Daily nasal spray of hPTH(1-34) for 3 months increases bone mass in osteoporotic subjects: a pilot study

Formulation and In Vitro Characterization of a Vacuum-Dried Drug–Polymer Thin Film for Intranasal Application

Intranasal drug applications show significant therapeutic potential for diverse pharmaceutical modalities. Because the formulation applied to the nasal cavity is discharged to the pharyngeal side by mucociliary clearance, the formulation should be dissolved effectively in a limited amount of mucus within its retention time in the nasal cavity. In this study, to develop novel formulations with improved dissolution behavior and compatibility with the intranasal environment, a thin-film formulation including drug and polymer was prepared using a vacuum-drying method. The poorly water-soluble drugs ketoprofen, flurbiprofen, ibuprofen, and loxoprofen were dissolved in a solvent comprising water and methanol, and evaporated to obtain a thin film. Physical analyses using differential scanning calorimetry (DSC), powder X-ray diffraction analysis (PXRD), and scanning electron microscopy SEM revealed that the formulations were amorphized in the film. The dissolution behavior of the drugs was investigated using an in vitro evaluation system that mimicked the intranasal physiological environment. The amorphization of drugs formulated with polymers into thin films using the vacuum-drying method improved the dissolution rate in artificial nasal fluid. Therefore, the thin film developed in this study can be safely and effectively used for intranasal drug application.

Development and in vivo evaluation of intranasal formulations of parathyroid hormone (1-34)

For efficient intranasal transport of parathyroid hormone (1-34) [PTH(1-34)], there is a great medical need to investigate permeation enhancers for intranasal formulations. In this study, the development of PTH(1-34) intranasal formulations was conducted. Based on conformation and chemical stability studies, the most preferable aqueous environment was determined to be 0.008 M acetate buffer solution (ABS). Subsequently, citric acid and Kolliphor^® HS·15 were compared as permeation enhancers. The mechanisms of action of citric acid and Kolliphor^® HS·15 were investigated using an in vitro model of nasal mucosa, and Kolliphor^® HS·15 led to higher permeability of fluorescein isothiocyanate-labeled PTH(1-34) (FITC-PTH) by enhancing both the transcellular and paracellular routes. Moreover, citric acid showed severe mucosal toxicity resulting in cilia shedding, while Kolliphor^® HS·15 did not cause obvious mucosa damage. Finally, Kolliphor^® HS·15 was studied as a permeation enhancer using a liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The results showed that 5% and 10% Kolliphor^® HS·15 increased the bioavailability of PTH(1-34) to 14.76% and 30.87%, respectively. In conclusion, an effective and biosafe PTH(1-34) intranasal formulation was developed by using 10% Kolliphor^® HS·15 as a permeation enhancer. Intranasal formulations with higher concentrations of Kolliphor^® HS·15 for higher bioavailability of PTH(1-34) could be further researched.

Nasal Administration and Plasma Pharmacokinetics of Parathyroid Hormone Peptide PTH 1-34 for the Treatment of Osteoporosis

Nasal delivery of large peptides such as parathyroid 1-34 (PTH 1-34) can benefit from a permeation enhancer to promote absorption across the nasal mucosa into the bloodstream. Previously, we have published an encouraging bioavailability (78%), relative to subcutaneous injection in a small animal preclinical model, for a liquid nasal spray formulation containing the permeation enhancer polyethylene glycol (15)-hydroxystearate (Solutol^® HS15). We report here the plasma pharmacokinetics of PTH 1-34 in healthy human volunteers receiving the liquid nasal spray formulation containing Solutol^® HS15. For comparison, data for a commercially manufactured teriparatide formulation delivered via subcutaneous injection pen are also presented. Tc-99m-DTPA gamma scintigraphy monitored the deposition of the nasal spray in the nasal cavity and clearance via the inferior meatus and nasopharynx. The 50% clearance time was 17.8 min (minimum 10.9, maximum 74.3 min). For PTH 1-34, mean plasma C_max of 5 pg/mL and 253 pg/mL were obtained for the nasal spray and subcutaneous injection respectively; relative bioavailability of the nasal spray was ≤1%. Subsequently, we investigated the pharmacokinetics of the liquid nasal spray formulation as well as a dry powder nasal formulation also containing Solutol^® HS15 in a crossover study in an established ovine model. In this preclinical model, the relative bioavailability of liquid and powder nasal formulations was 1.4% and 1.0% respectively. The absolute bioavailability of subcutaneously administered PTH 1-34 (mean 77%, range 55-108%) in sheep was in agreement with published human data for teriparatide (up to 95%). These findings have important implications in the search for alternative routes of administration of peptides for the treatment of osteoporosis, and in terms of improving translation from animal models to humans.

