ISSN:0884-0431    

DOI:10.1002/jbmr.5650100802

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe 25(OH)D3/1,25(OH)2D324‐hydroxylase (24‐hydroxylase) displays an induction profile responsive to vitamin D (D) abundance and is hence only observed in normal extracellular Ca2+concentrations. However, the participation of Ca2+in the expression of the 24‐hydroxylase gene in vivo is not known. The present studies investigate the role played by the circulating Ca2+and the D3and/or 1,25(OH)2D3status on the 1,25(OH)2D3‐mediated inducibility of the 24‐hydroxylase gene in rat duodenum. Hypocalcemic D‐depleted rats were supplemented with calcium alone to normalize serum Ca2+without normalizing the D3status or were acutely or chronically supplemented with D3or 1,25(OH)2D3. Messenger RNA for the 24‐hydroxylase was undetectable in the intestine of hypocalcemic D‐depleted rats, and short‐ or long‐term calcium supplementation was completely unsuccessful in inducing its expression. By contrast, acute 1,25(OH)2D3administration led to significant increases in the levels of expression of the gene which was independent of the calcium intake, the prevailing circulating Ca2+, and the D3or 1,25(OH)2D3status. Moreover, 24‐hydroxylase gene expression was only found to respond to acutely administered 1,25(OH)2D3, the mRNA levels being unaltered following continuous exposure to physiological or pharmacological doses of the hormone for 7 days. Time‐course studies revealed, however, that induction of the gene was clearly apparent early in the 1,25(OH)2D3supplementation course but gradually faded by 3 days to return to basal uninduced levels by 7 days, suggesting the presence of intestinal adaptation mechanism(s) which down‐regulated the responsiveness in the continuous presence of 1,25(OH)2D3. Our data show the lack of effect of calcium alone or in combination with 1,25(OH)2D3on the in vivo induction of the 24‐hydroxylase gene expression in rat intestine. By rapidly reacting to surges in 1,25(OH)2D3concentrations, the 24‐hydroxylase efficiently controls the amount of 1,25(OH)2D3in intestine as the first step in the biotransformation pathway aimed at the irreversible clearance of the secosteroid hormone. (J Bon

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100803

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

年代:1995

数据来源: WILEY

摘要:

AbstractOsteoclasts are multinucleated cells specific to bone tissue and of hemopoietic origin. They are formed by fusion of mononucleated cells in a manner related to the formation of macrophage polykarions. Subcutaneous implantation of mineralized bone particles induces multinucleated giant cell recruitment. There is controversy, however, about the nature of these cells. Although subcutaneous implantation of bone particles derived from warfarin‐treated animals has been applied as an in vivo model to study the role of osteocalcin in bone resorption, the exact nature of multinucleated cells elicited in this model is still unclear. In this paper, subcutaneous implants of bone particles from normal and warfarin‐treated rats were implanted in Sprague‐Dawley rats. Resorption was assessed in 12 and 16 day implants by chemical analysis (calcium content) and by histomorphometric measurement of the bone particle area and the number of multinucleated and tartrate‐resistant acid phosphatase‐positive cells. No significant difference in calcium content and bone area were observed, after 12 or after 16 days of implantation, between implants from normal and warfarin‐treated rats. The number of tartrate‐resistant acid phosphatase‐positive cells elicited by bone particles represented less than 25% of the number of multinucleated cells and did not differ between bone particles from normal and warfarin‐treated rats. By electron microscopy, a majority of multinucleated cells did not show a ruffled border in contact with bone particles, and their morphological features were suggestive of a foreign body giant cell reaction. In our experience this model appears to elicit only a few osteoclasts among multinucleated macrophagic cells and may not be the most appropriate one for the study of resorption of normal or osteocal

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100804

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

年代:1995

数据来源: WILEY

摘要:

AbstractLoss of skeletal weight bearing or physical unloading of bone in the growing animal inhibits bone formation and induces a bone mineral deficit. To determine whether the inhibition of bone formation induced by skeletal unloading in the growing animal is a consequence of diminished sensitivity to growth hormone (GH) we studied the effects of skeletal unloading in young hypophysectomized rats treated with GH (0, 50, 500 μg/100 g body weight/day). Skeletal unloading reduced serum osteocalcin, impaired uptake of3H‐proline into bone, decreased proximal tibial mass, and diminished periosteal bone formation at the tibiofibular junction. When compared with animals receiving excipient alone, GH administration increased bone mass in all animals. The responses in serum osteocalcin, uptake of3H‐proline and45Ca into the proximal tibia, and proximal tibial mass in non‐weight bearing animals were equal to those in weight bearing animals. The responses in trabecular bone volume in the proximal tibia and bone formation at the tibiofibular junction to GH, however, were reduced significantly by skeletal unloading. Bone unloading prevented completely the increase in metaphyseal trabecular bone normally induced by GH and severely dampened the stimulatory effect (158% vs. 313%,p<0.002) of GH on periosteal bone formation. These results suggest that while GH can stimulate the overall accumulation of bone mineral in both weight bearing and non‐weight bearing animals, skeletal unloading selectively impairs the response of trabecular bone and periosteal bone formation to the anabolic actio

