bluuebunny/crossref_metadata_2025 huggingface dataset:
Interrelationships Between Structural Parameters of Cancellous Bone Reveal Accelerated Structural Change at Low Bone Volume
Authors: Parkinson Ian H , Fazzalari Nicola L
Published: April 2006

This study shows that change to cancellous bone structure is bone volume-dependent in a nonlinear manner. At low bone volume (<15%), trabecular thickness and trabecular separation change at a much greater rate than at higher bone volume. This suggests that the structural integrity of the cancellous bone may become rapidly compromised when bone volume falls below a critical value.

Introduction: While bone mass is the major determinant of bone strength, this mass-based paradigm does not fully account for the contribution of the bone microstructure to mechanical efficiency. Geometric models of cancellous bone structure have been formulated based on stylized representations of the trabecular elements, where the relationships between bone volume and bone surface of cancellous bone are complex and reflect the modulating effect on the cancellous bone structure of bone remodeling at the trabecular surfaces. Using the plate model of cancellous bone structure, the interrelationships between parameters of cancellous bone structure have been studied.

Materials and Methods: Two hundred eighty histological sections of human cancellous bone from eight skeletal sites were analyzed. The structural parameters of cancellous bone (BV/TV, BS/TV, BS/BV, Tb.Th, Tb.Sp, Tb.N, and TBPf) were obtained.

Results and Conclusions: This study shows that change to cancellous bone structure is bone volume-dependent in a nonlinear manner. At low bone volume (<15%), structural parameters of cancellous bone, such as trabecular thickness and trabecular separation, change at a much greater rate than at higher bone volume. This suggests that the structural integrity of the cancellous bone may become rapidly compromised when bone volume falls below a critical value. These data describe the complex relationships between bone mass and structure in cancellous bone that are often overlooked in the mass-based paradigm of bone strength. Histomorphometric descriptors of cancellous bone structure highlight the potential for accelerated deterioration of the structure with low bone volume, which leads to increased risk of fracture. From a clinical viewpoint, estimation of an individual's fracture risk is constrained to noninvasive techniques, which only provide bone mineral density or bone mineral content. Therefore, there is a need to better correlate measurement of bone mass with measurements of structural parameters.
A Prospective Study of Risedronate on Regional Bone Metabolism and Blood Flow at the Lumbar Spine Measured by18F-Fluoride Positron Emission Tomography
Authors: Frost Michelle L , Cook Gary JR , Blake Glen M , Marsden Paul K , Benatar Nigel A , Fogelman Ignac
Published: April 2006

The effect of risedronate on bone metabolism at the lumbar spine was assessed in 18 women who had a18F-fluoride PET scan at baseline and after 6 months of therapy. The net plasma clearance of fluoride to bone mineral reflecting osteoblastic activity decreased significantly after therapy.

Introduction: Quantitative radionuclide studies of bone reflect bone blood flow and regional osteoblastic activity, and the latter should change after treatment with a bisphosphonate, although this has not been previously demonstrated. The aim of this study was to examine regional18F-fluoride kinetics in the lumbar spine measured by18F-fluoride positron emission tomography (PET) before and after treatment with risedronate.

Materials and Methods: Eighteen women, with a mean age of 67.0 years and a T-score of less than −2 at the spine or hip, had a dynamic PET scan of the lumbar spine after the injection of 90 MBq18F-fluoride ion at baseline and 6 months after commencing risedronate therapy. The arterial plasma input function was derived using aorta arterial activity from the PET image. Time-activity curves were measured by placing regions of interest over the lumbar vertebrae. A three-compartmental model was used to calculate bone blood flow (K1) and the net plasma clearance of tracer to bone mineral (Ki). Rate constants k2, k3, and k4, which describe transport between plasma, the extracellular fluid (ECF) compartment, and the bone mineral compartment, respectively, were also measured.

Results: Mean vertebral Ki decreased significantly by 18.4% from baseline (3.32 × 10−2 ml/min/ml) to 6 months post-treatment (2.71 × 10−2 ml/min/ml; p = 0.04). This decrease was similar in magnitude to the decrease observed for bone-specific alkaline phosphatase, a marker of bone formation. There was no significant difference in K1 from baseline (1.49 × 10−1 ml/min/ml) to 6 months after treatment (1.38 × 10−1 ml/min/ml; p > 0.05). There was a significant increase in k2, reflecting the reverse transport of fluoride from the extravascular tissue compartment to plasma, after 6 months of treatment (2.90 × 10−1/min versus 4.43 × 10−1/min; p = 0.01). No significant changes were seen for k3 or k4. There was a significant decrease from baseline in the fraction of tracer in the extravascular tissue space that underwent specific binding to the bone matrix (k3/[k2 + k3]), decreasing by 18.1% (p = 0.02).

Conclusion: K i, the net plasma clearance to bone mineral reflecting regional osteoblastic activity, displayed a significant decrease after 6 months of antiresorptive therapy. This is the first study to show a direct metabolic effect of antiresorptive therapy on skeletal kinetics at the clinically important site of the lumbar spine. The use of18F-fluoride PET may provide a useful noninvasive tool to assess novel treatments currently being developed for osteoporosis.
Gender Differences in Mortality After Hip Fracture: The Role of Infection
Authors: Wehren Lois E , Hawkes William G , Orwig Denise L , Hebel J Richard , Zimmerman Sheryl I , Magaziner Jay
Published: April 2006

Possible explanations for the observed gender difference in mortality after hip fracture were examined in a cohort of 804 men and women. Mortality during 2 years after fracture was identified from death certificates. Men were twice as likely as women to die, and deaths caused by pneumonia/influenza and septicemia showed the greatest increase.

