A highly sensitive bioassay for PTH using ROS 17/2.8 subclonal cells

Use of isolated mature osteoblasts in abundance acts as desired-shaped bone regeneration in combination with a modified poly-DL-lactic-co-glycolic acid (PLGA)-collagen sponge

Controlled regeneration of bone or cartilage has recently begun to facilitate a host of novel clinical treatments. An osteoblast line, which we isolated is able to form new bone matrix in vivo within 2 days and exhibits a mature osteoblast phenotype both in vitro and in vivo. Using these cells, we show that cuboidal bones can be generated into a predesigned shaped-bone with high-density bone trabeculae when used in combination with a modified poly-DL-lactic-co-glycolic acid (PLGA)-collagen sponge. PLGA coated with collagen gel serves as a good scaffold for osteoblasts. These results indicate that mature osteoblasts, in combination with a scaffold such as PLGA-collagen sponge, show promise for use in a custom-shaped bone regeneration tool for both basic research into osteogenesis and for development of therapeutic applications.

Beta-adrenergic receptor kinase-1 acutely regulates PTH/PTHrP receptor signalling in human osteoblastlike cells

To investigate whether G protein-coupled receptor kinases (GRKs) are involved in the regulation of the PTH/PTHrPR, we have established mutant SaOS-2 cells which stably overexpress (> 10-20-fold) a dominant negative form of the beta-adrenergic receptor kinase-1 (beta ARK-1). Acute (< or = 2 h) incubation with hPTH (1-34) induced significantly less (by up to 50%) downregulation of the PTH/PTHrPR in beta ARK-1 mutant SaOS-2 cells than observed in wild-type cells. Pretreatment of wild-type cells with PTH for 2 h induced homologous cAMP desensitisation to a second challenge with PTH, while the effect was blunted by up to 60% in beta ARK-1 mutant cells. We conclude that activation of beta ARK-1 (or a closely related GRK) is a critical component of the acute phase (< or = 2 h) of PTH-induced receptor downregulation and homologous cAMP desensitisation of the PTH/PTHrPR.

Humoral factors of ascites sarcoma 180 stimulate osteoblastic UMR 106-01 cell proliferation and bone resorption via signal transduction pathways, which are clearly different from those of parathyroid hormone

Ascites sarcoma 180 (S180A) is a transplantable tumor that induces hypercalcemia in tumor-bearing mice and stimulates bone resorption in cultured neonatal mouse calvaria without parathyroid hormone (PTH)-like activity. The serum-free conditioned media of S180A cell cultures (S180A-CM) stimulated [3H]thymidine incorporation (178.3% of the control) and inhibited alkaline phosphatase activity (39.0% of the control) in the osteoblastic osteosarcoma cell line UMR 106-01, contrary to PTH. To investigate signal transduction by S180A-CM, we determined the levels of intracellular free calcium ([Ca2+]i), inositol 1,4,5-triphosphate (IP3), 1,2-diacylglycerol (DAG), phosphatidylcholine (PC) and protein kinase (PK) C activity in UMR 106-01 cells. PTH and PTH-related protein (PTHrP), both potent bone-resorbing factors (BRFs), caused an increase in [Ca2+]i and stimulated IP3 production, whereas S180A-CM had little or no effect on these parameters. On the other hand, S180A-CM stimulated DAG production, accompanied by PC breakdown, and the translocation of PKC activity from the cytosol to the membrane fraction. Sphingosine, a specific PKC inhibitor, inhibited bone-resorbing activity (BRA) in S180A-CM more effectively than PTH or PTHrP-stimulated resorption. H-7, an inhibitor of both cAMP-dependent PKA and PKC, completely inhibited BRA in S180A-CM. These results suggest that BRFs of S180A-CM stimulate osteoblastic cell proliferation and bone resorption via two signal transduction pathways, which are different from those of PTH: 1) activation of PKC by DAG resulting from PC hydrolysis and 2) activation of PKA subsequent to prostaglandin E2 production by bone.

