Delivery of parathyroid hormone for the treatment of osteoporosis

New Targets and Emergent Therapies for Osteoporosis

The 11 existing FDA-approved osteoporosis drug treatments include hormone replacement therapy, 2 SERMs (raloxifene and bazedoxifene), 5 inhibitors of bone-resorbing osteoclasts (4 bisphosphonates and anti-RANKL denosumab), 2 parathyroid hormone analogues (teriparatide and abaloparatide), and 1 WNT signaling enhancer (romosozumab). These therapies are effective and provide multiple options for patients and physicians. As the genomic revolution continues, potential novel targets for future drug development are identified. This review takes a wide perspective to describe potentially rewarding topics to explore, including knowledge of genes and pathways involved in bone cell metabolism, the utility of animal models, targeting drugs to bone, and ongoing advances in drug design and delivery.

Does short-term weekly teriparatide improve healing in unstable intertrochanteric fractures?

Slow recovery after hip fracture has been associated with negative consequences. Thus, there is medical need to improve healing and functional recovery after intertrochanteric fracture. The aim of this study was to measure whether short-term teriparatide would improve healing in intertrochanteric fractures after internal fixation as measured by (1) clinical scores, (2) radiographic fracture healing, and (3) complication rates. We retrospectively reviewed 96 patients (average age, 82 years) who underwent closed reduction and internal fixation with proximal femoral nail (PFN) for unstable intertrochanteric fractures between 2014 and 2016. Of the 96 patients, 56 patients were treated with a PFN alone (group 1). These patients were compared with 46 patients for whom the same device was used and a weekly subcutaneous injection of PTH 1-34 (teriparatide) was prescribed postoperatively (group 2). Questionnaire surveys or telephone interviews were conducted, and patients completed a self-report Harris hip score and visual analog scale scores. The radiological time to fracture healing was assessed as the primary end point. Postoperative complication rates were compared. Functional outcomes at 6 months after surgery were similar in both groups. There were no differences between groups in the proportion of patients achieving radiographic fracture healing. The frequency of patients reporting adverse events was 20% (10 of 50) in group 1 versus 17% (8 of 46) in group 2 ( p = 0.744). Short-term teriparatide did not improve radiographic signs of fracture healing of an intertrochanteric fracture and reduce the incidence of complications. The effect of teriparatide on fracture healing remains uncertain. Further multicenter prospective studies are needed to demonstrate objective long-term results of parathyroid hormone therapy in patient with hip fracture.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Reversal of Osteopenia in Ovariectomized Rats by Pentoxifylline: Evidence of Osteogenic and Osteo-Angiogenic Roles of the Drug

Pentoxifylline (PTX) is a non-selective phosphodiesterase inhibitor and is used for the management of intermittent claudication. We tested whether PTX has oral efficacy in stimulating new bone formation. Rat calvarial osteoblasts (RCO) were used to study the effect of PTX on osteoblast differentiation and angiogenesis. Pharmacokinetic and pharmacodynamic studies were carried out in rats to determine an oral dose of PTX. In ovariectomized (OVX) rats with osteopenia, the effect of PTX on various skeletal parameters was studied, and compared with teriparatide. Effect of PTX on angiogenic signaling was studied by immunoblotting and relevant pharmacologic inhibitors. Bone vascularity was measured by intravenous injection of polystyrene fluorospheres followed by in vivo imaging, and angiogenesis was studied in vitro by tubulogenesis of endothelial cells and in vivo by Matrigel plug assay. Effective concentration (EC₅₀) of PTX in RCO was 8.2 nM and plasma PTX level was 7 nM/mL after single oral dosing of 25 mg/kg, which was 1/6th the clinically used dose. At this dose, PTX enhanced bone regeneration at femur osteotomy site and completely restored bone mass, microarchitecture, and strength in OVX rats. Furthermore, PTX increased surface referent bone formation parameters and serum bone formation marker (PINP) without affecting the resorption marker (CTX-1). PTX increased the expression of vascular endothelial growth factor and its receptor in bones and osteoblasts. PTX also increased skeletal vascularity, tubulogenesis of endothelial cells and in vivo angiogenesis. Taken together, our study suggested that PTX at 16% of adult human oral dose completely reversed osteopenia in OVX rats by osteogenic and osteo-angiogenic mechanisms.

Short-term daily teriparatide improve postoperative functional outcome and fracture healing in unstable intertrochanteric fractures

BACKGROUND

There has been heightened interest in the effect of osteoanabolic agents on acceleration of fracture healing.

OBJECTIVES

The purpose of this study was to identify whether short-term daily teriparatide prescribed for osteoporosis treatment would improve postoperative outcomes including clinical scores, radiographic healing, and complication rates.