Introduction: Men are more likely to die after hip fracture than women. Gender differences in predisposing factors and causes of death have not been systematically studied.

Materials and Methods: Participants (173 men and 631 women) in the Baltimore Hip Studies cohort enrolled in 1990 and 1991, at the time of hospitalization for hip fracture, were followed longitudinally for 2 years. Cause-specific mortality 1 and 2 years after hip fracture, identified from death certificates, was compared by gender and to population rates.

Results and Conclusions: Men were twice as likely as women to die during the first and second years after hip fracture (odds ratio [OR], 2.28; 95% CI, 1.47, 3.54 and OR, 2.21; 95% CI, 1.48, 3.31). Prefracture medical comorbidity, type of fracture, type of surgical procedure, and postoperative complications did not explain the observed difference. Greatest increases in mortality, relative to the general population, were seen for septicemia (relative risk [RR], 87.9; 95% CI, 16.5, 175 at 1 year and RR, 32.0; 95% CI, 7.99, 127 at 2 years) and pneumonia (RR, 23.8; 95% CI, 12.8, 44.2 at 1 year and RR, 10.4; 95% CI, 3.35, 32.2 at 2 years). The magnitude of increase in deaths caused by infection was greater for men than for women in both years. Mortality rates for men and women were similar if deaths caused by infection were excluded (3.46 [1.79, 6.67] and 2.47 [1.63, 3.72] at 1 year and 0.96 [0.48, 1.91] and 1.26 [0.80, 1.98] at 2 years). Deaths related to infections (pneumonia, influenza, and septicemia) seem to be largely responsible for the observed gender difference. In conclusion, an increased rate of death from infection and a gender difference in rates persists for at least 2 years after the fracture.
Racial Differences in Bone Mineral Density in Older Men
Authors: George Asha , Tracy J Kathleen , Meyer Walter A , Flores Raymond H , Wilson P David , Hochberg Marc C
Published: April 2006

Studies have examined factors related to BMD in older white, but not black, men. We measured BMD in older white and black men and examined factors related to racial differences in BMD. Black men had significantly higher adjusted BMD at all sites. These results may explain, in part, the lower incidence of fractures in older black men.

Introduction: Several studies have examined factors associated with bone mineral density (BMD)in older men. None, however, have had sufficient numbers of black men to allow for meaningful comparisons by race.

Materials and Methods: A total of 503 white and 191 black men aged 65 and older(75.1 ± 5.8 and 72.2 ± 5.7 years, respectively) were recruited from the Baltimore metropolitan area. All men completed a battery of self-administered questionnaires, underwent a standardized examination, and had BMD measured at the femoral neck, lumbar spine, and total body. Data were analyzed using multiple variable linear regression models, adjusted for potential confounding variables; two-way interactions with main effects were included in models where appropriate.

Results: Black men had significantly higher adjusted BMD at the femoral neck (difference 0.09 [95% CI: 0.07, 0.12] mg/cm2), lumbar spine (0.07 [0.04, 0.10] mg/cm2), and total body (0.06 [0.03, 0.08] mg/cm2) than white men.

Conclusions: Older black men have significantly higher BMD than older white men, even after adjustment for factors associated with BMD. These differences, especially at the femoral neck, may explain the reduced incidence of hip fracture in black compared with white men.
Mechanisms of Tumor Metastasis to the Bone: Challenges and Opportunities
Authors: Reddi A Hari , Roodman David , Freeman Colette , Mohla Suresh
Published: April 2006

In human cancers, bone is a common site for metastasis. It is well known that metastasis is the cause of morbidity and mortality in patients with cancer. Both breast and prostate carcinomas have a propensity to metastasize to bone. In general, metastatic breast cancers result in osteolytic lesions. On the other hand, prostate cancer metastases are osteoblastic and result in osteosclerosis. Thus, bone formation and bone resorption are at the crux of the cancer metastasis problem. For example, in the prostate, there is a vicious cycle of metastasis to bone (Fig. 1). Metastases to bone causes excruciating bone pain, pathological fractures, and eventually death, and therefore is a serious challenge to both bone biologists and cancer cell biologists. The stromal-epithelial interactions in breast and prostate are critical in initiation of carcinogenesis and the progression of the metastatic cascade to bone (Fig. 2). Over a hundred years ago, Stephen Paget enunciated the seed and soil hypothesis in which seeds of metastatic cancer cells of breast preferentially settle in the soil of bone matrix. Thus, the prostate/breast cancer bone interface and continuum has continuously presented challenges and opportunities and were discussed at a recent workshop.
A Proteome Study of Secreted Prostatic Factors Affecting Osteoblastic Activity: Galectin-1 Is Involved in Differentiation of Human Bone Marrow Stromal Cells
Authors: Andersen Helle , Jensen Ole N , Moiseeva Elena P , Eriksen Erik F
Published: April 2006

