Effects of bone in vitro of bovine parathyroid hormone and synthetic fragments representing residues 1-34, 2-34 and 3-34

Analysis of correlation between estradiol and fracture of femur neck

Osteoporosis is a major public health challenge all over the world. Estrogen hormone was cited amongst other hormones to be an efficient hormone for the production and maintenance of bone density. This study was designed with the purpose of evaluating and analyzing the estradiol effect on fractures of femur neck in the Iranian society. This study evaluated men over 50 years of age suffering with mild trauma (falling off the same level height or lower) and with a fracture on their femur neck. Also, their serum level of estradiol was measured with an ELISA method. Using this procedure, the patients were assigned into groups with either normal estradiol serum level (10pg/ml and higher) or with lower than normal level (lower than 10 pg/ml). A control group including 50-year-old and older men without hip fracture, or its history, was chosen to access their estradiol serum level. Data collected from these two groups were statistically compared. A total of 120 patients were evaluated (60 in the control and 60 in the test group). The mean age of patients in the control and test groups were 67.9±10.22 and 69.5±8.84 years, respectively (p=0.376). Smoker patients’ percentages in the control and test groups were 35% and 31.7%, respectively (p=0.699). On the basis of the serum estradiol level, patients’ percentages with low estradiol level in control and test groups were 10% and 16.7%, respectively (p=0.283). The only significant factor in predicting serum estradiol level was smoking. In conclusion, in this study it was observed that fractures of the femoral neck following a mild trauma were not correlated to low level of serum estradiol.

Muscle-bone and fat-bone interactions in regulating bone mass: do PTH and PTHrP play any role?

Metabolic bone disease occurs when there is a net loss in bone density. Osteoporosis, the most common metabolic bone disease, is a devastating problem and an increasingly major public health issue. A substantial body of evidence in the elderly population indicates that a relationship exists between the components of body weight and various measures of bone/mass, density, and function. Both muscle and fat contribute to the body's total weight and the intimate associations of muscle, fat, and bone are known. But the close functional interactions between muscle and bone or fat and bone are largely unidentified and have drawn much attention in recent years. Each of these tissues not only responds to afferent signals from traditional hormone systems and the central nervous systems but also secretes factors with important endocrine functions. Studies suggest that during growth, development, and aging, the relationship of muscle and fat with the skeleton possibly governs bone homeostasis and turnover. A better understanding of the endocrine function and the cellular and molecular mechanisms and pathways linking muscle or adipose tissues with bone anabolism and catabolism is a new avenue for novel pathways for anabolic drug discovery. These in turn will likely lead to more rational therapy toward increasingly prevalent disorders like osteoporosis. In this review, some of the recent works on the interaction of bone with muscle and fat are highlighted, and in so doing the role of parathyroid hormone (PTH), and PTH-related peptide (PTHrP) is surveyed.

The structure of secretin family GPCR peptide ligands: implications for receptor pharmacology and drug development

The secretin family G protein-coupled receptors, characterized by a large N-terminal extracellular domain and seven transmembrane helices, are drug targets in many diseases, including migraine, cardiovascular disease, diabetes, osteoporosis and inflammatory disorders. Their activating ligands are peptides with an average length of 30 amino acids. In this article we review the available structural data for these peptides and how this explains their activity. We emphasize how this information may be used to accelerate the development of new drugs against these receptors.

Osteoporotic fracture and parathyroid hormone

Osteoporosis and age-related bone loss is associated with changes in bone remodeling characterized by decreased bone formation relative to bone resorption, resulting in bone fragility and increased risk of fractures. Stimulating the function of bone-forming osteoblasts, is the preferred pharmacological intervention for osteoporosis. Recombinant parathyroid hormone (PTH), PTH(1-34), is an anabolic agent with proven benefits to bone strength and has been characterized as a potential therapy for skeletal repair. In spite of PTH's clinical use, safety is a major consideration for long-term treatment. Studies have demonstrated that intermittent PTH treatment enhances and accelerates the skeletal repair process via a number of mechanisms. Recent research into the molecular mechanism of PTH action on bone tissue has led to the development of PTH analogs to control osteoporotic fractures. This review summarizes a number of advances made in the field of PTH and bone fracture to combat these injuries in humans and in animal models. The ultimate goal of providing an alternative to PTH, currently the sole anabolic therapy in clinical use, to promote bone formation and improve bone strength in the aging population is yet to be achieved.

