Modulation of ovariectomy-related bone loss by parathyroid hormone in rats

Studies were carried out to examine whether parathyroid hormone (PTH) will prevent the age-related bone loss that results from ovarian hormone deficiency and to explore the mechanism of its action. Ovariectomy caused a significant decrease in bone density in the distal metaphysis and mid-diaphysis, but not in the vertebra and proximal metaphysis. The decrease was prevented by PTH injection and in all the bones examined PTH administration increased bone density and bone calcium content above the levels in sham-operated controls. Similar findings were made in bone hydroxyproline levels. PTH treated ovariectomized animals had lower serum 25(OH)vitamin D and higher 1,25(OH)2 vitamin D levels than ovariectomized and sham operated animals that received solvent vehicle. Compared to the sham operated controls, ovariectomy caused a 4.5-fold increase in the number of tartrate resistant acid phosphatase (TRAP) positive multinuclear cells. This increase did not occur in PTH-treated animals. We conclude that PTH is effective in preventing ovarian hormone deficiency bone loss in rats. PTH may mediate this effect partly by stimulating osteoblastic bone formation and partly by increasing 1,25(OH)2 vitamin D-mediated calcium absorption. The data from TRAP positive multinuclear cells indicate that an etiologic component of ovarian hormone deficiency bone loss is the expansion of a pool of osteoclast progenitors and that the bone anabolic action of PTH involves, in part, a decrease in bone resorption as a result of the suppression of the proliferation of osteoclast progenitors.     

PTH对破骨细胞骨吸收功能的影响及成骨细胞介导作用

采用分离、培养兔破骨细胞和成骨细胞的方法，体外研究甲状旁腺激素（ＰＴＨ）对破骨细胞骨吸收功能的影响，以及成骨细胞和破骨细胞之间的相互作用。结果表明，ＰＴＨ对破骨细胞的骨吸收功能无直接影响，但在成骨细胞参与下，ＰＴＨ对破骨细胞性骨吸收有明显的促进作用。说明成骨细胞在ＰＴＨ调节破骨细胞功能活动中有着重要的介导作用。     

Bone healing induced by local delivery of an engineered parathyroid hormone prodrug

Regenerative medicine requires innovative therapeutic designs to accommodate high morphogen concentrations in local depots, provide their sustained presence, and enhance cellular invasion and directed differentiation. Here we present an example for inducing local bone regeneration with a matrix-bound engineered active fragment of human parathyroid hormone (PTH_1–34), linked to a transglutaminase substrate for binding to fibrin as a delivery and cell-invasion matrix with an intervening plasmin-sensitive link (TGplPTH_1–34). The precursor form displays very little activity and signaling to osteoblasts, whereas the plasmin cleavage product, as it would be induced under the enzymatic influence of cells remodeling the matrix, was highly active. In vivo animal bone-defect experiments showed dose-dependent bone formation using the PTH–fibrin matrix, with evidence of both osteoconductive and osteoinductive bone-healing mechanisms. Results showed that this PTH-derivatized matrix may have potential utility in humans as a replacement for bone grafts or to repair bone defects.     

Inflammatory lesions and bone resorption induced in the rat periodontium by lipoteichoic acid ofStreptococcus mutans

Severe inflammatory lesions were induced in the periodontal tissues of the rat following the intragingival injection of lipoteichoic acid (LTA) fromStreptococcus mutans. There was no difference in the severity and distribution of the lesions between nonimmunized rats and animals immunized against LTA after antigenic challenge. The lesions are characterized by the occurrence of granulation tissue, massive infiltration of PMNs, abscess formation, bone resorption, and new bone formation. Deacylated LTA and saline caused relatively mild inflammation, and no significant bone resorption or new bone formation was evident. The peak response was reached after 3 intragingival injections. The mechanisms by which LTA caused the pathological alterations in the rat periodontium and the possible relations of this experimental model to periodontal disease in the human are discussed.     

The role of cytokines in the regulation of local bone resorption.

The skeleton is a complex organ that has a variety of functions. It provides a supportive framework for the body, it is the site of hematopoiesis, and it is the principal storehouse for calcium reserves. Recently, it has become clear that the multiple cell types within bone may interact by producing paracrine factors. These substances were originally recognized as either the products of activated immune cells (cytokines) or as local growth factors. However, they appear to have potent effects on both the cells responsible for the structural integrity of the skeleton and the cells involved in hematopoiesis. In humans the skeleton is constantly remodeling. The cells involved in maintaining the skeleton fall into two broad categories: those responsible for the removal of bone (bone resorption) and those responsible for bone formation. This review concentrates on defining the effects that locally produced factors have on bone-resorbing cells and on the interactions between hematopoietic cells that reside in the skeleton and the cells responsible for maintaining skeletal integrity.     