Prostate cancer cells metastasize to bone causing a predominantly osteosclerotic response. It has been shown that cells from the human prostate cancer cell line PC3 secrete factors that influence the behavior of osteoblast-like cells. Some of these factors with mitogenic activity have been found to be proteins with molecular weights between 20 and 30 kDa, but the identity of the osteoblastic mitogenic factor or factors produced by prostate cancer cells is still unknown. Therefore, the aim of this study was to characterize the protein profile of conditioned medium (CM) from PC3 cells in the molecular weight range from 5 to 30 kDa using proteome analysis. A protein profile of the CM from PC3 cells was performed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Thirty protein spots with molecular weights ranging from 5 to 30 kDa were analyzed by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). One of these spots was identified as galectin-1. We examined whether PC3 CM, recombinant galectin-1 alone, or combined with insulin-like growth factor-I (IGF-I) had any effects on the proliferation or differentiation of human bone marrow stromal (hBMS) cells. Furthermore, we tested whether adhesion of PC3 cells to plastic, laminin, fibronectin, and collagen type I was influenced by lactose, which inhibits galectin-1. Galectin-1 (1000 ng/ml) inhibited the proliferation of hBMS cells up to 70 ± 12% (treated/control) of control in contrast to PC3 CM, which induced hBMS cell proliferation by 3-fold. This effect was abolished by IGF-I. PC3 CM and galectin-1 in concentrations of 10 and 1000 ng/ml increased the alkaline phosphatase (ALP) activity of hBMS cells up to 175 ± 27%, 137 ± 8%, and 131 ± 11%, respectively, compared with ALP activity of untreated cells, and inhibited the secretion of osteocalcin (OC) up to 81 ± 3%, 93 ± 1%, and 58 ± 2%, respectively, compared with OC secretion of untreated cells. These effects were affected by IGF-I. Lactose inhibited adhesion of PC3 cells to plastic, fibronectin, laminin, and collagen type I up to 58 ± 4%, 30 ± 12, 72 ± 9%, and 86 ± 4%. In conclusion, galectin-1 modulated osteoblastic proliferation and differentiation. These effects were affected by IGF-I. Thus, galectin-1 is likely be involved in the osteoblastic response, caused by prostate cancer cells metastasizing into bone, by affecting the matrix mineralization.
Antagonistic Effects of Different Classes of Bisphosphonates in Osteoclasts and Macrophages In Vitro
Authors: Frith Julie C. , Rogers Michael J.
Published: April 2006

Nitrogen-containing bisphosphonates, such as alendronate and ibandronate, inhibit bone resorption by preventing protein prenylation in osteoclasts, whereas non-nitrogen-containing bisphosphonates, such as clodronate, are metabolized to nonhydrolyzable analogs of ATP, resulting in osteoclast apoptosis. Because these two classes of bisphosphonates have different molecular mechanisms of action, we examined in vitro whether combined treatment with clodronate and alendronate would alter antiresorptive effectiveness. Although, in cultures of rabbit osteoclasts, the antiresorptive effect of 10 μM alendronate was increased by the addition of clodronate, the effect of higher concentrations of alendronate was not altered by addition of clodronate. Furthermore, the inhibition of protein prenylation in osteoclasts caused by higher alendronate concentrations was partially prevented by cotreatment with clodronate. As in osteoclasts, the inhibition of protein prenylation in J774 cells caused by alendronate or ibandronate treatment was dose-dependently prevented by cotreatment with clodronate. Furthermore, alendronate-induced J774 apoptosis was significantly inhibited in the presence of clodronate. The presence of clodronate also decreased the short-term cellular uptake of [14C]ibandronate. These observations suggest that combined treatment with clodronate could enhance the antiresorptive effect of a low concentration of nitrogen-containing bisphosphonate, but clodronate can also antagonize some of the molecular actions and effects of higher concentrations of nitrogen-containing bisphosphonates. The exact molecular basis for the antagonistic effects between bisphosphonates remain to be determined, but could involve competition for cellular uptake by a membrane-bound transport protein.
Cathepsin K mRNA and Protein Expression in Prostate Cancer Progression
Authors: Brubaker KD , Vessella RL , True LD , Thomas R , Corey E
Published: April 2006

Prostate cancer (CaP) is the most commonly diagnosed malignancy in men and is often associated with bone metastases, which cause much of the morbidity associated with CaP. Lesions associated with CaP generally exhibit increased bone formation and resorption. Increased bone resorption may release factors from the extracellular matrix that contribute to tumor growth. Cathepsin K (cat K) is a cysteine protease that exhibits strong degradative activity against the extracellular matrix and is involved in osteoclast-mediated bone destruction. In this study, we analyzed the expression of cat K in CaP cell lines and patient samples. Cat K message was detected in CaP cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and in primary CaP and metastases by in situ hybridization. Immunohistochemistry revealed variable expression of cat K in primary CaP samples, as well as nonosseous metastases, whereas expression in bone metastases was significantly higher than in primary CaP, and normal prostate tissues were negative. Cat K protein was detected in CaP cell lines by Western blotting after immunoprecipitation. Cat K enzymatic activity was also detected in CaP cell lines by a fluorogenic assay and by an assay for degradation of collagen type I. Increased levels of NTx, a marker of bone matrix degradation mediated primarily by cat K, were also detected in sera of patients with CaP bone metastases. We hypothesize that CaP-expressed cat K may contribute to the invasive potential of CaP, while increased expression in bone metastases is consistent with a role in matrix degradation.
Endoglin Is Expressed on Human Chondrocytes and Forms a Heteromeric Complex With Betaglycan in a Ligand and Type II TGFβ Receptor Independent Manner
Authors: Parker Wendy L , Goldring Mary B , Philip Anie
Published: April 2006

