Anabolic therapy for osteoporosis: Parathyroid hormone

Implantable biosensors and their contribution to the future of precision medicine

Precision medicine can be defined as the prevention, investigation and treatment of diseases taking individual variability into account. There are multiple ways in which the field of precision medicine may be advanced; however, recent innovations in the fields of electronics and microfabrication techniques have led to an increased interest in the use of implantable biosensors in precision medicine. Implantable biosensors are an important class of biosensors because of their ability to provide continuous data on the levels of a target analyte; this enables trends and changes in analyte levels over time to be monitored without any need for intervention from either the patient or clinician. As such, implantable biosensors have great potential in the diagnosis, monitoring, management and treatment of a variety of disease conditions. In this review, we describe precision medicine and the role implantable biosensors may have in this field, along with challenges in their clinical implementation due to the host immune responses they elicit within the body.

Glucocorticoid-induced osteoporosis: treatment update and review

Glucocorticoid-induced osteoporosis (GIO) is a serious consequence of glucocorticoid therapy leading to fractures in 30-50% of patients. A wide range of protective medications have been studied in this condition including calcium, vitamin D, vitamin D analogs, oral and intravenous bisphosphonates, sex hormones, anabolic agents and calcitonin. The mechanism of action, and evidence for these therapies, are reviewed - focusing on important trials and new evidence. Recently published guidelines are also reviewed and compared. Bisphosphonates are currently the recommended first-line therapy for the prevention and treatment of GIO. They have been shown to increase bone mineral density (BMD) at the spine and hip and to decrease the incidence of vertebral fractures (especially in postmenopausal women). Testosterone therapy and female hormone replacement therapy (HRT) have been found to increase lumbar spine BMD in hypogonadal patients on glucocorticoid therapy, but effects on hip BMD have not been consistent and there is no fracture data in the GIO population. Similarly, calcitonin increases lumbar spine BMD but has no proven fracture efficacy. The effect of selective estrogen receptor modulators, the oral contraceptive pill and strontium on GIO is relatively unknown. Parathyroid hormone (PTH 1-34) and zoledronic acid have emerged as exciting new options for the treatment of GIO. Both therapies have been found to result in gains in BMD at the spine and hip that are either noninferior or superior to those seen with oral bisphosphonate therapy. PTH 1-34 has also been found to decrease the incidence of new vertebral fractures and may be an option in high-risk patients established on long-term glucocorticoid therapy.

Teriparatide in bisphosphonate-resistant osteoporosis: microarchitectural changes and clinical results after 6 and 18 months

A number of osteoporotic patients under bisphosphonate treatment present persistent fragility fractures and bone loss despite good compliance. The objective of this 18-month prospective study was to investigate the effect of teriparatide [rhPTH(1-34)] in 25 female osteoporotics who were inadequate responders to oral bisphosphonates and to correlate microarchitectural changes in three consecutive iliac crest biopsies measured by micro-computed tomography (μCT) with bone mineral density (BMD) and bone serum markers. Scanned biopsies at baseline (M0), 6 months (M6), and 18 months (M18) demonstrated early significant (P < 0.01) increases in bone volume per tissue volume (+34%) and trabecular number (+14%) at M6 with only moderate changes in most μCT structural parameters between M6 and M18. μCT-measured bone tissue density was significantly decreased at M18, expressing an overall lower degree of tissue mineralization characteristic for new bone formation despite unchanged trabecular thickness due to increased intratrabecular tunneling at M18. μCT results were consistent with serum bone turnover markers, reaching maximal levels of bone alkaline phosphatase and serum β-crosslaps at M6, with subsequent decline until M18. BMD assessed by DXA demonstrated persistent increases at the lumbar spine until M12, whereas no significant change was observed at the hip. Type (alendronate/risedronate) and duration (3.5 ± 4 years) of prior bisphosphonate treatment did not influence outcome on μCT, BMD, or bone marker results. The overall results indicate a positive ceiling effect of teriparatide on bone microarchitecture and bone markers after 6 and 12 months for lumbar spine BMD, with no additional gain until M18 in bisphosphonate nonresponders.