Influence of Dosing Interval and Administration on the Bone Metabolism, Skeletal Effects, and Clinical Efficacy of Parathyroid Hormone in Treating Osteoporosis: A Narrative Review

Recombinant human parathyroid hormone (PTH) is the key anabolic agent used for preventing fracture in postmenopausal women with osteoporosis. In bone metabolism, PTH signaling is mediated through a G protein–coupled receptor that affects various post‐receptor signaling pathways. Results of preclinical and clinical studies have shown that PTH improves both the structure and strength of bone tissue. Once daily subcutaneous injection of the PTH fragment, teriparatide (PTH [1‐34]), is the most commonly recommended formulation and dosing strategy in clinical practice. However, other dosing intervals, formulations, and routes have been investigated in preclinical and clinical studies. In particular, once‐weekly and cyclical administration have been investigated mainly as a means of reducing the high direct costs of treatment. In preclinical studies, bone formation/resorption markers, bone mineral density measurements, and histomorphometric parameters improved with both once‐daily and once‐weekly administration. However, the magnitude and duration of such improvements were generally greater with once‐daily PTH administration. In clinical studies, reductions in fracture incidence were also noted with both once‐daily and once‐weekly PTH administration, although improvements in nonvertebral fractures are less evident with once‐weekly administration. This narrative review details the differences between PTH formulation and dosing strategies in relation to preclinical and clinical efficacy/safety parameters, although it should be stressed that no head‐to‐head studies allow direct comparisons. This review also seeks to outline practical considerations involved with PTH prescribing and new directions in research regarding routes of administration. © 2017 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Preparation and in vivo evaluation of an orally available enteric-microencapsulated parathyroid hormone (1-34)-deoxycholic acid nanocomplex

The N-terminal 34-amino-acid peptide fragment of human parathyroid hormone PTH (1-34), is used clinically to treat osteoporosis; however, it is currently administered by a once-daily subcutaneous injection, resulting in poor patient compliance. We have developed enteric microcapsules containing an ionic nanocomplex between PTH (1-34) and lysine-linked deoxycholic acid (LysDOCA) for the oral delivery of PTH (1-34). We measured the particle size of the PTH/LysDOCA complex and assessed its biological activity by determining the cAMP content in MC3T3-E1 cells. We also assessed its permeability across a Caco-2 cell monolayer and the bioavailability of the intrajejunally administered PTH/LysDOCA complex compared with PTH (1-34) in rats. In addition, the antiosteoporotic activity of the PTH/LysDOCA complex, encapsulated in an enteric carrier by coaxial ultrasonic atomization, was evaluated after it was orally administered to ovariectomized (OVX) rats. The formation of an ionic complex between PTH (1-34) and LysDOCA produced nanoparticles of diameter 33.0±3.36 nm, and the bioactivity of the complex was comparable with that of PTH (1-34). The Caco-2 cell permeability and AUClast value of the PTH/LysDOCA (1:10) nanocomplex increased by 2.87- and 16.3-fold, respectively, compared with PTH (1-34) alone. Furthermore, the OVX rats treated with oral PTH/LysDOCA-loaded enteric microcapsules showed an increase in bone mineral density (159%), bone volume fraction (175%), and trabecular number (174%) compared with those in the OVX control group. Therefore, the PTH/LysDOCA nanocomplex oral delivery system is a promising treatment modality for osteoporosis because it improves osteogenesis and trabecular connectivity.