Previous work has implicated transforming growth factor β (TGFβ) as an essential mediator of cartilage repair and TGFβ signaling as a requirement for the maintenance of articular cartilage in vivo. However, the mechanisms regulating TGFβ action in chondrocytes are poorly understood. Endoglin, an accessory receptor of the TGFβ receptor superfamily, is highly expressed on endothelial cells and has been shown to potently modulate TGFβ responses. It is not known whether chondrocytes express endoglin or whether it modulates TGFβ signaling in these cells. In this study, we show that endoglin is expressed on human chondrocytes at levels comparable with endothelial cells and that it forms higher order complexes with the types I and II TGFβ receptors. More importantly, we show that endoglin forms a heteromeric complex with betaglycan on these cells at endogenous receptor concentrations and ratios. Endoglin complexes with betaglycan in a ligand-independent and -dependent manner as indicated by co-immunoprecipitation in the absence of TGFβ and after affinity labeling with radiolabeled TGFβ, respectively. Also, the endoglin-betaglycan association can occur independently of the type II TGFβ receptor. These findings, taken together with the available evidence that endoglin and betaglycan are potent modulators of TGFβ signal transduction, imply that the complex formation between endoglin and betaglycan may be of critical significance in the regulation of TGFβ signaling in chondrocytes.
Relative Contributions of Bone Density, Bone Turnover, and Clinical Risk Factors to Long-Term Fracture Prediction
Authors: Melton L Joseph , Crowson Cynthia S , O'Fallon W Michael , Wahner Heinz W , Riggs B Lawrence
Published: April 2006

Long-term fracture prediction using bone mineral density remains controversial, as does the additional contribution from assessing bone turnover or clinical risk factors. We measured bone mineral density at various sites, along with biochemical markers of bone turnover, sex steroid levels, and over 100 clinical variables, at baseline on an age-stratified sample of 304 Rochester, MN women in 1980. The 225 postmenopausal women were subsequently followed for 3146 person-years (median, 16.2 years per subject), wherein they experienced 302 new fractures: 81% resulted from minimal or moderate trauma and 60% of these involved the proximal femur, thoracic or lumbar vertebrae, or distal forearm. Accounting for multiple fractures per subject, these osteoporotic fractures together were best predicted by baseline femoral neck bone mineral density (age-adjusted hazard ratio [HR] per SD decrease, 1.37; 95% CI, 1.10–1.70); 19 moderate trauma forearm fractures were best predicted by distal radius bone mineral content, whereas 28 hip fractures and 100 vertebral fractures were best predicted by femoral neck bone mineral density. Femoral neck bone mineral density performed comparably in predicting osteoporotic fracture risk within the first decade of follow-up (HR, 1.38; 95% CI, 1.10–1.74) as well as more than 10 years after baseline (HR, 1.39; 95% CI, 1.05–1.84). The older biochemical markers were not associated with fractures, but serum “free” estradiol index was independently predictive of short- and long-term fracture risk. Consistent clinical risk factors were not identified, but statistical power was limited. Identifying patients at increased long-term risk of fracture is challenging, but it is reassuring that femoral neck bone mineral density can predict osteoporotic fractures up to 20 years later.
Ten-Year Longitudinal Relationship Between Physical Activity and Lumbar Bone Mass in (Young) Adults
Authors: Bakker Ingrid , Twisk Jos WR , Van Mechelen Willem , Roos Jan C , Kemper Han CG
Published: April 2006

Little is known about the influence of long-term daily physical activity (PA) on lumbar bone mass after peak bone mass has been reached, that is, during [young] adulthood. The purpose of this study was to investigate the longitudinal relationship between PA and lumbar bone mineral density (LBMD) in healthy subjects over a 10-year period. The data reported here relate to 225 male and 241 female participants in the Amsterdam Growth and Health Longitudinal Study, who were measured at the mean ages of 27, 32, and/or 36. LBMD, habitual daily PA, total body weight, and calcium intake were assessed at each measurement point. The effects of two aspects of PA were analyzed: the mechanical (MECHPA; sum of all ground reaction forces) and metabolic (METPA; weighted metabolic score of intensity, frequency, and duration) components, each within a separate model. Multilevel analysis was used to investigate the relationship between PA and LBMD over the 10-year period. Gender, total body weight, and calcium intake were included in the analysis as covariates. The results indicated that MECHPA was a significant positive linear predictor of LBMD for males (r = 0.09; p < 0.001) but not for females. For the METPA, no linear longitudinal relationship with LBMD was found. The results suggest that there is a metabolic threshold at which extra PA becomes “deleterious” and METPA in its totality becomes ineffective for LBMD. It is concluded that during the (young) adult period, between 27 and 36 years of age, PA causing mechanical loading on the skeleton has a small positive influence on LBMD in males.
Hormone Replacement Therapy Dissociates Fat Mass and Bone Mass, and Tends to Reduce Weight Gain in Early Postmenopausal Women: A Randomized Controlled 5-Year Clinical Trial of the Danish Osteoporosis Prevention Study
Authors: Jensen LB , Vestergaard P , Hermann AP , Gram J , Eiken P , Abrahamsen B , Brot C , Kolthoff N , Sørensen OH , Beck-Nielsen H , Nielsen S Pors , Charles P , Mosekilde L
Published: April 2006

