The aminobisphosphonate risedronate preserves localized mineral and material properties of bone in the presence of glucocorticoids

Instrumented nanoindentation in musculoskeletal research

Musculoskeletal tissues, such as bone, cartilage, and muscle, are natural composite materials that are constructed with a hierarchical structure ranging from the cell to tissue level. The component differences and structural complexity, together, require comprehensive multiscale mechanical characterization. In this review, we focus on nanoindentation testing, which is used for nanometer to sub-micrometer length scale mechanical characterization. In the following context, we will summarize studies of nanoindentation in musculoskeletal research, examine the critical factors that affect nanoindentation testing results, and briefly summarize other commonly used techniques that can be conjoined with nanoindentation for synchronized imaging and colocalized characterization.

A multiscale study of structural and compositional changes in a natural nanocomposite: Osteoporotic bone with chronic endogenous steroid excess

Glucocorticoid (or steroid) induced osteoporosis (GIOP) is the leading form of secondary osteoporosis, affecting up to 50% of patients receiving chronic glucocorticoid therapy. Bone quantity (bone mass) changes in GIOP patients alone are inadequate to explain the increased fracture risk, and bone material changes (bone quality) at multiple levels have been implicated in the reduced mechanics. Quantitative analysis of specific material-level changes is limited. Here, we combined multiscale experimental techniques (scanning small/wide-angle X-ray scattering/diffraction, backscattered electron imaging, and X-ray radiography) to investigate these changes in a mouse model (Crh^-120/+) with chronic endogenous steroid production. Nanoscale degree of orientation, the size distribution of mineral nanocrystals in the bone matrix, the spatial map of mineralization on the femoral cortex, and the microporosity showed significant changes between GIOP and the control, especially in the endosteal cortex. Our work can provide insight into the altered structure-property relationship leading to lowered mechanical properties in GIOP. SIGNIFICANCE STATEMENT: As a natural nanocomposite with a hierarchical structure, bone undergoes a staggered load transfer mechanism at the nanoscale. Disease and age-related deterioration of bone mechanics are caused by changes in bone structure at multiple length scales. Although clinical tools such as dual-energy X-ray absorptiometry (DXA) can be used to assess the reduction of bone quantity in these cases, little is known about how altered bone quality in diseased bone can increase fracture risk. It is clear that high-resolution diagnostic techniques need to be developed to narrow the gap between the onset and diagnosis of fracture-related changes. Here, by combining several scanning probe methods on a mouse model (Crh^-120/+) of glucocorticoid-induced osteoporosis (GIOP), we developed quantitative and spatially resolved maps of ultrastructural changes in collagen fibrils and mineral nanocrystals, mineralization distribution (microscale), and morphology (macroscale) across femoral osteoporotic bone. Our results indicate that the altered bone remodelling in GIOP leads to 1) heterogeneous bone structure and mineralization, 2) reduced degree of orientation of collagen fibrils and mineral nanocrystals, and 3) reduced length and increased thickness of mineral nanocrystals, which contribute to mechanical abnormalities. The combined multiscale experimental approach presented here will be used to understand musculoskeletal degeneration in aging and osteoporosis.

Fifty years of bisphosphonates: What are their mechanical effects on bone?

After fifty years of experience with several generations of bisphosphonates (BPs), and 25 years after these drugs were approved for use in humans, their mechanical effects on bone are still not fully understood. Certainly, these drugs have transformed the treatment of osteoporosis in both men and women. There is no question that they do prevent fractures related to low bone mass, and there is widespread agreement that they increase strength and stiffness of the vertebrae. There is less consensus, however, about their effects on cortical bone, or on bone tissue properties in either trabecular or cortical bone, or their effects with longer periods of treatment. The consensus of most studies, both those based on ovariectomized and intact animal models and on testing of human bone, is that long-term treatment and/or high doses with certain BPs make the bone tissue more brittle and less tough. This translates into reduced energy to fracture and potentially a shorter bone fatigue life. Many studies have been done, but Interpretation of the results of these studies is complicated by variations in which BP is used, the animal model used, dose, duration, and methods of testing. Duration effects and effects on impact properties of bone are gaps that should be filled with additional testing.

Investigation of bone matrix composition, architecture and mechanical properties reflect structure-function relationship of cortical bone in glucocorticoid induced osteoporosis

Glucocorticoid induced osteoporosis (GIOP) is the most common negative consequence of long-term glucocorticoid treatment, leading to increased fracture risk followed by loss of mobility and high mortality risk. These biologically induced changes in bone quality at molecular level lead to changes both in bone matrix architecture and bone matrix composition. However, the quantitative details of changes in bone quality - and especially their link to reduced macroscale mechanical properties are still largely missing. In this study, a mouse model for glucocorticoid-induced osteoporosis (GIOP) was used to investigate mechanical and material alterations in bone cortex (natural nanocomposite) at different scale. By combining quantitative backscattered electron (qBSE) imaging, nanoindentation and high brilliance synchrotron X-ray nanomechanical imaging on a genetically modified mouse model of GIOP, we were able to quantify the local indentation modulus, mineralization distribution and the alterations of nanoscale structures and deformation mechanisms in the mid-diaphysis of femur, and relate them to the macroscopic mechanical changes. Our results showed clear and significant changes in terms of material quality of bone at nanoscale and microscale, which manifests itself in development of spatial heterogeneities in mineralization and indentation moduli across the bone organ, with potential implications for increased fracture risk.

