Human parathyroid hormone gene (PTH) is on short arm of chromosome 11

The human gene for parathyroid hormone (PTH) was chromosomally mapped using human-rodent hybrids and Southern filter hybridization of cell hybrid DNA. A recombinant DNA probe containing human PTHcDNA insert (pPTHm122) hybridized to a 3.7-kb fragment in human DNA cleaved with the restriction enzyme EcoRI. By correlating the presence of this fragment in somatic cell hybrid DNA with the human chromosomal content of the hybrid cells, the PTHgene was mapped to the short arm of the chromosome 11.     

Parathyroid hormone (PTH) assay of parathyroid cysts examined by fine-needle aspiration biopsy

The authors report three cases of parathyroid cysts examined by the fine-needle aspiration biopsy technic. A presumptive diagnosis of parathyroid cyst was made when characteristic water-clear fluid was aspirated. The diagnosis was then confirmed by parathyroid hormone (PTH) assay. The authors believe that the C-terminal/midmolecule determination should be the assay of choice, because the N-terminal-specific assay gave normal or slightly elevated results in all the cases studied. If only an N-terminal-specific PTH assay is obtained, potential for a false negative diagnosis exists. With a correct PTH assay, a specific diagnosis of parathyroid cyst can be rendered, which enables appropriate treatment of total fluid aspiration, which thereby eliminates the need for thyroid hormone treatment or surgery in most cases. A discussion of PTH assays is presented along with speculations concerning the secretion of PTH by the parathyroid gland. The previous literature detailing cytologic findings and the PTH assays of parathyroid cysts diagnosed by the fine-needle aspiration biopsy are reviewed.     

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。     

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.     

Effect of parathyroid hormone PTH (1-34) on hemopoietic and stromal stem cells

Long-term administration of parathyroid hormone causing activation and proliferation of osteoblasts to mice increases the concentration of primitive hemopoietic precursor cells (cobblestone area-forming cells) in long-living bone marrow culture after 28–35 days. The concentrations of later precursors forming colonies in the spleen and the concentration of cobblestone-area forming cells in long-living bone marrow culture after 7 days decrease, while the concentration of more differentiated cells forming colonies in the culture does not change. Transplantation of the bone marrow from mice treated with parathyroid hormone under the renal capsule of syngeneic recipients results in the formation of a focus of ectopic hemopoiesis not differing by size from the control. Injection of parathyroid hormone to mice during the growth of the ectopic focus did not modulate its size. These foci tolerate retransplantation procedure similarly as controls. Hence, parathyroid hormone has no effect on mesenchymal stem cells responsible for transfer of the stromal microenvironment. Therefore, the number of stem hemopoietic cells in the body is regulated by not stromal stem cells, but their better differentiated descendants.Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 138, No. 12, pp. 645–648, December, 2004This revised version was published online in April 2005 with a corrected cover date.     

Role of parathyroid hormone (PTH) and PTH-related protein (PTHrP) in regulating mineral homeostasis during fetal development

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) play complementary and overlapping roles in regulating fetal mineral homeostasis. PTHrP is expressed within the growth plate, directs endochondral bone formation, and determines the fate of chondrocytes before bone formation can be initiated. It is expressed in placenta and is present at high levels in the fetal circulation. It stimulates placental calcium (and possibly magnesium) transfer and raises blood mineral levels above ambient maternal values in order to effect mineralization of the skeleton. It does not upregulate in response to absence of PTH or hypocalcemia, and thus, its secretion may be regulated autonomously or in response to placental signals. PTH is expressed in fetal parathyroids and placenta. Despite circulating at low levels, it has a more dominant effect than PTHrP in regulating the blood calcium and ensuring adequate mineralization of the skeleton. It may also have effects on bone formation in the steps that occur after apoptosis of hypertrophic chondrocytes. Unlike PTHrP, it increases with fetal hypocalcemia, but its secretion is constrained by the calcium-sensing receptor to maintain the adult calcium level, well below what the fetus normally achieves. PTH also stimulates placental calcium transfer, and its absence disrupts placental expression of calciotropic and cation transporter genes.     