The aim of this study was to study the influence of hormone replacement therapy (HRT) on weight changes, body composition, and bone mass in early postmenopausal women in a partly randomized comprehensive cohort study design. A total of 2016 women ages 45–58 years from 3 months to 2 years past last menstrual bleeding were included. One thousand were randomly assigned to HRT or no HRT in an open trial, whereas the others were allocated according to their preferences. All were followed for 5 years for body weight, bone mass, and body composition measurements. Body weight increased less over the 5 years in women randomized to HRT (1.94 ± 4.86 kg) than in women randomized to no HRT (2.57 ± 4.63, p = 0.046). A similar pattern was seen in the group receiving HRT or not by their own choice. The smaller weight gain in women on HRT was almost entirely caused by a lesser gain in fat. The main determinant of the weight gain was a decline in physical fitness. Women opting for HRT had a significantly lower body weight at inclusion than the other participants, but the results in the self-selected part of the study followed the pattern found in the randomized part. The change in fat mass was the strongest predictor of bone changes in untreated women, whereas the change in lean body mass was the strongest predictor when HRT was given. Body weight increases after the menopause. The gain in weight is related to a decrease in working capacity. HRT is associated with a smaller increase in fat mass after menopause. Fat gain protects against bone loss in untreated women but not in HRT-treated women. The data suggest that women's attitudes to HRT are more positive if they have low body weight, but there is no evidence that the conclusions in this study are skewed by selection bias.
Distinct Anabolic Response of Osteoblast to Low-Intensity Pulsed Ultrasound
Authors: Naruse Kouji , Miyauchi Akimitsu , Itoman Moritoshi , Mikuni-Takagaki Yuko
Published: April 2006

Low-intensity pulsed ultrasound, a form of mechanical energy transmitted as high-frequency acoustical pressure waves, provides noninvasive therapeutic treatment for accelerating fracture repair and distraction osteogenesis. Relatively young osteoblasts respond to ultrasound by transiently upregulating message levels of immediate-early genes as well as that of osteocalcin and insulin-like growth factor I (IGF-I). Osteocytes derived from newborn rat tibia and calvaria responded to a lesser extent only in c-fos and cyclooxygenase-2 (COX-2) messages. Compared with the stretched osteocytes, which use stretch-activated and parathyroid hormone (PTH)-potentiated Ca2+ influx as an entry route to the protein kinase A (PKA) signal transduction pathways, there was no evidence of Ca2+ internalization by any of the cells tested on exposure to the ultrasound. On the other hand, inhibitors of p38 mitogen-activated protein kinase (MAPK) and upstream phosphoinositide 3-kinase (PI3K) blocked COX-2 and osteocalcin upregulation by the ultrasound-exposed ST2, murine bone marrow-derived cells. This is distinct from the aforementioned osteocytic response to low-frequency stretching and implies the involvement of integrins. Our findings suggested that accelerated fracture repair and distraction osteogenesis by the low-intensity pulsed ultrasound depend, at least in part, on the stimulation of osteoblastic cells at relatively early stages of osteogenic lineage. Bone is under control of multiple regulatory mechanisms so that diverse physical forces can be reflected to the microenvironment of each cell, in turn, to the entire bone.
Bone Loss Detection in Rats Using a Mouse Densitometer
Authors: Binkley N , Dahl DB , Engelke J , Kawahara-Baccus T , Krueger D , Colman RJ
Published: April 2006

Estrogen-depletion bone-loss studies often use ovariectomized (ovx) rats and measure bone mineral density in vivo or ex vivo using DXA. Recently, a portable densitometer (PIXImus) was developed for mouse research; however, its use in rats is unclear. This study compared the ability of PIXImus and a standard densitometer (DPXL) to detect ovx-induced bone loss in rats both in vivo and ex vivo. Additionally, instrument accuracy was assessed by comparing measured bone mass with ash weight. Finally, the use of two distal femur regions of interest (ROI) to detect ovx-induced bone loss was evaluated. Twenty-three 6-month-old nulliparous female Sprague-Dawley rats were randomly assigned to sham or ovx groups. Distal femur bone mineral density was assessed at baseline and at 1 and 2 months postoperatively, using a PIXImus and DPXL densitometer. At 3 months postoperatively, all animals were killed, and ex vivo femur scans obtained. Distal femur bone loss was demonstrable by 1 month post-ovx using either densitometer. With the PIXImus, a 4-mm ROI demonstrated greater bone loss (p < 0.05) than an 8-mm ROI. Using the 4-mm ROI, similar amounts of bone loss were detected by the PIXImus and DPXL: 22.2% and 22.4%, respectively, at 2 months post-ovx. Total femur bone mineral content was overestimated by the PIXImus but highly correlated with the DPXL measurement (r = 0.988) and ash weight (r = 0.998). Given its comparability to standard DXA plus its rapid scan speed and portability, the PIXImus is useful in evaluating ovx-induced osteopenia in rats.
Growth Hormone Increases Bone Mineral Content in Postmenopausal Osteoporosis: A Randomized Placebo-Controlled Trial
Authors: Landin-Wilhelmsen Kerstin , Nilsson Anders , Bosaeus Ingvar , Bengtsson Bengt-Åke
Published: April 2006