METHODS

Between 2014 and 2017, we retrospectively assessed 112 patients who underwent closed reduction and internal fixation with proximal femoral nail (PFN) for unstable intertrochanteric fractures. In 60 of 112 patients, patients were treated with a PFN alone (group I). These patients were compared with 52 patients for whom the same device was used and a daily subcutaneous injection of teriparatide (1-34 PTH, Forsteo®) was prescribed postoperatively (group II). Teriparatide was administered by nurses during a hospital stay and then self-injection was monitored by follow-up visits to the outpatient clinic after discharge. Questionnaire surveys were conducted and patients completed a self-report Harris hip score (HHS) and visual analog scale (VAS) scores.

RESULTS

Teriparatide therapy significantly increased HHS (p = 0.02) and decreased VAS pain scores (p = 0.008). The mean time to fracture healing post-operatively was 14.8 weeks (SD 7.1) and 12.1 weeks (SD 6.4) in group I and II, respectively (p = 0.002). The frequency of patients reporting postoperative complications was also markedly reduced in the teriparatide-treated groups (p = 0.028).

CONCLUSIONS

Short-term daily teriparatide used for osteoporosis treatment improved radiographic fracture healing of a hip fracture and reduced complication rates. However, because of the limited power of the study, additional randomized placebo-controlled trials are needed to determine the potential benefit of PTH as an adjunct to enhance fracture healing and its efficacy in broader populations with varying comorbidities and fracture types.

Oral dosing of pentoxifylline, a pan-phosphodiesterase inhibitor restores bone mass and quality in osteopenic rabbits by an osteogenic mechanism: A comparative study with human parathyroid hormone

The non-selective phosphodiesterase inhibitor pentoxifylline (PTX) is used for the treatment of intermittent claudication due to artery occlusion. Previous studies in rodents have reported salutary effects of the intraperitoneal administration of PTX in segmental bone defect and fracture healing, as well as stimulation of bone formation. We determined the effect of orally dosed PTX in skeletally mature ovariectomized (OVX) rabbits with osteopenia. The half-maximal effective concentration (EC₅₀) of PTX in rabbit bone marrow stromal cells was 3.07 ± 1.37 nM. The plasma PTX level was 2.05 ± 0.522 nM after a single oral dose of 12.5mg/kg, which was one-sixth of the adult human dose of PTX. Four months of daily oral dosing of PTX at 12.5 mg/kg to osteopenic rabbits completely restored bone mineral density, bone mineral content (BMC), microarchitecture and bone strength to the level of the sham-operated (ovary intact) group. The bone strength to BMC relationship between PTX and sham was similar. The bone restorative effect of PTX was observed in both axial and appendicular bones. In osteopenic rabbits, PTX increased serum amino-terminal propeptide, mineralized nodule formation by stromal cells and osteogenic gene expression in bone. PTX reversed decreased calcium weight percentage and poor crystal packing found in osteopenic rabbits. Furthermore, similar to parathyroid hormone (PTH), PTX had no effect on bone resorption. Taken together, our data show that PTX completely restored bone mass, bone strength and bone mineral properties by an anabolic mechanism. PTX has the potential to become an oral osteogenic drug for the treatment of post-menopausal osteoporosis.

The administration of intermittent parathyroid hormone affects functional recovery from trochanteric fractured neck of femur: a randomised prospective mixed method pilot study

Aims

We wished to assess the feasibility of a future randomised controlled trial of parathyroid hormone (PTH) supplements to aid healing of trochanteric fractures of the hip, by an open label prospective feasibility and pilot study with a nested qualitative sub study. This aimed to inform the design of a future powered study comparing the functional recovery after trochanteric hip fracture in patients undergoing standard care, versus those who undergo administration of subcutaneous injection of PTH for six weeks.

Patients and Methods

We undertook a pilot study comparing the functional recovery after trochanteric hip fracture in patients 60 years or older, admitted with a trochanteric hip fracture, and potentially eligible to be randomised to either standard care or the administration of subcutaneous PTH for six weeks. Our desired outcomes were functional testing and measures to assess the feasibility and acceptability of the study.

Results

A total of 724 patients were screened, of whom 143 (20%) were eligible for recruitment. Of these, 123 were approached and 29 (4%) elected to take part. However, seven patients did not complete the study. Compliance with the injections was 11 out of 15 (73%) showing the intervention to be acceptable and feasible in this patient population.

Take home message: Only 4% of patients who met the inclusion criteria were both eligible and willing to consent to a study involving injections of PTH, so delivering this study on a large scale would carry challenges in recruitment and retention. Methodological and sample size planning would have to take this into account. PTH administration to patients to enhance fracture healing should still be considered experimental.

Cite this article: Bone Joint J 2016;98-B:840–5.

