CAMKK2 is upregulated in primary human osteoarthritis and its inhibition protects against chondrocyte apoptosis.

OBJECTIVE: To investigate the role of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) in human osteoarthritis. MATERIALS AND METHODS: Paired osteochondral plugs and articular chondrocytes were isolated from the relatively healthier (intact) and damaged portions of human femoral heads collected from patients undergoing total hip arthroplasty for primary osteoarthritis (OA). Cartilage from femoral plugs were either flash frozen for gene expression analysis or histology and immunohistochemistry. Chondrocyte apoptosis in the presence or absence of CAMKK2 inhibition was measured using flow cytometry. CAMKK2 overexpression and knockdown in articular chondrocytes were achieved via Lentivirus- and siRNA-mediated approaches respectively, and their effect on pro-apoptotic and cartilage catabolic mechanisms was assessed by immunoblotting. RESULTS: CAMKK2 mRNA and protein levels were elevated in articular chondrocytes from human OA cartilage compared to paired healthier intact samples. This increase was associated with elevated catabolic marker matrix metalloproteinase 13 (MMP-13), and diminished anabolic markers aggrecan (ACAN) and type II collagen (COL2A1) levels. OA chondrocytes displayed enhanced apoptosis, which was suppressed following pharmacological inhibition of CAMKK2. Levels of MMP13, pSTAT3, and the pro-apoptotic marker BAX became elevated when CAMKK2, but not its kinase-defective mutant was overexpressed, whereas knockdown of the kinase decreased the levels of these proteins. CONCLUSIONS: CAMKK2 is upregulated in human OA cartilage and is associated with elevated levels of pro-apoptotic and catabolic proteins. Inhibition or knockdown of CAMKK2 led to decreased chondrocyte apoptosis and catabolic protein levels, whereas its overexpression elevated them. CAMKK2 may be a therapeutic target to prevent or mitigate human OA.

Bone quality in an ovariectomized monkey animal model treated with two doses of teriparatide for either 18 months, or 12 months followed by withdrawal for 6 months.

Previous studies of ovariectomized (OVX) monkeys, treated with recombinant human parathyroid hormone (PTH) (1-34) at 1 or 5 µg/kg/day for 18 months or for 12 months followed by 6 months withdrawal from treatment, displayed significant changes in geometry, histomorphometry, and bone quality, but without strict tissue age criteria, of the midshaft humerus. Since bone quality significantly depends on tissue age among other factors, the aim of the present study was to establish the bone-turnover independent effects of two doses of PTH, as well as the effects of treatment withdrawal on bone quality by measuring bone material composition at precisely known tissue ages ranging from osteoid, to mineralized tissue older than 373 days. Raman microspectroscopic analysis of bone tissue from the mid-shaft humerus of OVX monkeys demonstrated that the clinically relevant dose of PTH administered for 18 months reverses the effects of ovariectomy on bone quality when compared against SHAM. Both doses investigated in this study restore the mineralization regulation mechanisms to SHAM levels. The study also showed that the beneficial effects induced by 12 months of clinically relevant PTH therapy were sustained after six months of therapy withdrawal.

Systemic inhibition or global deletion of CaMKK2 protects against post-traumatic osteoarthritis.