Pulsed electromagnetic fields modify the adverse effects of glucocorticoids on bone architecture, bone strength and porous implant osseointegration by rescuing bone-anabolic actions

Long-term glucocorticoid therapy is known to induce increased bone fragility and impaired skeletal regeneration potential. Growing evidence suggests that pulsed electromagnetic fields (PEMF) can accelerate fracture healing and increase bone mass both experimentally and clinically. However, how glucocorticoid-treated bone and bone cells respond to PEMF stimulation remains poorly understood. Here we tested the effects of PEMF on bone quantity/quality, bone metabolism, and porous implant osseointegration in rabbits treated with dexamethasone (0.5 mg/kg/day, 6 weeks). The micro-CT, histologic and nanoindentation results showed that PEMF ameliorated the glucocorticoid-mediated deterioration of cancellous and cortical bone architecture and intrinsic material properties. Utilizing the new porous titanium implant (Ti2448) with low toxicity and low elastic modulus, we found that PEMF stimulated bone ingrowth into the pores of implants and enhanced peri-implant bone material quality during osseous defect repair in glucocorticoid-treated rabbits. Dynamic histomorphometric results revealed that PEMF reversed the adverse effects of glucocorticoids on bone formation, which was confirmed by increased circulating osteocalcin and P1NP. PEMF also significantly attenuated osteocyte apoptosis, promoted osteoblast-related osteocalcin, Runx2 and Osx expression, and inhibited osteocyte-specific DKK1 and Sost expression (negative regulators of osteoblasts) in glucocorticoid-treated skeletons, revealing improved functional activities of osteoblasts and osteocytes. Nevertheless, PEMF exerted no effect on circulating bone-resorbing cytokines (serum TRAcP5b and CTX-1) or skeletal gene expression of osteoclast-specific markers (TRAP and cathepsin K). PEMF also significantly upregulated skeletal gene expression of canonical Wnt ligands (Wnt1, Wnt3a and Wnt10b), whereas PEMF did not alter non-canonical Wnt5a expression. This study demonstrates that PEMF treatment improves bone mass, strength and porous implant osseointegration in glucocorticoid-treated rabbits by promoting potent bone-anabolic action, which is associated with canonical Wnt-mediated improvement in osteoblast and osteocyte functions. This study provides a new treatment alternative for glucocorticoid-related bone disorders in a convenient and non-invasive manner.

A novel technique with reduced computed tomography exposure to predict vertebral compression fracture: a finite element study based on rat vertebrae

Vertebral compression fractures are a significant clinical issue with an annual incidence of approximately 750,000 cases in the USA alone. Mechanical properties of vertebrae are successfully evaluated through finite element (FE) models based on vertebrae CT. However, clinical drawbacks associated to radiation transmission encouraged to explore the possibility to use selected or reduced portions of the vertebra. The objective of our study was to develop a new procedure to predict vertebral compression fracture from sub-volumes. We reconstructed rat vertebras from micro-CT of thoracic and lumbar groups. Each vertebra was partitioned into three sub-volumes of different axial thickness. FE simulating compression tests were performed on each model to evaluate their failure load and stiffness. Using a power function, a high correlation was found for stiffness and strength. The sub-volume with three fifths thickness had a failure load of 180.7 ± 19.2 N for thoracic and of 209.5 ± 27.4 N for the lumbar vertebra. These values were not significantly different from the values found for the entire vertebra (p > 0.05). Based on our findings, failure loads and stiffnesses obtained with reduced CT scans can be successfully used to predict full vertebral failure. This sub-region analysis and power relationship suggests that one can limit radiation exposure to patients when bone characterization is needed. Graphical abstract Estimated mechanical properties in relation to the extent of the computed tomography reconstruction.