The control of bone growth by parathyroid hormone,leptin, & statins

There is a need for anabolic drugs that can stimulate bone growth, improve bone microarchitecture, accelerate fracture healing and thus restore bone strength to oteoporotics. The anabolic agents currently leading the way to the clinic are the parathroid hormone (PTH) and some of its adenylyl cyclase-stimulating fragments. Here we discuss what is known about the genes and their products that are stimulated by PTHR1 receptor signals and in four ways cause a large accumulation of bone-building osteoblasts. We will also discuss the currently controversial anabolic activity of the cholesterol-lowering statins and outline a possible mechanism by which they might stimulate BMP-2 expession and bone growth. Finally, we will present the growing evidence for the body's "fat-o-stat" cytokine-leptin-indirectly restraining bone growth via a hypothalamic factor and at the same serving as a local autocrine/paracrine stimulator of osteoblast activity via IGF-I and an inhibitor of osteoclast generation by stimulating osteoblastic cells' antiosteoclast OPG (osteoprotegerin) expression and reducing their proosteoclast RANKL expression.     

The role of collagenase in bone resorption. An overview

Since its discovery, vertebrate collagenase is postulated to be the key enzyme for collagen degradation, but the evidence for its participation in bone resorption was, until recently, very weak. The osteoclast, which is the major bone resorbing cell, does apparently not produce collagenase but lysosomal acid proteinases, including collagenolytic cysteine proteinases, whose involvement in bone resorption is supported by many observations. Recent reports indicating 1) that osteoblasts produce and secrete collagenase in response to bone resorbing hormones and 2) that bone resorption is inhibited by a specific collagenase inhibitor, have reintroduced collagenase as a plausible participant in the mechanisms of bone resorption. Moreover bone resorbing agents do not act directly on osteoclasts, but on osteoblasts which, by an unknown mechanism, induce the osteoclasts to excavate bone matrix. Collagenase could participate in the control of bone resorption by degrading the unmineralized collagen which seems to shield the underlying bone from osteoclastic attack. In addition, collagenase, stored as a latent proenzyme in the mineralized matrix, might cooperate with the lysosomal cysteine proteinases in the subosteoclastic lysis of demineralized collagen.     

Parathyroid hormone induces bone resorption in human peripheral blood mononuclear cells

Osteoclasts are known to derive from a macrophage colony-stimulating factor (M-CSF)-dependent precursor shared with macrophages. Cells capable of forming osteoclasts are present in peripheral blood. We characterized this population by incubating human peripheral blood mononuclear cells (PBMCs) with osteoclast-inductive UMR 106 cells, human macrophage colony stimulating factor (hM-CSF) and parathyroid hormone (PTH) or 1,25(OH)₂vitamin D3 on slices of devitalised cortical bone. We found that PBMCs were capable of substantial bone resorption, to levels comparable to those of haemopoietic tissue. Cells plated at very low densities and screened for the presence or absence of excavations revealed a linear relationship (r = 0.994) between the number of cells plated and the number of excavations formed. The limiting dilution analysis suggested that 1 in every 300–600 plated cells (0.15–0.3% of the PBMC population) had the capacity to resorb bone. The precursor was found in the rapidly adherent fraction, and typically generated very small numbers of excavations, suggesting that it was a relatively mature cell type. Co-cultures of PBMCs with UMR 106 cells would not generate osteoclasts without PTH/1,25(OH)₂vitamin D3, even with M-CSF, indicating that osteoclast-induction by stromal cells is not attributable to hormonal induction of M-CSF in UMR 106 cells, but that PTH induces some other activity, necessary for osteoclast but not macrophage formation, in UMR 106 cells. Osteoclasts did not form if PTH was omitted in the first few days of the culture period. Thus, osteoclasts appear to form not from cells committed to macrophage differentiation, but from a discrete subpopulation of relatively mature bipotential or osteoclast-committed precursors which, in the absence of an osteoclast-inductive stimulus, become irreversibly lost to the osteoclast lineage.     

The possible role of the fibroblast in granuloma-induced bone resorption in the rat.

Granulomas were produced over the calvaria of rats by injection of a mixture of turpentine and peanut oil. The granulomas induced localised areas of bone resorption and these resorptive lesions were examined at the fine structural level. A close association was found between osteoclasts and fibroblasts at resorbing surfaces. Furthermore, fibroblasts but not osteoclasts were observed to engulf and phagocytose bone collagen fibrils. It is suggested that the fibroblast either alone or in collaboration with the osteoclast is involved in the destruction of bone collagen during chronic inflammatory disorder of bone.     

The role of a parathyroid hormone analogue in the pathogenesis of malignant hypercalcemia

Patients with malignant hypercalcemia can display not only an increase in bone resorption, but also changes in the renal tubular reabsorption of calcium and phosphate similar to those found in primary hyperparathyroidism. A protein of tumoral origin likely responsible for this syndrome has been described. Even if produced by another gene than parathyroid hormone, it shares a homology in the aminoterminus and seems to exert a similar spectrum of action. Besides its role in malignant hypercalcemia, this analogue may be involved in physiological regulatory processes.     