OBJECTIVE: To investigate the role of Ca2+/calmodulin-dependent protein kinase 2 (CaMKK2) in post-traumatic osteoarthritis (PTOA). METHODS: Destabilization of the medial meniscus (DMM) or sham surgeries were performed on 10-week-old male wild-type (WT) and Camkk2-/- mice. Half of the DMM-WT mice and all other cohorts (n = 6/group) received tri-weekly intraperitoneal (i.p.) injections of saline whereas the remaining DMM-WT mice (n = 6/group) received i.p. injections of the CaMKK2 inhibitor STO-609 (0.033 mg/kg body weight) thrice a week. Study was terminated at 8- or 12-weeks post-surgery, and knee joints processed for microcomputed tomography imaging followed by histology and immunohistochemistry. Primary articular chondrocytes were isolated from knee joints of 4-6-day-old WT and Camkk2-/- mice, and treated with 10 ng/ml interleukin-1ß (IL)-1ß for 24 or 48 h to investigate gene and protein expression. RESULTS: CaMKK2 levels and activity became elevated in articular chondrocytes following IL-1ß treatment or DMM surgery. Inhibition or absence of CaMKK2 protected against DMM-associated destruction of the cartilage, subchondral bone alterations and synovial inflammation. When challenged with IL-1ß, chondrocytes lacking CaMKK2 displayed attenuated inflammation, cartilage catabolism, and resistance to suppression of matrix synthesis. IL-1ß-treated CaMKK2-null chondrocytes displayed decreased IL-6 production, activation of signal transducer and activator of transcription 3 (Stat3) and matrix metalloproteinase 13 (MMP13), indicating a potential mechanism for the regulation of inflammatory responses in chondrocytes by CaMKK2. CONCLUSIONS: Our findings reveal a novel function for CaMKK2 in chondrocytes and highlight the potential for its inhibition as an innovative therapeutic strategy in the prevention of PTOA.

Proposed pathogenesis for atypical femoral fractures: lessons from materials research.

Atypical femoral fractures (AFFs) have been well defined clinically and epidemiologically. Less clear are the underlying mechanisms responsible. This commentary points out the likely sources of decreased resistance to fracture using lessons from bone material studies and biomechanics. We hypothesize that the key element in the cascade of events leading to failure of the largest and strongest bone in the human body is long-term suppression of normal bone turnover caused by exposure to potent anti-remodeling agents, most notably the bisphosphonates (BPs). Suppressed bone turnover produces changes in bone that alter its material quality and these changes could lead to adverse effects on its mechanical function. At the submicroscopic [<1 µm] level of collagen fibrils, suppression of bone turnover allows continued addition of non-enzymatic cross links that can reduce collagen's plasticity and this in turn contributes to reduced bone toughness. Further, adverse changes in hydroxyapatite crystalline structure and composition can occur, perhaps increasing collagen's brittleness. At the microscopic level [~1-500 µm] of the bone-matrix structure, suppressed bone turnover allows full mineralization of cortical bone osteons and results in a microstructure of bone that is more homogeneous. Both brittleness and loss of heterogeneity allow greater progression of microscopic cracks that can occur with usual physical activity; in crack mechanical terms, normal mechanisms that dissipate crack tip growth energy are greatly reduced and crack progression is less impeded. Further, the targeted repair of cracks by newly activated BMUs appears to be preferentially suppressed by BPs. We further hypothesize that it is not necessary to have accumulation of many cracks to produce an AFF, just one that progresses - one that is not stopped by bone's several protective mechanisms and is allowed to penetrate through a homogeneous environment. The remarkable straight transverse fracture line is an indicator of the slow progression of a "mother crack" and the failure of usual mechanisms to bridge or deflect the crack. Research in AFF mechanisms has been focused at the organ level, describing the clinical presentation and radiologic appearance. Although today we have not yet connected all the dots in the pathophysiology of BP-induced AFF, recent advances in measuring bone mechanical qualities at the submicroscopic and tissue levels allow us to explain how spontaneous catastrophic failure of the femur can occur.

Three years of alendronate treatment does not continue to decrease microstructural stresses and strains associated with trabecular microdamage initiation beyond those at 1 year.