Eighty osteoporotic, postmenopausal women, 50–70 years of age, with ongoing estrogen therapy (HRT), were randomized to recombinant human growth hormone (GH), 1.0 U or 2.5 U/day, subcutaneous, versus placebo. This study was double-blinded and lasted for 18 months. The placebo group then stopped the injections, but both GH groups continued for a total of 3 years with GH and followed for 5 years. Calcium (750 mg) and vitamin D (400 U) were given to all patients. Bone mineral density and bone mineral content were measured with DXA. At 18 months, when the double-blind phase was terminated, total body bone mineral content was highest in the GH 2.5 U group (p = 0.04 vs. placebo). At 3 years, when GH was discontinued, total body and femoral neck bone mineral content had increased in both GH-treated groups (NS between groups). At 4-year follow-up, total body and lumbar spine bone mineral content increased 5% and 14%, respectively, for GH 2.5 U (p = 0.01 and p = 0.0006 vs. placebo). Femoral neck bone mineral density increased 5% and bone mineral content 13% for GH 2.5 U (p = 0.01 vs. GH 1.0 U). At 5-year follow-up, no differences in bone mineral density or bone mineral content were seen between groups. Bone markers showed increased turnover. Three fractures occurred in the GH 1.0 U group. No subjects dropped out. Side effects were rare. In conclusion, bone mineral content increased to 14% with GH treatment on top of HRT and calcium/vitamin D in postmenopausal women with osteoporosis. There seems to be a delayed, extended, and dose-dependent effect of GH on bone. Thus, GH could be used as an anabolic agent in osteoporosis.
Association of a Haplotype (196Phe/532Ser) in the Interleukin-1-Receptor-Associated Kinase (IRAK1) Gene With Low Radial Bone Mineral Density in Two Independent Populations
Authors: Ishida Ryota , Emi Mitsuru , Ezura Yoichi , Iwasaki Hironori , Yoshida Hideyo , Suzuki Takao , Hosoi Takayuki , Inoue Satoshi , Shiraki Masataka , Ito Hiromoto , Orimo Hajime
Published: April 2006

Osteoporosis, a multifactorial common disease, is believed to result from the interplay of multiple environmental and genetic determinants, including factors that regulate bone mineral density. Interleukin-1 (IL-1) is one of the most potent bone-resorbing factors, and interleukin-1-associated kinase 1 (IRAK1) is an essential effector of the IL-1 receptor signaling cascade. In genetic studies of two independent populations of postmenopausal women (cohort A: 220 individuals and cohort T: 126 individuals) from separated geographical regions of Japan, we found that radial bone mineral density levels had similar associations with IRAK1 genotypes in both populations. Two amino acid-substituting variations in the gene, encoding Phe196Ser and Ser532Leu, were in complete linkage disequilibrium (D′ = 1.0000, r2 = 1.0000, χ2 = 192.000, p = 1.2 × 10−43), and we found two exclusive haplotypes (196F/532S, frequency 0.74; 196S/532L, frequency 0.26) of the IRAK1 gene among our test subjects. In both populations, a significant association with decreased radial bone mineral density was identified with haplotype 196F/532S (in cohort A: r = 0.21, p = 0.0017; in cohort T: r = 0.23, p = 0.011). Radial bone mineral density was lowest among 196F/532S homozygotes, highest among 196S/532L homozygotes, and intermediate among heterozygotes. Accelerated bone loss also correlated with the 196F/532S haplotype in a 5-year follow-up. These results suggest that variation of IRAK1 may be an important determinant of postmenopausal osteoporosis, in part through the mechanism of accelerated postmenopausal bone loss.
Abnormal Regulation of Renal 25-Hydroxyvitamin D-1α-Hydroxylase Activity in X-Linked Hypophosphatemia: A Translational or Post-Translational Defect
Authors: Fujiwara Ikuma , Aravindan Rolands , Horst Ron L , Drezner Marc K
Published: April 2006

The hyp mouse exhibits abnormal metabolic/hormonal regulation of renal 25(OH)D-1α-hydroxylase activity. Whether this results from aberrant transcriptional regulation of the 1α-hydroxylase gene, CYP27B1, remains unknown. To investigate this possibility, we compared phosphate and parathyroid hormone effects on renal proximal convoluted tubule and thyrocalcitonin effects on proximal straight tubule enzyme activity and mRNA expression in normal and hyp mice. We assayed 25(OH)D-1α-hydroxylase activity by measuring 1,25(OH)2D production and mRNA by ribonuclease protection. Phosphate-depleted mice exhibited a 3-fold increment of 25(OH)D-1α-hydroxylase activity compared with normals, whereas hyp mice displayed no enhanced enzyme function. Phosphate-depleted mice concurrently displayed a 2-fold increase in mRNA transcripts; in contrast, despite failure to alter enzyme activity, hyp mice exhibited a similar increment in mRNA transcripts. Parathyroid hormone stimulation of normal mice increased 25(OH)D-1α-hydroxylase activity 10-fold, while eliciting only a 2-fold increment in hyp mouse enzyme function. This disparity occurred despite increments of mRNA transcripts to comparable levels (22.2 ± 3.5- vs. 19.9 ± 1.8-fold). The dissociation between phosphate- and parathyroid hormone-mediated transcriptional activity and protein function was not universal. Thus, thyrocalcitonin stimulation of normal and hyp mice resulted in comparable enhancement of mRNA transcripts and enzyme activity. These observations indicate that abnormal regulation of vitamin D metabolism in hyp mice occurs in the proximal convoluted tubule and results, not from aberrant transcriptional regulation, but from a defect in translational or post-translational activity.
Effects of Cyclosporine on Osteoclast Activity: Inhibition of Calcineurin Activity With Minimal Effects on Bone Resorption and Acid Transport Activity
Authors: Williams John P , Mckenna Margaret A , Thames Allyn M , McDONALD Jay M
Published: April 2006