Oxidation of recombinant human parathyroid hormone: effect of oxidized position on the biological activity

PURPOSE

To determine the oxidation products of recombinant human parathyroid hormone (rhPTH) treated with H2O2, the amino acid residue oxidized, and the biological activity of the oxidation products.

METHODS

Oxidized residues were determined by CNBr cleavage, trypsin digestion and subsequent fast atom bombardment mass spectrometry. The biological activity of each oxidized rhPTH was examined in rat osteosarcoma cell adenylate cyclase assay.

RESULTS

Three oxidized products were isolated, namely, Met at position 8 (Met8) sulfoxide, Met at position 18 (Met18) sulfoxide and both positions Met sulfoxide. It appears that the Met8 and Met18 oxidized forms are intermediates in the generation of the Met doubly oxidized form. All oxidized forms possessed reduced biological activity, more so for oxidation at Met8 than at Met18.

CONCLUSIONS

The region around Met8 is important for the activity of the parathyroid hormone.

Involvement of alkaline phosphatase in the modulation of receptor signaling in osteoblasts: evidence for a difference between human parathyroid hormone-related protein and human parathyroid hormone

We have previously reported that alkaline phosphatase (ALPase) is functionally involved in calcium uptake by several osteoblast-like cell lines. We have extended these studies to investigate the actions of ALPase on the cAMP response to and the receptor binding of human parathyroid hormone (hPTH) and human parathyroid hormone-related protein (hPTHrP). Pretreatment of human osteoblast-like SaOS-2 cells with human placental ALPase (hpALPase) inhibited the cAMP response to hPTH(1-34) but had no effect on the actions of hPTHrP(1-34) or vasoactive intestinal peptide. The inhibitory effect was reversed by L-Phe-Gly-Gly, an inhibitor of hpALPase. Treatment of SaOS-2 cells with hpALPase modestly reduced the binding of hPTH to 70% of control values, with little or no effect on the binding of hPTHrP. Bovine kidney and calf intestine ALPases were without effect on either the cAMP response or binding of hPTH or hPTHrP in SaOS-2 cells. In rat osteoblast-like ROS 17/2.8 cells, hpALPase had no effect on cAMP production stimulated by hPTH(1-34) or hPTHrP(1-34), arguing against a nonspecific effect of hpALPase. We suggest that, in SaOS-2 cells, the common PTH/PTHrP receptor can differentiate between the agonist activities of hPTH and hPTHrP by a mechanism that is sensitive to hpALPase.

Passive immunization with anti-parathyroid hormone-related protein monoclonal antibody markedly prolongs survival time of hypercalcemic nude mice bearing transplanted human PTHrP-producing tumors

Malignancy-associated hypercalcemia is mainly caused by excessive production of parathyroid hormone-related protein (PTHrP) by the tumor. Using anti-PTHrP-(1-34) monoclonal murine antibody (anti-PTHrP MoAb), we studied whether repeated injection of the homologous antibody would continuously decrease the serum calcium concentration in hypercalcemic nude mice bearing transplanted human PTHrP-producing tumors, leading to prolongation of their survival time. Daily SC injections of anti-PTHrP MoAb decreased the serum calcium concentration almost to within the normal range in nude mice bearing transplanted human PTHrP-producing tumors (T3M-1, EC-GI, PC-3, and FA-6) but not in a nude mouse bearing a transplanted parathyroid carcinoma. The antibody did not affect FA-6 tumor growth either in vitro or in vivo. Pancreatic carcinoma cells (FA-6), which caused the most severe hypercalcemia, were inoculated into 6-week-old nude mice. When severe hypercalcemia (approximately 19 mg/dl) had developed, daily SC injection of anti-PTHrP MoAb was started. Within 18 days of this time point, all untreated tumor-bearing mice (n = 10) died of hypercalcemia and cachexia, whereas all the treated mice (n = 10) showed an increase in body weight and survived for at least 25 days. Histologic examination of the treated mice revealed a marked decrease in osteoclastic bone resorption, without toxicologic findings in the kidney and liver. These results suggest that passive immunization against PTHrP can continuously ameliorate the hypercalcemia and markedly prolong the survival time of severely hypercalcemic, tumor-bearing mice. If a human monoclonal antibody against PTHrP-(1-34) could be developed, then passive immunization would be potentially one of the most effective therapies for patients with malignancy-associated hypercalcemia due to excessive production of PTHrP.