UNLABELLED: The effects of a 3-year alendronate treatment on trabecular stresses/strains associated with microdamage initiation were investigated using finite element modeling (FEM). Severely damaged trabeculae in the low-dose treatment group were associated with increased stresses compared with the high-dose treatment group (p = 0.006) and approached significance in the control group (p = 0.02). INTRODUCTION: Alendronate, a commonly prescribed anti-remodeling agent, decreases fracture risk in the vertebrae, hip, and wrist of osteoporotic individuals. However, evaluation of microdamage accumulation in animal and human studies shows increased microdamage density relative to controls. Microstructural von Mises stresses associated with severe and linear damage have been found to decrease after 1 year of alendronate treatment. In the present study, stresses/strains associated with damage were assessed after 3 years of treatment to determine whether they continued to decrease with increased treatment duration. METHODS: Microdamaged trabeculae visualized with fluorescent microscopy were associated with stresses and strains obtained using image-based FEM. Stresses/strains associated with severe, diffuse, and linearly damaged and undamaged trabeculae were compared among groups treated for 3 years with an osteoporotic treatment dose of alendronate, a Paget's disease treatment dose of alendronate, or saline control. Architectural characteristics and mineralization were also analyzed from three-dimensional microcomputed tomography reconstructed images. RESULTS: Severely damaged trabeculae in the osteoporotic treatment dose group were associated with increased stress compared with the Paget's disease treatment dose group (p = 0.006) and approached significance compared to the control group (p = 0.02). Trabecular mineralization in severely damaged trabeculae of the low-dose treatment group was significantly greater compared to severely damaged trabeculae in the high-dose treatment and control group, suggesting that changes at the tissue level may play a role in these findings. CONCLUSIONS: Trabecular level stresses associated with microdamage do not continue to decrease with prolonged alendronate treatment. Changes in mineralization may account for these findings.

Why bones bend but don't break.

The musculoskeletal system is adept at dissipating potentially damaging energy that could accelerate fracture consequent to multiple loading cycles. Microstructural damage reduces bone's residual properties, but prevents high stresses within the material by dissipating energy that can lead to eventual failure. Thus skeletal microdamage can be viewed as an adaptive process to prevent bone failure by dissipating energy. Because a damaged bone has reduced strength and stiffness, it must be repaired, so bone has evolved a system of self-repair that relies on microdamage-stimulated signaling mechanisms. When repair cannot occur quickly enough, low energy stress fractures can occur. The regulating effects of muscle also prevent failure by controlling where high stresses occur. Acting synergistically, muscle forces dissipate energy by appropriately regulating accelerations and decelerations of the limbs during movement. When muscles become fatigued, these functions are constrained, larger amounts of energy are imparted to bone, increasing the likelihood of microstructural damage and fracture. Thus, healthy bones are maintained by the ability of the musculoskeletal system to dissipate the energy through synergistic muscular activity and through the maintenance of microstructural and material properties that allow for crack initiation, but also for their repair.

Issues in modern bone histomorphometry.

This review reports on proceedings of a bone histomorphometry session conducted at the Fortieth International IBMS Sun Valley Skeletal Tissue Biology Workshop held on August 1, 2010. The session was prompted by recent technical problems encountered in conducting histomorphometry on bone biopsies from humans and animals treated with anti-remodeling agents such as bisphosphonates and RANKL antibodies. These agents reduce remodeling substantially, and thus cause problems in calculating bone remodeling dynamics using in vivo fluorochrome labeling. The tissue specimens often contain few or no fluorochrome labels, and thus create statistical and other problems in analyzing variables such as mineral apposition rates, mineralizing surface and bone formation rates. The conference attendees discussed these problems and their resolutions, and the proceedings reported here summarize their discussions and recommendations.

Compromised osseous healing of dental extraction sites in zoledronic acid-treated dogs.

UNLABELLED: The goal of this study was to document how treatment with high doses of zoledronic acid affects dental extraction healing. Our results, showing significantly compromised osseous healing within the socket as well as presence of exposed bone and development of a sequestrum in one animal, provide a building block toward understanding osteonecrosis of the jaw. PURPOSE: The goal of this study was to document how treatment with a bisphosphonate affects the bone tissue following dental extraction. METHODS: Skeletally mature female beagle dogs were either untreated controls (CON) or treated with intravenous zoledronic acid (ZOL). Following the extraction of the fourth premolars, healing was allowed for 4 or 8 weeks. Properties of the extraction site were assessed using microcomputed tomography (micro-CT) and dynamic histomorphometry. RESULTS: The initial infilling of the extraction socket with bone was not affected by ZOL, but subsequent removal of this bone was significantly suppressed compared to CON. After 8 weeks of healing, the alveolar cortical bone adjacent to the extraction socket had a remodeling rate of ∼50% per year in CON animals while ZOL-treated animals had a rate of <1% per year. One ZOL-treated animal developed exposed bone post-extraction which eventually led to the formation of a sequestrum. Assessment of the sequestrum with micro-CT and histology showed that it had features consistent with those reported in humans with osteonecrosis of the jaw. CONCLUSIONS: These results, showing significantly compromised post-extraction osseous healing as well as presence of exposed bone and development of a sequestrum in one ZOL animal, provide a building block toward understanding the pathophysiology of osteonecrosis of the jaw.