Glucocorticoids cause mandibular bone fragility and suppress osteocyte perilacunar-canalicular remodeling

Osteocytes support dynamic, cell-intrinsic resorption and deposition of bone matrix through a process called perilacunar/canalicular remodeling (PLR). In long bones, PLR depends on MMP13 and is tightly regulated by PTH, sclerostin, TGFβ, and glucocorticoids. However, PLR is regulated differently in the cochlea, suggesting a mechanism that is anatomically distinct. Unlike long bones, the mandible derives from neural crest and exhibits unique susceptibility to medication and radiation induced osteonecrosis. Therefore, we sought to determine if PLR in the mandible is suppressed by glucocorticoids, as it is in long bone. Hemimandibles were collected from mice subcutaneously implanted with prednisolone or vehicle containing pellets for 7, 21, or 55 days (n = 8/group) for radiographic and histological analyses. Within 21 days, micro-computed tomography revealed a glucocorticoid-dependent reduction in bone volume/total volume and trabecular thickness and a significant decrease in bone mineral density after 55 days. Within 7 days, glucocorticoids strongly and persistently repressed osteocytic expression of the key PLR enzyme MMP13 in both trabecular and cortical bone of the mandible. Cathepsin K expression was significantly reduced only after 55 days of glucocorticoid treatment, at which point histological analysis revealed a glucocorticoid-dependent reduction in the lacunocanalicular surface area. In addition to reducing bone mass and suppressing PLR, glucocorticoids also reduced the stiffness of mandibular bone in flexural tests. Thus, osteocyte PLR in the neural crest-derived mandible is susceptible to glucocorticoids, just as it is in the mesodermally-derived femur, highlighting the need to further study PLR as a target of drugs, and radiation in mandibular osteonecrosis.

Assessing bone quality through mechanical properties in postmenopausal trabecular bone

BACKGROUND

The inner structure of trabecular bone is a result of structural optimization provided by remodeling processes. Changes in hormonal status related to menopause cause bone tissue loss and micro-architectural deterioration with a consequent susceptibility to fracture. Accumulation of micro-damage in bone, as a function of the rate of production and rate of repair, underlies the development of stress fractures, increasing fragility associated to age and osteoporosis, especially in transmenopausal women.

PATIENTS AND METHODS

Quasi-static and nano-dynamic mechanical characterization were undertaken in trabecular bone from femoral neck biopsies of postmenopausal women. AFM (Atomic Force Microscopy) complementary studies were performed to determine nano-roughness (SRa) and the fibrils width of collagen. Nanoindentations were used to quantify transmenopausal changes in intrinsic mechanical properties of trabecular bone: hardness (Hi), modulus of Young (Ei), complex modulus (E*), tan delta (δ), storage modulus (E') and loss modulus (E").

RESULTS

As result of the quasi-static measurements, 0.149 (0.036) GPa and 2.95 (0.73) GPa of Hi and Ei were obtained, respectively. As result of the nano-dynamic measurements, 17.94 (3.15), 0.62 (0.10), 13.79 (3.21 and 6.39 (1.28) GPa of E*, tan (δ), E' and E" were achieved, respectively. 101.07 SRa and 831.28 nm of fibrils width were additionally obtained.

CONCLUSIONS

This study poses a first approach to the measurement of bone quality in postmenopausal trabecular bone by combining quasi-static, nano-DMA analysis and tribology of dentin surface through AFM characterization.

Biochemical assessment of nanostructures in human trabecular bone: Proposal of a Raman microspectroscopy based measurements protocol

BACKGROUND

Improvements to the understating of the compositional contributions of bone mineral and organic components to the competence of trabecular bone are crucial. The purpose of this study was to propose a protocol to study biochemical composition of trabecular bone, based on two combined Raman analysis methodologies.

MATERIAL AND METHODS

Both cluster and single point Raman mappings were obtained, in order to assess bone degeneration associated with aging, disease, or injury, and to help in the evaluation and development of successful therapies. In this study, human trabecular bone has been analysed throughout a) Raman cluster analysis: bone mineral content, carbonate-to-phosphate ratio (both from the mineral components), the crosslinking and nature/secondary structure of collagen (both from the organic components); and b) Single point Raman spectra, where Raman points related to the minerals and organic components were also obtained, both techniques were employed in spectra attained at 400 to 1700 cm^-1.

RESULTS

Multivariate analysis confirmed: 1) the different spectral composition, 2) the existence of centroids grouped by chemical affinity of the various components of the trabecular bone, and 3) the several traces of centroids and distribution of chemical compositional clusters.

CONCLUSIONS

This study is important, because it delivers a study protocol that provides molecular variations information in both mineral and collagen structure of trabecular bone tissue. This will enable clinicians to benefit knowing the microstructural differences in the bone subjected to degeneration of their patients.

Nanostructure in the trabecular bone of postmenopausal women: Mechanical and chemical analysis

The possibility of diagnosis and prediction of multiple disorders in trabecular bone through nano-biomechanics and chemical analysis are summarized. Improvements to the understating of the compositional contributors of bone mineral and organic components to mechanical competence are crucial. Viscoelastic properties and Raman characterization have been used to evaluate possible alterations of the trabecular bone associated with aging, disease, or injury. In this study, the trabecular bone of postmenopausal women has been analyzed throughout. (a) Nanomechanical characterization, by using nano-DMA: complex modulus, tan δ, loss modulus (E'), and storage modulus (E'); and (b) Raman analysis: relative presence of minerals, carbonate-to-phosphate ratio (both from the mineral components), the crosslinking and nature/secondary structure of collagen (both from the organic components). Complementary nano-morphological studies were done assessing roughness (SRa) and collagen fibrils width, on this trabecular bone. A general idea of the behavior of the viscoelastic performance can be obtained by the Tan δ (E″/E'), that achieved 0.98GPa of damping. 249nm and 0.898μm of SRa roughness and fibrils width were obtained, respectively. The relative presence of minerals, the carbonate-to-phosphate ratio, the crosslinking and the nature/secondary structure of collagen, between 700 and 1700cm^-1, were also obtained, in order to propose a study protocol for trabecular bone characterization.

