Ability Of Parathyroid Hormone Research Articles

Changes in serum fibroblast growth factor 2 in patients with glucocorticoid-induced osteoporosis treated with human parathyroid hormone (1–34)

Since the ability of parathyroid hormone (PTH) to increase osteoblast maturation and activity is associated with basic fibroblast growth factor (bFGF) we determined the changes in serum bFGF levels in patients treated with human parathyroid hormone (hPTH) (1-34) for 12 months and 12 months follow up. All studied subjects (n=51) had postmenopausal osteoporosis, had been receiving long-term treatment with glucocorticoid plus estrogen or estrogen/progesterone and were randomly allocated either to a group receiving hPTH, 400 U/day (n=28), or to a control group (n=23). Osteocalcin (OST), bone-specific alkaline phosphatase (BSAP) and bFGF were monitored at the baseline, every 3 months for 18 months, and at 24 months. In the hPTH group, OST increased by more than 150% above baseline at 3 months and was maintained at this level throughout the treatment period. BSAP had increased more than 80% over the baseline level at 3 months and was maintained at 90% above baseline for the next 9 months. bFGF levels had increased by 45% at 3 months, 60% at 6 to 9 months (P<0.05) and had increased more than 90% from baseline by 12 months (P<0.05). We found that daily hPTH injections increased bFGF levels. These results support the hypothesis that up-regulation of bFGF could play a role in the osteoblastic response to PTH.

Identification of parathyroid hormone-regulated proteins in mouse bone marrow cells by proteomics

The ability of parathyroid hormone (PTH) to enhance bone formation has recently been exploited in the treatment of osteoporosis. Several studies have suggested that the activation of bone marrow stromal cells could be preceded to show the anabolic effect of PTH on bone formation, but little is known of PTH-regulated proteins in bone marrow cells. Therefore, protein profiling in the intermittent PTH-treated bone marrow cells was evaluated using proteomics. Daily treatment for 5 days consisting of subcutaneous injection of either 150 μg/kg per day of mouse PTH (1–84) or vehicle (0.9% normal saline) was performed on the ICR mouse. At the end of the treatment period, bone marrow cells were separated and used in proteomics. The expression levels of seven proteins including vimentin were decreased, but those of four proteins including calreticulin and thioredoxin domain containing 7 protein (Txnde7) were increased. Among these, the decrease of vimentin and the increase of both calreticulin Txnde7 in mRNA levels were confirmed by semi-quantitative RT-PCR. In PTH-treated mouse MC3T3-E1 osteoblast cells, mRNA expression levels were not totally consistent with the results observed in proteomics. In conclusion, the differentially expressed proteins in bone marrow cells depending on PTH could be highly linked to the differentiation of osteoprogenitor cells in the bone marrow into preosteoblast cells.

Parathyroid hormone activates adhesion in bone marrow stromal precursor cells.

The ability of parathyroid hormone (PTH) to enhance bone formation has recently been exploited in the treatment of osteoporosis. However, the underlying mechanisms are unknown. Osteoblasts, the bone-forming cells, derive from multipotential bone marrow stromal precursors called colony-forming units-fibroblastic (CFU-F) upon culture ex vivo. Adhesion of such stromal precursors to bone is likely to be an early event in the anabolic response of bone to PTH. To test this, we measured the number of CFU-F that could be extracted from murine bone marrow after administration of an anabolic dose of PTH. We found that a very early response is a dramatic reduction, starting within 2 h, in the number of CFU-F that could be extracted from their bone marrow. We then tested whether PTH has the ability to activate adhesion of CFU-F in vitro. For this, bone marrow cells were incubated in PTH for varying times. Non-adherent cells were then removed, and the adherent cells were incubated in PTH-free medium for 14 days to assess, as colony formation, the number of CFU-F that had adhered in the preceding period. We found that incubation in PTH caused a substantial increase in the number of CFU-F that adhered within 24 h. This increase was abrogated by peptidic inhibitors of integrins. The increase did not seem to be mediated through a PTH-induced increase in interleukin-6, since interleukin-6 had no effect on CFU-F numbers when substituted for PTH. Similarly, adhesion was unaffected by incubation of bone marrow cells in dibutyryl cyclic AMP, nor by inhibitors or donors of nitric oxide. However, activation of CFU-F in vitro by PTH was strongly inhibited by indomethacin and mimicked by prostaglandin E(2), and indomethacin reversed the PTH-mediated reduction of CFU-F that could be extracted from mouse bone marrow. These results suggested that PTH rapidly activates adhesion of CFU-F to plastic or bone surfaces. This activation may represent an early event in the anabolic response of bone cells to PTH.