Ovariectomy stimulates and bisphosphonates inhibit intracortical remodeling in the mouse mandible.

OBJECTIVE: The pathophysiology of osteonecrosis of the jaw (ONJ) is thought to be linked to suppression of intracortical remodeling. The aim of this study was to determine whether mice, which normally do not undergo appreciable amounts of intracortical remodeling, could be stimulated by ovariectomy to remodel within the cortex of the mandible and if bisphosphonates (BPs) would suppress this intracortical remodeling. MATERIAL AND METHODS: Skeletally mature female C3H mice were either ovariectomized (OVX) or SHAM operated and treated with two intravenous doses of zoledronic acid (ZOL, 0.06 mg/kg body weight) or vehicle (VEH). This ZOL dose corresponds to the dose given to patients with cancer on a mg/kg basis, adjusted for body weight. Calcein was administered prior to sacrifice to label active formation sites. Dynamic histomorphometry of the mandible and femur was performed. RESULTS: Vehicle-treated OVX animals had significantly higher (eightfold) intracortical remodeling of the alveolar portion of the mandible compared to sham--this was significantly suppressed by ZOL treatment. At all skeletal sites, overall bone formation rate was lower with ZOL treatment compared to the corresponding VEH group. CONCLUSIONS: Under normal conditions, the level of intracortical remodeling in the mouse mandible is minimal but in C3H mice it can be stimulated to appreciable levels with ovariectomy. Based on this, if the suppression of intracortical remodeling is found to be part of the pathophysiology of ONJ, the ovariectomized C3H mouse could serve as a useful tool for studying this condition.

The influence of vitamin E on immune function and response to vaccination in older horses.

Horses have an increased susceptibility to infection because of a decline in immune function with advancing age. Vitamin E has been found to play a key role in normal immune system function. The purpose of the study was to examine the effect of vitamin E supplementation on immune function and response to vaccination in older horses. Predominantly older horses (18.9 +/- 1.3 yr, range 7 to 26 yr; 523 +/- 38 kg of BW) were supplemented orally once daily for 16 wk with either all-rac-alpha-tocopheryl acetate (15 IU/kg of BW; n = 8) or a placebo (n = 8). One horse from each group was removed from the study for reasons not related to the study. Serum alpha-tocopherol concentration, neutrophil and monocyte bacterial killing ability, lysozyme activity, immunoglobulin concentration (IgG(a), IgG(b), IgG(T), and IgM), and neutralizing antibody production to West Nile virus vaccination were determined. The overall serum alpha-tocopherol concentration of the vitamin E-supplemented horses was greater than that of placebo-supplemented horses (P < 0.001). Bacterial killing capacity of monocytes and neutrophils increased in the vitamin E-supplemented horses (P < 0.05). Vitamin E-supplemented horses had greater serum IgG(a) (P < 0.001) and IgG(T) (P = 0.003) concentrations but produced less serum IgG(b) (P = 0.023) than placebo-supplemented horses. There was no effect of vitamin E supplementation on IgM production. The neutralizing antibody response to vaccination against West Nile virus was unaffected by vitamin E supplementation. There was a continuous increase in serum lysozyme concentration in placebo-supplemented horses, whereas serum lysozyme concentration did not increase until wk 12 in vitamin E-supplemented horses. In conclusion, vitamin E supplementation of predominantly older horses differentially modulated general cell-mediated and humoral immune function. Further research is needed to fully understand the effect of vitamin E on the immune function of horses.

Histomorphometric changes by teriparatide in alendronate-pretreated women with osteoporosis.

