ISSN:0884-0431    

DOI:10.1002/jbmr.5650110502

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

年代:1996

数据来源: WILEY

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110503

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

年代:1996

数据来源: WILEY

摘要:

AbstractOsteoblasts arise from partially differentiated osteogenic progenitor cells (OPCs) which in turn arise from undifferentiated marrow stromal mesenchymal stem cells (MSCs). It has been postulated that age‐related defects in osteoblast number and function may be due to quantitative and qualitative stem cell defects. To examine this possibility, we compared osteogenic stem cell number and in vitro function in marrow cells from 4‐month‐old and 24‐month‐old male BALB/c mice. Histologic studies demonstrated that these mice undergo age‐related bone loss resembling that seen in humans. In primary MSC cultures grown in media supplemented with 10 nM dexamethasone, cultures from older animals yielded an average of 41% fewer OPC colonies per given number of marrow cells plated (p<0.001). This implies that for a given number of marrow cells there are fewer stem cells with osteogenic potential in older animals than there are in younger animals. The basal proliferative rate in cultures from older animals, as measured by3H‐thymidine uptake, was more than three times that observed in cultures from young animals (p<0.005). However, the increase in proliferative response to serum stimulation was 10‐fold in the younger cultures (p<0.001) and insignificant (p<0.4) in the older cultures. Colonies in both age groups became alkaline phosphatase positive at the same rate, and virtually all colonies were positive after 12 days of culture. Cultures from both age groups produced abundant type I collagen. These studies suggest that defects in the number and proliferative potential of MSCs may underlie age‐related defects in osteoblast nu

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110504

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

年代:1996

数据来源: WILEY

摘要:

AbstractActivation of the G protein–coupled receptor for parathyroid hormone (PTH)/PTH‐related protein (PTHrP) produces homologous desensitization of receptor signaling. We have shown recently that the opossum PTH/PTHrP receptor stably expressed in human embryonic kidney (HEK) 293 cells is phosphorylated upon agonist binding and upon activation of serine/threonine protein kinases (PKA and PKC), an event which for some G protein‐coupled receptors has been linked to desensitization. To locate the sites of phosphorylation, mutated forms of the opossum PTH/PTHrP receptor were stably expressed in HEK 293 cells, and ligand‐stimulated receptor phosphorylation was evaluated. The five serine and threonine residues of the third cytoplasmic loop of the receptor were not required for receptor phosphorylation. Basal and ligand‐induced phosphorylation were, however, completely abolished upon deletion of all but the 16 juxtamembrane residues of the cytoplasmic C‐terminal tail of the receptor, even though this truncated receptor resembled the wild‐type receptor in its level of expression based on Western blotting and radioligand binding. To identify further the phosphorylation sites, the 129 amino acid C‐terminal tail of the rat PTH/PTHrP receptor was expressed inE. colias a recombinant glutathione S‐transferase fusion protein. Elimination of a single PKA consensus site in the tail (serine 491) resulted in ≥90% loss of PKA‐mediated phosphorylation, identifying this as the preferential site for PKA, with two other sites (serine 473 and/or 475) being minor sites. Phosphorylation by PKC occurred largely in the proximal portion of the tail, whereas β‐adrenergic receptor kinase 1 (βARK1) phosphorylated more distally in the tail. The ability of these kinases to phosphorylate the PTH/PTHrP receptor at distinct sites on the cytoplasmic tail may allow differential regulation of receptor

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110505

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

年代:1996

数据来源: WILEY

摘要:

AbstractBisphosphonates (BPs) are used for the treatment of both benign and malignant diseases characterized by increased bone resorption. Because of their potential nephrotoxicity, currently available BPs have to be administered by slow intravenous infusion, with conventional doses requiring an infusion time of at least 2 h. In the present investigation, we evaluated the safety and efficacy of the new BP ibandronate as administered by intravenous bolus injection. On day 0, 15 normocalcemic breast cancer patients with bone metastases were treated with 3 mg of ibandronate injected intravenously over 60–120 s. Ibandronate treatment led to significant decreases in serum levels of calcium (p<0.0001) and phosphate (p<0.0001) and to subsequent increases in serum concentrations of parathyroid hormone (p<0.0001) and calcitriol (p<0.0001). Moreover, there was a significant reduction in the urinary excretion of calcium (p<0.0001), pyridinoline (p<0.001), and deoxypyridinoline (p<0.0001). Three serious adverse events were observed: vomiting (WHO grade 3), pulmonary infection (WHO grade 2), and deterioration of a pre‐existing impaired glucose tolerance (WHO grade 3). Only vomiting appeared to be related to administration of the drug. The most frequent nonserious adverse events were 10 cases of transient clinically asymptomatic hypocalcemia and 8 cases of asymptomatic hypophosphatemia. Serum levels of creatinine and urea nitrogen did not increase, nor did creatinine clearance deteriorate. When tested with the dipstick method, proteinuria was present in five (33%) patients prior to ibandronate treatment (median protein concentration, 30 mg/dl). Following the BP injection, seven (47%) patients showed slight (highest protein concentration, 30 mg/dl) transient proteinuria at at least one time point, of which six cases appeared in conjunction with leucocyturia and three with microhematuria. Side effects specific to aminosubstituted BPs (fever, reduction in white blood cell counts, and lymphocyte counts) were not seen in these 15 patients. In conclusion, a single intravenous injection of 3 mg of ibandronate significantly inhibited osteoclast activity as reflected by the decrease in serum calcium and in urinary parameters of bone resorption. Serum creatinine levels and estimates of creatinine clearance were not affected by therapy. However, before repeated bolus injections of ibandronate at this dosage can be recommended for further clinical trials, whether a relationship exists between the transient pathological urinary findings and injected ibandronate needs to be determi

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110506

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe sensitivity of bone mineral density (BMD) as a predictor of fracture risk is limited by the fact that this index does not take into account the geometrical and material characteristics of bone. In contrast, both BMD and bone architecture influence the quality factor (QF), the fraction of the inverse of the energy lost in one cycle of deformation. In this study we have compared the sensitivity of a QF analyzer and dual‐energy X‐ray absorptiometry (DXA) in detecting the changes induced by ovariectomy (OVX) on the QF, impact strength, and BMD of the femur of mature rats. QF and BMD were measured noninvasively before and 4 weeks after OVX or sham operation using a QF analyzer developed in our laboratory and a Hologic QDR 2000 bone densitometry, respectively. Impact strength was measured in excised femurs at the end of the study. The in vivo short‐term precision (coefficient of variation) of the QF analyzer was 1.9%. BMD and QF measurements were highly correlated (r= 0.80,p<0.0001). At baseline, QF and BMD were similar in OVX and sham‐operated rats. At 4 weeks, BMD was 14.7 + 0.9% lower than at baseline (p<0.001) in OVX rats and 5.3 + 1.3% lower in sham‐operated rats (p<0.05). QF decreased 36.0 + 2.8% (p<0.0001) in OVX and 10.6 + 3.6% in sham rats (p<0.01). As a result, at 4 weeks the difference between sham‐operated and OVX rats was larger (p<0.05) by QF than by BMD. Moreover, QF correlated better than BMD with impact strength and the difference in impact strength between sham and OVX mice was closer to that in QF than that in BMD. These data demonstrate that QF analysis is a precise technique that is more sensitive than DXA in detecting the changes in bone density and strength induced by OVX. QF analysis may represent a new, simple, and economic technique for predicting fr

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110507

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

年代:1996

数据来源: WILEY

摘要:

AbstractTherapies utilizing intermittent human parathyroid hormone(1–34) (hPTH[1–34]) in combination with other agents have recently been proposed as possible anabolic regimens for the treatment of osteoporosis. We conducted a 24 week study in aged beagle dogs to determine the effects of intermittent hPTH(1–34) administered alone or in combination with 1,25‐dihydroxyvitamin D3(1,25(OH)2D3) on the endosteal remodeling in cancellous and cortical bone. Additionally, we tested the interaction between hPTH(1–34) and a new potent bisphosphonate, risedronate. The three treatment groups were compared with a vehicle control group. Kinetic reconstruction of the remodeling unit revealed substantial differences between the groups in resorption and formation at the basic multicellular unit level. Although the estimates of final erosion depth were unaffected by treatment, tunneling resorption was noted in six of the eight dogs administered hPTH(1–34) alone. These qualitative morphological changes in the resorption lacunae were attenuated or absent in dogs administered hPTH(1–34) in combination with either 1,25(OH)2D3or risedronate. Functional periods for resorption were significantly increased, and the resorption rates were significantly decreased in the hPTH(1–34) + risedronate group. Analyses of the formative site demonstrated that the wall thickness was significantly increased and the bone balance significantly more positive in all three hPTH(1–34) treatment groups. The most positive bone balance was achieved in the combined hPTH(1–34) + risedronate group (+15.6 + 14.2 mm,p<0.05). Increases in the mineral apposition rate in the early phases of the formative period suggest that an increase in osteoblastic activity (number or function) may contribute to the increase in wall thickness. Treatment with hPTH(1–34) alone or in combination with 1,25(OH)2D3caused an approximately 2‐fold increase in the activation frequency in cancellous bone, which was essentially normalized to control values by the coadministration of risedronate. The impact of these changes on the cancellous bone microstructure was significant only in the combined hPTH(1–34) + risedronate group where normalized bone turnover in the face of a positive bone balance effected a significant increase in the trabecular thickness. Analyses of sequential fluorochrome labels, administered to reconstruct the temporal changes in intracortical activation, demonstrated the presence of an apparent cyclic pattern of activation in the cortex of placebo‐treated dogs. Generally, activation was increased throughout the study in dogs administered hPTH(1–34) alone or in combination. However, in the hPTH(1–34) + risedronate group, activation was significantly blunted toward the end of the study, and the cyclic pattern of activation was modulated. These data suggest that intermittent hPTH(1–34) in combination with risedronate may be superior to hPTH(1–34) in combination with 1,25(OH)2D3as a therapeutic regimen for osteoporosis due to the protective effect of this bisphosphonate on the

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110508

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

年代:1996

数据来源: WILEY

摘要:

AbstractIntermittent parathyroid hormone (PTH) therapy increases bone mass. The purpose of this study was to determine if analogs of human PTH(1–34) (hPTH[1–34]), which differ from the native sequence in their receptor‐activating properties, could promote bone formation in an ovariectomized (OVX) osteopenic rat model. We synthesized two hPTH(1–34) analogs with single substitutions for serine in the 3‐position that in vitro are partial agonists in kidney. In the renal cell line OK, maximal cyclic adenosine monophosphate (cAMP) activation by [His3]hPTH(1–34) was 50%, and maximal cAMP activation by [Leu3]hPTH(1–34) was 20% of that produced by hPTH(1–34). Both analogs were full agonists in UMR‐106 rat osteosarcoma cells and other bone‐derived systems, but both had reduced potency compared with hPTH(1–34). Six‐month‐old retired breeder Sprague‐Dawley rats were ovariectomized, and five animals underwent sham operation. On day 56 post‐OVX, five sham‐operated and five pre‐PTH treatment OVX animals were sacrificed, and the remaining animals were randomized into 10 groups of six animals each. All other animals were injected with one of the hPTH analogs or hPTH(1–34) at 0,4,40, or 400 μg/kg of body weight (BW)/day and were killed on day 84. Histomorphometry of the proximal tibia metaphysis and biochemical markers of bone turnover (osteocalcin and pyridinoline cross‐links) were the primary endpoints. The cancellous bone volume was significantly lower at day 56 post‐OVX (pretreatment) and at day 84 post‐OVX (post‐vehicle treatment) than at baseline. None of the compounds significantly increased the cancellous bone volume. Trabecular number declined after OVX and did not change with hPTH treatment. In contrast, the trabecular thickness declined after OVX but was higher after treatment with 40 μg/kg of BW/day or 400 μg/kg of BW/day of hPTH(1–34). In OVX rats, the mineralizing surface was higher than baseline at day 56 and fell toward control levels by day 84. All three peptides produced marked dose‐related increases in the mineralizing surface and bone formation rates, but the two analogs were less potent than hPTH(1–34). Likewise, all peptides produced significant dose‐related increases in the serum osteocalcin level. The osteoclast surface was not affected by OVX but was decreased with medium and high doses of hPTH(1–34). Pyridinoline cross‐link excretion was not significantly affected by treatment with hPTH(1–34) but responded with a dose‐dependent decrease to treatment with [His3]hPTH(1–34). These data suggest that bone selective analogs of hPTH(1–34) maintain the ab