PTH and PTHrP signaling in osteoblasts

The striking clinical benefit of PTH in osteoporosis began a new era of skeletal anabolic agents. Several studies have been performed, new studies are emerging out and yet controversies remain on PTH anabolic action in bone. This review focuses on the molecular aspects of PTH and PTHrP signaling in light of old players and recent advances in understanding the control of osteoblast proliferation, differentiation and function.

Effects of transient PTH on early proliferation, apoptosis, and subsequent differentiation of osteoblast in primary osteoblast cultures

In primary calvarial osteoblast cultures derived from transgenic mice expressing green fluorescent protein (GFP) under the control of 3.6-kb Col1a1 promoter, the emergence of GFP signal marks the transition of multipotential osteoprogenitors into preosteoblasts. Early transient treatment (days 1-7) of these cultures with parathyroid hormone (PTH) has an anabolic effect that is not associated with an increase in total DNA content or cell number in day 21 cultures. In the present study, the effect of early PTH treatment on cell proliferation and apoptosis was examined in greater detail in GFP(+) and GFP(-) cells using flow cytometry. In preconfluent cultures, PTH significantly reduced the proportion of cells in S phase but increased those in G(0)/G(1) and G(2)+M phases in both GFP(+) and GFP(-) subpopulations. PTH decreased apoptosis only in GFP(-) but not GFP(+) cells, indicating an increased survival of GFP(-) cells. In contrast, PTH did not change the amounts of cell proliferation and apoptosis seen in either compartment after these cultures reached confluence. To further assess the effect of early PTH treatment on osteogenic differentiation, secondary cultures of sorted GFP(+) or GFP(-) cells were obtained from day 7 primary cultures that had been treated for 1 wk with PTH. This treatment resulted in larger areas of GFP expression accompanied by increased xylenol orange/von Kossa staining in the secondary cultures of GFP fractions. Early transient PTH treatment appears to enhance the commitment of progenitor cells to an osteogenic fate and results in a higher proportion of cells that achieve full osteoblast differentiation.

Backbone-methylated Analogues of the Principle Receptor Binding Region of Human Parathyroid Hormone

We have used backbone N-methylations of parathyroid hormone (PTH) to study the role of these NH groups in the C-terminal amphiphilic alpha-helix of PTH (1-31) in binding to and activating the PTH receptor (P1R). The circular dichroism (CD) spectra indicated the structure of the C-terminal alpha-helix was locally disrupted around the methylation site. The CD spectra differences were explained by assuming a helix disruption for four residues on each side of the site of methylation and taking into account the known dependence of CD on the length of an alpha-helix. Binding and adenylyl cyclase-stimulating data showed that outside of the alpha-helix, methylation of residues Asp30 and Val31 had little effect on structure or activities. Within the alpha-helix, disruption of the structure was associated with increased loss of activity, but for specific residues Val21, Leu24, Arg25, and Leu28 there was a dramatic loss of activities, thus suggesting a more direct role of these NH groups in correct P1R binding and activation. Activity analyses with P1R-delNT, a mutant with its long N-terminal region deleted, gave a different pattern of effects and implicated Ser17, Trp23, and Lys26 as important for its PTH activation. These two groups of residues are located on opposite sides of the helix. These results are compatible with the C-terminal helix binding to both the N-terminal segment and also to the looped-out extracellular region. These data thus provide direct evidence for important roles of the C-terminal domain of PTH in determining high affinity binding and activation of the P1R receptor.

Parathyroid hormone secretion and action: evidence for discrete receptors for the carboxyl-terminal region and related biological actions of carboxyl- terminal ligands

PTH is a major systemic regulator of the concentrations of calcium, phosphate, and active vitamin D metabolites in blood and of cellular activity in bone. Intermittently administered PTH and amino-terminal PTH peptide fragments or analogs also augment bone mass and currently are being introduced into clinical practice as therapies for osteoporosis. The amino-terminal region of PTH is known to be both necessary and sufficient for full activity at PTH/PTHrP receptors (PTH1Rs), which mediate the classical biological actions of the hormone. It is well known that multiple carboxyl-terminal fragments of PTH are present in blood, where they comprise the major form(s) of circulating hormone, but these fragments have long been regarded as inert by-products of PTH metabolism because they neither bind to nor activate PTH1Rs. New in vitro and in vivo evidence, together with older observations extending over the past 20 yr, now points strongly to the existence of novel large carboxyl-terminal PTH fragments in blood and to receptors for these fragments that appear to mediate unique biological actions in bone. This review traces the development of this field in the context of the evolution of our understanding of the "classical" receptor for amino-terminal PTH and the now convincing evidence for these receptors for carboxyl-terminal PTH. The review summarizes current knowledge of the structure, secretion, and metabolism of PTH and its circulating fragments, details available information concerning the pharmacology and actions of carboxyl-terminal PTH receptors, and frames their likely biological and clinical significance. It seems likely that physiological parathyroid regulation of calcium and bone metabolism may involve receptors for circulating carboxy-terminal PTH ligands as well as the action of amino-terminal determinants within the PTH molecule on the classical PTH1R.