Response of immortalized murine cementoblasts/periodontal ligament cells to parathyroid hormone and parathyroid hormone-related protein in vitro

Cementum is an essential component of the periodontium, but the mechanisms involved in regulating the activity of this tissue are poorly understood. As one approach to better defining the cellular and molecular properties of cementum and the associated ligament, immortalized murine cell populations expressing gene markers associated with both cementoblasts (CM) and periodontal ligament cells (PDL), termed CM/PDL cells, were established. To further characterize these cells, their responsiveness to parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) was examined. CM/PDL cells were tested for the presence of steady state PTH-1 receptor mRNA using Northern blot analysis. In addition, the ability of PTH and PTHrP to stimulate cAMP production and c- fos mRNA expression in CM/PDL cells was determined, using a cAMP-binding assay and northern blot hybridization, respectively. Rat osteosarcoma cells (ROS 17/2.8) were used as a positive control and human periodontal ligament cells as a negative control. Northern blot analysis demonstrated that cells within the CM/PDL cell population expressed PTH-1 receptor mRNA. Both PTH (1–34) and PTHrP (1–34) increased cAMP and c- fos mRNA in CM/PDL cells. Furthermore, PTHrP treatment for either 24 or 48 h downregulated expression of transcripts for bone sialoprotein, osteocalcin and PTH-1 receptor by CM/PDL cells and abolished CM/PDL cell-mediated mineralization in vitro. These results indicate that cells within the CM/PDL population are targets for PTH and PTHrP action and that PTHrP may play an important part in regulating the biomineralization of cementum.

In vitro effect of hormones and growth factors on the incorporation of [ 3H]leucine, [ 35S]sulfate and [ 3H]proline by chondrocytes of aging mice

The ability of parathyroid hormone (PTH 1–84), dexamethasone, prostaglandin E 1 (PGE 1), prostaglandin E 2 (PGE 2) and human transforming growth factor beta (hTGF-β) to stimulate the synthesis of matrical components in articular cartilage of aging mice, was studied in an organ culture system. A marked age-dependent decrease was observed in the synthesis of sulfated glycosaminoglycans (GAGs), protein, collagen disgestible protein (CDP) and non-collagen protein (NCP) between 1 and 18 months of age. The addition of hTGF-β (1 ng/ml) into the culture medium resulted in a significant ( P < 0.01) increase of both protein and sulfated GAGs in condylar cartilage from animals aged 1, 3, 6 and 12 months. PGE 2 (10 μg/ml) induced [ 3H]leucine and [ 35S]SO 4 incorporation into condylar cartilage from 1, 3 and 6 months old animals. A stimulatory effect of PGE 1 (10 μg/ml) on [ 3H]leucine incorporation was noted at 1 and 3 months of age. The effect of PTH appeared to be stimulatory only for protein synthesis in young (1 and 3 months old) animals, whereas it had no effect at 6, 12 and 18 months of age. In contrast, dexamethasone exerted a stimulatory effect on young adults (6 months old) and in matured (12 months old) animals, respectively and a slight inhibitory effect on young (1 and 3 months old) animals. [ 3H]Proline incorporation was enhanced by all the factors tested in 1-month-old animals. In cultures from 6- and 18-months old animals only PGE 1 and PGE 2 appeared to be stimulatory. It is concluded that synthesis of protein, sulfated GAGs and collagen by chondrocytes from maturing and osteoarthritic senescent animals can be stimulated by hormones and growth factors. The efficiency of this response, however, varied according to the animal's age and the factor studied.

Effects of transforming growth factor-α on parathyroid hormone- and parathyroid hormone-related protein- mediated bone resorption and adenylate cyclase stimulation in vitro

The effects of transforming growth factor-α (TGFα) were determined on the ability of parathyroid hormone (PTH) or parathyroid hormone-related protein (PTHrP) to stimulate bone resorption and adenylate cyclase in vitro. Bovine PTH-(1–34) and human PTHrP-(1–34) were equipotent in their ability to stimulate bone resorption in neonatal mouse calvaria with maximal stimulation (2.9 and 2.8-fold increases in 45Ca release, respectively) at a concentration of 10 nM. Combinations of TGFα with bPTH-(1–34) or hPTHrP-(1–34) had additive effects on their ability to stimulate bone resorption when submaximal concentrations of the agonists were used. There was no evidence of synergism between TGFα and bPTH-(1–34) or hPTHrP-(1–34) in their ability to stimulate bone resorption in vitro, nor was TGFα able to increase bone resorption induced by maximal concentrations of bPTH-(1–34) or hPTHrP-(1–34). TGFα potentiated the effects of either bPTH-(1–34) or hPTHrP-(1–34) on the stimulation of adenylate cyclase in osteoblast-like ROS 17 2.8 cells. These data indicate that TGFα has additive effects with submaximal concentrations of PTH or PTHrP on their ability to stimulate bone resorption which may be important in the pathogenesis of humoral hypercalcemia of malignancy.

