ISSN:0884-0431    

DOI:10.1002/jbmr.5650071002

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

年代:1992

数据来源: WILEY

摘要:

AbstractA causal role in age‐related bone loss has been attributed to alterations in vitamin D status, the bone mineral regulating hormones, and/or renal function. We assessed biochemical parameters of bone metabolism and renal function in healthy subsets of young and old men (n= 191) and women (n= 120) and evaluated the relationships between these parameters and bone mineral density (BMD) in the radius, spine, and femur. There were no significant associations between BMD at any site and serum 25‐OHD, 1,25‐(OH)2D, PTH, or creatinine clearance in either young men or in young or old women, after controlling for age. In old men, however, lower radius BMD was significantly related to higher PTH and higher 1,25‐(OH)2D and marginally related to lower 25‐OHD values. In young men, there were unexpected but significant associations between lower femoral neck BMD and higher serum osteocalcin and urinary calcium/creatinine excretion after age adjustment. In old women, lower spine and radius BMD was also significantly correlated with higher serum osteocalcin. In this healthy, vitamin D‐replete population, there were significant cross‐sectional declines in BMD in the femur in young and old men and at all sites in old women. Elevated remodeling may be an important feature that contributes to reduced femoral BMD in young men and reduced spine and radius BMD in old women. However, compromised renal function or levels of 1,25‐(OH)2D or elevated PTH appear to be neither necessary nor relevant as determinants of osteopenia in the spine or femur in these normal, health

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071003

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

年代:1992

数据来源: WILEY

摘要:

AbstractAlthough much is known about the hormonal regulation of osteoblastic cell differentiation, much less is known about the nuclear regulatory molecules that affect this process. We analyzed the expression of several regulatory molecules of the helix‐loop‐helix (H‐L‐H) group in primary mouse calvarial cells and in MC3T3‐E1 mouse osteoblastic cells in situations representing different degrees of cellular differentiation. H‐L‐H class regulators are known to participate directly in directing cell fate and differentiation decisions in other mesodermal lineages. Two of the molecules that we studied, Id and E12, have well‐established roles in this process. The other, mTwi, the murine homolog of theDrosophila twistgene, is a newly cloned mammalian H‐L‐H gene. Levels of E12 RNA remained unchanged during differentiation. On the other hand, in both primary osteoblastic cells and MC3T3‐E1 cells, the abundance of Id and mTwi declined with cell maturation; mTwi less dramatically than Id. That Id expression is causally related to differentiation is suggested by the finding that MC3T3‐E1 cells transfected with an Id‐expression plasmid fail to undergo differentiation. We conclude that helix‐loop‐helix regulatory genes are expressed in mouse osteoblastic cells, where they are likely to participate in differentiation. The E12 gene product is likely to function as a positive modulating factor. In contrast, Id inhibits differentiation, probably by sequestering other H‐L‐H gene regulators, including E12, in inactive complexes. The precise role of mTwi is more speculative at this time, but the observed pattern of expression is consistent with a role in early and midmesodermal specification that is

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071004

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

年代:1992

数据来源: WILEY

摘要:

AbstractWe previously established that normal articular chondrocytes, like macrophages, express class II major histocompatibility antigens, present antigen, and induce mixed and autologous lymphocyte stimulation. In a recent study using the trapped indicator 2′,7′‐dichlorofluorescein diacetate, we were able to measure levels of intracellular hydrogen peroxide within normal articular chondrocytes (J Immunol 245:690–696, 1990). In the present study, we utilized the technique of chemiluminescence and the biochemical method of quantitating hydrogen peroxide release to measure the production of reactive oxygen intermediates by articular chondrocytes. Chondrocytes, in suspension or adherent to coverslips, showed luminol‐dependent chemiluminescence that was dependent on the number and viability of cells. There was a dose‐dependent increase in chemiluminescence in response to soluble stimuli, such as phorbol myristate acetate (PMA), concanavalin A (ConA), and f‐Met‐Leu‐Phe (FMLP). Azide inhibited chemiluminescence, suggesting that the light emission in chondrocytes is myeloperoxidase dependent. The antioxidant, catalase, inhibited chemiluminescence but superoxide dismutase had no effect, suggesting that luminol‐dependent chemiluminescence in chondrocytes mostly measured hydrogen peroxide. Chemiluminescence was also observed in fragments of live cartilage tissue, indicating that chondrocytes that are cartilage matrix bound can generate the respiratory burst response. Using the scopoletin oxidation assay, we confirmed the release of increasing amounts of hydrogen peroxide by chondrocytes exposed to interleukin‐1, rabbit interferon, and tumor necrosis factor α. Tumor necrosis factor α had both priming and enhancing effects on reactive oxygen intermediate production by chondrocytes. Reactive oxygen intermediates have been shown to play a significant role in matrix degradation. We suggest that reactive oxygen intermediates produced by chondrocytes play an important role in the degradation

