Comparing and contrasting the effects of strontium ranelate and other osteoporosis drugs on microarchitecture

Comparison of parathyroid hormone and strontium ranelate in combination with whole-body vibration in a rat model of osteoporosis

We investigated the combinatorial effects of whole-body vertical vibration (WBVV) with the primarily osteoanabolic parathyroid hormone (PTH) and the mainly antiresorptive strontium ranelate (SR) in a rat model of osteoporosis. Ovariectomies were performed on 76 three-month-old Sprague-Dawley rats (OVX, n = 76; NON-OVX, n = 12). After 8 weeks, the ovariectomized rats were divided into 6 groups. One group (OVX + PTH) received daily injections of PTH (40 µg/kg body weight/day) for 6 weeks. Another group (OVX + SR) was fed SR-supplemented chow (600 mg/kg body weight/day). Three groups (OVX + VIB, OVX + PTH + VIB, and OVX + SR + VIB) were treated with WBVV twice a day at 70 Hz for 15 min. Two groups (OVX + PTH + VIB, OVX + SR + VIB) were treated additionally with PTH and SR, respectively. The rats were killed at 14 weeks post-ovariectomy. The lumbar vertebrae and femora were removed for biomechanical and morphological assessment. PTH produced statistically significant improvements in biomechanical and structural properties, including bone mineral density (BMD) and trabecular bone quality. In contrast, SR treatment exerted mild effects, with significant effects in cortical thickness only. SR produced no significant improvement in biomechanical properties. WBVV as a single or an adjunctive therapy produced no significant improvements. In conclusion, vibration therapy administered as a single or dual treatment had no significant impact on bones affected by osteoporosis. PTH considerably improved bone quality in osteoporosis cases and is superior to treatment with SR.

Osteoporosis drug effects on cortical and trabecular bone microstructure: a review of HR-pQCT analyses

With the development of new non-invasive analytical techniques and particularly the advent of high-resolution peripheral quantitative computed tomography (HRpQCT) it is possible to assess cortical and trabecular bone changes under the effects of ageing, diseases and treatments. In the present study, we reviewed the treatment-related effects on bone parameters assessed by HRpQCT imaging. We identified 12 full-length articles published in peer-reviewed journals describing treatment-induced changes assessed by HRpQCT. The design of these studies varied a lot in terms of duration and methodology: some of them were open-labelled, others were double-blind, placebo-controlled or double-blind, double-dummy, active controlled. In addition, the sample size in these studies ranged from 11 to 324 patients. Motion artifacts occurring during data acquisition were sometimes a real challenge particularly at the radius leading sometimes to exclude the analysis at the radius due to the uninterpretability of microstructural parameters. Responses to therapies were treatment-specific and divergent effects in cortical and trabecular bone with antiresorptive or anabolic agents were observed. Standardization of bone microarchitecture parameters (including porosity) and bone strength estimates by finite element analysis (FEA) are mandatory. The additional value of microarchitecture and FEA estimates changes with therapies in terms of improvement in fracture outcomes which have to be adequately assessed in clinical trials with fracture end point. Data from these reviewed studies advance our understanding of the microstructural consequences of osteoporosis and highlight potential differences in bone quality outcomes within therapies.

Challenges in longitudinal measurements with HR-pQCT: evaluation of a 3D registration method to improve bone microarchitecture and strength measurement reproducibility

Definition of identical regions between repeated computed tomography (CT) scans is a key factor to monitor changes in bone microarchitecture. In longitudinal studies, accurate determination of the volume of interest (VOI), using three dimensional (3D) registration may improve precision. Therefore, the aim of our study was to investigate the short-term reproducibility of bone geometry, density, microstructure and biomechanical parameters assessed by HR-pQCT and micro-finite element (μFE) derived analyses, using the cross-sectional area (CSA) registration method in comparison with the use of 3D registration, to find overlapping regions between scans. Fifteen healthy individuals (aged 21-47 years) underwent 3 separate scans at the distal radius and tibia, within a one-month interval. Reproducibility was assessed after double contouring the cortical compartment and after applying three different methods to determine the common region between repeated scans: (i) the VOI was determined with no registration, i.e., on 110 slices, (ii) the VOI was determined after CSA-based registration, and (iii) the VOI was determined after 3D registration. Both pre- and post-registration short-term reproducibility for each subject was determined. With no registration, CVrms of geometry parameters ranged from 0.5 to 3.7%, showing a slight variation in the CSA between scans. When the CSA registration method was employed, the variability of geometry (CVrms<1.8%) and density parameters (CVrms<1.8%), was better than that obtained without registration. By removing the effect of repositioning, the 3D registration further improved the reproducibility of cortical bone measurements compared to other methods. Indeed, significant improvements were found for cortical geometry and microstructure measurements (CVrms ranged from 0.4% to 10.7% at both sites; p<0.05), whereas the impact on trabecular bone measurements was restricted to its geometry parameter. The repositioning error was significantly reduced, most markedly at the radius compared to the tibia. For μFE measures, the impact of 3D registration on whole bone stiffness was negligible, indicating adequate assessment of longitudinal changes in estimated biomechanical properties, even without registration. In conclusion, we have shown that the 3D registration improved the identification of the common region retained for longitudinal analysis, contributing to improve the reproducibility of cortical bone parameter measurements. We also quantified the minimally detectable bone changes to help designing future studies with HR-pQCT.

