ISSN:0884-0431    

DOI:10.1002/jbmr.5650060202

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

年代:1991

数据来源: WILEY

摘要:

AbstractSerum osteocalcin was remarkably and significantly (‐34 and −41% in two separate experiments;p<0.001) lower in rats fed an 8% (w/v) ethanol liquid diet (ELD) for 1 week than in rats fed an isocaloric control liquid diet (CLD). In a longer experiment that spanned 4 weeks, the ELD rats were given 6% ethanol on day 4, increased stepwise to 8% by day 9, and then maintained at 8% until day 28, when the experiment was terminated. Again, serum osteocalcin was much lower (‐32%,p<0.001) in the ELD‐fed rats than in CLD‐fed rats. Even in rats fed only a 6% ELD for 12 days, serum osteocalcin was lower (‐33%,p<0.001) than in controls. Also, the femora were weaker, more compliant, and more ductile in ELD‐ than in CLD‐fed rats, findings that confirmed our earlier, related work. The fall in serum osteocalcin in ELD‐fed rats is associated with a fall in femur ash weight and bone strength. There were significant correlations between serum osteocalcin and bone strength(r= 0.80;p<0.001) and between serum osteocalcin and bone stiffness(r= 0.83;p<0.001). Serum ionized calcium, like osteocalcin, was consistently lower in rats given ethanol for 1 or 4 weeks than in controls. From these experiments we conclude that excessive ethanol consumption inhibits osteoblastic activity as indicated by the reduced serum osteocalcin. The inhibition is also associated with other deleterious effects of ethanol on bone, including ash weight, bone strength, and bone stiffness. These results in rats suggest that serum osteocalcin may be a useful biologic marker of bone status in a

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060203

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe roles of parathyroid hormone (PTH) and calcitonin (CT) in the pathogenesis of familial benign hypercalcemia (FBH, or hypocalciuric hypercalcemia) are uncertain. Thus we performed studies in 26 patients with FBH, 12 patients with primary hyperparathyroidism (HPT), and 20 normal volunteers, to answer these questions: are plasma levels of intact or biologically active PTH frequently elevated in FBH? Is plasma intact PTH nonsuppressible during calcium infusion? Is there blunting of the C cell CT response to calcium infusion as occurs in primary HPT? We used three methods for measurement of PTH: a mid region‐specific radioimmunoassay (iPTH, antiserum GP‐1M), an extraction‐concentration bioassay (bioPTH, stimulation of cAMP generation in osteoblastlike cells), and a two‐site immunoradiometric assay (IRMA) for intact PTH. PTH levels were significantly elevated in primary HPT by all three methods, but mean PTH was normal in FBH and 85–92% of values overlapped the normal range. During 5 minute calcium infusions (2 mg Ca2+per kg) iPTH values fell little, but bioPTH and intact PTH fell sharply in all three groups. Mean calcium‐induced decreases of intact and bioPTH were indistinguishable from normal in FBH, but PTH levels generally remained elevated at 5 minutes in primary HPT. In FBH basal and postinfusion CT levels were normal. The data show that, in the majority of patients with FBH, PTH concentrations and bioactivity in blood are within the normal range and are suppressed rapidly to very low levels with further increases of calcium. The data suggest that the abnormality of parathyroid function in FBH differs from that in primary HPT. There was no deficiency of CT or C cell responsiveness in FBH, another difference from primary HPT. Nonetheless, in 8–15% of cases, measurement of PTH could not discriminate FBH fro

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060204

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe studied the mechanism of impaired calcium absorption with aging in 51 healthy women whose ages ranged from 26 to 88 years. Serum concentrations of 1,25‐dihydroxyvitamin D [1,25‐(OH)2D, mean of four measurements per subject] increased with age by 22%(P<0.05) but, by split‐point analysis, plateaued or decreased slightly after age 65. In a subset of 20 subjects, [3H]1,25‐(OH)2D3kinetic analysis showed that this increase with age resulted from both increased production and decreased metabolic clearance of 1,25‐(OH)2D. Despite the increase in serum 1,25‐(OH)2D concentration, true calcium absorption did not change with age. The expected inverse correlation between true fractional calcium absorption and dietary calcium intake, however, was easily demonstrated(r= 0.66,P<0.001). Serum intact parathyroid hormone (PTH) increased with age by 35%(P<0.02) and serum bone gla protein (BGP, osteocalcin) increased by 47%(P<0.001); the increases in serum PTH and serum BGP were directly correlated(r= 0.32,P<0.05). The data are consistent with the following hypothetical model: (1) intestinal resistance to 1,25‐(OH)2D action accounts for the increase in serum 1,25‐(OH)2D concentrations with aging with no change in true calcium absorption; (2) this results in a compensatory increase in PTH secretion and in 1,25‐(OH)2D production that prevents true calcium absorption from decreasing; (3) the previously described defect in 25‐hydroxyvitamin D (25‐OHD) 1α‐hydroxylase activity in aging animals and humans acccounts for the leveling off in serum 1,25‐(OH)2D concentration after age 65 years; and (4) the secondary hyperparathyroidism leads to increased bone turnover and thus contribute