Biological action of parathyroid hormone (PTH)-related peptide (PTHrP) mediated either by the PTH/PTHrP receptor or the nucleolar translocation in chondrocytes

Parathyroid hormone (PTH)-related peptide (PTHrP) has been believed to act by binding the common receptor to PTH (PTH/PTHrP receptor). However, PTHrP is localized not only in the secretory pathway, but also in nucleoli by virtue of its nucleolar targeting signal (NTS). This review demonstrates the bipartite action of PTHrP on chondrocytes, the receptor-mediated and -independent signaling pathway. Mice with deletion of the PTHrP gene were characterized by a chondrodysplasia due to markedly reduced proliferation of epiphyseal chondrocytes. The PTH/PTHrP receptor was localized mainly in proliferative chondrocytes in the epiphyseal cartilage, indicating that PTHrP modulates normal proliferation via the receptor. In contrast to the receptor-mediated action, the mid-region of the amino acid sequence of PTHrP contains an NTS. The PTHrP-translation was found to initiate from both methionine-coding AUG and downstream leucine-coding CUGs in its signal sequence. When translated from CUGs, PTHrP accumulated in the nucleoli, and the translation from AUG localized PTHrP in both the Golgi apparatus and nucleoli. Therefore, nucleolar PTHrP appears to be derived from the translation initiating from both AUG and CUGs. A chondrocytic cell line expressing a full-length PTHrP, but not PTHrP lacking NTS, were resistant to apoptosis caused by serum depletion, suggesting that the nucleolar PTHrP in chondrocytes serves as a survival factor against apoptosis. Thus, PTHrP regulates chondrocyte proliferation, differentiation and apoptosis by mediating its receptor or acting directly on the nucleolus.     

Immunological evidences for the presence of small late carboxylterminal fragment(s) of human parathyroid hormone (PTH) in circulation in man

Two antisera, C-52 and C-97, raised against bovine (b)PTH(1-84) in guinea pigs, were evaluated with 125I-[tyr53] human (h)PTH(53-84) as tracer and intact hPTH(1-84) and synthetic hPTH(39-84), representative of large carboxylterminal ("C") fragments found in circulation, as standards. In both assays, hPTH(39-84) was 5-6 times more potent than hPTH(1-84) on a molar basis in displacing the tracer. With both antisera, progressive deletion at the aminoterminal end of large "C" fragments, as in hPTH(53-84) and hPTH(65-84), lead to decreased immunoreactivity, hPTH(69-84) being non-immunoreactive. The mid-carboxylterminal fragments, hPTH(44-68) and hPTH(39-68), did not react in either assay. Each antiserum measured known quantities of pure hPTH(1-84) or hPTH(39-84) standards similarly. Serum PTH values obtained with antiserum C-97 were about 3 times higher in renal failure, 1.75 times higher in normal individuals and those with primary hyperparathyroidism, while similar to values measured with antiserum C-52 in individuals with secondary hyperparathyroidism without renal failure or with pseudohypoparathyroidism. When circulating PTH taken from patients with these disorders was fractionated by gel chromatography, both antisera recognized similar peaks of intact hPTH(1-84) and of large "C" fragments while antiserum C-97 further recognized a peak of smaller "C" fragments. This explained the different clinical behavior of the latter antiserum. Our findings demonstrate the existence of small late "C" fragments in circulation. They further suggest an influence of serum calcium and of renal function on the quantity of these fragments.     

A synthetic bone implant macroscopically identical to cancellous bone

Macroporous hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) are widely used as synthetic bone replacement materials due to their high biocompatibility and osteoconductive properties. The level of porosity, pore size distribution, pore morphology, and the degree of pore interconnectivity in such grafts significantly influences the extent of bone ingrowth. It has been hypothesised that an ideal implant macrostructure may be similar in morphological characteristics to the inorganic matrix of the bone it is replacing. However, to date, clinically available synthetic materials differ structurally from cancellous bone.