Strain dependent differences in glucocorticoid-induced bone loss between C57BL/6J and CD-1 mice

We have investigated the effect of long-term glucocorticoid (GC) administration on bone turnover in two frequently used mouse strains; C57BL/6J and CD1, in order to assess the influence of their genetic background on GC-induced osteoporosis (GIO). GIO was induced in 12 weeks old female C57BL/6J and CD1 mice by subcutaneous insertion of long-term release prednisolone or placebo pellets. Biomechanical properties as assessed by three point bent testing revealed that femoral elasticity and strength significantly decreased in CD1 mice receiving GC, whereas C57BL/6J mice showed no differences between placebo and prednisolone treatment. Bone turnover assessed by microcomputer tomography revealed that contrary to C57BL/6J mice, prednisolone treated CD1 mice developed osteoporosis. In vitro experiments have underlined that, at a cellular level, C57BL/6J mice osteoclasts and osteoblasts were less responsive to GC treatment and tolerated higher doses than CD1 cells. Whilst administration of long-term release prednisolone pellets provided a robust GIO animal model in 12 weeks old CD1 mice, age matched C57BL/6J mice were not susceptible to the bone changes associated with GIO. This study indicates that for the induction of experimental GIO, the mouse strain choice together with other factors such as age should be carefully evaluated.

Improved Mobilization of Exogenous Mesenchymal Stem Cells to Bone for Fracture Healing and Sex Difference

Mesenchymal stem cell (MSC) transplantation has been tested in animal and clinical fracture studies. We have developed a bone-seeking compound, LLP2A-Alendronate (LLP2A-Ale) that augments MSC homing to bone. The purpose of this study was to determine whether treatment with LLP2A-Ale or a combination of LLP2A-Ale and MSCs would accelerate bone healing in a mouse closed fracture model and if the effects are sex dependent. A right mid-femur fracture was induced in two-month-old osterix-mCherry (Osx-mCherry) male and female reporter mice. The mice were subsequently treated with placebo, LLP2A-Ale (500 μg/kg, IV), MSCs derived from wild-type female Osx-mCherry adipose tissue (ADSC, 3 x 10⁵ , IV) or ADSC + LLP2A-Ale. In phosphate buffered saline-treated mice, females had higher systemic and surface-based bone formation than males. However, male mice formed a larger callus and had higher volumetric bone mineral density and bone strength than females. LLP2A-Ale treatment increased exogenous MSC homing to the fracture gaps, enhanced incorporation of these cells into callus formation, and stimulated endochondral bone formation. Additionally, higher engraftment of exogenous MSCs in fracture gaps seemed to contribute to overall fracture healing and improved bone strength. These effects were sex-independent. There was a sex-difference in the rate of fracture healing. ADSC and LLP2A-Ale combination treatment was superior to on callus formation, which was independent of sex. Increased mobilization of exogenous MSCs to fracture sites accelerated endochondral bone formation and enhanced bone tissue regeneration. Stem Cells 2016;34:2587-2600.

Multiscale alterations in bone matrix quality increased fragility in steroid induced osteoporosis

A serious adverse clinical effect of glucocorticoid steroid treatment is secondary osteoporosis, enhancing fracture risk in bone. This rapid increase in bone fracture risk is largely independent of bone loss (quantity), and must therefore arise from degradation of the quality of the bone matrix at the micro- and nanoscale. However, we lack an understanding of both the specific alterations in bone quality n steroid-induced osteoporosis as well as the mechanistic effects of these changes. Here we demonstrate alterations in the nanostructural parameters of the mineralized fibrillar collagen matrix, which affect bone quality, and develop a model linking these to increased fracture risk in glucocorticoid induced osteoporosis. Using a mouse model with an N-ethyl-N-nitrosourea (ENU)-induced corticotrophin releasing hormone promoter mutation (Crh(-120/+)) that developed hypercorticosteronaemia and osteoporosis, we utilized in situ mechanical testing with small angle X-ray diffraction, synchrotron micro-computed tomography and quantitative backscattered electron imaging to link altered nano- and microscale deformation mechanisms in the bone matrix to abnormal macroscopic mechanics. We measure the deformation of the mineralized collagen fibrils, and the nano-mechanical parameters including effective fibril modulus and fibril to tissue strain ratio. A significant reduction (51%) of fibril modulus was found in Crh(-120/+) mice. We also find a much larger fibril strain/tissue strain ratio in Crh(-120/+) mice (~1.5) compared to the wild-type mice (~0.5), indicative of a lowered mechanical competence at the nanoscale. Synchrotron microCT show a disruption of intracortical architecture, possibly linked to osteocytic osteolysis. These findings provide a clear quantitative demonstration of how bone quality changes increase macroscopic fragility in secondary osteoporosis.