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060205

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

年代:1991

数据来源: WILEY

摘要:

AbstractHigh levels of interleukin‐6 (IL‐6) have been detected in synovial fluid from patients with inflammatory arthropathies associated with local bone resorption, suggesting a role for IL‐6 as a local regulator of bone resorption and remodeling. In the present study we examined the effects of IL‐6 on [3H]thymidine ([3H]TdR) incorporation, collagen synthesis, and alkaline phosphatase activity in UMR‐106–01 rat osteoblastic osteosarcoma cells. IL‐6 stimulated a dose‐dependent increase in [3H]TdR incorporation that was maximal at 1000 U/ml (+147% of basal,p<0.005) in osteoblastlike cells that were in a logarithmic phase of growth. The increase in [3H]TdR incorporation was maximal between 12 and 24 h and was neutralized by pretreatment with the polyclonal rabbit antibody to IL‐6. IL‐6 also increased cell number and the secretion of prostaglandin E2in UMR‐106–01 cells in logarithmic growth phase. The stimulation of [3H]TdR incorporation and release of PGE2into the culture medium by IL‐6 was inhibited by indomethacin. A 24 h exposure of the osteoblastlike cells to 1000 U/ml of IL‐6 reduced [3H]proline incorporation into collagenase‐digestible (CDP) protein to 73% of control values(p<0.01). Noncollagen protein (NCP) synthesis was inhibited to 80% of control values(p<0.01) by 1000 U/ml of IL‐6. The inhibitory effect was relatively greater on CDP than on NCP and consequently resulted in a decrease in the percentage of collagen synthesis. Alkaline phosphatase activity was not altered in these cells after a 24 h exposure to 1–1000 U/ml of IL‐6. These results indicate that IL‐6 has a direct effect on osteoblastlike cells, stimulating DNA synthesis via a prostaglandin‐dependent mechanism and suppressing col

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060206

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

年代:1991

数据来源: WILEY

摘要:

AbstractInterleukin 6 (IL‐6) exerts well‐established effects on cells of the immune system as well as on various other cell types. It has been implicated in the control of connective tissue cells in such conditions as rheumatoid arthritis and osteoporosis. We have investigated the effects of recombinant human interleukin‐6 (rhIL‐6) on human osteoblastlike cells derived from explants of trabecular bone. ROS 17/2.8 cells were used as an additional osteoblastlike cell model system.We were unable to identify any effects of rhIL‐6 (5–5000 pg/ml) on the proliferation, alkaline phosphatase activity, osteocalcin production, or release of cytokines or prostaglandins by either osteoblastlike cell model system. Since we have shown previously that these cells release IL‐6 in culture, we used a sheep anti‐human IL‐6 antibody to investigate the possibility that (1) action of added exogenous IL‐6 could be masking endogenous production, and (2) endogenous IL‐6 may regulate the effects of osteotropic agents on the osteoblastlike cells. Presence of the antibody exerted no detectable effects on 1,25‐(OH)2D3‐stimulated alkaline phosphatase or on proliferation or TNF production enhanced by IL‐1. Thus IL‐6 does not appear to be involved in the regu

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060207

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

年代:1991

数据来源: WILEY

摘要:

AbstractA parathyroid hormone‐related protein (PTHrP) is the probable cause of humoral hypercalcemia in malignancy, but its normal physiologic role remains unknown. Since current evidence suggests that PTHrP may have a role in embryonic development, we cloned a genomic fragment that encodes chicken PTHrP (cPTHrP) and studied the expression of PTHrP in developing chick embryos. Blot hybridization of chicken genomic DNA with a cPTHrP genomic DNA probe showed a single band, suggesting that a single‐copy gene encodes cPTHrP. By screening a chicken genomic library with the human probe an open reading frame was identified that corresponds to the human PTHrP (hPTHrP) exon IV. Compared to the human sequence the 5′ splice junction is highly conserved and the two predicted propeptide residues are identical. The sequence predicts a mature peptide of 139 amino acids; all of the first 21 and 94 of the first 112, but only 8 of the final 27 residues of cPTHrP are identical to the human sequence. The structural features required for PTH receptor binding and activation are highly conserved between chicken and hPTHrP. Poly(A)‐enriched RNA from 3–15 day chicken embryos was surveyed by hybridization to the chicken probe. A hybridizing band of 1.45 kb was found in tissues derived from all three germ layers, including brain, heart, lung, liver, gizzard, intestine, chorioallantoic membrane, yolk sac, and skeletal muscle. An additional 1.2 kb hybridizing band was found in some tissues. The conservation of the PTHrP sequence between chicken and mammals supports the view that PTHrP has an important physiologic role. The presence of PTHrP mRNA in early embryos suggests that this role may be in embryonic de

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060208

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

年代:1991

数据来源: WILEY

摘要:

AbstractProstaglandins (PG) act as direct inhibitors of mature osteoclasts, but although resorption‐inhibition is also observed initially PG increase bone resorption in organ culture. This suggests that PG influence bone resorption in organ culture through actions on cell types other than mature osteoclasts. We have therefore tested the effects of PG E1, E2, and F2αon the differentiation of osteoclastic phenotype in mouse bone marrow cultures using bone resorption and calcitonin receptors (CTR) as markers of osteoclastic differentiation. We found that PGE2(10−6–10−9M) and PGE1(10−6–10−7M) induced a significant increase in CTR‐positive cell numbers, to levels five to eight times those seen in controls and similar to the number induced by 1,25‐dihydroxyvitamin D3[1,25‐(OH)2D3]. Bone resorption was increased (10−7M PGE2and 10−6M PGE1) in association with the increased CTR‐positive cell numbers, suggesting that the PG also induced resorptive function. 1,25‐(OH)2D3increased both the number of CTR‐positive cells and the extent of resorption per cell; the additional presence of PG did not affect the number of CTR‐positive cells but did reduce bone resorption compared with 1,25‐(OH)2D3alone. PGF2αhad no significant effect on CTR‐positive cell induction or bone resorption. The results suggest that PGE1and E2induce osteoclastic differentiation in mouse bone marrow cultures and inhibit the function of the osteoclasts thus formed. The explanation for this apparently paradoxical behavior may be that osteoclast generation occurs in a different microenvironment from that in which osteoclast function is regulated and that PG production may be inversely modulated at the two sites, in response to a given stimulus,

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060209

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

年代:1991

数据来源: WILEY

摘要:

AbstractTransforming growth factor (TGF) β1is a multifunctional cytokine with powerful effects on osteoblastic cells. Its role in the regulation of osteoclast generation and function, however, is unclear. It has been reported both to stimulate and to inhibit resorption in organ culture and to inhibit multinuclear cell formation in bone marrow cultures. We tested the effects of TGF‐β1on bone resorption by osteoclasts isolated from neonatal rat long bones. We found potent stimulation of osteoclastic bone resorption, mediated by osteoblastic cells, with an EC50of 10 pg/ml, considerably lower than that of well‐documented osteotropic hormones. Stimulation was not mediated by Swiss mouse 3T3 cells, a nonosteoblastic cell line. TGF‐β1strongly inhibited the generation of calcitonin receptor (CTR)‐positive cells in mouse bone marrow cultures, but as for isolated osteoclasts, bone resorption per CTR‐positive cell was increased. The inhibition of CTR‐positive cell formation was associated with suppression of maturation of other bone marrow derivatives and may be related more to the known ability of TGF‐β1to suppress the proliferation of primitive hematopoietic cells than to a specific role of TGF‐β1in o

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060210

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

年代:1991

数据来源: WILEY

摘要:

AbstractOur earlier results indicated that the binding moiety of the renal PTH receptor is an 85 kD protein that is susceptible to proteolytic cleavage to a 70 kD form that supports high‐affinity binding and Gscoupling, and to a 50–55 kD form that contains the ligand binding domain but does not couple to Gs. In the present study we used [125I]hPTHrP‐(1–34)amide and a chemical cross‐linking technique to discern the structural features of the intact 85 kD PTH/PTHrP receptor that are retained in the proteolyzed forms to “structurally map” the receptor. The results of lectin chromatography and endoglycosidase treatment show that the paritally proteolyzed receptor forms retain the complex, N‐linked glycans present on the intact receptor. This conclusion is further supported by the finding that wheat germ agglutinin was equally effective at competitively inhibiting specific [125I]hPTHrP‐(1–34)A binding to the 70 kD form and the intact 85 kD receptor. Specific binding of [125I]hPTHrP‐(1–34)A to the intact 85 kD receptor or to the 70 kD form was completely abolished by treatment with disulfide reducing agents, and both partially proteolyzed receptor forms (70‐ and 50 kD) were shown to retain the small (≤ 14 kD) labeled fragment that is released from the intact receptor by disulfide reduction. Lectin chromatography and endoglycosidase treatment revealed that the ≤ 14 kD receptor component is not glycoslyated. The ≤ 14 kD fragment does not contain a transmembrane spanning region, as its release from the membrane can be affected without detergent solubilization. Identical partial proteolytic maps of the receptor were obtained whether the receptor was covalently labeled with [125I]hPTHrP‐(1–34)amide or [125I]bPTH‐(1–34). These results suggest a model of the renal PTH/PTHrP receptor binding moiety as a single‐chain protein in which the sites of glycosylation, ligand binding, and the functionally critical disulfide bonds are in extracellular domains near one end of the protein and the sites of proteolysis reside near the other end of the protein. These studies also provide further confirmation that PTH and PTHrP bind to a structurally indistinguishable renal receptor and validate the use of PTHrP as a ligand for studies designed to

ISSN:0884-0431    

DOI:10.1002/jbmr.5650060211

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

年代:1991

数据来源: WILEY