Transcriptional regulation of BMP2 expression by the PTH-CREB signaling pathway in osteoblasts

Intermittent application of parathyroid hormone (PTH) has well established anabolic effects on bone mass in rodents and humans. Although transcriptional mechanisms responsible for these effects are not fully understood, it is recognized that transcriptional factor cAMP response element binding protein (CREB) mediates PTH signaling in osteoblasts, and that there is a communication between the PTH-CREB pathway and the BMP2 signaling pathway, which is important for osteoblast differentiation and bone formations. These findings, in conjunction with putative cAMP response elements (CREs) in the BMP2 promoter, led us to hypothesize that the PTH-CREB pathway could be a positive regulator of BMP2 transcription in osteoblasts. To test this hypothesis, we first demonstrated that PTH signaling activated CREB by phosphorylation in osteoblasts, and that both PTH and CREB were capable of promoting osteoblastic differentiation of primary mouse osteoblast cells and multiple rodent osteoblast cell lines. Importantly, we found that the PTH-CREB signaling pathway functioned as an effective activator of BMP2 expression, as pharmacologic and genetic modulation of PTH-CREB activity significantly affected BMP2 expression levels in these cells. Lastly, through multiple promoter assays, including promoter reporter deletion, mutation, chromatin immunoprecipitation (ChIP), and electrophoretic mobility shift assay (EMSA), we identified a specific CRE in the BMP2 promoter which is responsible for CREB transactivation of the BMP2 gene in osteoblasts. Together, these results demonstrate that the anabolic function of PTH signaling in bone is mediated, at least in part, by CREB transactivation of BMP2 expression in osteoblasts.

The hedgehog/Gli signaling paradigm in prostate cancer

Hedgehog is a ligand-activated signaling pathway that regulates Gli-mediated transcription. Although most noted for its role as an embryonic morphogen, hyperactive hedgehog also causes human skin and brain malignancies. The hedgehog-related gene anomalies found in these tumors are rarely found in prostate cancer. Yet surveys of human prostate tumors show concordance of high expression of hedgehog ligands and Gli2 that correlate with the potential for metastasis and therapy-resistant behavior. Likewise, prostate cancer cell lines express hedgehog target genes, and their growth and survival is affected by hedgehog/Gli inhibitors. To date, the preponderance of data supports the idea that prostate tumors benefit from a paracrine hedgehog microenvironment similar to the developing prostate. Uncertainty remains as to whether hedgehog's influence in prostate cancer also includes aspects of tumor cell autocrine-like signaling. The recent findings that Gli proteins interact with the androgen receptor and affect its transcriptional output have helped to identify a novel pathway through which hedgehog/Gli might affect prostate tumor behavior and raises questions as to whether hedgehog signaling in prostate cancer cells is suitably measured by the expression of Gli target genes alone.

PTH analogues and osteoporotic fractures

IMPORTANCE OF THE FIELD

At present there are two parathyroid hormone (PTH) analogues (PTH 1 - 34 and PTH 1 - 84) registered for the treatment of established osteoporosis in postmenopausal women (PTH 1 - 34 and PTH 1 - 84) and in men (PTH 1 - 34 only) who are at increased risk of having a fracture.

AREAS COVERED IN THIS REVIEW

The efficacy and safety of PTH 1 - 34 and PTH 1 - 84 in the management of osteoporosis is evaluated by reviewing published literature and presentations from scientific meetings through to 2010.

WHAT THE READER WILL GAIN

This review focuses on data on fracture risk reduction and safety endpoints of PTH analogues. The adverse reactions reported most are nausea, pain in the extremities, headache and dizziness.

TAKE HOME MESSAGE

Exogenous PTH analogues, given as daily subcutaneous injections, stimulate bone formation, increase bone mass and bone strength, and improve calcium balance. In postmenopausal women with osteoporosis, PTH analogues reduced the risk of vertebral (PTH 1 - 34 and PTH 1 - 84) and non-vertebral fractures (only PTH 1 - 34). In men and women with glucocorticosteroid-induced osteoporosis, PTH 1 - 34 reduced the risk of vertebral fractures. In general, PTH analogues are well tolerated with an acceptable safety profile: they can be used for the prevention and treatment of fractures in postmenopausal women with severe, established osteoporosis.

Milk ribonuclease-enriched lactoferrin induces positive effects on bone turnover markers in postmenopausal women

Current treatments for postmenopausal osteoporosis suffer from side effects. Safe and natural milk proteins, ribonuclease, and lactoferrin promote formation of new capillaries and bone formation. A ribonuclease-enriched lactoferrin supplement studied here, demonstrates significant reduction in resorption and increase in formation, towards restoring the balance of bone turnover within 6 months.

INTRODUCTION

Osteoporosis, a major health issue among postmenopausal women, causes increased bone resorption and reduced bone formation. A reduction in angiogenesis could also contribute to this imbalance. Current treatments such as hormone replacement therapy and bisphosphonates have drawbacks of severe side effects. Milk ribonuclease (RNase) is known to promote angiogenesis and lactoferrin (LF) to stimulate bone formation by osteoblasts. We examine the effect of ribonuclease-enriched lactoferrin supplement on the bone health of postmenopausal women.

METHODS

A total of 38 healthy, postmenopausal women, aged 45 to 60 years were randomized into placebo or RNAse-enriched-LF (R-ELF) supplement groups. The bone health status was monitored by assessing bone resorption markers, serum N-telopeptides (NTx), and urine deoxypyridinoline (Dpd) crosslinks and serum bone formation markers, bone-specific alkaline phosphatase (BAP), and osteocalcin (OC).