Sclerostin-antibody treatment of glucocorticoid-induced osteoporosis maintained bone mass and strength

This study was to determine if antibody against sclerostin (Scl-Ab) could prevent glucocorticoid (GC)-induced osteoporosis in mice. We found that Scl-Ab prevented GC-induced reduction in bone mass and bone strength and that the anabolic effects of Scl-Ab might be partially achieved through the preservation of osteoblast activity through autophagy.

INTRODUCTION

Glucocorticoids (GCs) inhibit bone formation by altering osteoblast and osteocyte cell activity and lifespan. A monoclonal antibody against sclerostin, Scl-Ab, increased bone mass in both preclinical animal and clinical studies in subjects with low bone mass. The objectives of this study were to determine if treatment with the Scl-Ab could prevent loss of bone mass and strength in a mouse model of GC excess and to elucidate if Scl-Ab modulated bone cell activity through autophagy.

METHODS

We generated reporter mice that globally expressed dsRed fused to LC3, a protein marker for autophagosomes, and evaluated the dose-dependent effects of GCs (0, 0.8, 2.8, and 4 mg/kg/day) and Scl-Ab on autophagic osteoblasts, bone mass, and bone strength.

RESULTS

GC treatment at 2.8 and 4 mg/kg/day of methylprednisolone significantly lowered trabecular bone volume (Tb-BV/TV) at the lumbar vertebrae and distal femurs, cortical bone mass at the mid-shaft femur (FS), and cortical bone strength compared to placebo (PL). In mice treated with GC and Scl-Ab, Tb-BV/TV increased by 60-125 %, apparent bone strength of the lumbar vertebrae by 30-70 %, FS-BV by 10-18 %, and FS-apparent strength by 13-15 %, as compared to GC vehicle-treated mice. GC treatment at 4 mg/kg/day reduced the number of autophagic osteoblasts by 70 % on the vertebral trabecular bone surface compared to the placebo group (PL, GC 0 mg), and GC + Scl-Ab treatment.

CONCLUSIONS

Treatment with Scl-Ab prevented GC-induced reduction in both trabecular and cortical bone mass and strength and appeared to maintain osteoblast activity through autophagy.

Prevention of glucocorticoid induced bone changes with beta-ecdysone

Beta-ecdysone (βEcd) is a phytoecdysteroid found in the dry roots and seeds of the asteraceae and achyranthes plants, and is reported to increase osteogenesis in vitro. Since glucocorticoid (GC) excess is associated with a decrease in bone formation, the purpose of this study was to determine if treatment with βEcd could prevent GC-induced osteoporosis. Two-month-old male Swiss-Webster mice (n=8-10/group) were randomized to either placebo or slow release prednisolone pellets (3.3mg/kg/day) and treated with vehicle control or βEcd (0.5mg/kg/day) for 21days. GC treatment inhibited age-dependent trabecular gain and cortical bone expansion and this was accompanied by a 30-50% lower bone formation rate (BFR) at both the endosteal and periosteal surfaces. Mice treated with only βEcd significantly increased bone formation on the endosteal and periosteal bone surfaces, and increased cortical bone mass were their controls to compare to GC alone. Concurrent treatment of βEcd and GC completely prevented the GC-induced reduction in BFR, trabecular bone volume and partially prevented cortical bone loss. In vitro studies determined that βEcd prevented the GC increase in autophagy of the bone marrow stromal cells as well as in whole bone. In summary, βEcd prevented GC induced changes in bone formation, bone cell viability and bone mass. Additional studies are warranted of βEcd for the treatment of GC induced bone loss.

Effect of sequential treatments with alendronate, parathyroid hormone (1-34) and raloxifene on cortical bone mass and strength in ovariectomized rats

Anti-resorptive and anabolic agents are often prescribed for the treatment of osteoporosis continuously or sequentially for many years. However their impact on cortical bone quality and bone strength is not clear.

METHODS

Six-month old female rats were either sham operated or ovariectomized (OVX). OVX rats were left untreated for two months and then were treated with vehicle (Veh), hPTH (1-34) (PTH), alendronate (Aln), or raloxifene (Ral) sequentially for three month intervals, for a total of three periods. Mid-tibial cortical bone architecture, mass, mineralization, and strength were measured on necropsy samples obtained after each period. Bone indentation properties were measured on proximal femur necropsy samples.