Molecular mechanisms of bone resorption by the osteoclast

The osteoclast is a multinucleated cell that is actively engaged in the synthesis of lysosomal enzymes, their vectorial transport toward the apical membrane, and the secretion of these enzymes at its apical pole. These secreted enzymes are targeted to the apical ruffled-border membrane by mechanisms that involve cation-independent mannose-6-phosphate receptors. These receptors bind to an enzyme-linked mannose-6-phosphate recognition marker in the Golgi complex, and the enzyme-ligand-receptor complex, carried within small coated transport vesicles, dissociates upon reaching the low pH established in the bone-resorbing compartment by the osteoclast. The apical bone-resorbing compartment is sealed off by the attachment of the osteoclast to the calcified matrix and is actively acidified by the osteoclast. The plasma membrane of the cell is divided into distinct domains. The apical membrane at the ruffled-border shares common antigenic determinants with lysosomal and endosomal membranes, including a 100 kD protein and proton pumps that may be involved in the acidification of the extracellular resorbing compartment. The basolateral membrane is highly enriched in carbonic anhydrase, and bicarbonate-chloride exchange appears to regulate the intracellular pH of this cell. These observations are consistent with a scheme in which, in the low pH environment of the bone-resorbing lacuna produced by the osteoclast, the mineral phase dissolves, exposing the organic matrix to the action of the secreted enzymes. The activity of these enzymes is in turn presumably favored by the acidic milieu. All constituents of the matrix, whether mineral or organic, then would be reduced to their elemental forms (ions and amino acids) extracellularly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of parathyroid hormone by heparin in vitro

Pieces of the parietal bone of inbred C57BL/Mib mice aged 3 days were grown in culture for 3 days. The following substances were added to the culture medium: 0.01 unit/ml (series I) and 0.1 unit/ml (series II) parathormone, 0.1 unit/ml (series III) and 1 unit/ml (series IV) heparin, and 0.01 unit/ml parathormone +0.1 unit/ml heparin (series V). Resorption of bone tissue of the explants was observed in the experiments of series II and V, but not in those of series I, III, and IV. Parathormone (0.01 unit/ml), combined with heparin (0.1 unit/ml), stimulated resorption of the bone tissue of the explant (series V), whereas if added separately in the same dose it had no such action.Laboratory of Experimental Genetics, Institute of Medical Genetics, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. P. Avtsyn.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 80, No. 9, pp. 97–99, September, 1975.     

鸟氨酸脱羧酶/多胺系统在大鼠缺血预适应心肌保护中的作用

目的：探讨鸟氨酸脱羧酶（ODC）/多胺系统在缺血预适应（IPC）心肌保护中的作用。方法:应用离体灌流大鼠心脏复制模拟心肌缺血/再灌注模型。心脏随机分为6组：对照组 (control)、缺血/再灌注组 (IR)、弱缺血预适应组 (IPCw)、强缺血预适应组 (IPCs)、IPCw+多胺抑制剂组 (DF-EG-IPCw)和IPCs+多胺抑制剂组(DF-EG-IPCs)。免疫印迹法定量分析多胺合成限速酶鸟氨酸脱羧酶 (ODC)的表达;高效液相色谱测定心肌组织中的多胺（腐胺、精脒、精胺）含量;Powerlab多导生理记录系统记录心脏功能;氯化三苯基四氮唑 (TTC) 染色检测心肌梗死面积;TUNEL方法检测细胞凋亡率,比较其中的差异性。结果:（1）与对照组比,IR组ODC表达下调,腐胺含量增加,精胺含量减少,总多胺池减少（P<0.05）,此时心功能下降（LVDP、HR、CF均低于对照组,P<0.05）,心肌梗死面积及心肌细胞凋亡率增加（P<0.05）;（2）与IR组比,弱及强缺血预处理组（IPCw、IPCs）心肌ODC表达上调,腐胺含量减少,精胺含量增加,总多胺池增加（P<0.05或P<0.01）,此时大鼠心功能有明显改善（LVDP、HR、CF与IR组比,P<0.05）,心肌梗死面积及心肌细胞凋亡率均明显降低（P<0.01）;（3）给予多胺抑制剂后,心肌ODC表达,腐胺、精脒、精胺及总多胺池含量均明显降低（DF-EG-IPCw组 vs IPCw组;DF-EG-IPCs组vs IPCs组,P<0.05或P<0.01）,心功能明显下降（P<0.05）,心肌梗死面积及细胞凋亡率均明显增加（P<0.05）。结论:缺血预适应能明显上调大鼠心肌ODC/多胺系统,减轻缺血/再灌注心肌损伤;多胺合成代谢抑制剂取消了预适应介导的心功能改善、缩小心肌梗死面积及减少心肌细胞凋亡的作用,提示ODC/多胺系统可能参与了缺血预适应介导的心肌保护作用。