Parathyroid hormone and parathyroid hormone-related protein exert both pro- and anti-apoptotic effects in mesenchymal cells

During bone formation, multipotential mesenchymal cells proliferate and differentiate into osteoblasts, and subsequently many die because of apoptosis. Evidence suggests that the receptor for parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP), the PTH-1 receptor (PTH-1R), plays an important role in this process. Multipotential mesenchymal cells (C3H10T1/2) transfected with normal or mutant PTH-1Rs and MC3T3-E1 osteoblastic cells were used to explore the roles of PTH, PTHrP, and the PTH-1R in cell viability relative to osteoblastic differentiation. Overexpression of wild-type PTH-1R increased cell numbers and promoted osteocalcin gene expression versus inactivated mutant receptors. Furthermore, the effects of PTH and PTHrP on apoptosis were dramatically dependent on cell status. In preconfluent C3H10T1/2 and MC3T3-E1 cells, PTH and PTHrP protected against dexamethasone-induced reduction in cell viability, which was dependent on cAMP activation. Conversely, PTH and PTHrP resulted in reduced cell viability in postconfluent cells, which was also dependent on cAMP activation. Further, the proapoptotic-like effects were associated with an inhibition of Akt phosphorylation. These data suggest that parathyroid hormones accelerate turnover of osteoblasts by promoting cell viability early and promoting cell departure from the differentiation program later in their developmental scheme. Both of these actions occur at least in part via the protein kinase A pathway.

Analogues of human parathyroid hormone (1-31)NH(2): further evaluation of the effect of conformational constraint on biological activity

A series of conformationally-restricted analogues of hPTH was prepared, based on the parent peptide agonist, cyclo(Lys(18)-Asp(22))[Ala(1),Nle(8),Lys(18),Asp(22),Leu(27)]hPTH(1-31)NH(2) (2, EC(50)=0.29nM). Truncation of 2 at either the N- or C-termini resulted in peptides with reduced agonist activity as measured by stimulation of adenylate cyclase activity in the rat osteosarcoma cell line (ROS 17/2.8). Alanine- and glycine-scanning at the N-terminus of 2 was consistent with data previously obtained on linear hPTH(1-34). Other locations within the primary sequence of hPTH(1-31)NH(2) were evaluated by the placement of the [i, i+4] lactam constraining element. Ring size and lactam orientations at the 18-22 positions were also examined.

Pulmonary delivery of drugs for bone disorders

As the population ages, osteoporosis becomes a growing public health concern. Current treatments provide patients with limited clinical improvement, numerous side effects, and no cure. The naturally-occurring peptides calcitonin and parathyroid hormone, which regulate bone metabolism, offer alternative treatment options. Clinical studies indicate the usefulness of calcitonin and parathyroid hormone in osteoporosis and Paget's disease of bone. For the peptides to become viable therapies, formulations must be developed that bypass the need for injection. Pulmonary delivery of calcitonin and parathyroid hormone appears likely in the near future.

Analysis of signaling pathways used by parathyroid hormone to activate the c-fos gene in human SaOS2 osteoblast-like cells

We have evaluated the signaling pathways activated by parathyroid hormone (PTH) in SaOS2 human osteoblastlike cells correlating with induction of the c-fos proto-oncogene. Human PTH(1-34) (hPTH[1-34]) and hPTH(1-34) Nle8,18 Tyr34 induced the expression of c-fos mRNA in quiescent SaOS2 cells in a concentration-dependent manner. N-terminal truncations of hPTH(1-34) that fail to activate protein kinase A (PKA) also abolished c-fos mRNA induction. In gel retardation assays hPTH(1-34) led to a change in the mobility of specific, cyclic adenosine monophosphate (cAMP) response element binding protein (CREB)-containing protein-DNA complexes identical to that caused by other activators of PKA. The appearance of this altered mobility complex correlated temporally with the induction of c-fos mRNA. Using a c-fos serum response element probe, a slowed protein DNA complex appeared upon serum, epidermal growth factor, and basic fibroblast growth factor treatment. This slowed complex reflects phosphorylation of the transcription factor ternary complex factor (TCF) mediated via activation of the mitogen-activated protein (MAP) kinase pathway. The MAP kinase cascade is also activated by protein kinase C (PKC), and treatment with phorbol ester led to the induced TCF shift. In contrast, PTH did not produce this shift, ruling out PTH activation of c-fos via PKC and the MAP kinase signaling cascade. Further evidence for this was the lack of effect of the highly selective PKC inhibitor CGP 41251 on c-fos induction by hPTH(1-34). The janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling cascade targets the v-sis-inducible element in the c-fos promoter via the induced binding of STATs. Interferon gamma rapidly induced STAT binding in SaOS2 cells, unlike PTH. Thus, PTH induction of c-fos transcription appears to occur principally through activation of PKA that then targets CREB and the c-fos calcium/cAMP response element.

