ISSN:0884-0431    

DOI:10.1002/jbmr.5650110902

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.5650110903

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:

AbstractKnee joints from cynomolgus monkeys of both genders and a wide range of ages were examined to characterize further the natural history of osteoarthritis (OA) in these animals. The objectives of this study were to characterize better the subchondral bone changes previously noted in this disease, to determine whether the severity of OA in these animals is affected by age or weight, and to determine whether males and females are affected similarly. As had been seen in previous studies, the medial tibial plateau was the most severely affected site. The thickness of the subchondral plate in the medial tibial plateau increased with increasing severity of articular cartilage lesions in both males and females; however, in monkeys with subchondral plate thicknesses less than 400 μm, articular cartilage lesions were essentially absent. Subchondral plate thickness increased with increasing weight in both genders, but females had a higher subchondral plate thickness than males for a given body weight. There was no correlation between bone volume in the proximal tibial epiphysis and articular cartilage lesions of OA. The prevalence and severity of OA in the medial tibial plateau increased with increasing age, but were not affected by gender or weight. Although there was no correlation between articular cartilage lesions and body mass index or weight, the waist/hip circumference ratio and severity of articular cartilage lesions were correlated in the female monkeys. This work provides evidence that thickening of the subchondral bone plate may be more important than the volume of epiphyseal/metaphyseal cancellous bone in determining the biomechanical stresses in the joint and in influencing the development of articular cartilage lesions

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110904

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:

AbstractWe studied the effects of parathyroid hormone (PTH) on PTH parathyroid hormone related peptide (PTHrP) receptor mRNA level, PTHrP binding, and PTH‐stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblasts, derived from fetal rat calvariae (ROB). Cells isolated during 10–70 minutes of collagenase treatment were seeded at a density of 25,000 cells/cm2and cultured for 4 days. These cells show a fast increase in cAMP production after stimulation for 5 minutes with 20 nM bovine parathyroid hormone(1‐34) (bPTH(1‐34)). When ROB are incubated with bPTH(1‐34) (0.04–40 nM) for 24 h, a dose‐dependent decrease of the PTH/PTHrP receptor mRNA level, PTHrP binding, and PTH‐stimulated cAMP accumulation can be observed. Pretreatment of ROB with a high concentration of bPTH(1‐34) (40 nM) leads within 15 minutes to a decrease in PTH‐stimulated cAMP accumulation. However, it takes ≥3 h before a significant decrease in PTH/PTHrP receptor mRNA level can be observed. Also a significant decrease in PTHrP binding is observed after only 4 h of incubation with bPTH(1‐34). Compared with bPTH(1‐34), pretreatment of ROB with bPTH(3‐34) (40 and 100 nM) for 24 h causes smaller decreases in PTH‐stimulated cAMP accumulation, PTHrP binding, and in the PTH/PTHrP receptor mRNA level. We investigated the possible involvement of the protein kinase A signaling pathway in the regulation of the PTH/PTHrP receptor mRNA expression. Both forskolin and (Bu)2AMP decreased PTHrP binding and PTH/PTHrP mRNA levels. These observations suggest that chronic activation of the PKA signaling pathway may down‐regulate PTH/PTHrP receptor expression and thus hormone responsiveness in “normal” osteoblasts. In short, we found that the decrease of the PTH‐stimulated cAMP accumulation after long‐term pretreatment with bPTH(1‐34) is correlated with both PTH/PTHrP receptor mRNA level and PTHrP binding. These data also suggest that the initial desensitization (<30 minutes) of PTH‐stimulated cAMP responsiveness by pretreatment with a high concentration of bPTH(1‐34) (40 nM) is not dependent on the number of available PTH/PTHrP receptors. The protein kinase A signaling pathway is involved in the regulation of the PTH/PTHrP receptor, but, regarding the effect of bPTH(3

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110905

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:

AbstractSeveral studies have shown the presence of hysteresis of the parathyroid hormone (PTH)‐calcium relationship in both normal humans and hemodialysis patients; for hypocalcemia, hysteresis is defined as a lower PTH level for the same serum calcium during the recovery from than the induction of hypocalcemia. However, some have questioned whether hysteresis is only a function of the rate and/or direction of change in calcium, and others have proposed that hysteresis is due to depletion of PTH stores. To address these issues, two groups of dogs were studied. To induce hypocalcemia, sodium EDTA (50 mg/kg) was infused either over 60 (termed slow) or 30 (termed fast) minutes; immediately after the cessation of the ethylenediamine tetracetate (EDTA) infusion, calcium chloride (0.75 mEq/kg) was infused over 60 or 30 minutes, respectively, to correct the hypocalcemia. The EDTA infusion produced a linear decrease in serum calcium by progressively increasing the infusion rate at regular intervals. A second cycle of hypocalcemia and recovery using the same protocol was started immediately after the completion of the first cycle. To determine whether a nonlinear decrease in the serum calcium affected the PTH response to hypocalcemia, a third group of dogs, termed superfast, was studied; in this group, EDTA was infused for 30 minutes at a constant rate of 50 mg/kg. The hysteretic loops of PTH produced by the two sequential slow and fast cycles and the superfast cycle during the induction of and recovery from hypocalcemia were similar. Moreover, the maximal PTH level for the two sequential slow and fast cycles and the superfast cycle was not different even though the rates of calcium decrease varied and the calcium decrease was nonlinear in the superfast cycle. In conclusion, (1) since hysteresis was reproducible and the maximal PTH was not different during two sequential cycles of hypocalcemia, hysteresis is not due to PTH depletion; (2) the PTH‐calcium curve is not affected by the rate at which hypocalcemia is induced: and (3) the maximal PTH level is not influenced by either the rate or linearity of the reduction in serum calc

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110906

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:

AbstractWe evaluated in normal and hypophosphatemic (Hyp) mice whether changes in serum levels of osteocalcin in response to dietary phosphate supplementation, parathyroid hormone (PTH) and 1,25‐dihydroxyvitamin D3(1,25(OH)2D3) administration were related to perturbations in calcium phosphate homeostasis. In normal mice, serum osteocalcin levels were not altered by phosphate supplementation. In contrast, phosphate supplementation in Hyp mice led to a 2‐fold decrease in serum osteocalcin to normal levels after 3 days and to an increase in osteocalcin levels after 14 days. The decrease in osteocalcin was associated with normophosphatemia, severe hypocalcemia, and marked increases in circulating 1,25(OH)2D3levels, whereas the increase in osteocalcin levels was associated with normophosphatemia and no change in serum calcium and 1,25(OH)2D3. Administration of PTH decreased serum osteocalcin in both genotypes. Infusion of 1,25(OH)2D3for 3 days elicited increases in serum osteocalcin and calcium levels in normal mice, whereas in Hyp mice it produced significant decreases in osteocalcin levels and no change in serum calcium. However, with a more prolonged infusion of 1,25(OH)2D3, hypercalcemia and increases in serum osteocalcin were induced in mutant mice. Our results suggest that the abnormal osteocalcin response of Hyp mice is not directly attributable to an osteoblast dysfunction but is secondary, at least in part, to perturbations in factors that modulate the osteoblast activity, especially serum calcium and/or

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110907

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:

AbstractConflicting results have been reported on the association between restriction fragment length polymorphisms (RFLPs) at the vitamin D receptor (VDR) gene locus (i.e., forBsmI,ApaI, andTaqI) and bone mineral density (BMD). We analyzed this association in a large population‐based sample (n= 1782) of men and women aged 55–80 years using a novel direct haplotyping polymerase chain reaction (PCR) test to monitor the three polymorphic sites simultaneously. The direct haplotyping test we developed demonstrated a larger degree of genetic polymorphism at the VDR gene locus than described until now. None of the individual RFLPs were associated with BMD at the proximal femur. By analyzing allele dose effects, we identified a VDR haplotype allele weakly associated with low BMD. This allele, as one representative of the group of b alleles, is different from theBsmI allele previously reported by other groups to be associated with low BMD. This suggests allelic heterogeneity at the VDR locus in relation to BMD. Our results indicate at most a small effect of the VDR genotype on BMD in this elderly population. Since anonymous polymorphisms were analyzed, alternative explanations for our results include linkage to another nearby bone‐metabolism related

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110908

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 structure‐activity relations and signal transduction pathways for the anabolic effects of prostaglandins were examined in cultured fetal rat calvariae. In the presence of cortisol prostaglandins of the E and F series (10−9to 10−5M) produced a dose‐related increase in [3H]thymidine incorporation up to 4‐fold at 24 h. Prostaglandin E2(PGE2) was also effective in the absence of cortisol. Butaprost (10−6M), a selective EP‐2 receptor agonist, produced partial stimulation. Prostaglandin D2, prostacyclin, sulprostone, an EP‐1 and EP‐3 receptor agonist, and fluprostenol, an FP receptor agonist, were ineffective. Forskolin (10−4M) increased [3H] thymidine incorporation 3‐fold, while phorbol myristate acetate (PMA) (10−6M) produced a 1.8‐fold increase. Isobutylmethylxanthine (IBMX) increased [3H] thymidine incorporation in control cultures, in the absence of cortisol, and increased the response to PGE2in control and cortisol‐treated cultures. [3H] proline incorporation into collagen and noncollagen protein was measured in the continuous presence of prostaglandins and cortisol for 72–96 h (continuous model) or when prostaglandins and cortisol were applied for 24 h, followed by culture for 48 h in control medium (on/off model). The effects on collagen were greater than on noncollagen proteins, so that the percent of collagen synthesis increased. The effects of prostaglandins and forskolin paralleled their mitogenic effects. PMA increased only noncollagen protein. Indomethacin did not diminish the anabolic response, while aphidicolin produced only partial inhibition. We conclude that the anabolic effects of prostaglandins on replication and differentiation of osteoblasts are likely to be mediated by an EP‐2 receptor th