Novel therapies for osteoporosis

Since the identification of osteoporosis as a major health issue in aging populations and the subsequent development of the first treatment modalities for its management, considerable progress has been made in our understanding of the mechanisms controlling bone turnover and disease pathophysiology, thus enabling the pinpointing of new targets for intervention. This progress, along with advances in biotechnology, has rendered possible the development of ever more sophisticated treatments employing novel mechanisms of action. Denosumab, a monoclonal antibody against RANKL, approved for the treatment of postmenopausal and male osteoporosis, significantly and continuously increases bone mineral density (BMD) and maintains a low risk of vertebral, non-vertebral, and hip fractures for up to 8 years. Currently available combinations of estrogens with selective estrogen receptor modulators moderately increase BMD without causing the extra-skeletal adverse effects of each compound alone. The cathepsin K inhibitor odanacatib has recently been shown to decrease vertebral, non-vertebral, and hip fracture rates and is nearing approval. Romosozumab, an anti-sclerosin antibody, and abaloparatide, a PTH-related peptide analog, are at present in advanced stages of clinical evaluation, so far demonstrating efficaciousness together with a favorable safety profile. Several other agents are currently in earlier clinical and preclinical phases of development, including dickkopf-1 antagonists, activin A antagonists, β-arrestin analogs, calcilytics, and Src tyrosine kinase inhibitors.

Novel approaches to the treatment of osteoporosis

Despite the availability of efficacious treatments for fracture reduction in patients with osteoporosis, there are still unmet needs requiring a broader range of therapeutics. In particular, agents that are capable of replacing already lost bone and that also drastically reduce the risk of non-vertebral fractures are needed. Studies of rare bone diseases in humans and animal genetics have identified targets in bone cells for the development of therapies for osteoporosis with novel mechanisms of action. Here, we review these new developments, with emphasis on inhibitors of cathepsin K in osteoclasts and sclerostin in osteocytes, which are currently studied in phase 3 clinical trials.

Emerging therapies for the treatment of osteoporosis

Osteoporosis is a chronic disease of the osseous system characterized by decreased bone strength and increased fracture risk. It is due to an imbalance in the dynamic ongoing processes of bone formation and bone resorption. Currently available osteoporosis therapies like bisphosphonates, selective estrogen receptor modulators (SERMs), and denosumab are anti-resorptive agents. Parathyroid hormone analogs like teriparatide are the only anabolic agents currently approved for osteoporosis treatment. The side-effects and limited efficacy of the presently available therapies has encouraged extensive research into the pathophysiology of the disease and newer drug targets for its treatment. The novel anti-resorptive agents being developed are newer SERMs, osteoprotegerin, c-src (cellular-sarcoma) kinase inhibitors, αVβ3 integrin antagonists, cathepsin K inhibitors, chloride channel inhibitors, and nitrates. Upcoming anabolic agents include calcilytics, antibodies against sclerostin and Dickkopf-1, statins, matrix extracellular phosphoglycoprotein fragments activin inhibitiors, and endo-cannabinoid agonists. Many of these new drugs are still in development. This article provides an insight into the emerging drugs for the treatment of osteoporosis.

Parathyroid hormone and parathyroid hormone-related protein analogs as therapies for osteoporosis

Osteoporotic fractures result in significant morbidity and mortality. Anabolic agents reverse the negative skeletal balance that characterizes osteoporosis by stimulating osteoblast-dependent bone formation to a greater degree than osteoclast-dependent bone resorption. Parathyroid hormone (PTH) and parathyroid hormone- related protein (PTHrP) are peptide hormones, which have anabolic actions when administered intermittently. The only FDA-approved anabolic bone agent for the treatment of osteoporosis in the United States is PTH 1-34, or teriparatide, administered by daily subcutaneous injections. However, PTH 1-84 is also available in Europe. Synthetic human PTHrP 1-36 and a PTHrP 1-34 analog, BA058, have also been shown to increase lumbar spine bone density. These agents and several other PTH and PTHrP analogs, including some which are not administered as injections, continue to be investigated as potential anabolic therapies for osteoporosis.

Treating osteoporosis by targeting parathyroid hormone to bone

Osteoporosis is a major public health problem despite widespread use of bisphosphonate therapy. PTH(1-34) is a more effective treatment; but its use has been limited by side effects (hypercalcemia, tumor risk) and inconvenient dosing (daily injection). Long-acting forms of PTH are also effective but cause severe hypercalcemia, presumably from effects in kidney. We hypothesized that targeted delivery of PTH to bone using a collagen binding domain (PTH-CBD) could reduce hypercalcemia. PTH-CBD is cleared from serum within 12hours after subcutaneous administration. In ovariectomized rats, monthly administration of PTH-CBD increased spinal BMD by 14.2% with no associated hypercalcemia. Such bone-targeted anabolic agents may ultimately allow the superior efficacy of anabolic therapy to be obtained with the dosing convenience of bisphosphonates.