RESULTS

Eight or more months of estrogen deficiency in rats resulted in decreased cortical bone area and thickness. Treatment with PTH for 3months caused the deposition of endocortical lamellar bone that increased cortical bone area, thickness, and strength. These improvements were lost when PTH was withdrawn without followup treatment, but were maintained for the maximum times tested, six months with Ral and three months with Aln. Pre-treatment with anti-resorptives was also somewhat successful in ultimately preserving the additional endocortical lamellar bone formed under PTH treatment. These treatments did not affect bone indentation properties.

SUMMARY

Sequential therapy that involved both PTH and anti-resorptive agents was required to achieve lasting improvements in cortical area, thickness, and strength in OVX rats. Anti-resorptive therapy, either prior to or following PTH, was required to preserve gains attributable to an anabolic agent.

Short-courses of dexamethasone abolish bisphosphonate-induced reductions in bone toughness

Atypical femoral fractures, which display characteristics of brittle material failure, have been associated with potent remodeling suppression drugs. Given the millions of individuals treated with this class of drugs it is likely that other factors play a role in these fractures. Some evidence suggests that concomitant use of corticosteroids may contribute to the pathogenesis although data in this area is lacking. The goal of this study was to assess the combined role of bisphosphonates and dexamethasone on bone mechanical properties. Skeletally mature beagle dogs were either untreated controls, or treated with zoledronic acid (ZOL), dexamethasone (DEX), or ZOL + DEX. Zoledronic acid (0.06 mg/kg) was given monthly via IV infusion for 9 months. DEX (5 mg) was administered daily for one week during each of the last three months of the 9 month experiment. Ribs were harvested and assessed for bone geometry, mechanical properties, and remodeling rate (n = 3-6 specimens per group). DEX significantly suppressed intracortical remodeling compared to vehicle controls while both ZOL and the combination of DEX + ZOL nearly abolished intracortical remodeling. ZOL treatment resulted in significantly lower bone toughness, determined from 3-point bending tests, compared to all other treatment groups while the toughness in ZOL + DEX animals was identical to those of untreated controls. These findings suggest that short-courses of dexamethasone not only do not adversely affect toughness in the setting of bisphosphonates, but also actually reverse the adverse effects of its treatment. Understanding the mechanism for this tissue-level effect could lead to novel approaches for reducing the risk of atypical femoral fractures.

Prolonged alendronate treatment prevents the decline in serum TGF-β1 levels and reduces cortical bone strength in long-term estrogen deficiency rat model

INTRODUCTION

While the anti-resorptive effects of the bisphosphonates (BPs) are well documented, many questions remain about their mechanisms of action, particularly following long-term use. This study evaluated the effects of alendronate (Ale) treatment on TGF-β1 signaling in mesenchymal stem cells (MSCs) and osteocytes, and the relationship between prolonged alendronate treatment on systemic TGF-β1 levels and bone strength.

METHODS

TGF-β1 expression and signaling were evaluated in MSCs and osteocytic MLO-Y4 cells following Ale treatment. Serum total TGF-β1 levels, a bone resorption marker (DPD/Cr), three-dimensional microCT scans and biomechanical tests from both the trabecular and cortical bone were measured in ovariectomized rats that either received continuous Ale treatment for 360 days or Ale treatment for 120 days followed by 240 days of vehicle. Linear regression tests were performed to determine the association of serum total TGF-β1 levels and both the trabecular (vertebrae) and cortical (tibiae) bone strength.

RESULTS

Ale increased TGF-β1 signaling in the MSCs but not in the MLO-Y4 cells. Ale treatment increased serum TGF-β1 levels and the numbers of TGF-β1-positive osteocytes and periosteal cells in cortical bone. Serum TGF-β1 levels were not associated with vertebral maximum load and strength but was negatively associated with cortical bone maximum load and ultimate strength.

CONCLUSIONS

The increase of serum TGF-β1 levels during acute phase of estrogen deficiency is likely due to increased osteoclast-mediated release of matrix-derived latent TGF-β1. Long-term estrogen-deficiency generally results in a decline in serum TGF-β1 levels that are maintained by Ale treatment. Measuring serum total TGF-β1 levels may help to determine cortical bone quality following alendronate treatment.

Prednisolone treatment and restricted physical activity further compromise bone of mdx mice

OBJECTIVES

The purpose of this study was to determine the extent to which prednisolone treatment and restricted physical activity caused deleterious changes in inherently compromised mdx bone.

METHODS

Four week-old male mdx mice (n=36) were treated for 8-wk either with or without prednisolone (0.8-1.3 mg/kg/d) and were housed in traditional or small cages (restricted activity). Tibial bone strength, geometry, and intrinsic material properties were assessed at the mid-shaft by three-point bending and micro-computed tomography (μCT).

RESULTS

Three-point bending results showed that both prednisolone and restricted activity reduced bone strength (7%), however stiffness was only reduced in restricted-activity mice. μCT analyses showed that cortical bone area and cortical thickness were 13% smaller in restricted-activity mice, and may have accounted for their compromised bone strength. Intrinsic material properties, including volumetric bone mineral density (vBMD) and modulus of elasticity, were not impacted by either treatment, however, vBMD tended to be lower in restricted-activity mice (p=0.06).