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100805

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

年代:1995

数据来源: WILEY

摘要:

AbstractTo examine the relation of the vitamin D status and the remaining estrogen activity with bone turnover and bone mineral density (BMD) in elderly women, BMD was measured at both hips using dual‐energy X‐ray absorptiometry and at the distal radius using single photon absorptiometry, in 330 healthy women aged 70 and over. Vitamin D metabolites, sex hormone binding globulin (SHBG), PTH(1–84), osteocalcin, alkaline phosphatase, and hydroxyproline and calcium excretion in 2 h fasting urine were measured. Multiple linear regression was used to adjust for potential confounders. In 65% of the women, serum 25(OH)D was below 30 nmol/l. Only values below a threshold for 25(OH)D were negatively related to serum PTH(1–84) (p= 0.02, threshold at 25 nmol/l) and to osteocalcin levels (p= 0.04, threshold at 30 nmol/l). BMD of the femoral neck and trochanter was positively related to serum 25(OH)D (left neckp= 0.001) with thresholds at 30 nmol/l whereas the distal radius was not (p= 0.32). Serum PTH was negatively related to BMD at all measurement sites (allp<0.001). Serum SHBG, an inverse measure of estrogen activity, was positively related to osteocalcin levels (p= 0.004) and the urinary hydroxyproline/creatinine ratio (p= 0.002) and negatively related to the BMD of the trochanter (left trochanterp= 0.02) and the distal radius (p= 0.001). We conclude that in elderly women, serum 25(OH)D levels below 30 nmol/l are associated with secondary hyperparathyroidism and increased bone turnover. SHBG is positively related to bone turnover. Vitamin D deficiency especially influences BMD of the femoral neck, a cortical area. SHBG mainly influences BMD at the trochanteric region and distal radius, predominantly trabecular areas, which may reflect the effects of remaining estrogen a

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100806

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

年代:1995

数据来源: WILEY

摘要:

AbstractRecent evidence indicates that phosphatidylcholine breakdown by phospholipase D (PLD) is an important cellular control mechanism. We investigated the signaling pathway participating in prostaglandin E2(PGE2)–induced PLD activation in osteoblast‐like MC3T3‐E1 cells. PGE2stimulated PLD activity, as measured by choline generated from phosphatidylcholine, just after the stimulation. The reaction reached a plateau 15 minutes later. PGE2stimulated PLD activity in a dose‐related manner and also increased inositol phosphate (IP) formation. However, the EC50value for PGE2‐induced IP formation is lower than that for PLD activation. 12‐O‐Tetradecanoylphorbol‐13‐acetate (TPA), a protein kinase C (PKC) activator, stimulated PLD activity, and a combination of PGE2and TPA potentiated it in an additive manner. Although NaF, a heterotrimeric GTP‐binding protein activator, significantly stimulated PLD activity, this effect was not augmented by combination with PGE2. PGE2‐induced PLD activity was markedly suppressed by either chelating extracellular Ca2+by EGTA or pertussis toxin. These findings suggest that osteoblasts might have at least two PLD activation mechanisms which involve PKC‐dependent or ‐independent pathways. However, present results indicate that PKC is unlikely to be essential to PGE2‐induced PLD activation. On the contrary, pertussis toxin‐sensitive GTP‐binding protein and extracellular Ca2+might play important roles in the pathway

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100807

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

年代:1995

数据来源: WILEY

摘要:

AbstractBisphosphonates are used increasingly in normocalcemic patients for treating tumor‐induced osteolysis (TIO) but little is known about the metabolic effects and the most appropriate therapeutic regimen. In 21 patients with breast cancer and TIO, we determined the biochemical effects of a single infusion of pamidronate given at 30 mg (n= 5), 60 mg (n= 5), 90 mg (n= 5), or 120 mg (n= 6). Patients received no other systemic antineoplastic therapy during the trial. We selected patients with baseline fasting urinary Ca/Creat (creatinine)>0.105 mg/mg (median value of our normal range) and they were followed weekly for up to 14 weeks. The biochemical effects were maximal at day 7. For the whole group, mean (± SEM) Ca/Creat levels fell from 0.208 ± 0.018 to 0.048 ± 0.008 mg/mg on day 7 and remained significantly (p<0.01) lower than baseline up to day 56. Hydroxyproline excretion fell to a lesser degree, from 7.0 ± 1.2 to 4.0 ± 0.6 mg × 100/mg of Creat. The falls in Ca/Creat and hydroxyproline excretion were dose‐related (ANCOVA,p<0.05). Changes in serum parameters of calcium metabolism were, however, not significantly dose‐related. Serum Ca levels fell from 9.3 ± 0.1 to 8.7 ± 0.1 mg/dl on day 7, but no patients developed symptomatic hypocalcemia, and the decrease within each dose group was significant only at 120 mg. Ca2+levels followed a similar pattern. There was a slight increase in Mg levels and a pronounced fall in Pilevels, from 3.6 ± 0.2 to 2.8 ± 0.1 mg/dl. Intact PTH levels increased from 29 ± 4 to 91 ± 13 pg/ml and remained significantly (p<0.05) elevated up to day 28. The concentration of 1,25(OH)2vitamin D increased from 20 ± 2 to 45 ± 4 pg/ml, but the osteocalcin concentration did not change significantly. We subsequently treated 11 cancer patients with bone metastases and low urinary Ca/Creat levels (<0.105 mg/mg) with 30 or 60 mg of pamidronate. The changes in biochemical parameters of bone metabolism were similar to those described above, confirming the safety of these doses of pamidronate in patients without evidence of increased bone resorption. In summary, single pamidronate infusions, given at doses from 30 to 120 mg, dose‐dependently inhibited bone resorption in patients with bone metastases. Pamidronate also induced marked but transient changes in blood parameters of calcium metabolism, especially at a dose of 120 mg. Our data suggest that 90 mg of pamidronate is adequate to inhibit bone resorption in th