Cryopreservation of parathyroid tissue after parathyroid surgery for renal hyperparathyroidism: does it really make sense?

BACKGROUND

Metachronous autotransplantation of cryopreserved parathyroid tissue is a technique for treating postoperative hypoparathyroidism after parathyroid surgery for renal hyperparathyroidism (rHPT). The aim of the present study was to evaluate our institution's experience with metachronous autotransplantation to analyze the role of cryopreservation in the treatment of rHPT and to determine for whom and when cryopreservation of parathyroid tissue should be deemed necessary.

METHODS

A prospective database of patients with rHPT who underwent surgery between 1976 and 2011 was screened for patients with hypoparathyroidism who received a metachronous autotransplantation. Data were analyzed regarding clinical data, histopathological findings of the cryopreserved parathyroid tissues, and patient outcome after metachronous replantation of parathyroid tissue.

RESULTS

Fifteen of 883 patients with rHPT underwent a metachronous autotransplantation under local anesthesia at a mean time of 23 months following the last cervical surgery. Histopathology of the parathyroid tissue chosen for transplantation revealed a necrosis rate of 0 % in 14 and 70 % in one patient. Mean preoperative serum calcium and parathyroid hormone (PTH) levels were 2.0 mmol/l and 3.7 pg/ml, respectively. Autotransplantation raised mean serum calcium and PTH levels to 2.2 mmol/l and 97.5 pg/ml, respectively, after a mean follow-up of 78 months.

CONCLUSIONS

Metachronous autotransplantation following parathyroid surgery in patients with rHPT effectively normalizes PTH and calcium levels. The success rate is high if an adequate cryopreservation procedure is applied. However, it is rarely necessary, and therefore the cryopreservation of parathyroid tissue in all patients has to be questioned, at least from an economic point of view.

Anabolic therapies for osteoporosis

As the first FDA-approved anabolic agent for osteoporosis, teriparatide has proven effective for people at highest risk of fracture, despite limitations of expense, route of delivery, and length of treatment. Available data show that combination therapy with teriparatide and antiresorptive agents does not offer a therapeutic advantage. However, treatment with an antiresorptive agent after teriparatide discontinuation is essential to prevent the ensuing bone loss. Although pretreatment with bisphosphonates may somewhat attenuate the anabolic effect of teriparatide, significant gains in bone mineral density are still achieved and prior bisphosphonate use should not dissuade clinicians from using teriparatide in select patients.

Regulation of osteoblast differentiation by interleukin-11 via AP-1 and Smad signaling

Mechanical stress and parathyroid hormone (PTH) are major stimulators, and aging and glucocorticoids excess are important suppressors of osteoblast differentiation. Mechanical stress and PTH stimulate interleukin (IL)-11 expression in cells of osteoblast lineage by enhancing transcription of IL-11 gene via an increase in intracellular Ca²⁺. The elevated Ca²⁺ activates extracellular signal-regulated kinase (ERK) to enhance phosphorylation of cyclic AMP response element-binding protein (CREB), which binds to the fosB gene promoter and enhances ΔFosB expression. ΔFosB dimerizes with JunD on the IL-11 gene promoter to enhance its transcription. Both mechanical stress and PTH also stimulate phosphorylation of Smad1 via an activation of protein kinase Cδ (PKCδ). Phosphorylated Smad1 binds to the IL-11 gene promoter and forms complex with ΔFosB/JunD to further enhance IL-11 gene transcription. The increased IL-11 then suppresses expression of Wnt inhibitors, including Dickkopf 1 (Dkk1) and 2, and enhances Wnt signaling to stimulate osteoblast differentiation and inhibit adipocyte differentiation. The suppression of osteoblast differentiation by aging involves a decrease in IL-11 gene transcription by a reduction in JunD binding to the activator protein (AP)-1 site of the IL-11 gene promoter. Glucocorticoids inhibit transcriptional activation of IL-11 gene by an interaction of glucocorticoid-glucocorticoid receptor (GR) complex with ΔFosB/JunD heterodimer. Thus, factors that enhance osteoblast differentiation stimulate, and those which suppress osteoblast differentiation inhibit IL-11 gene transcription, and IL-11 enhances Wnt signaling by suppressing expression of its inhibitors. These observations are consistent with the notion that IL-11 mediates stimulatory and inhibitory signals of osteoblast differentiation by affecting Wnt signaling.

