Long-term safety of antiresorptive treatment: bone material, matrix and mineralization aspects

Assessment of Collagen-Based Nanostructured Biomimetic Systems with a Co-Culture of Human Bone-Derived Cells

Osteoporosis is a worldwide disease resulting in the increase of bone fragility and enhanced fracture risk in adults. In the context of osteoporotic fractures, bone tissue engineering (BTE), i.e., the use of bone substitutes combining biomaterials, cells, and other factors, is considered a potential alternative to conventional treatments. Innovative scaffolds need to be tested in in vitro systems where the simultaneous presence of osteoblasts (OBs) and osteoclasts (OCs), the two main players of bone remodeling, is required to mimic their crosstalk and molecular cooperation. To this aim, two composite materials were developed, based on type I collagen, and containing either strontium-enriched mesoporous bioactive glasses or rod-like hydroxyapatite nanoparticles. The developed nanostructured systems underwent genipin chemical crosslinking and were then tested with an indirect co-culture of human trabecular bone-derived OBs and buffy coat-derived OC precursors, for 2–3 weeks. The favorable structural and biological properties of the materials proved to successfully support the viability, adhesion, and differentiation of cells, encouraging a further investigation of the developed bioactive systems as biomaterial inks for the 3D printing of more complex scaffolds for BTE.

Bone matrix quality in paired iliac bone biopsies from postmenopausal women treated for 12 months with strontium ranelate or alendronate

Bone quality is altered mainly by osteoporosis, which is treated with modulators of bone quality. Knowledge of their mechanisms of action is crucial to understand their effects on bone quality. The goal of our study was to compare the action of alendronate (ALN) and strontium ranelate (SrRan) on the determinants of bone quality. The investigation was performed on over 60 paired human iliac biopsies. Paired samples correspond to biopsies obtained from the same patient, one before treatment (baseline) and one after 12 months of treatment, in postmenopausal women with osteoporosis. Vibrational spectroscopy (Raman and FTIRM) and nanoindentation were used to evaluate the effect of both drugs on bone quality at the ultrastructural level. Outcomes measured by vibrational spectroscopy and nanoindentation are sensitive to bone age. New bone packets are distinguished from old bone packets. Thus, the effect of bone age is distinguished from the treatment effect. Both drugs modify the mineral and organic composition in new and old bone in different fashions after 12 months of administration. The new bone formed during ALN administration is characterized by an increased mineral content, carbonation and apatite crystal size/perfection compared to baseline. Post-translational modifications of collagen are observed through an increase in the hydroxyproline/proline ratio in new bone. The proteoglycan content is also increased in new bone. SrRan directly modulates bone quality through its physicochemical actions, independent of an effect on bone remodeling. Strontium cations are captured by the hydrated layer of the mineral matrix. The mineral matrix formed during SrRan administration has a lower carbonate content and crystallinity after 12 months than at baseline. Strontium might create bonds (crosslinks) with collagen and noncollagenous proteins in new and old bone. The nanomechanical properties of bone were not modified with either ALN or SrRan, probably due to the short duration of administration. Our results show that ALN and SrRan have differential effects on bone quality in relation to their mechanism of action.

Handling Parathormone Receptor Type 1 in Skeletal Diseases: Realities and Expectations of Abaloparatide

Musculoskeletal disorders represent an elevated socioeconomic burden for developed aging societies. Osteoporosis (OP) has been treated with antiresorptive therapies or with teriparatide that was until recently the only anabolic therapy. However, approval of osteoporosis treatment in postmenopausal women with abaloparatide, which is an analog of parathyroid hormone-related peptide (PTHrP), has created a new alternative for OP management. The success of this new treatment is related to differential mechanisms of activation of PTH receptor type 1 (PTH1R) by abaloparatide and PTH. Here, we address the distinguishing mechanisms of PTH1R activation; the effects of PTH1R stimulation in osteoblast, osteocytes, and chondrocytes; the differences between PTH and abaloparatide actions on PTH1R; potential safety concerns; and future perspectives about abaloparatide use in other musculoskeletal disorders.