Cyclosporine results in rapid and profound bone loss in transplant patients, an effect ascribed to osteoclasts. Cyclosporine, complexed with the appropriate immunophilin, inhibits calcineurin (the calcium/calmodulin dependent serine/threonine phosphatase) activity. We tested the hypothesis that cyclosporine inhibits calcineurin activity in osteoclasts, resulting in stimulation of osteoclast activity. We compared the effects of cyclosporine A and the calmodulin antagonist, tamoxifen, on bone resorption by avian osteoclasts. Tamoxifen inhibits bone resorption ∼60%, whereas cyclosporine A only inhibited bone resorption 12%. One-hour treatment with 100 nM cyclosporine inhibited osteoclast calcineurin activity 70% in whole cell lysates, whereas 10 μM tamoxifen only inhibited calcineurin activity 25%. We compared the effects of cyclosporine A and tamoxifen on acid transport activity in isolated membrane vesicles and in isolated membrane vesicles obtained from osteoclasts treated with cyclosporine A or tamoxifen under conditions that inhibit calcineurin activity. Direct addition of cyclosporine A in the acid transport assay, or pretreatment of cells with cyclosporine A followed by membrane isolation, had no effect on acid transport activity in membrane vesicles. In contrast, direct addition of tamoxifen to membranes inhibits acid transport activity, an effect that can be prevented by addition of exogenous calmodulin. Furthermore, acid transport activity was also inhibited in membrane vesicles isolated from cells treated with tamoxifen. In conclusion, cyclosporine A inhibits osteoclast calcineurin activity; however, calcineurin inhibition does not correspond to a significant effect on acid transport activity in isolated membrane vesicles or bone resorption by osteoclasts.
Zoledronic Acid Treatment of 5T2MM-Bearing Mice Inhibits the Development of Myeloma Bone Disease: Evidence for Decreased Osteolysis, Tumor Burden and Angiogenesis, and Increased Survival
Authors: Croucher Peter I , De Raeve Hendrik , Perry Mark J , Hijzen Anja , Shipman Claire M , Lippitt Jennifer , Green Jonathan , Van Marck Eric , Van Camp Ben , Vanderkerken Karin
Published: April 2006

Multiple myeloma is characterized by the growth of plasma cells in the bone marrow and the development of osteolytic bone disease. Myeloma cells are found closely associated with bone, and targeting this environment may therefore affect both the bone disease and the growth of myeloma cells. We have investigated the effect of the potent bisphosphonate, zoledronic acid, on the development of bone disease, tumor burden, and disease-free survival in the 5T2MM model of myeloma. 5T2MM murine myeloma cells were injected intravenously into C57BL/KaLwRij mice. After 8 weeks, all animals had a paraprotein. Animals were treated with zoledronic acid (120 μg/kg, subcutaneously, twice weekly) or vehicle, from the time of tumor cell injection or from paraprotein detection for 12 or 4 weeks, respectively. All animals injected with tumor cells developed osteolytic lesions, a decrease in cancellous bone volume, an increase in osteoclast perimeter, and a decrease in bone mineral density. Zoledronic acid prevented the formation of lesions, prevented cancellous bone loss and loss of bone mineral density, and reduced osteoclast perimeter. Zoledronic acid also decreased paraprotein concentration, decreased tumor burden, and reduced angiogenesis. In separate experiments, Kaplan-Meier analysis demonstrated a significant increase in survival after treatment with zoledronic acid when compared with control (47 vs. 35 days). A single dose of zoledronic acid was also shown to be effective in preventing the development of osteolytic bone disease. These data show that zoledronic acid is able to prevent the development of osteolytic bone disease, decrease tumor burden in bone, and increase survival in a model of established myeloma.
S100A4: A Novel Negative Regulator of Mineralization and Osteoblast Differentiation
Authors: Duarte Wagner R , Shibata Tatsuya , Takenaga Keizo , Takahashi Etsuko , Kubota Kaori , Ohya Keiichi , Ishikawa Isao , Yamauchi Mitsuo , Kasugai Shohei
Published: April 2006

S100A4 is an intracellular calcium-binding protein expressed by osteoblastic cells. However, its roles in bone physiology are unknown. Because before matrix mineralization, its expression is markedly diminished, we hypothesized that S100A4 negatively regulates the mineralization process. In this study, we investigated the effects of the inhibition of S100A4 synthesis on osteoblast differentiation and in vitro mineralized nodule formation. Inhibition of S100A4 synthesis was achieved by an antisense approach in the mouse osteoblastic cell line MC3T3-E1. Cell clones that synthesized low levels of S100A4 (AS clones) produced markedly increased number of mineralized nodules at much earlier stages in comparison with controls as demonstrated by Alizarin red S and von Kossa staining. The expression of type I collagen (COLI) and osteopontin (OPN) increased in AS clones compared with controls. Bone sialoprotein (BSP) and osteocalcin (OCN), molecules associated with mineralization and markers for mature osteoblastic phenotype, were expressed in AS clones before their detection in controls. Because S100A4 was not localized in the nucleus of MC3T3-E1 cells and AS clones, it is unlikely that S100A4 directly regulates the expression of these genes. Moreover, the expression of Cbfa1/Osf-2 and Osx, transcription factors necessary for the expression of osteoblast-associated genes, remained unchanged in AS clones, indicating that S100A4 may be downstream to these transcription factors. These findings indicate that S100A4 is a novel negative regulator of matrix mineralization likely by modulating the process of osteoblast differentiation.
Enhancement of Fibronectin Synthesis and Fibrillogenesis by BMP-4 in Cultured Rat Osteoblast
Authors: Tang Chih-Hsin , Yang Rong-Sen , Liou Houng-Chi , Fu Wen-Mei
Published: April 2006