Lipid-based nanocarriers for oral peptide delivery

This article is aimed to overview the lipid-based nanostructures designed so far for the oral administration of peptides and proteins, and to analyze the influence of their composition and physicochemical (particle size, zeta potential) and pharmaceutical (drug loading and release) properties, on their interaction with the gastro-intestinal environment, and the subsequent PK/PD profile of the associated drugs. The ultimate goal has been to highlight and comparatively analyze the key factors that may be determinant of the success of these nanocarriers for oral peptide delivery. The article ends with some prospects on the challenges to be addressed for the intended commercial success of these delivery vehicles.

The administration of intermittent parathyroid hormone affects functional recovery from pertrochanteric fractured neck of femur: a protocol for a prospective mixed method pilot study with randomisation of treatment allocation and blinded assessment (FRACTT)

INTRODUCTION

Pertrochanteric hip fractures occur in an elderly population and cause considerable morbidity and loss of functional ability as the fracture heals. Recently, parathyroid hormone (PTH), which is licensed for the treatment of osteoporosis, has been shown to potentially accelerate bone healing in animal and human studies. If its administration could allow a faster functional recovery after pertrochanteric hip fracture, then a patient's hospital stay may be reduced and rehabilitation could be potentially accelerated. PTH can currently only be administered by subcutaneous injection. The acceptability of this intervention is unknown in this elderly population. The aim of this pilot study is to inform the design of a future powered study comparing the functional recovery after pertrochanteric hip fracture in patients undergoing standard care versus those who undergo administration of subcutaneous injection of PTH.

METHODS AND ANALYSIS

The study is an open label, prospective, randomised, comparative pilot study with blinded outcomes assessment to establish feasibility of the trial design. Patients will be randomised to receive a 6-week course of PTH or usual treatment. Functional outcomes will be assessed at 6 weeks and 12 weeks. Blinded assessment will be used to minimise the effect of bias of an open label study design. A nested qualitative study will investigate the patient experience of, and expectations following, hip fracture and the patient important aspects of recovery compared with the outcome measures proposed.

RESULTS

Results will be analysed to establish the potential recruitment, compliance and retention rates using 95% CIs, and trial outcomes quoted with SDs and 95% CIs for the effect size.

ETHICS AND DISSEMINATION

The study has been approved by the South West 2 Research Ethics committee (reference 10/H0206/34). The findings of this study will be disseminated to the medical community via presentations to orthopaedic, orthogeriatric and osteoporosis societies, and their relevant specialist journals.

TRIAL REGISTRATION

ISRCTN Register reference number: ISRCTN03362357. Eudract Number: 2010-020081-22.

Opportunities and challenges for oral delivery of hydrophobic versus hydrophilic peptide and protein-like drugs using lipid-based technologies

Peptide and protein-like drugs are macromolecules currently produced in increasing numbers by the pharmaceutical biotechnology industry. The physicochemical properties of these molecules pose barriers to oral administration. Lipid-based drug-delivery systems have the potential to overcome these barriers and may be utilized to formulate safe, stable and efficacious oral medicines. This review outlines the design of such lipid-based technologies. The mechanisms whereby these formulations enhance the absorption of lipophilic versus hydrophilic peptide and protein-like drugs are discussed. In the case of lipophilic compounds, the advantages of lipid-based drug-delivery systems including increased solubilization, decreased intestinal efflux, decreased intracellular metabolism and possible lymphatic transport are well established as is evident from the success of Neoral® and other drug products on the market. In contrast, with respect to hydrophilic compounds, the situation is more complex and, while promising formulation approaches have been studied, issues including reproducibility of response, intersubject variability and duration of response require further optimization before commercially viable products are possible.

Calcilytics: antagonists of the calcium-sensing receptor for the treatment of osteoporosis

The only bone anabolic agents currently available on the market are based on the parathyroid hormone (PTH). Secretion of endogenous PTH is controlled by a calcium-sensing receptor at the surface of the parathyroid glands. Antagonists of this receptor (calcilytics) induce the release of the hormone. Provided the effect of the calcilytic is of short duration, a bone anabolic effect should also result. Although the first calcilytic series became known approximately 10 years ago, the number of different structural types is still small today. This article outlines the quest from hits to potent development candidates of all relevant calcilytic series currently known. Even after the front-runners unexpectedly failed in the clinic, the approach for an oral alternative to parenteral PTH remains highly attractive.