Parathyroid hormone fragment [3–34] stimulates protein kinase C (PKC) activity in rat osteosarcoma and murine T-lymphoma cells

The parathyroid hormone (PTH) fragment [1–34] strongly stimulated both adenylate cyclase and membrane-associated PKC activities in rat 17/2 osteosarcoma cells. By contrast, the PTH [3–34] fragment, which was unable to stimulate adenylate cyclase, remained a potent stimulator of membrane-associated PKC activity in these cells. Both PTH fragments also strongly stimulated membrane-PKC activity in cyc − S49T-lymphoma cells possessing a defective adenylate cyclase system. This ability of PTH [3–34] to stimulate membrane-associated PKC activity could explain the residual bioactivity of this fragment.

Effect of parathyroid hormone on renin secretion.

The ability of parathyroid hormone (PTH) to increase renin secretion was investigated in pentobarbital-anesthetized dogs. An intravenous infusion of bovine PTH 1-34, at the dose of 0.028 microgram/kg-1 min-1 increased renin secretion by 149% (501 +/- 105 to 1249 +/- 309 ng hr-1 min-1); renin secretion returned to control values during the recovery period. In order to determine whether PTH acted directly on the kidney to increase renin secretion, PTH was infused into the right renal artery at doses of 0.0014 to 0.0028 microgram/kg-1 min-1 and renin secretion from the right kidney was compared to that from the left (control) kidney. Renin secretion from the right (PTH-infused) kidney was not greater than control values for that kidney or different from the renin secretory rate of the left (control) kidney. In contrast, the excretion rates of both phosphate and sodium from the right kidney were greater than control values and from the excretion rates of the left kidney. These data suggest that PTH, while acting directly on the kidney to increase phosphate and sodium excretion, does not elevate renin secretion by a direct renal action.

Lipopolysaccharide-induced bone resorption is mediated by prostaglandins.

Abstract In organ cultures of new-born mouse calvaria both bovine parathyroid hormone and a lipopolysaccharide preparation from E. coli promoted bone resorption. Dead bone cultures did not respond to either of these agents. When bone prostaglandin synthesis was inhibited by indomethacin the lipopolysaccharide no longer promoted bone resorption. Similar treatment did not affect the ability of parathyroid hormone to cause bone dissolution.

Glucocorticoid Potentiation of the Adenosine 3′,5′- Monophosphate Response to Parathyroid Hormone in Cultured Rat Bone Cells*

We have previously demonstrated the presence of glucocorticoid receptors in bone cells and have suggested that direct inhibition of cell proliferation may contribute to glucocorticoid-induced osteoporosis. The present studies examine the issue of whether glucocorticoids might also alter bone status by interacting with parathyroid hormone (PTH) a major regulator of bone homeostasis. Since cyclic AMP (cAMP) is the putative mediator of PTH-induced inhibition of collagen synthesis as well as resorption, we assessed the ability of dexamethasone to modulate the cAMP response to PTH. Bone cells from calvaria of 20-21 day fetal rats were cultured for 6–7 days and the ability of PTH to stimulate cAMP was measured. The cells responded to both the synthetic (1–34) fragment and native PTH with a dose-dependent increase in cAMP. Dexamethasone treatment did not alter base-line levels of cAMP but did potentiate the cAMP response to PTH: 1- to 2- fold when assayed in the presence of theophylline and 2- to 4-fold in its a...

Early effect of 25-hydroxycholecalciferol (25-OH-D 3) and 1,25-dihydroxycholecalciferol (1,25-(OH) 2-D 3) on the ability of parathyroid hormone (PTH) to elevate cyclic AMP of intact bone cells

25-OH-D 3 and 1,25-(OH) 2-D 3 had no effects by themselves on the cyclic AMP levels of isolated bone cells but enhanced the stimulation seen following an exposure with submaximal concentrations of PTH for as little as 2 minutes. Preincubation with the 25-OH-D 3 or 1,25-(OH) 2-D 3 resulted in a time dependent decrease in the enhancement of PTH response over a 1 hr period. It is, therefore, suggested that cyclic AMP may be involved in some aspects of the action of vitamin D 3 derivatives on bone cells.