Bortezomib prevents ovariectomy-induced osteoporosis in mice by inhibiting osteoclast differentiation

Bone homeostasis is achieved through coordinated activities of bone-forming osteoblasts and bone-resorbing osteoclasts. When the balance is skewed in favor of osteoclasts due to hormonal or inflammatory issues, pathologic bone loss occurs leading to conditions such as osteoporosis, rheumatoid arthritis, and periodontitis. Bortezomib is the first in-class of proteasome inhibitors used as an anti-myeloma agent. In the present study, we show that bortezomib directly inhibited the receptor activator of nuclear factor κB ligand (RANKL)-dependent osteoclast differentiation of mouse bone marrow macrophages. Bortezomib significantly reduced the induction of osteoclast marker genes and proteins including nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1). The intraperitoneal injection of bortezomib reduced ovariectomy-induced osteoclastogenesis and protected the mice from bone loss. These data propose novel use of bortezomib as a potential anti-resorptive agent.

Bone-seeking agents for the treatment of bone disorders

The targeting and delivery of therapeutic and diagnostic agents to bone tissue presents both a challenge and opportunity. Osteoporosis, Paget's disease, cancer, and bone metastases are all skeletal diseases whose treatment would benefit from new targeted therapeutic strategies. Osteoporosis, in particular, is a very prevalent disease, affecting over one in three women and one in five men in Canada alone with the cost to the healthcare system estimated at over $2.3 billion in 2010. Bone tissue is often considered a rigid structure when in reality there is a process of continuous remodeling that takes place via complex endocrine-regulated cell signaling pathways in addition to the signaling pathways unique to bone tissue. It is these specific boneremodeling processes that provide unique targeting opportunities but also present a number of challenges.

Alendronate induces osteoclast precursor apoptosis via peroxisomal dysfunction mediated ER stress

Nitrogen-containing bisphosphonates including alendronate (ALN) are the current first line antiresorptive drug in treating osteoporosis. In our study, we found that ALN administration impaired the secretion of platelet derived growth factor-BB (PDGF-BB), the most important angiogenic cytokines produced by preosteoclast (POC), in both sham and ovariectomized (OVX) mice. To further understand this phenomenon, we induced bone marrow macrophages (BMMs) to POCs in vitro and detected the effects of ALN particularly in POCs. The proapoptotic effect of ALN in POCs was confirmed by flow cytometry. On the molecular level, we found that farnesyl diphosphate synthase (FDPS) inhibition of ALN led to peroxisomal dysfunction and up regulation of cytoprotective protein glucose-regulated protein (GRP) 78. Peroxisomal dysfunction further induced endoplasmic reticulum (ER) stress in POCs and finally resulted in cell apoptosis marked by reduced expression of B-cell lymphoma 2 (Bcl-2) and increased expressions of CCAAT/enhancer binding protein homologous protein (CHOP), Bcl2 associated X (Bax), and cleaved caspase-3. We concluded that ALN has no selectivity in inhibiting POC and mature osteoclast. For POCs, ALN inhibition of FDPS leads to peroxisomal dysfunction, which further mediates ER stress and finally causes cell apoptosis. Considering that decreased angiogenesis is also an important issue in treating osteoporosis, how to preserve pro-angiogenic POCs while depleting mature osteoclasts is a problem worthy to be solved.

Insights into the bisphosphonate holiday: a preliminary FTIRI study

Bone composition evaluated by FTIRI analysis of iliac crest biopsies from post-menopausal women treated with alendronate for 10 years, continuously or alendronate for 5 years, followed by a 5-year alendronate-holiday, only differed with the discontinued biopsies having increased cortical crystallinity and heterogeneity of acid phosphate substitution and decreased trabecular crystallinity heterogeneity.

INTRODUCTION

Bisphosphonates (BP) are the most commonly used and effective drugs to prevent fragility fractures; however, concerns exist that prolonged use may lead to adverse events. Recent recommendations suggest consideration of a BP "holiday" in individuals taking long-term BP therapy not at high risk of fracture. Data supporting or refuting this recommendation based on bone quality are limited. We hypothesized that a "holiday" of 5 years would cause no major bone compositional changes.