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110909

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:

AbstractBasic fibroblast growth factor (bFGF) is a potent mitogen for bone. In this study, we utilized the clonal rat osteoblastic cell line, Py1a, to examine signal transduction by bFGF and to determine the role of mitogen activated protein kinases (MAPK) and induction ofc‐fosmRNA in the mitogenic response to bFGF. Stimulation of [3H]thymidine incorporation (TDR) into DNA by bFGF was determined in the presence of phorbol myristate acetate of (PMA) to down‐regulate the protein kinase C (PKC) pathway, genistein, an inhibitor of tyrosine kinase and H‐7, a PKC inhibitor, bFGF 10−8M and PMA 10−7M increased TDR by 242 and 245%, respectively. Treatment with bFGF or PMA for 5 or 30 minutes increased tyrosine phosphorylation of multiple proteins, and immunoblotting with MAPK‐specific antibody revealed that two of these bands were the 42 and 44 kD isoforms of MAPK. PMA and bFGF inducedc‐fosmRNA expression at 30 minutes. Genistein at 10 μg/ml blocked the mitogenic effect of bFGF and partially inhibited the mitogenic effect of PMA. Genistein at 100 μg/ml also blocked both bFGF‐ and PMA‐induced increases inc‐fosmRNA. A 24 h pretreatment with PMA at 10−7M inhibited the mitogenic response, tyrosine phosphorylation of MAPK, and induction ofc‐fosmRNA subsequent to the addition of PMA, but not bFGF. H‐7 at 50 μM blocked bFGF‐induced mitogenesis and c‐fosinduction, but did not inhibit bFGF‐induced tyrosine phosphorylation of MAPK. In this study, we show that the signaling pathway of bFGF and PMA are similar in that they both induce tyrosine phosphorylation of MAP kinases and activate c‐fos. However, the signaling pathways ultimately diverge in that once the PKC pathway is down‐regulated by PMA pretreatment or blocked by the PKC inhibitor H‐7, tyrosine phosphorylation of MAP kinase, c‐fosinduction, and the mitogenic effect of PMA is blocked. In contrast, down‐regulation of the PKC pathway inhibits c‐fosand the mitogenic response to bFGF, but not bFGF's eff

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110910

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:

AbstractMesenchymal progenitors cells can be isolated from rat bone marrow and mitotically expanded in vitro. When these cells, which we operationally call mesenchymal stem cells (MSCs), are placed in an appropriate environment, they have the capacity to differentiate into bone and/or cartilage. This capacity is called osteochondrogenic potential. In this study, preconfluent MSCs were exposed in vitro to 5 ng/ml transforming growth factor‐β1 (TGF‐β1) or platelet‐derived growth factor, isoform BB (PDGF‐BB) for a pulse of 48 h and assayed for cell proliferation, alkaline phosphatase activity, and osteochondrogenic potential; untreated MSC's served as controls. In these cell culture conditions, TGF‐β1 or PDGF‐BB had similar effects on proliferation and alkaline phosphatase activity. Both growth factors increased cell proliferation and decreased alkaline phosphatase activity of MSCs. Sister cultures of TGF‐β1‐ or PDGF‐BB‐treated MSCs and untreated MSCs were trypsinized. For each type of culture, the trypsinised MSCs were split in two parts: one part was replated in an osteogenic medium to assess its in vitro osteogenic potential, whereas the other part was seeded into porous calcium phosphate ceramics and implanted subcutaneously in syngeneic rats to assess its in vivo osteochondrogenic potential. PDGF‐pretreated MSCs showed no difference in in vivo and in vitro osteochondrogenesis from that of control MSCs, while TGF‐β1 pretreatment blocked the osteochondrogenic potential of MSCs when assayed in vitro for bone nodule formation. However, when tested in vivo, TGF‐β1‐pretreated MSCs were able to form bone and cartilage. These data show that measurements of proliferation and alkaline phosphatase activity of preconfluent MSCs immediately after exposure to growth factor were not predictive of their subsequent osteochondrogenic potential. Moreover, the variation of the osteochondrogenic potential of MSCs after exposure to growth factor was further modulated by the environme

ISSN:0884-0431    

DOI:10.1002/jbmr.5650110911

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