CONCLUSIONS

These data show that prednisolone treatment and restricted physical activity independently accentuate reductions in the strength and geometry of mdx bone, but do not influence intrinsic material properties.

Recurrent fractures in an elderly patient with systemic lupus erythematosus

Glucocorticoid-induced osteoporosis (GIO) is an important problem that remains undertreated, even by rheumatologists. We present a case of an elderly patient with systemic lupus erythematosus diagnosed more than 40 years ago, who suffered from recurrent fractures and attendant complications despite a bone mineral density (BMD) score in the osteopenic range and treatment with bisphosphonates. With improved treatment and outcome of lupus, an increasing number of elderly patients who are susceptible to osteoporotic fractures are expected. This case serves to highlight that rheumatic disease patients on steroids should be screened for GIO, as effective treatment and preventive measures are available. Teriparatide is a promising treatment for patients who have failed bisphosphonate treatment or who are at high risk for fracture. We should also bear in mind that BMD scores alone are not indicative of fracture risk, and other tools such as the WHO-FRAX (Fracture risk assessment tool), serum vitamin D3 levels and bone turnover markers should be used where appropriate. Other measures including attention to factors that contribute to falls should also be considered, necessitating a multi-disciplinary approach.

Glucocorticoid-induced osteoporosis in growing mice is not prevented by simultaneous intermittent PTH treatment

Glucocorticoids (GCs) are widely used in medicine for treatment of chronic diseases. Especially in children, prolonged treatment causes growth retardation and early onset of osteoporosis. Human parathyroid hormone (PTH) has an anabolic effect on bone when administrated intermittently. The aim of the present study was to examine whether a combined therapy of dexamethasone (DEX) and PTH could prevent the detrimental effects of GC on cortical and trabecular bone in the femur and vertebrae of growing mice. Three-week-old female FVB mice were treated with control, DEX, PTH, or a combination of DEX and PTH by daily subcutaneous injections. After 4 weeks, animals were killed and the femur and L5 vertebra were isolated. Cortical and trabecular bone parameters and relative calcium density were measured by high-resolution X-ray micro-computed tomography (micro-CT). In the femur, PTH can reverse the effects of DEX on bone volume to control. However, it cannot reverse the undermineralization, which most likely is a strong contributor to bone fragility. In the vertebra, PTH improves bone volume to some extent but does not restore the values to normal. It augments the negative effect of DEX on mineralization. We conclude that the detrimental effects of DEX in the growing skeleton cannot be prevented by simultaneous PTH treatment.

Comparison of the effect of vitamin K(2) and risedronate on trabecular bone in glucocorticoid-treated rats: a bone histomorphometry study

PURPOSE

To compare the effect of vitamin K(2) and risedronate on trabecular bone in glucocorticoid (GC)-treated rats.

MATERIALS AND METHODS

Forty-eight Sprague-Dawley female rats, 3 months of age, were randomized by the stratified weight method into 5 groups according to the following treatment schedule: age-matched control, GC administration, and GC administration with concomitant administration of vitamin K(2), risedronate, or vitamin K(2) + risedronate. GC (methylprednisolone sodium succinate, 5.0 mg/kg) and risedronate (10 microg/kg) were administered subcutaneously three and five times a week, respectively. Vitamin K(2) (menatetrenone, 30 mg/kg) was administered orally three times a week. At the end of the 8-week experiment, bone histomorphometric analysis was performed on trabecular bone of the tibial proximal metaphysis.

RESULTS

GC administration decreased trabecular bone mass compared with age-matched controls because of decreased bone formation (mineralizing surface, mineral apposition rate, and bone formation rate) and increased bone erosion. Vitamin K(2) attenuated GC-induced trabecular bone loss by preventing GC-induced decrease in bone formation (mineralizing surface) and subsequently reducing GC-induced increase in bone erosion. Risedronate prevented GC-induced trabecular bone loss by preventing GC-induced increase in bone erosion although it also suppressed bone formation (mineralizing surface, mineral apposition rate, and bone formation rate). Vitamin K(2) mildly attenuated suppression of bone formation (mineralizing surface) and bone erosion caused by risedronate without affecting trabecular bone mass when administered in combination.

CONCLUSION

The present study showed differential effect of vitamin K(2) and risedronate on trabecular bone in GC-treated rats.