A method is described for the macrostructural replication of cancellous bone. Reproduction involves a multistage process requiring the manipulation of positive and negative forms of the inorganic matrix. By infiltration of a wax negative mould of cancellous bone with a ceramic slip, followed by removal of the wax, and firing, it is possible to produce a positive replica of the original cancellous macrostructure.

Optimisation of slip preparation conditions (pH and percentage deflocculant addition) and sintering conditions have allowed successful replication of cancellous bone using several bioceramic compositions including HA, β-TCP, and HA/β-TCP.     

Expression of parathyroid hormone-related peptide (PthrP) and its receptor (PTH1R) during the histogenesis of cartilage and bone in the chicken mandibular process

The purpose of this study was to examine the expression and actions of parathyroid hormone-related protein (PTHrP) when skeletal histogenesis occurs in the chicken mandible. Prior to the appearance of skeletal tissues, PTHrP and PTH1R were co-expressed by cells in the ectoderm, skeletal muscle, peripheral nerve and mesenchyme. Hyaline cartilage was first observed at HH stage 27 when many but not all chondroblasts expressed PTHrP and PTH1R. By stage 34, PTHrP and PTH1R were not detected in chondrocytes but were expressed in the perichondrium. Alkaline phosphatase (AP)-positive preosteoblasts and woven bone appeared at stages 31 and 34, respectively. Preosteoblasts, osteoblasts and osteocytes co-expressed PTHrP and PTH1R. Treatment with chicken PTHrP (1-36) increased cAMP in mesenchyme from stage 26 embryos. Continuous exposure to chicken PTHrP (1-36) for 14 days increased cartilage nodule number and decreased AP while intermittent exposure did not affect cartilage nodule number and increased AP in cultures of stage 26 mesenchymal cells. Adding a neutralizing anti-PTHrP antibody to the cultures reduced cartilage nodule number and did not affect AP. These findings show that PTHrP and PTH1R are co-expressed by extraskeletal and skeletal cells before and during skeletal tissue histogenesis, and that PTHrP may influence skeletal tissue histogenesis by affecting the differentiation of mandibular mesenchymal cells into chondroblasts and osteoblasts.     

Production and characterisation of monoclonal antibodies to parathyroid hormone (1-34)

Monoclonal antibodies to the biologically active N terminal region of parathyroid hormone (PTH) suitable for use in the measurement of circulating PTH concentrations have proved difficult to produce. In this study, no serum PTH antibody titres could be detected in mice using synthetic human PTH (1-34) (free or coupled to albumin) or PTH (1-10) (coupled to keyhole limpet haemocyanin) as immunogen. A consistent response to PTH (1-34) peptide was obtained in DA rats. We have produced five monoclonal antibodies to PTH (1-34) derived from the fusion of DA rat spleen cells and the mouse myeloma line X63 Ag.8.653. Bulk production of the antibodies was achieved using congenitally athymic mice for ascites production. Antibody assessment studies revealed the antibodies to be sensitive to the oxidation state of the methionine residues in PTH (1-34). Two of the antibodies, 3B3 and 6E3, were shown to be of potential use in measuring circulating PTH (1-84) when used in combination with available antibodies to C terminal PTH. A third antibody, 4G3, which failed to recognise PTH (1-84) when used in combination with 3B3, formed the basis of a specific assay for PTH (1-34).     

Osteoporosis: A bone turnover defect resulting from an elevated parathyroid hormone concentration within the bone-marrow cavity?