The skeletal extracellular matrix produced by osteoblasts contains the glycoprotein fibronectin (Fn), which regulates the adhesion, differentiation, and function of osteoblasts. Fn fibrillogenesis is involved in the process of bone mineralization. Bone morphogenetic proteins (BMPs) can be isolated from organic bone matrix and are able to initiate de novo cartilage and bone formation. In this study, the effect of BMP-4 on Fn fibrillogenesis in cultured rat osteoblasts was examined. BMP-4 enhanced Fn synthesis and extracellular Fn assembly in primary cultured osteoblasts. In addition, the extracellular assembly of Fn from exogenously applied soluble human Fn was also increased by BMP-4. It has been reported that α5β1 integrin is related to Fn fibrillogenesis. The synthesis of both α5 and β1 integrins was upregulated by BMP-4. Immunocytochemistry showed that the clustering of α5 and β1 integrins was also increased by BMP-4. BMP-4 increased fibril formation of Fn and the adhesion of osteoblasts onto Fn matrix, which was inhibited by disintegrin triflavin and Gly-Arg-Gly-Asp-Ser (GRGDS) peptide. Phosphorylation of extracellular signal-regulated kinase (ERK) and focal adhesion kinase (FAK) was increased by BMP-4. Enhancement of extracellular Fn fibrillogenesis and the mRNA expression of β1 integrin by BMP-4 were inhibited by ERK kinase (MEK) inhibitor PD98059. These results suggest that the enhancement of extracellular Fn fibrillogenesis by BMP-4 in cultured osteoblasts is related to the increase of the synthesis of Fn and clustering of α5 and β1 integrins. ERK is involved in the signaling pathway of BMP-4 in regulating Fn fibrillogenesis in osteoblasts.
Long-Term Treatment of Incadronate Disodium Accumulates Microdamage but Improves the Trabecular Bone Microarchitecture in Dog Vertebra
Authors: Komatsubara Satoshi , Mori Satoshi , Mashiba Tasuku , Ito Masako , Li Jiliang , Kaji Yoshio , Akiyama Tomoyuki , Miyamoto Kensaku , Cao Yongping , Kawanishi Jun , Norimatsu Hiromichi
Published: April 2006

This study aimed to investigate the effect of long-term suppression of bone resorption by bisphosphonate on the microstructure, accumulation of microdamage, and mechanical properties of trabecular bone. Twenty-nine 1-year-old beagles (15 males, 14 females) were divided into three groups. The control group (CNT) was treated daily with vehicle, and the other two groups were treated with incadronate at a dose of 0.3 mg/kg/day (LOW) or 0.6 mg/kg/day (HIGH) orally for 3 years. After death, the second thoracic vertebra was scanned with microcomputed tomography (micro-CT) and assigned to histomorphometric and microdamage measurements. The fourth lumbar vertebra was mechanically tested by compression. Incadronate concentration in bone was measured in the 11th thoracic vertebra. Micro-CT analysis demonstrated a platelike trabecular structure and increased concave surface of trabeculae in the thoracic vertebra of incadronate-treated groups. Three-year incadronate treatment significantly suppressed trabecular activation rates by 56% in LOW and 67% in HIGH without impairment of mineralization, and increased microdamage accumulation in both incadronate-treated groups. Trabecular bone volume was significantly increased in both LOW and HIGH groups, and vertebral strength was significantly increased in the HIGH group compared with the CNT group. However, intrinsic material properties such as normalized ultimate stress and normalized toughness were reduced in incadronate-treated groups. Incadronate concentration in bone was dose-dependent. This study suggests that long-term suppression of bone remodeling increases microdamage accumulation, but this is not necessarily associated with vertebral fragility because of compensated increase of bone mass and improved microarchitecture.
Suture Growth Modulated by the Oscillatory Component of Micromechanical Strain
Authors: Kopher Ross A , Mao Jeremy J
Published: April 2006

Sutures are fibrous connective tissue articulations between intramembranous craniofacial bones. Sutures are composed of fibroblastic cells with their matrices in the center and osteogenic cells in the periphery producing a matrix that is mineralized during skeletal growth. Whether oscillatory forces stimulate sutural growth is unknown. In the present work, we applied static and cyclic forces with the same peak magnitude of 5N to the maxilla in growing rabbits and quantified (1) acute in vivo sutural bone strain responses and (2) chronic growth responses in the premaxillomaxillary suture (PMS) and nasofrontal suture (NFS). Bone strain recordings showed that the waveforms of static force and 1-Hz cyclic force were expressed as corresponding static and cyclic sutural strain patterns in both the PMS and NFS, with the mean peak PMS strain (−1451 ± 137 με for the cyclic and −1572 ± 138 με for the static) approximately 10-fold higher than the mean peak NFS strain (124 ± 9 με for the cyclic and 134 ± 9 με for the static). Strain polarity was the opposite: compressive for the PMS but tensile for the NFS. However, on application of repetitive 5N cyclic and static forces in vivo for 10 minutes/day over 12 days, cyclic loading induced significantly greater sutural widths for the compressed PMS (95.1 ± 8.3 μm) than sham control (69.8 ± 8.2 μm) and static loading (58.9 ± 2.8 μm; p < 0.01). Interestingly, the same trend was true for the NFS under tensile strain: significantly greater sutural width for cyclic loading (267.4 ± 64.2 μm) than sham control (196.0 ± 10.1 μm) and static loading (169.9 ± 11.4 μm). Cell counting in 110 × 110 μm grids laid over sutures disclosed significantly more sutural cells on repetitive cyclic loading than sham control and static loading (p < 0.05) for both the PMS and NFS. Fluorescent labeling of newly formed sutural bone demonstrated more osteogenesis on cyclic loading in comparison with sham control and static loading. Thus, the oscillatory component of cyclic force or more precisely the resulting cyclic strain experienced in sutures is a potent stimulus for sutural growth. The increased sutural growth by cyclic mechanical strain in the tensed NFS and compressed PMS suggests that both microscale tension and compression induce anabolic sutural growth response.