RESULTS

R-ELF supplementation demonstrated a decrease in urine Dpd levels by 14% (19% increase for placebo) and serum NTx maintained at 24% of the baseline (41% for placebo), while serum BAP and OC levels showed a 45% and 16% elevation (25% and 5% for placebo).

CONCLUSIONS

R-ELF supplementation demonstrated a statistically significant reduction in bone resorption and increase in osteoblastic bone formation, to restore the balance of bone turnover within a short period.

Effects of two years of daily teriparatide treatment on BMD in postmenopausal women with severe osteoporosis with and without prior antiresorptive treatment

Previous antiresorptive (AR) treatment may influence the response to teriparatide. We examined BMD response and safety in a subgroup of 503 postmenopausal women with osteoporosis who received teriparatide for 24 mo. Patients were divided into three groups based on their prior AR treatment: treatment-naïve (n = 84); pretreated with no evidence of inadequate treatment response (n = 134); and pretreated showing an inadequate response to AR treatment (n = 285), which was predefined based on the occurrence of fractures, persistent low BMD, and/or significant BMD loss while on therapy. Changes in BMD from baseline were analyzed using mixed model repeated measures. Lumbar spine BMD increased significantly from baseline at 6, 12, 18, and 24 mo in all three groups. The mean gain in spine BMD over 24 mo was greater in the treatment-naïve group (0.095 g/cm(2); 13.1%) than in the AR pretreated (0.074 g/cm(2); 10.2%; p < 0.005) and inadequate AR responder (0.071 g/cm(2); 9.8%; p < 0.001) groups. The corresponding increases in total hip BMD were 3.8%, 2.3%, and 2.3%, respectively. Early decreases in hip BMD in the inadequate AR responder group were reversed by 18 mo of treatment. Increases in BMD between 18 and 24 mo were highly significant. Nausea (13.3%) and arthralgia (11.7%) were the most commonly reported adverse events. Asymptomatic hypercalcemia was reported in 5.0% of patients. Teriparatide treatment for 24 mo is associated with a significant increase in BMD in patients with and without previous AR use. Prior AR treatment modestly blunted the BMD response to teriparatide. Safety was consistent with current prescribing label information.

Risedronate did not block the maximal anabolic effect of PTH in aged rats

The study was designed to investigate if pre-treating rats with a therapeutic equivalent dose of risedronate blunted the anabolic effects of PTH, and whether a withdrawal period prior to PTH treatment would alter any effect of risedronate on PTH treatment. Skeletally mature rats were treated for 18 weeks with vehicle, risedronate, or risedronate for 8 weeks followed by vehicle for 10 weeks (withdrawal period). At the end of this period, animals were treated for a further 12 weeks with PTH or PTH vehicle. Trabecular and cortical bone mass were monitored by serial pQCT, or by DXA and microCT. Bone histomorphometry was performed on the proximal tibiae and tibial shafts for bone turnover parameters at week 40. Risedronate alone moderately increased while PTH alone markedly increased trabecular bone mass at the proximal tibial (35% and 200%, respectively) and lumbar vertebral body (14% and 36%, respectively). The maximum bone gains were similar with and without pretreatment with risedronate as compared to the PTH alone. Continuous administration of risedronate for 18 weeks prior to PTH treatment had lower percentage increases in proximal tibial BMD during the first 8 weeks of PTH treatments, and had lower active bone forming surface and bone formation rates after being treated with PTH 12 weeks as compared to the PTH alone group. However, with the 10-week withdrawal period, risedronate did not blunt the stimulatory effect of PTH on osteoblast activity as shown by similar bone formation rates as with PTH alone. Our findings suggest that while risedronate pretreatment may slow the bone anabolic response to PTH, a withdrawal period prior to PTH treatment allows osteoblastic activity to respond normally to PTH stimulation.

Biological options to enhance periprosthetic bone mass

There is a potential for the use of pharmacological agents to enhance the quality of bone around a total hip or knee prosthesis, reducing the risk of implant failure or periprosthetic fracture. Bisphosphonates are currently used for the management of postmenopausal osteoporosis and recent investigations also suggest a potential role for the management of postoperative periprosthetic bone loss. Current evidence suggests that the short-term gains may not be sustained in the long term. Teriparatide and parathyroid hormone 1-84 have been licensed to treat postmenopausal osteoporosis and may also be investigated for the potential to enhance periprosthetic bone mass. In addition, other agents such as calcitonin and strontium ranelate, non-anabolic agents such as doxycycline, and recombinant OPG adeno-associated virus (rAAV) gene therapy, may in the future provide solutions for enhancing periprosthetic bone mass.