METHODS

We analyzed the 31 available biopsies from the FLEX-Long-term Extension of FIT (Fracture Intervention Trial) using Fourier transform infrared imaging (FTIRI). Biopsies from two groups of post-menopausal women, a "Continuously treated group" (N = 16) receiving alendronate for ~ 10 years and a "Discontinued group" (N = 15), alendronate treated for 5 years taking no antiresorptive medication during the following 5 years. Iliac crest bone biopsies were provided at 10 years.

RESULTS

Key FTIRI parameters, mineral-to-matrix ratio, carbonate-to-phosphate ratio, acid phosphate substitution, and collagen cross-link ratio as well as heterogeneity of these parameters were similar for Continuously treated and Discontinued groups in age-adjusted models. The Discontinued group had 2% greater cortical crystallinity (p = 0.01), 31% greater cortical acid phosphate heterogeneity (p = 0.02), and 24% lower trabecular crystallinity heterogeneity (p = 0.02).

CONCLUSIONS

Discontinuation of alendronate for 5 years did not affect key FTIRI parameters, supporting the hypothesis that discontinuation would have little impact on bone composition. Modest differences were observed in three parameters that are not likely to affect bone mechanical properties. These preliminary data suggest that a 5-year BP holiday is not harmful to bone composition.

Graphene-Based MicroRNA Transfection Blocks Preosteoclast Fusion to Increase Bone Formation and Vascularization

The objective of this study is to design a graphene-based miRNA transfection drug delivery system for antiresorptive therapy. An efficient nonviral gene delivery system is developed using polyethylenimine (PEI) functionalized graphene oxide (GO) complex loaded with miR-7b overexpression plasmid. GO-PEI complex exhibits excellent transfection efficiency within the acceptable range of cytotoxicity. The overexpression of miR-7b after GO-PEI-miR-7b transfection significantly abrogates osteoclast (OC) fusion and bone resorption activity by hampering the expression of an essential fusogenic molecule dendritic cell-specific transmembrane protein. However, osteoclastogenesis occurs without cell-cell fusion and preosteoclast (POC) is preserved. Through preservation of POC, GO-PEI-miR-7b transfection promotes mesenchymal stem cell osteogenesis and endothelial progenitor cells angiogenesis in the coculture system. Platelet-derived growth factor-BB secreted by POC is increased by GO-PEI-miR-7b both in vitro and in vivo. In treating osteoporotic ovariectomized mice, GO-PEI-miR-7b significantly enhances bone mineral density, bone volume as well as bone vascularization through increasing CD31^hiEmcn^hi cell number. This study provides a cell-cell fusion targeted miRNA transfection drug delivery strategy in treating bone disorders with excessive osteoclastic bone resorption.

Histomorphometric and osteocytic characteristics of cortical bone in male subtrochanteric femoral shaft

The histomorphometric properties of the subtrochanteric femoral region have rarely been investigated. The aim of this study was to investigate the age-associated variations and regional differences of histomorphometric and osteocytic properties in the cortical bone of the subtrochanteric femoral shaft, and the association between osteocytic and histological cortical bone parameters. Undecalcified histological sections of the subtrochanteric femoral shaft were obtained from cadavers (n = 20, aged 18-82 years, males). They were cut and stained using modified Masson-Goldner stain. Histomorphometric parameters of cortical bone were analysed with ×50 and ×100 magnification after identifying cortical bone boundaries using our previously validated method. Within cortical bone areas, only complete osteons with typical concentric lamellae and cement line were selected and measured. Osteocytic parameters of cortical bone were analyzed under phase contrast microscopy and epifluorescence within microscopic fields (0.55 mm² for each). The cortical widths of the medial and lateral quadrants were significantly higher than other quadrants (P < 0.01). Osteonal area per cortical bone area was lower and cortical porosities were higher in the posterior quadrant than in the other quadrants (P < 0.05). Osteocyte lacunar number per cortical bone area was found higher in the young subjects (≤ 50 years) than in the older ones (> 50 years) both before and after adjustments for body height and weight (P < 0.05). Moreover, significant but low correlations were found between the cortical bone and osteocytic parameters (0.20 ≤ R²  ≤ 0.35, P < 0.05). It can be concluded that in healthy males, the cortical histomorphometric parameters differ between the anatomical regions of the subtrochanteric femoral shaft, and are correlated with the osteocytic parameters from the same site. These findings may be of use when discussing mechanisms that predispose patients to decreasing bone strength.