SUMMARY: The level of increased bone formation after 24 months of treatment with teriparatide (rhPTH (1-34), TPTD) is similar in patients who were either treatment-naïve (TN) or had lower bone turnover initially due to previous alendronate (ALN) therapy. INTRODUCTION: Bone anabolic effects of TPTD in postmenopausal women with osteoporosis may be blunted during the initial phase after switching from ALN to TPTD. To explore the long-term implications, we examined histomorphometric and biochemical markers of bone turnover of patients on TPTD therapy after long-term ALN treatment. METHODS: Paired biopsies were obtained after tetracycline double labeling at baseline and after 24 months of TPTD treatment from 29 ALN-pretreated (64.5 ± 16.4 months) and 16 TN patients. Biochemical markers were measured at baseline, during the treatment, or at study end. RESULTS: Compared with the baseline, after 24-month TPTD, activation frequency (Ac.F.) and osteoid surface (OS) increased in both groups: 0.11-0.34 cycles per year, 3.96-9.8% in the ALN-pretreated group and 0.19-0.33 cycles per year, 6.2-11.3% (p < 0.05) in the TN group, respectively. Biochemical and histomorphometric markers correlated positively both at baseline and endpoint. Serum amino terminal propeptide of type I procollagen (PINP) correlated with Ac.F. (r = 0.57, p < 0.001 and r = 0.48, p < 0.01) and OS (r = 0.51, p < 0.01 and r = 0.56, p < 0.01) at baseline and endpoint, respectively. Following 3 months of treatment, increases in biochemical markers like PINP predicted the increase in Ac.F. (r = 0.52, p < 0.01) and OS (r = 0.54, p < 0.01) after 24 months. CONCLUSIONS: The increased level of formation is similar in patients who were either TN or had lower bone turnover initially due to previous ALN therapy. Elevated bone formation in postmenopausal women with osteoporosis was sustained over a 24-month period by TPTD. Biochemical markers of bone formation are a good surrogate for the assessment of TPTD effects.

Heritability of lumbar trabecular bone mechanical properties in baboons.

Genetic effects on mechanical properties have been demonstrated in rodents, but not confirmed in primates. Our aim was to quantify the proportion of variation in vertebral trabecular bone mechanical properties that is due to the effects of genes. L3 vertebrae were collected from 110 females and 46 male baboons (6-32 years old) from a single extended pedigree. Cranio-caudally oriented trabecular bone cores were scanned with microCT then tested in monotonic compression to determine apparent ultimate stress, modulus, and toughness. Age and sex effects and heritability (h(2)) were assessed using maximum likelihood-based variance components methods. Additive effects of genes on residual trait variance were significant for ultimate stress (h(2)=0.58), toughness (h(2)=0.64), and BV/TV (h(2)=0.55). When BV/TV was accounted for, the residual variance in ultimate stress accounted for by the additive effects of genes was no longer significant. Toughness, however, showed evidence of a non-BV/TV-related genetic effect. Overall, maximum stress and modulus show strong genetic effects that are nearly entirely due to bone volume. Toughness shows strong genetic effects related to bone volume and shows additional genetic effects (accounting for 10% of the total trait variance) that are independent of bone volume. These results support continued use of bone volume as a focal trait to identify genes related to skeletal fragility, but also show that other focal traits related to toughness and variation in the organic component of bone matrix will enhance our ability to find additional genes that are particularly relevant to fatigue-related fractures.

Mandibular necrosis in beagle dogs treated with bisphosphonates.

OBJECTIVES - To test the effect of bisphosphonate (BP) treatment for up to 3 years on bone necrosis and osteocyte death in the mandible using a canine model. MATERIALS AND METHODS - Dogs were treated with clinical doses of oral alendronate (ALN, 0.2 or 1.0 mg/kg/day) for 1 or 3 years. In a separate study, dogs were treated with i.v. zoledronate (ZOL) at 0.06 mg/kg/day for 6 months. En bloc staining was used to identify necrotic areas in the mandible; viable osteocytes were identified using lactate dehydrogenase. RESULTS - None of the treatments was associated with exposed bone, but 17-25% of dogs treated for 1 year and 25-33% of dogs treated for 3 years with ALN showed pockets of dead bone. Necrotic areas had no viable osteocytes and were void of patent canaliculi. No control animals demonstrated necrotic bone. ZOL treatment for 6 months was associated with osteocyte death greater than that seen in animals treated with ALN or saline. It is not clear whether osteocyte death occurs because of direct toxic effects of BPs, or because suppressed remodelling fails to renew areas that naturally undergo cell death. Necrotic areas are also associated with bone other than the mandible, e.g. the rib, which normally undergo high rates of remodelling. CONCLUSIONS - Reduced remodelling rate using BPs may contribute to the pathogenesis of bone matrix necrosis. The development of an animal model that mimics important aspects of BP-related osteonecrosis of the jaw is important to understanding the pathogenesis of osteonecrosis.