Prolonged treatments with antiresorptive agents and PTH have different effects on bone strength and the degree of mineralization in old estrogen-deficient osteoporotic rats

Current approved medical treatments for osteoporosis reduce fracture risk to a greater degree than predicted from change in BMD in women with postmenopausal osteoporosis. We hypothesize that bone active agents improve bone strength in osteoporotic bone by altering different material properties of the bone. Eighteen-month-old female Fischer rats were ovariectomized (OVX) or sham-operated and left untreated for 60 days to induce osteopenia before they were treated with single doses of either risedronate (500 microg/kg, IV), zoledronic acid (100 microg/kg, IV), raloxifene (2 mg/kg, PO, three times per week), hPTH(1-34) (25 microg/kg, SC, three times per week), or vehicle (NS; 1 ml/kg, three times per week). Groups of animals were killed after days 60 and 180 of treatment, and either the proximal tibial metaphysis or lumbar vertebral body were studied. Bone volume and architecture were assessed by muCT and histomorphometry. Measurements of bone quality included the degree of bone mineralization (DBM), localized elastic modulus, bone turnover by histomorphometry, compression testing of the LVB, and three-point bending testing of the femur. The trabecular bone volume, DBM, elastic modulus, and compressive bone strength were all significantly lower at day 60 post-OVX (pretreatment, day 0 study) than at baseline. After 60 days of all of the bone active treatments, bone mass and material measurements agent were restored. However, after 180 days of treatment, the OVX + PTH group further increased BV/TV (+30% from day 60, p < 0.05 within group and between groups). In addition, after 180 days of treatment, there was more highly mineralized cortical and trabecular bone and increased cortical bone size and whole bone strength in OVX + PTH compared with other OVX + antiresorptives. Treatment of estrogen-deficient aged rats with either antiresorptive agents or PTH rapidly improved many aspects of bone quality including microarchitecture, bone mineralization, turnover, and bone strength. However, prolonged treatment for 180 days with PTH resulted in additional gains in bone quality and bone strength, suggesting that the maximal gains in bone strength in cortical and trabecular bone sites may require a longer treatment period with PTH.

Glucocorticoid-induced bone loss in mice can be reversed by the actions of parathyroid hormone and risedronate on different pathways for bone formation and mineralization

OBJECTIVE

Glucocorticoid excess decreases bone mineralization and microarchitecture and leads to reduced bone strength. Both anabolic (parathyroid hormone [PTH]) and antiresorptive agents are used to prevent and treat glucocorticoid-induced bone loss, yet these bone-active agents alter bone turnover by very different mechanisms. This study was undertaken to determine how PTH and risedronate alter bone quality following glucocorticoid excess.

METHODS

Five-month-old male Swiss-Webster mice were treated with the glucocorticoid prednisolone (5 mg/kg in a 60-day slow-release pellet) or placebo. From day 28 to day 56, 2 groups of glucocorticoid-treated animals received either PTH (5 microg/kg) or risedronate (5 microg/kg) 5 times per week. Bone quality and quantity were measured using x-ray tomography for the degree of bone mineralization, microfocal computed tomography for bone microarchitecture, compression testing for trabecular bone strength, and biochemistry and histomorphometry for bone turnover. In addition, real-time polymerase chain reaction (PCR) and immunohistochemistry were performed to monitor the expression of several key genes regulating Wnt signaling (bone formation) and mineralization.

RESULTS

Compared with placebo, glucocorticoid treatment decreased trabecular bone volume (bone volume/total volume [BV/TV]) and serum osteocalcin, but increased serum CTX and osteoclast surface, with a peak at day 28. Glucocorticoids plus PTH increased BV/TV, and glucocorticoids plus risedronate restored BV/TV to placebo levels after 28 days. The average degree of bone mineralization was decreased after glucocorticoid treatment (-27%), but was restored to placebo levels after treatment with glucocorticoids plus risedronate or glucocorticoids plus PTH. On day 56, RT-PCR revealed that expression of genes that inhibit bone mineralization (Dmp1 and Phex) was increased by continuous exposure to glucocorticoids and glucocorticoids plus PTH and decreased by glucocorticoids plus risedronate, compared with placebo. Wnt signaling antagonists Dkk-1, Sost, and Wif1 were up-regulated by glucocorticoid treatment but down-regulated after glucocorticoid plus PTH treatment. Immunohistochemistry of bone sections showed that glucocorticoids increased N-terminal Dmp-1 staining while PTH treatment increased both N- and C-terminal Dmp-1 staining around osteocytes.

CONCLUSION

Our findings indicate that both PTH and risedronate improve bone mass, degree of bone mineralization, and bone strength in glucocorticoid-treated mice, and that PTH increases bone formation while risedronate reverses the deterioration of bone mineralization.

Measurement of the toughness of bone: a tutorial with special reference to small animal studies

Quantitative assessment of the strength and toughness of bone has become an integral part of many biological and bioengineering studies on the structural properties of bone and their degradation due to aging, disease and therapeutic treatment. Whereas the biomechanical techniques for characterizing bone strength are well documented, few studies have focused on the theory, methodology, and various experimental procedures for evaluating the fracture toughness of bone, i.e., its resistance to fracture, with particular reference to whole bone testing in small animal studies. In this tutorial, we consider the many techniques for evaluating toughness and assess their specific relevance and application to the mechanical testing of small animal bones. Parallel experimental studies on wild-type rat and mouse femurs are used to evaluate the utility of these techniques and specifically to determine the coefficient of variation of the measured toughness values.