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071005

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe present study was undertaken to clarify the relationship between c‐fosand c‐junprotooncogene expression and the differentiation and/or proliferation of osteoblasts, using osteoblast‐like MC3T3‐E1 (E1) cells. c‐fosmRNA was barely detectable, whereas c‐junmRNA was constitutively expressed in E1 cells after serum deprivation for 24–72 h. When serum was added, a rapid and transient induction of c‐fosand c‐junmRNAs was observed. The c‐fosand c‐junmRNAs reached peak levels at 30 minutes, with a rapid disappearance of c‐fosmRNA within 3 h and a much slower decrease in c‐junmRNA. The addition of serum together with cycloheximide, an inhibitor of protein synthesis, resulted in the superinduction of both c‐fosand c‐junmRNAs. Among various growth factors, PDGF, EGF, and bFGF mimicked the serum effect, whereas IGF‐I and TGF‐β failed to induce c‐fosand c‐junmRNA. The effects of PDGF, EGF, and bFGF were completely abolished by pretreatment with actinomycin D, an inhibitor of RNA synthesis, suggesting a transcriptional mechanism. Nuclear runoff experiments showed that the transcription rate of c‐fosand c‐junprotooncogenes was increased by serum and growth factors. The effects of PDGF, EGF, and bFGF were inhibited by H‐7 or staurosporine, inhibitors of protein kinase C (PKC), but not by HA1004 with a much weaker inhibitory activity, suggesting the involvement of PKC for the activation of the protooncogenes. PDGF, EGF, and bFGF, which induced the expression of c‐fosand c‐junprotooncogenes, stimulated the proliferation of E1 cells, whereas IGF‐I and TGF‐β, which failed to induce the expression of the protooncogenes, had no effect or an inhibitory effect on the proliferation of E1 cells, respectively. In addition, when the protooncogene induction was inhibited by H‐7, but not by HA1004, the proliferative responses to the growth factors were also completely abolished. Although E1 cells are known to develop osteoblastic phenotypes during prolonged culture period, the expression of c‐fosand c‐junmRNAs was not altered during 2–28 days of culture at various stages of differentiation. These results suggest that the expression of c‐fosand c‐junprotooncogenes may play a role as an immediate early event in the

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071006

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

年代:1992

数据来源: WILEY

摘要:

AbstractProstaglandin E2is produced by bone cells and increases cyclic AMP in these cells. Like PTH and dibutyryl cyclic AMP, PGE2is a potent stimulator of IGF‐I synthesis in cultured rat osteoblasts and inhibits DNA synthesis and type I procollagen gene expression. In addition, PGE2inhibits the response of the cells toward IGF‐I after 1 day but not after 4 days of incubation. Rat calvaria osteoblasts constitutively release IGFBPsinto the culture medium, in particular IGFBP‐2 and IGFBP‐3. Like growth hormone, PGE2stimulates the accumulation of IGFBP‐3. PGE2rapidly increases IGF‐I and IGFBP‐3 mRNA expression in calvaria cells, with a time course clearly different from that observed in response to growth hormone. Thus, PGE2modifies not only the synthesis of IGF‐I but also that of IGFBP‐3 i

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071007

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

年代:1992

数据来源: WILEY

摘要:

AbstractDespite radiographic and histologic evidence of trabecular bone density changes within and adjacent to osseous metastases, there currently exist no data to demonstrate whether these changes are important in predicting the risk of fracture. To determine if these density changes result in significant reductions in mechanical properties, trabecular bone specimens were prepared from lower thoracic and lumbar vertebrae from two cadavers with radiographic, gross, and histologic evidence of lytic and/or blastic osseous metastases. Each specimen was classified as normal, lytic, or blastic based on appearance in fine‐grain radiographs of 8–9 mm thick coronal plane sections. Specimens were tested to failure in uniaxial compression, and tissue and apparent densities were measured. Mean tissue densities were within normal ranges. The mean apparent density for all specimens combined was within the normal range for human vertebrae, and the mean apparent density for radiographically normal (0.131 g/ml) and lytic (0.111 g/ml) specimens was less than the mean apparent density of blastic (0.182 g/ml) specimens (p<0.02). The moduli of lytic and blastic specimens were less than for normal specimens (p0.1). Apparent density explained significant fractions of the variations in both modulus (p<0.001) and strength (p<0.001). The data suggest that blastic changes associated with osseous metastases to trabecular bone disrupt the normal dependence of trabecular mechanical properties on apparent density, but lytic changes do not. These data also suggest that fracture risk predictors that utilize bone density to estimate stiffness or strength should adjust for the effects of metasta

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071008

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

年代:1992

数据来源: WILEY

摘要:

AbstractDiffusion chambers with rat bone marrow cells and demineralized bone matrix (DBM) were implanted subcutaneously to syngeneic 8‐week‐old rats and were harvested every week 3–7 weeks after implantation, and histochemical examination, determination of alkaline phosphatase activity, total calcium and phosphorus, the bone‐specific vitamin K‐dependent gla‐containing protein (BGP) content, and detection of BGP mRNA relative to mineralization were performed. Alkaline phosphatase in diffusion chamber implants reached the highest activity at 4 weeks and then decreased. Calcium and phosphorus deposits occurred at 4 weeks after implantation and were followed by marked increases until 7 weeks, which was comparable to the accumulation of BGP. The BGP gene within the diffusion chambers began to be expressed at 5 weeks, and its expression increased markedly at 7 weeks after implantation. At 4–5 weeks after implantation, new bone adjacent to the membrane filters and cartilage toward the center of the diffusion chamber were observed histochemically. Light microscopic and immunohistologic examinations of chambers with marrow cells and DBM revealed production of mineralized matrices, typical of bone characterized by the appearance of BGP and mineralized nodules. In contrast, bone marrow cells alone did not show extensive bone formation and yielded very low values for these biochemical parameters. The present experiments demonstrate the potential of bone marrow cells and DBM to produce not only cartilage formation but also membranous bone formation associated with increasing expression of BGP mRNA during the later stages of bone formation, as well as a marked accumu

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071009

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe disparity in fracture incidence and bone mass in women of European (white) and African (black) ancestry is of unknown etiology. To determine if racial differences in bone mass reflected racial differences in the mechanisms of bone turnover underlying bone mineral loss, we measured serum osteocalcin, serum alkaline phosphatase, fasting urinary calcium and hydroxyproline excretion, 24 h urinary excretion of calcium and sodium, and dietary intakes of calcium and vitamin D in 263 healthy pre‐, peri‐, and postmenopausal white and black women. In addition, radial and spinal bone density were measured cross‐sectionally for comparison with biochemical measures of bone turnover. The biochemical parameters thought to reflect bone resorption (fasting urinary calcium and hydroxyproline excretions) were lower in black than in white women throughout the age and menopausal stages studied. The parameters thought to reflect bone formation (alkaline phosphatase and osteocalcin), were similar in the two racial groups among the premenopausal women, but osteocalcin was significantly lower among the peri‐ and postmenopausal blacks. Cross sectionally measured radial bone density increased with age in premenopausal black women, but it did not change with age in the white premenopausal subjects, a statistically significant difference. In peri‐ and postmenopausal women radial density declined significantly with years after menopause in both racial groups, but the rate of decline was significantly slower in the black women. Lumbar bone density in premenopausal white and black women did not change with age. After menopause lumbar bone density declined significantly and similarly in both racial groups. The biochemical findings and the densitometric data at the radial site are consistent, both suggesting lower bone resorption and lower rates of cortical bone loss in pre‐ and postmenopausal black women than in whites. Together these findings indicate that racial differences in bone density result, at least in part, from measurable racial differences in bone homeostasis and support the hypothesis of a more positive bone balance in both pre‐ and postmenopausa

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071010

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

年代:1992

数据来源: WILEY

摘要:

AbstractCyclosporine A (CsA) administered to the male and female rat produces high‐turnover osteopenia. Prostaglandins have both bone‐resorbing and bone‐forming properties, but administration of prostaglandin E2(PGE2) to the rat in vivo produces a net increase in cancellous bone. To investigate the effects of PGE2on CsA‐induced alteration in bone mass, 43 male Sprague‐Dawley rats (9 weeks old) were administered 15 mg/kg of CsA by oral gavage and/or 6 mg/kg of PGE2by subcutaneous injection daily for 21 days according to the following protocol: group A was an age‐matched control; group B received CsA only; group C received PGE2only; and group D received CsA and PGE2. Serum was assayed on days 0, 7, 14, and 21 for bone gla protein (BGP), PTH, and 1,25‐dihydroxyvitamin D [1,25‐(OH)2D]. A computerized image analysis system was used for bone histomorphometry of the proximal tibial metaphysis after double tetracycline labeling. Compared to control animals (group A), treatment with CsA alone (group B) and PGE2alone (group C) significantly elevated BGP levels. Combination therapy (group D) resulted in BGP levels that were significantly higher on days 7 and 14 than with either agent alone. 1,25‐(OH)2D was significantly elevated in the CsA group only (group B). Therapy with CsA alone (group B) resulted in a significant osteopenia. The concurrent administration of PGE2with CsA (group D) alleviated the altered bone mass induced by CsA alone by adding a significant amount of additional bone. This report confirms and extends the current knowledge of the different effects of CsA and PGE2on bone mineral metabolism and demonstrates that PGE2can alleviate the deleterious effec

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071011

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

年代:1992

数据来源: WILEY