The biphasic effect of triiodothyronine compared to bone resorbing effect of PTH on bone modelling of mouse long bone in vitro

To examine the effects of T3 on fetal long bone modelling the radii and ulnae of 16 day old fetal mice were grown in vitro for two days. Their growth, mineralization, and resorption were assessed by measuring diaphyseal length, calcium and phosphorus content, hydroxyproline content, and the release of incorporated 45Ca. The effects of T3 were compared to the effects of 1-34 PTH, a known resorbing agent, on the same system. Devitalized bones were used as a control. The results showed that T3 had a biphasic effect. At high concentrations (10(-5) M-10(-6) M) T3 inhibited the growth of the bones as indicated by their diaphyseal length and hydroxyproline content. Calcium and phosphorus content were significantly decreased while 45Ca release was increased. Similar effects were also found after the addition of 1-34 PTH to the media. However, T3, at lower concentrations (10(-7) M-10(-9) M), stimulated the growth and calcification of the bones as indicated by an increase in diaphyseal length and the hydroxyproline, calcium, and phosphorus content. 45Ca release was significantly decreased at these concentrations. Neither T3 nor 1-34 PTH affected devitalized bones in the same system. The results suggest that at physiological concentrations, T3 has a direct, anabolic effect on bone, which may explain its major role in the growth process of various species. At high doses, however, T3 stimulates bone resorption in a way similar to PTH.

Stimulation of alkaline phosphatase activity in cultured neonatal mouse calvarial bone cells by parathyroid hormone

The effect of parathyroid hormone (PTH) on alkaline phosphatase activity was examined in confluent, serum-free primary cultures of neonatal mouse calvarial cells. It was found that synthetic bPTH-(1-34) caused an increase in the specific activity of skeletal alkaline phosphatase isoenzyme by 18 hours. Between 10 and 500 ng/ml, the magnitude of the change was directly related to peptide concentration. The change occurred in the absence of any effect on cell number, total cell protein, or DNA and was not the result of an effect on either proliferation or survival of a specific cell population. Results of histochemical studies indicate that bPTH-(1-34) caused an increase in the proportion of cells containing enzyme activity. The response was duplicated by intact bPTH-(1-84) and DBcAMP, but not by oxidized bPTH-(1-34) or insulin and did not require prostaglandin synthesis or hydroxylation of 25-hydroxyvitamin D3. These results demonstrate that bPTH has a direct effect on osteoblast maturation in vitro, that the effect is specific for PTH, and suggest that it is mediated by cAMP.

Semi-preparative high-performance liquid chromatographic purification of a 28-amino acid synthetic parathyroid hormone antagonist

Structure-activity studies of parathyroid hormone (PTH) over the last decade have led to the design and synthesis of a peptide hormone inhibitor of PTH action in vivo, [Tyr-34]bPTH-(7-34)amide. To evaluate the biological properties of this 28-amino acid hormone analogue, sufficient amounts of the peptide needed to be prepared in a high state of purity to permit continuous infusion in groups of animals for periods of several hours. For this purpose, gel chromatography followed by semi-preparative, reversed-phase high-performance liquid chromatography (HPLC) using a lyophilizable solvent gradient system of acetonitrile in 0.1% trifluoroacetic acid was utilized. In a parallel purification scheme, gel filtration followed by ion-exchange chromatography was employed. Comparison of yields and product purity were determined by a battery of chemical analytical techniques. Semi-preparative HPLC generated a highly purified product; substantial heterogeneity was detected in the ion-exchange-purified material. The HPLC-purified product retains the biological activities of binding to PTH receptors in vitro and inhibiting PTH action in vivo.