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110509

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

年代:1996

数据来源: WILEY

摘要:

AbstractDual X‐ray absorptiometry (DXA) is widely used to monitor treatment efficacy in reducing the rate of bone mineral loss. In order to assure the validity of these measurements, instrument quality control of the DXA scanners becomes very important. This paper compares five quality control procedures (visual inspection, Shewhart chart with sensitizing rules, Shewhart chart with sensitizing rules and a filter for clinically insignificant mean changes, moving average chart and standard deviation, and cumulative sum chart [CUSUM]) in their ability to identify scanner malfunction by means of (1) an analysis of five longitudinal phantom data sets that had been collected during a clinical trial and (2) an analysis of simulated data sets. The visual inspection method is relatively subjective and depends on the operator's experience and attention. The regular Shewhart chart with sensitizing rules has a high false alarm rate. The Shewhart chart with sensitizing rules and an additional filter for clinically insignificant mean changes has the lowest false alarm rate but a relatively low sensitivity. The CUSUM method has good sensitivity and a low false alarm rate. In addition, this method provides an estimate of the date a change in the DXA scanner performance might have occurred. The method combining a moving average chart and a moving standard deviation chart came closest to the performance of the CUSUM method. Comparing the advantages and disadvantages of all methods, we propose the use of the CUSUM method as a quality control procedure for monitoring DXA scanner performance. For clinical trials use of the more intuitive Shewhart charts may be acceptable at the individual sites provided their scanner performance is followed up by CUSUM analysis at a central quality assurance cente

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110510

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn fundamental osteoporosis research precise and accurate assessment of the mineral quantity in histological bone sections is of particular importance when studying the local effects of implants releasing bone modulating agents. A potentially useful technique to estimate the bone mineral density (BMD) is dual‐energy X‐ray absorptiometry (DXA). A highly collimated (0.13 mm) Hologic 2000 with a line spacing and point resolution of 0.13 mm was used. The mineral content was measured in regions of 3.1 mm2. A ceramic hydroxyapatite (CHA) phantom was developed as a reference standard. The phantom was made of a single‐phase hydroxyapatite starting powder by compressing and sintering at 1000°C. The true density was 3.14 + 0.001 g/cm3. The calcium/phosphorus ratio was close to the theoretical one of 1.67. The mean precision error expressed as the coefficient of variation (CV) of the mineral density (MD) measurements of the phantoms with thicknesses of 1, 2, and 3 mm was 0.2%. Embedded undecalcified alveolar bone sections of dogs (0.0015‐1 mm in thickness) were scanned simultaneously with a phantom 1 mm in thickness. The precision error (CV) of the BMD measurements calculated by DXA for sections ≥0.1 mm and with a BMD ≥0.14 g/cm2was 0.81%. There was a linear relationship between the BMD calculated by DXA and the estimated BMD in the histological bone sections by means of the true density of the phantom. It is concluded that DXA using a standard CHA phantom is a precise and accurate method to measure MD changes as small as 1% in histological bone areas of 3.1 mm2provided that the loss or gain in BMD is

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110511

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

年代:1996

数据来源: WILEY