Nuclear receptors in bone physiology and diseases

During the last decade, our view on the skeleton as a mere solid physical support structure has been transformed, as bone emerged as a dynamic, constantly remodeling tissue with systemic regulatory functions including those of an endocrine organ. Reflecting this remarkable functional complexity, distinct classes of humoral and intracellular regulatory factors have been shown to control vital processes in the bone. Among these regulators, nuclear receptors (NRs) play fundamental roles in bone development, growth, and maintenance. NRs are DNA-binding transcription factors that act as intracellular transducers of the respective ligand signaling pathways through modulation of expression of specific sets of cognate target genes. Aberrant NR signaling caused by receptor or ligand deficiency may profoundly affect bone health and compromise skeletal functions. Ligand dependency of NR action underlies a major strategy of therapeutic intervention to correct aberrant NR signaling, and significant efforts have been made to design novel synthetic NR ligands with enhanced beneficial properties and reduced potential negative side effects. As an example, estrogen deficiency causes bone loss and leads to development of osteoporosis, the most prevalent skeletal disorder in postmenopausal women. Since administration of natural estrogens for the treatment of osteoporosis often associates with undesirable side effects, several synthetic estrogen receptor ligands have been developed with higher therapeutic efficacy and specificity. This review presents current progress in our understanding of the roles of various nuclear receptor-mediated signaling pathways in bone physiology and disease, and in development of advanced NR ligands for treatment of common skeletal disorders.

The effect of PTH(1-84) or strontium ranelate on bone formation markers in postmenopausal women with primary osteoporosis: results of a randomized, open-label clinical trial

We explored the effects of PTH(1-84) compared with strontium ranelate on bone remodeling as measured by bone remodeling markers in postmenopausal women with osteoporosis. Biochemical markers of bone formation were significantly increased after treatment with PTH(1-84) but not strontium ranelate, indicating a different mechanism of action between these agents.

INTRODUCTION

PTH(1-84) and strontium ranelate (SR) are both known to reduce fracture risk in osteoporosis. Measuring changes in biochemical markers of bone turnover induced by these agents can help in characterizing the action of PTH(1-84) and SR on bone remodeling.

METHODS

A 24-week, randomized, open-label, parallel group, phase IV trial was conducted in 81 postmenopausal women with primary osteoporosis (≥50 years of age, lumbar spine, or total hip T-score ≤-2.5 SD) to assess the effect of SR as compared to PTH(1-84) on bone formation markers P1NP and BSAP. The bone resorption marker CTX was also measured. Subjects were randomly assigned to receive daily either 100 μg PTH(1-84) (n = 41) (subcutaneous injection) or oral 2 g SR (n = 40) for 24 weeks with daily supplements of 800 IU vitamin D(3) and 1,000 mg calcium. Patient-reported outcomes were collected to investigate the effect of treatment on quality of life (QoL).

RESULTS

Percentage changes from baseline in P1NP and BSAP were significantly increased for PTH(1-84) by week 24 compared with SR (p < 0.0001). Significant changes from baseline in P1NP and BSAP were noted for PTH(1-84) from week 4 onwards; no significant changes were noted for SR. A trend towards a positive impact on QoL was seen with PTH(1-84) treatment. Safety profiles concur with previous analyses.

CONCLUSIONS

PTH(1-84) had a more rapid and higher effect on bone formation markers compared to SR, indicating that SR has a different mode of action on bone remodeling than the bone building agent PTH(1-84) in postmenopausal women with osteoporosis.

Denosumab and bisphosphonates: different mechanisms of action and effects

To treat systemic bone loss as in osteoporosis and/or focal osteolysis as in rheumatoid arthritis or periodontal disease, most approaches target the osteoclasts, the cells that resorb bone. Bisphosphonates are currently the most widely used antiresorptive therapies. They act by binding the mineral component of bone and interfere with the action of osteoclasts. The nitrogen-containing bisphosphonates, such as alendronate, act as inhibitors of farnesyl-pyrophosphate synthase, which leads to inhibition of the prenylation of many intracellular signaling proteins. The discovery of RANKL and the essential role of RANK signaling in osteoclast differentiation, activity and survival have led to the development of denosumab, a fully human monoclonal antibody. Denosumab acts by binding to and inhibiting RANKL, leading to the loss of osteoclasts from bone surfaces. In phase 3 clinical studies, denosumab was shown to significantly reduce vertebral, nonvertebral and hip fractures compared with placebo and increase areal BMD compared with alendronate. In this review, we suggest that the key pharmacological differences between denosumab and the bisphosphonates reside in the distribution of the drugs within bone and their effects on precursors and mature osteoclasts. This may explain differences in the degree and rapidity of reduction of bone resorption, their potential differential effects on trabecular and cortical bone, and the reversibility of their actions.