ATF936, a novel oral calcilytic, increases bone mineral density in rats and transiently releases parathyroid hormone in humans

Parathyroid hormone (PTH), when injected daily as either the intact hormone PTH(1-84) or the active fragment PTH(1-34) (teriparatide), is an efficacious bone anabolic treatment option for osteoporosis patients. Injections lead to rapid and transient spikes in hormone exposure levels, a profile which is a prerequisite to effectively form bone. Oral antagonists of the calcium-sensing receptor (calcilytics) stimulate PTH secretion and represent thus an alternative approach to elevate hormone levels transiently. We report here on ATF936, a novel calcilytic, which triggered rapid, transient spikes in endogenous PTH levels when given orally in single doses of 10 and 30mg/kg to growing rats, and of 1mg/kg to dogs. Eight weeks daily oral application of 30mg/kg of ATF936 to aged female rats induced in the proximal tibia metaphysis increases in bone mineral density, cancellous bone volume and cortical and trabecular thickness as evaluated by computed tomography. In healthy humans, single oral doses of ATF936 produced peak PTH levels in plasma after a median time of 1h and levels returned to normal at 24-h post-dose. The average maximum PTH concentration increase from baseline was 1.9, 3.6, and 6.0-fold at doses of 40, 70, and 140mg. ATF936 was well tolerated. The sharp, transient increase in PTH levels produced by the oral calcilytic ATF936 was comparable to the PTH profile observed after subcutaneous administration of teriparatide. In conclusion, ATF936 might hold potential as an oral bone-forming osteoporosis therapy.

Repetition of continuous PTH treatments followed by periodic withdrawals exerts anabolic effects on rat bone

Various animal experiments and human studies have shown that intermittent injections of parathyroid hormone (PTH) exert anabolic effects on bone, whereas continuous PTH treatment decreases the bone mass and causes hypercalcemia in animals. However, limited data are available with regard to the effects of a repetitive regimen of continuous treatments of PTH followed by periodic withdrawals on the bone metabolism. We investigated the effects of this regimen by comparing the findings of intermittent and continuous PTH treatments in rats. Infusions of PTH for 24 h followed by 6-day withdrawal periods from PTH transiently increased the serum calcium levels on day 1, but these levels were within the normocalcemic range. The repetition of 4 cycles of continuous PTH infusions followed by PTH withdrawals as well as intermittent PTH treatment increased the trabecular bone thickness, osteoblast surface, and bone formation rate. Continuous PTH infusions followed by PTH withdrawals also increased the cortical thickness of the femoral diaphysis and the osteoid volume in trabecular bones, whereas the continuous treatment failed to induce these changes. These findings suggest that continuous PTH treatment followed by PTH withdrawal is a potential regimen that can induce the anabolic effects of PTH in bone metabolism without inducing hypercalcemia.

Specific aminopeptidases of excised human nasal epithelium and primary culture: a comparison of functional characteristics and gene transcripts expression

Objectives

To investigate whether growing human nasal epithelium as primary cultures alters aminopeptidase B (APB), aminopeptidase N (APN) and dipeptidyldipeptidase (DPPIV) metabolic characteristics, and mRNA gene transcript expression.

Methods

The formation of 7-amino-methyl coumarin from specific substrates for APN (l-alanine-4-methyl-coumaryl-7-amide, APB (l-arginine-4-methyl-coumaryl-7-amide) and DPPIV (glycyl-l-proline-4-methyl-coumaryl-7-amide) was used to estimate the Km, Vmax and the effect of aminopeptidases inhibitors on the enzymes. Polymerase chain reaction was used to investigate gene expression.

Key findings

Results of this study showed that: (1) both the excised tissues and primary cultures of human nasal epithelium expressed APN, APB and DPPIV activity; (2) the Km of APB, APN and DPPIV was not significantly different in cell and tissue homogenates; (3) except for APN, the Vmax was not significantly different in the two metabolism models; (4) there was no statistically significant difference in the behaviours of APB, APN and DPPIV in response to inhibition by puromycin and bestatin in the two models; (5) the mRNA transcripts that encode APB, APN and DPPIV were expressed in both cell culture and tissue homogenate.

Conclusions

Based on the results of this study, it may be concluded that nasal primary culture system is suitable for investigating peptide and protein metabolism and enzymatic stability in human nasal epithelium. Except for APN, the tissue culture conditions did not significantly alter the functional and molecular expression of the aminopeptidases.

Motivations and methods for analyzing pulsatile hormone secretion

Endocrine glands communicate with remote target cells via a mixture of continuous and intermittent signal exchange. Continuous signaling allows slowly varying control, whereas intermittency permits large rapid adjustments. The control systems that mediate such homeostatic corrections operate in a species-, gender-, age-, and context-selective fashion. Significant progress has been made in understanding mechanisms of adaptive interglandular signaling in vivo. Principal goals are to understand the physiological origins, significance, and mechanisms of pulsatile hormone secretion. Key analytical issues are: 1) to quantify the number, size, shape, and uniformity of pulses, nonpulsatile (basal) secretion, and elimination kinetics; 2) to evaluate regulation of the axis as a whole; and 3) to reconstruct dose-response interactions without disrupting hormone connections. This review will focus on the motivations driving and the methodologies used for such analyses.