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100808

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

年代:1995

数据来源: WILEY

摘要:

AbstractA gene encoding a possible novel human cathepsin, a cysteine proteinase that is distinct from previously characterized enzymes, has been identified by differential screening of a human osteoclastoma cDNA library. This molecule, termed cathepsin X, appears to represent the human homolog of the osteoclast‐expressed rabbit cathepsin OC‐2. Cathepsin X (GenBank accession number U20280) is 93.9% identical to OC‐2 at the amino acid level, and is 92% identical at the nucleotide level within the coding region. Cathepsin X is 52.2 and 46.9% identical to cathepsins S and L, respectively, and is therefore clearly distinct from these enzymes. Cathepsin X mRNA was localized to multinucleated giant cells within the osteoclastoma tumor by in situ hybridization. These data strongly support the hypothesis that cathepsin X represents a novel cysteine proteinase which is expressed at high levels in osteoc

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100809

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

年代:1995

数据来源: WILEY

摘要:

AbstractROB‐C26 (C26) is a multipotential, clonal cell line known to express several members of the TGF‐β superfamily and to become more osteoblastic (e.g., express higher levels of alkaline phosphatase) upon treatment with 10−6M retinoic acid (RA). We hypothesize that the expression of this more osteoblastic phenotype subsequent to RA exposure is the result of the treated cell's extracellular matrix (ECM) becoming a repository and active source of putative osteoinductive growth factors including, specifically, select members of the TGF‐β superfamily. To test this hypothesis, we isolated the ECM from RA‐treated and untreated C26 cells and assessed them for their ability to promote osteogenic differentiation in vivo and in vitro. We then explored whether the latter activities could be attributed specifically to TGF‐β1. We found that the ECM of treated cells isolated by cell lysis and extensive washing induced endochondral bone formation in vivo when implanted into the thigh muscles of athymic nude mice and stimulated alkaline phosphatase (ALP) activity in vitro in freshly plated C26 cells. This latter stimulation was comparable to levels observed with direct RA treatment. This latter in vitro activity was only very partially mimicked by the ECM prepared from untreated cells and not duplicated at all by RA‐treated collagen or the ECM from another RA‐treated multipotential cell line. Moreover, the in vivo osteoinductive effect of the treated C26 cell ECM was not duplicated by comparable ECM prepared from untreated cells. Finally, we also found that preincubation of the ECM with specific, neutralizing antibodies to either TGF‐β's 1, 2, and 3 or TGF‐β1 alone substantially reduced the ability of the ECM to stimulate ALP activity. This inhibitory effect was not seen using nonspecific IgG. These data identify the C26 cell line as a valuable model system for exploring cell‐matrix interaction in osteogenic differentiation, provide direct support for an autocrine role of the ECM in such differentiation, and suggest that TGF‐β1 is an important ECM‐based mediator in the regulat

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100810

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the rat tibial bone marrow cavity, following colchicine injection, there is a phase of osteogenesis in which bone trabeculae replace the necrotic bone marrow tissues and fill the marrow cavity. The newly formed bone is subsequently resorbed by osteoclasts and normal bone marrow is restored. In this study, we correlated these morphologic events with the pattern of gene expression of bone sialoprotein (BSP), an extracellular matrix protein in mineralized tissues, to elucidate the possible functions of BSP in bone formation and resorption in vivo. The expressions of osteopontin (OPN) and type I collagen were also examined. Northern hybridization of the tibia demonstrated that OPN mRNA was gradually increased and expressed at a maximal level 10 days after colchicine injection (during the bone resorption process), while BSP mRNA expression already reached a maximal level at day 6 (during the initial process of bone formation). Its expression was, thus, quite temporary at the beginning of bone formation and different from that of type I collagen, which was continually elevated from days 6 to 10. In situ hybridization of the newly formed bone induced in the tibia revealed that BSP mRNA was evenly expressed in most osteoblasts and osteocytes, moreover in interconnecting colonies of spindle‐shaped cells, possibly preosteoblasts, at day 6. At day 10, however, its expression became restricted to some cells on the bone surfaces, some osteoblasts, and most osteoclasts. These observations suggest that BSP may play an important role mainly in the initiation of bone formation and is also associated with the functions of osteoclast in viv

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100811

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

年代:1995

数据来源: WILEY