Summary Recently the bone-marrow cavity blood concentration of parathyroid hormone (PTH) has been shown to exceed that of the peripheral blood. As PTH is a primary modulator of bone cell activity, altered levels of the hormone in the bone-marrow blood may play a significant role in the aetiology of bone disease. We therefore measured PTH concentrations in marrow cavity and venous blood of 9 osteoporotic and 14 control subjects using sequence specific radioimmunoassays for intact and mid-carboxyl (Mid-C) regional human PTH (hPTH). Intact and Mid-C PTH levels were identical in the peripheral blood of control and osteoporotic subjects. Furthermore, bone-marrow cavity blood concentrations of Mid-C PTH, whilst universally higher than those found in peripheral blood, were also comparable in the osteoporotic and control subjects. The sole difference in the PTH composition of bone-marrow cavity blood from osteoporotic subjects was an increased concentration of intact PTH. The origins and consequences of elevated levels of intact PTH within the marrow cavity blood of osteoporotic subjects are discussed.Supported by the Deutsche Forschungsgemeinschaft and the Stiftung Volkswagenwerk     

Monoclonal antibodies to human parathyroid hormone (1-34) and their use in the immunocytochemical detection of parathyroid tumours

Monoclonal antibodies against the biologically active N-terminal fragment of human parathyroid hormone, hPTH (1-34), were produced. The procedure included the use of novel secondary immunization in vitro of mouse spleen cell cultures. Dissociated spleen cells from primary immunized Balb/c mice, were cultured for five days in the presence of thymocyte conditioned media (TCM) and synthetic hPTH (1-34). Contrary to previous findings by other workers, in our hands Balb/c mice responded well. Following immunization the spleen cells were fused with NSl myeloma cells and cultured for eleven days before screening for antibody. Using an enzyme linked immunosorbent assay (ELISA) a number of positive clones were detected. Positive cells were cloned by limiting dilution and fifteen specific monoclonal hybridomas were produced. The immunoglobulin class of the different monoclonal antibodies was found to be IgGl. The immunocytochemical reaction was tested with chief cell carcinoma tissue and found to be clearly positive.     

Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis

BACKGROUND: Once-daily injections of parathyroid hormone or its amino-terminal fragments increase bone formation and bone mass without causing hypercalcemia, but their effects on fractures are unknown. METHODS: We randomly assigned 1637 postmenopausal women with prior vertebral fractures to receive 20 or 40 microg of parathyroid hormone (1-34) or placebo, administered subcutaneously by the women daily. We obtained vertebral radiographs at base line and at the end of the study (median duration of observation, 21 months) and performed serial measurements of bone mass by dual-energy x-ray absorptiometry. RESULTS: New vertebral fractures occurred in 14 percent of the women in the placebo group and in 5 percent and 4 percent, respectively, of the women in the 20-microg and 40-microg parathyroid hormone groups; the respective relative risks of fracture in the 20-microg and 40-microg groups, as compared with the placebo group, were 0.35 and 0.31 (95 percent confidence intervals, 0.22 to 0.55 and 0.19 to 0.50). New nonvertebral fragility fractures occurred in 6 percent of the women in the placebo group and in 3 percent of those in each parathyroid hormone group (relative risk, 0.47 and 0.46, respectively [95 percent confidence intervals, 0.25 to 0.88 and 0.25 to 0.861). As compared with placebo, the 20-microg and 40-microg doses of parathyroid hormone increased bone mineral density by 9 and 13 more percentage points in the lumbar spine and by 3 and 6 more percentage points in the femoral neck; the 40-microg dose decreased bone mineral density at the shaft of the radius by 2 more percentage points. Both doses increased total-body bone mineral by 2 to 4 more percentage points than did placebo. Parathyroid hormone had only minor side effects (occasional nausea and headache). CONCLUSIONS: Treatment of postmenopausal osteoporosis with parathyroid hormone (1-34) decreases the risk of vertebral and nonvertebral fractures; increases vertebral, femoral, and total-body bone mineral density; and is well tolerated. The 40-microg dose increased bone mineral density more than the 20-microg dose but had similar effects on the risk of fracture and was more likely to have side effects.