Effect of parathyroid hormone on hypogonadism induced bone loss of proximal femur of orchiectomized rat

Purpose

Management of hypogonadism-induced osteoporosis in elderly men is still a challenge. We investigated the short-term effects of parathyroid hormone (PTH) treatments on strength, micro-architecture, and mineral density of trochanteric region of orchiectomized rat femur.

Methods

Eight-month-old male Sprague–Dawley rats (n = 44) were divided into two groups: (1) orchiectomized (ORX) and (2) sham group. Twelve weeks after orchiectomy, half of the orchiectomized animals were treated with daily subcutaneously injected PTH (0.040 mg/kg/BW) (ORX-PTH) for 5 weeks. The other half remained untreated (ORX). The sham-operated group was divided and treated in the same way (sham, sham-PTH). After 5 weeks, both femurs were excised for biomechanical and histomorphometric analysis, trabecular measurements, mineral content assessment, and immunofluorescence analysis.

Results

The femoral trochanteric strength after PTH treatment was enhanced in the breaking test (ORX-F_max = 158.7 N vs. ORX + PTH-F_max = 202 N). Stiffness of treated ORX animals reached nearly the levels observed in untreated sham rats. PTH therapy improved the trabecular connectivity, width, and area (ORX-Tb.Ar = 47.79% vs. ORX + PTH-Tb.Ar = 68.47%, P < 0.05) in the proximal femur. The treated rats showed significantly improved mineral content in ashed femurs (ORX-mineral content = 43.73% vs. ORX + PTH-mineral content = 49.49%) when compared to the untreated animals. A comparison of widths of fluorescence bands in cortical bone of the subtrochanteric cross-sections showed a significant increase in oppositions after the PTH therapy.

Conclusions

Our finding supports the hypothesis that PTH therapy seems to be a rational therapy in patients with hypogonadism induced bone loss and improves the bone strength of trochanteric region of rat femur.

Improvement of trochanteric bone quality in an osteoporosis model after short-term treatment with parathyroid hormone: a new mechanical test for trochanteric region of rat femur

We have examined the changes induced in the trochanteric region of femur of ovariectomized rat after administration of estradiol and parathyroid hormone. We have developed a reproducible biomechanical test and produced trochanteric fractures to evaluate stiffness and strength of this region in addition to histomorphometry.

INTRODUCTION

We investigated the short-term effects of parathyroid hormone (PTH) and estrogen (E) on the strength of the rat trochanteric region in a new mechanical test.

METHODS

Forty-four 3-month-old female Sprague-Dawley rats were ovariectomized and 8 weeks later treated with soy-free diet (C), daily applications of orally supplied E (0.5 mg/kg food) or subcutaneously injected PTH (0.014 mg/kg), for 5 weeks, and an additional untreated group was added as sham-operated. The femurs were examined for biomechanical and histomorphometric changes.

RESULTS

Our new mechanical test was validated in a right-left comparison. The PTH treatment induced significantly superior biomechanical results (F (max) = 225.3 N, stiffness = 314.9 N/mm) compared to E (F (max) = 182.9 N, stiffness = 237.2 N/mm), C (F (max) = 166.03 N, stiffness = 235.56 N/mm), and sham (F (max) = 192.1 N, stiffness = 267.2 N/mm). Animals of the PTH group demonstrated a significantly improved trabecular bone structure and area (75.67%) in comparison to the E (61.04%) and C (57.18%) groups.

CONCLUSION

Our new biomechanical test is valid and produces trochanteric fracture. Our results show that the short-term antiosteoporotic effects of PTH are in the trochanteric region of ovariectomized rat superior to E.

Full length parathyroid hormone, PTH(1-84), for the treatment of severe osteoporosis in postmenopausal women

OBJECTIVE

To review and analyse the evidence supporting the use of full length parathyroid hormone, PTH(1-84), in the treatment of osteoporosis based on a search of several literature sources; articles selected for review were published between 1990 and 2008.

BACKGROUND

PTH(1-84) is approved for the treatment of osteoporosis in postmenopausal women at high risk of fracture in Europe. It was well tolerated in clinical trials and demonstrated bone building properties and fracture prevention particularly for the lumbar spine in the treatment of postmenopausal women.