Design and validation of a knee brace with feedback to reduce the rate of loading.

The repetitive nature of walking can lead to repetitive stress and associated complications due to the rate of loading (ROL) experienced by the body at the initial contact of the foot with the ground. An individual's gait kinematics at initial contact has been suggested to give rise to the ROL, and a repetitive, high ROL may lead to several disorders, including osteoarthritis. We present the design, development, and validation of a knee brace that provides feedback to the user during gait. The feedback consists of an auditory signal when the specific parameters of knee angle or tibial acceleration 50 ms prior to contact are exceeded. Nine women were recruited for the gait analysis, and the gait characteristics with and without the brace and feedback are analyzed. Our results indicate that using a knee brace with feedback can effectively change the gait kinematics used during walking, leading to a reduced ROL experienced at initial contact. Using a knee brace with feedback is a novel approach to gait retraining. Al-though the kinetics of how the subjects change in gait pattern is unknown, the reduced ROL experienced is significant and warrants further investigation.

Changes in non-enzymatic glycation and its association with altered mechanical properties following 1-year treatment with risedronate or alendronate.

SUMMARY: One year of high-dose bisphosphonate (BPs) therapy in dogs allowed the increased accumulation of advanced glycation end-products (AGEs) and reduced postyield work-to-fracture of the cortical bone matrix. The increased accumulation of AGEs in these tissues may help explain altered bone matrix quality due to the administration of BPs in animal models INTRODUCTION: Non-enzymatic glycation (NEG) is a posttranslational modification of the organic matrix that results in the formation of advanced glycation end-products (AGEs). In bone, the accumulation of AGEs play an important role in determining fracture resistance, and elevated levels of AGEs have been shown to adversely affect the bone's propensity to brittle fracture. It was thus hypothesized that the suppression of tissue turnover in cortical bone due to the administration of bisphosphonates would cause increased accumulation of AGEs and result in a more brittle bone matrix. METHODS: Using a canine animal model (n = 12), we administered daily doses of a saline vehicle (VEH), alendronate (ALN 0.20, 1.00 mg/kg) or risedronate (RIS 0.10, 0.50 mg/kg). After a 1-year treatment, the mechanical properties, intracortical bone turnover, and the degree of nonenzymatic cross-linking of the organic matrix were measured from the tibial cortical bone tissue of these animals. RESULTS: There was a significant accumulation of AGEs at high treatment doses (+49 to + 86%; p < 0.001), but not at doses equivalent to those used for the treatment of postmenopausal osteoporosis, compared to vehicle. Likewise, postyield work-to-fracture of the tissue was significantly reduced at these high doses (-28% to -51%; p < 0.001) compared to VEH. AGE accumulation inversely correlated with postyield work-to-fracture (r (2) = 0.45; p < 0.001), suggesting that increased AGEs may contribute to a more brittle bone matrix. CONCLUSION: High doses of bisphosphonates result in the accumulation of AGEs and a reduction in energy absorption of cortical bone. The increased accumulation of AGEs in these tissues may help explain altered bone matrix quality due to the administration of BPs in animal models.

Alendronate treatment results in similar levels of trabecular bone remodeling in the femoral neck and vertebra.