Salmon stanniocalcin and bovine parathyroid hormone have dissimilar actions on mammalian bone

Stanniocalcin (STC), a calcium-regulating glycoprotein hormone isolated from the corpuscles of Stannius of salmon, was tested for effects on bone and calcium metabolism in mammalian species (rats and mice). STC generally failed to alter serum calcium of parathyroidectomized rats at concentrations equimolar with effective concentrations of parathyroid hormone (PTH). STC did not increase cAMP in ROS 17/2.8 or UMR-108 osteosarcoma cells, OK kidney cells, fetal rat limb bones, or neonatal mouse calvariae, and similarly failed to increase urinary cAMP in rats. STC did not consistently stimulate resorption in any of the rodent bone culture systems, although variable resorptive responses were elicited in fetal mouse calvariae. The results indicate that this fish hormone has limited, if any, PTH-like activity on calcium metabolism in mammalian systems.

Effects of glucocorticoids and calcitonin on parathyroid hormone-related protein (PTHrP) gene expression and PTHrP release in human cancer cells causing humoral hypercalcemia

Glucocorticoids are widely used for the treatment of malignancy-associated hypercalcemia to delay the occurrence of an escape phenomenon inherent in calcitonin therapy. Using parathyroid hormone-related protein (PTHrP)-producing squamous carcinoma cells (T3M-1 and EC-GI) established in our laboratory, we investigated the in vitro effects of glucocorticoids and calcitonin on PTHrP mRNA expression in the cells and release of PTHrP into the culture medium. The PTHrP gene was constitutively expressed in the logarithmic growth phase in both squamous carcinoma cell lines. When these cells became superconfluent, PTHrP mRNA expression was greatly diminished in T3M-1 cells but was not distinctly diminished in EC-GI cells. Hydrocortisone inhibited the PTHrP mRNA expression in T3M-1 cells and EC-GI cells in a dose-dependent manner. In accordance with the decreased expression of PTHrP mRNA, the release of immunoreactive as well as bioactive PTHrP also decreased in the conditioned medium of glucocorticoid-treated cells. The minimal effective concentration of prednisolone was about 10(-7) M, which is readily attainable in the serum of patients treated with the agent. Calcitonin and indomethacin did not affect the PTHrP mRNA expression or PTHrP release into the medium. Calcitonin did not modulate the hydrocortisone-induced inhibition of PTHrP production. These in vitro findings suggest that the combined use of glucocorticoids and calcitonin plays a beneficial role in the treatment of malignancy-associated hypercalcemia, since the steroid hormone can suppress PTHrP mRNA expression and release of bioactive PTHrP in certain PTHrP-producing tumors.

Hypercalcaemia and the synthesis of interleukin-1 by an ameloblastoma

A case of hypercalcaemia secondary to a long-standing solitary ameloblastoma is presented with evidence to suggest that the raised plasma calcium was the result of the secretion of interleukin-1 and a parathyroid hormone-like substances by the tumour. The aetiology of humoral hypercalcaemia of malignancy is discussed in relation to the role played by these substances.

In vitro and in vivo antagonists against parathyroid hormone-related protein

Four analogues of parathyroid hormone-related protein (PTHrP), PTHrP(7-34)NH2, (10-34)NH2, (15-34)NH2 and (20-34)NH2, were synthesized and their antagonistic activity against PTHrP(1-34) was examined in vitro and in vivo. In vitro studies revealed that all four analogues antagonized PTHrP-stimulated cyclic AMP production in rat osteosarcoma cells (ROS 17/2.8), and that PTHrP(7-34)NH2 and PTHrP(10-34)NH2 had potent antagonistic activity. In vivo experiments in nude mice also revealed that PTHrP(7-34)NH2 completely inhibited hypercalcemia induced by PTHrP(1-34), indicating that these analogues antagonize the effects of PTHrP(1-34) in vitro and in vivo.