RESULTS

The TOP clinical trial showed that PTH(1-84) treatment for 18 months resulted in a 61% reduction (p = 0.001) in new vertebral fracture incidence when compared with placebo and reduced the risk of a first vertebral fracture by 68% (p = 0.006) in women without a prevalent fracture at baseline. PTH(1-84) increased bone mineral density (BMD) at vertebral and non-vertebral sites the lumbar spine BMD increasing regardless of T-score, age, prior osteoporosis therapy or number of years post-menopause. The PaTH study showed that treatment with PTH(1-84) for 12 months increased BMD at the trabecular spine and hip. Lumbar spine BMD gains were largest with sequential administration of PTH(1-84) followed by alendronate but were smaller with concurrent administration involving anabolic and antiresorptive agents. Lumbar spine BMD increases were also seen in trials involving PTH with raloxifene and PTH in combination with hormone replacement therapy.

CONCLUSIONS

PTH(1-84) has demonstrated effective bone building qualities and extends the therapeutic options available to osteoporotic women. The use of PTH(1-84) followed by sequential administration of an antiresorptive has proved effective at increasing trabecular BMD and points towards new treatment regimens offering improvements in BMD and fracture prevention.

Effect of teriparatide on bone mineral density and biochemical markers in Japanese women with postmenopausal osteoporosis: a 6-month dose-response study

The dose-response efficacy and safety with three doses of teriparatide and placebo was assessed, using once-daily subcutaneous injections for 24 weeks, in Japanese postmenopausal women with osteoporosis at high risk of fracture for reasons of preexisting fracture(s), advanced age, and/or low bone mineral density (BMD). In this multicenter, randomized, placebo-controlled study, 159 subjects were randomized and 154 subjects were included for analysis. Teriparatide (10-microg, 20-microg, and 40-microg doses) showed a statistically significant increase with increasing treatment dose as assessed by the percent change of lumbar spine BMD from baseline to endpoint using Williams' test when compared with placebo (P < 0.001). The mean (+/-SD) percent change in lumbar spine, femoral neck, and total hip BMD with the 20-microg dose from baseline to endpoint was 6.40% +/- 4.76%, 1.83% +/- 7.13%, and 1.91% +/- 3.60%, respectively. Rapid and sustained increases in bone formation markers [type I procollagen N-terminal propeptide (PINP), type I procollagen C-terminal propeptide (PICP), and bone-specific alkaline phosphatase (BAP)], followed by late increases in a bone resorption marker [type I collagen cross-linked C-telopeptide (CTX)], were observed for the teriparatide treatment groups (20-microg, 40-microg), suggesting a persistent, positive, balanced anabolic effect of teriparatide. Optimal adherence was achieved by this daily self-injection treatment. Regarding safety, most of the adverse events were mild to moderate in severity. No study drug-or study procedure-related serious adverse events were reported during the treatment period. These results observed in Japanese patients may support the observation that teriparatide stimulates bone formation in patients with osteoporosis at a high risk of fracture.

Emerging pharmacologic therapies for osteoporosis

Osteoporotic fractures are an important public health problem, contributing substantially to morbidity and mortality in an ageing world population and consuming considerable health resources. Presently available pharmacologic therapies for prevention of fragility fractures are limited in scope, efficacy and acceptability to patients. Considerable efforts are being made to develop new, more effective treatments for osteoporosis, and to refine/optimize existing therapies. These novel treatments include an expanding array of drugs that primarily inhibit osteoclastic bone resorption: estrogenic compounds, bisphosphonates, inhibitors of receptor activator of NF-kappaB ligand signaling, cathepsin K inhibitors, c-src kinase inhibitors, integrin inhibitors and chloride channel inhibitors. The advent of intermittent parathyroid hormone (PTH) therapy has provided proof-of-principle that osteoblast-targeted (anabolic) agents can effectively prevent osteoporotic fractures, and is likely to be followed by the introduction of other therapies based on PTH (orally active PTH analogs, antagonists of the calcium sensing receptor, PTH-related peptide analogs) and/or agents that induce osteoblast anabolism by means of pathways involving key, recently identified, molecular targets (wnt-low-density lipoprotein receptor-related protein 5 signaling, sclerostin and matrix extracellular phosphoglycoprotein).