SUMMARY: We aimed to determine whether trabecular bone in sites that have different surface-based remodeling rates, the femoral neck and vertebra, are differently affected by alendronate treatment. Alendronate treatment resulted in similar levels of turnover in both sites, suggesting that a lower limit of bone turnover suppression with alendronate may exist. INTRODUCTION: Bone turnover suppression in sites that already have a low surface-based remodeling rate may lead to oversuppression that could have negative effects on the biomechanical properties of bone. The goal was to determine how alendronate suppresses bone turnover at sites with different surface-based remodeling rates. METHODS: Dynamic histomorphometric parameters were assessed in trabecular bone of the femoral neck and lumbar vertebrae obtained from skeletally mature beagles treated with saline (1 ml/kg/day) or alendronate (ALN 0.2 or 1.0 mg/kg/day). The ALN0.2 and ALN1.0 doses approximate, on a milligram per kilogram basis, the clinical doses used for the treatment of postmenopausal osteoporosis and Paget's disease, respectively. RESULTS: Alendronate treatment resulted in similar absolute levels of bone turnover in the femoral neck and vertebrae, although the femoral neck had 33% lower pre-treatment surface-based remodeling rate than the vertebra (p < 0.05). Additionally, the high dose of alendronate (ALN 1.0) suppressed bone turnover to similar absolute levels as the low dose of alendronate (ALN 0.2) in both sites. CONCLUSIONS: Alendronate treatment may result in a lower limit of trabecular bone turnover suppression, suggesting that sites of low pre-treatment remodeling rate are not more susceptible to oversuppression than those of high pre-treatment remodeling rate.

Strontium ranelate does not stimulate bone formation in ovariectomized rats.

INTRODUCTION: Strontium ranelate (SrR) is suggested to function as a dual-acting agent in the treatment of postmenopausal osteoporosis with anti-resorptive and anabolic skeletal benefits. We evaluated the effects of SrR on the skeleton in ovariectomized (OVX) rats and evaluated the influence of dietary calcium. METHODS: Three-month old virgin female rats underwent ovariectomy (OVX, n = 50) or SHAM surgery (SHAM, n = 10). Four weeks post-surgery, rats were treated daily by oral gavage with distilled water (10 ml/kg/day) or SrR (25 or 150 mg/kg/day) for 90 days. Separate groups of animals for each dose of SrR were fed a low (0.1%) or normal (1.19%) calcium (Ca) diet. Static and dynamic histomorphometry, DXA, mu-CT, mechanical testing, and serum and skeletal concentrations of strontium were assessed. RESULTS: SrR at doses of 25 and 150 mg/kg/day did not increase bone formation on trabecular or periosteal bone surfaces, and failed to inhibit bone resorption of trabecular bone regardless of Ca intake. There were no improvements in bone mass, volume or strength with either dose of SrR given normal Ca. CONCLUSION: These findings demonstrate that SrR at dosages of 25 and 150 mg/kg/day did not stimulate an anabolic bone response, and failed to improve the bone biomechanical properties of OVX rats.

The effect of the microscopic and nanoscale structure on bone fragility.

Bone mineral density is the gold-standard for assessing bone quantity and diagnosing osteoporosis. Although bone mineral density measurements assess the quantity of bone, the quality of the tissue is an important predictor of fragility. Understanding the macro- and nanoscale properties of bone is critical to understanding bone fragility in osteoporosis. Osteoporosis is a disease that affects more than 75 million people worldwide. The gold standard for osteoporosis prognosis, bone mineral density, primarily measures the quantity of bone in the skeleton, overlooking more subtle aspects of bone's properties. Bone quality, a measure of bone's architecture, geometry and material properties, is evaluated via mechanical, structural and chemical testing. Although decreased BMD indicates tissue fragility at the clinical level, changes in the substructure of bone can help indicate how bone quality is altered in osteoporosis. Additionally, mechanical properties which can quantify fragility, or bone's inability to resist fracture, can be changed due to alterations in bone architecture and composition. Recent studies have focused on examination of bone on the nanoscale, suggesting the importance of understanding the interactions of the mineral crystals and collagen fibrils and how they can alter bone quality. It is therefore important to understand alterations in bone that occur at the macro-, micro- and nanoscopic levels to determine what parameters contribute to decreased bone quality in diseased tissue.