Nonosteomalacic osteopathy associated with chronic hypophosphatemia

We studied bone histomorphometry in 19 patients with chronic hypophosphatemia related to an idiopathic renal phosphate wasting and without histological osteomalacia. Nine patients had renal lithiasis (group 1), three had radiological osteoporosis (group 2), and seven had lumbar pain (group 3). In the whole group of 19 patients, serum phosphate levels were low (24.9 +/- 2.1 mg/l), calcium in blood was normal, calcium in urine was increased, and iPTH was low. Histomorphometric data showed decreased osteoblastic surfaces with normal resorption surfaces, normal osteoid volume and calcification front. There was no correlation between serum phosphate level and histomorphometric parameters. There was no statistical difference between the data of the 3 groups of hypophosphatemic patients. We concluded that chronic hypophosphatemia in the adult doses not always lead to osteomalacia but to an unusual osteopathy characterized by an osteopenia due to an isolated decrease in bone formation. The respective importance of phosphate deficiency and of decreased iPTH level in the pathogenesis of this osteopathy is uncertain.

Parathyroid hormone stimulates bone formation and resorption in organ culture: evidence for a coupling mechanism

We have developed an in vitro system, using embryonic chicken tibiae grown in a serum-free medium, which exhibits simultaneous bone formation and resorption. Tibiae from 8-day embryos increased in mean (+/- SD) length (4.0 +/- 0.4 to 11.0 +/- 0.3 mm) and dry weight (0.30 +/- 0.04 to 0.84 +/- 0.04 mg) during 12 days in vitro. There was increased incorporation of [3H]proline into hydroxyproline (120 +/- 20 to 340 +/- 20 cpm/mg of bone per 24 hr) as a measure of collagen synthesis, as well as a 62 +/- 5% increase in total calcium and 45Ca taken up as an indication of active mineralization. A physiologic concentration (1 pM) of parathyroid hormone was found to stimulate bone resorption over control levels in this system. Parathyroid hormone stimulated the release of [3H]hydroxyproline from the bone shafts but not from the cartilage ends, indicating the specificity of the response. With 1 pM parathyroid hormone we observed an acute inhibition of bone formation, followed (after 12-16 hr) by a chronic stimulation of bone formation during the 12-day incubation. Both mineral uptake and matrix formation were enhanced at approximately the same rate during the 12-day incubation. The chronic enhancement of formation required parathyroid hormone only for the initial 8-10 hr of incubation. These results could be explained by the production or release of a factor from bone to stimulate formation in response to the acute increase in resorption--a "coupling factor." Indeed, dialyzed culture medium conditioned by actively resorbing bones stimulated bone formation over controls when added to organ cultures at a 1:20 dilution. The factor is larger than 12,000 daltons as determined by dialysis. The factor is specific for the bone shaft and did not affect the cartilage ends.

Comparison of the effects of a potent synthetic analog of bovine parathyroid hormone with native bPTH-(1-84) and synthetic bPTH-(1-34) on bone resorption and collagen synthesis

An analog of bobine PTH [nle-8, nle-18, tyr-34 bPTH-(1-34) amide, (PTH-Ana)] which is a potent stimulator of renal adenylate cyclase has been compared with the native hormone bPTH-(1-84) and the biologically active amino terminal portion, bPTH-(1-34), for its effects on bone resorption and bone collagen synthesis in organ culture. All three compounds stimulated the release of previously incorporated 45Ca from cultured fetal rat long bone shafts with similar dose-response curves at 10(-9) to 3 X 10(-8) M. All three compounds inhibited bone collagen synthesis as measured by incorporation of proline into collagenase digestible protein, whereas incorporation into noncollagen protein was not inhibited. The effects were dose related and decreases in percent collagen synthesis were significant at 10(-9) M. Thus PTH-Ana appears to have the same effects on bone resorption and collagen synthesis as bPTH-(1-84) and (1-34) and is likely to be a valid probe for investigating PTH receptors in bone as well as in kidney.

Mechanisms of hypercalcemia in malignancy

Various hormones have been implicated in the genesis of hypercalcemia in patients with malignancy. Ectopic secretion of PTH by tumor has been documented in only a few patients; rather, elevated levels of circulating iPTH have been presumed to reflect tumor production of hormone in most patients. Small fragments of PTH, as well as polypeptides larger than native PTH, have been described; their biological roles are unclear. The pattern of immunoreactivity, however, has been used to differentiate patients with ectopic hyperparathyroidism from patients with concomitant primary hyperparathyroidism. Vitamin D-like sterols produced by breast cancer seldom reach plasma levels necessary for physiological effects. Members of the prostaglandin family have been proposed to induce hypercalcemia through osteoclast activation or alteration of the immune system and also to affect the frequency of bone metastases. At present, no direct evidence is available to prove a direct role for these effects and prostaglandins are most useful as possible indicators of disease activity.