Vertebral Trabecular Bone Research Articles

A nonlinear micromechanical model for progressive damage of vertebral trabecular bones

A nonlinear micromechanical model for progressive damage of vertebral trabecular bones

Chronic Mild Stress Causes Bone Loss via an Osteoblast-Specific Glucocorticoid-Dependent Mechanism.

Chronic stress and depression are associated with alterations in the hypothalamic-pituitary-adrenal signaling cascade and considered a risk factor for bone loss and fractures. However, the mechanisms underlying the association between stress and poor bone health are unclear. Using a transgenic (tg) mouse model in which glucocorticoid signaling is selectively disrupted in mature osteoblasts and osteocytes [11β-hydroxysteroid-dehydrogenase type 2 (HSD2)OB-tg mice], the present study examines the impact of chronic stress on skeletal metabolism and structure. Eight-week-old male and female HSD2OB-tg mice and their wild-type (WT) littermates were exposed to chronic mild stress (CMS) for the duration of 4 weeks. At the endpoint, L3 vertebrae and tibiae were analyzed by micro-computed tomography and histomorphometry, and bone turnover was measured biochemically. Compared with nonstressed controls, exposure to CMS caused an approximately threefold increase in serum corticosterone concentrations in WT and HSD2OB-tg mice of both genders. Compared with controls, CMS resulted in loss of vertebral trabecular bone mass in male WT mice but not in male HSD2OB-tg littermates. Furthermore, both tibial cortical area and area fraction were reduced in stressed WT but not in stressed HSD2OB-tg male mice. Osteoclast activity and bone resorption marker were increased in WT males following CMS, features absent in HSD2OB-tg males. Interestingly, CMS had little effect on vertebral and long-bone structural parameters in female mice. We conclude that in male mice, bone loss during CMS is mediated via enhanced glucocorticoid signaling in osteoblasts (and osteocytes) and subsequent activation of osteoclasts. Female mice appear resistant to the skeletal effects of CMS.

Characterization of synthetic foam structures used to manufacture artificial vertebral trabecular bone

Artificial materials reflecting the mechanical properties of human bone are essential for valid and reliable implant testing and design. They also are of great benefit for realistic simulation of surgical procedures. The objective of this study was therefore to characterize two groups of self-developed synthetic foam structures by static compressive testing and by microcomputed tomography. Two mineral fillers and varying amounts of a blowing agent were used to create different expansion behavior of the synthetic open-cell foams. The resulting compressive and morphometric properties thus differed within and also slightly between both groups. Apart from the structural anisotropy, the compressive and morphometric properties of the synthetic foam materials were shown to mirror the respective characteristics of human vertebral trabecular bone in good approximation. In conclusion, the artificial materials created can be used to manufacture valid synthetic bones for surgical training. Further, they provide novel possibilities for studying the relationship between trabecular bone microstructure and biomechanical properties.

Regional Variations in Shear Strength and Density of the Human Thoracic Vertebral Endplate and Trabecular Bone.

Previous studies investigated the overall mechanical strength of the vertebral body; however, limited information is available on the biomechanical properties of different regions within the vertebral endplate and cancellous bone. In addition, the correlation between mechanical strength and various density measurements has not been studied yet. Thoracic (T10) vertebrae were harvested from fifteen human cadaveric spines (average age: 77 years old). Twelve cylindrical cores of 7.2 mm (diameter) by 3.2 mm (height) were prepared from each vertebral body. Shear was produced using a stainless steel tubular blade and measured with a load cell from a mechanical testing machine. Optical and bulk densities were calculated before mechanical testing. Apparent, material, and ash densities were measured after testing. Material density and shear strength increased from anterior to lateral regions of both endplate and cancellous bone. Endplate shear strength was significantly lower in the anterior (0.52 ± 0.08 MPa) than in the lateral region (2.72 ± 0.59 MPa) (p=0.017). Trabecular bone maximum load carrying capacity was 5 times higher in the lateral (12 ± 2.74 N) (p=0.09) and 4.5 times higher in the central (10 ± 2.24 N) (p=0.2) than in the anterior (2 ± 0.60 N) regions. Mechanical strength positively correlated with ash density, and even moreso with material density. Shear strength was the lowest at the anterior region and highest at the lateral region for both endplate and cancellous bone. Material density had the best correlation with mechanical strength. Newer spinal implants could optimize the loading in the lateral aspects of both endplate and cancellous bone to reduce the likelihood of screw loosening and the subsidence of disc replacement devices. This study was reviewed by the SUNY Downstate Medical Center IRB Committee; IRB#: 533603-2.

A new multiscale micromechanical model of vertebral trabecular bones.

A new three-dimensional (3D) multiscale micromechanical model has been suggested as adept at predicting the overall linear anisotropic mechanical properties of a vertebral trabecular bone (VTB) highly porous microstructure. A nested 3D modeling analysis framework spanning the multiscale nature of the VTB is presented herein. This hierarchical analysis framework employs the following micromechanical methods: the 3D parametric high-fidelity generalized method of cells (HFGMC) as well as the 3D sublaminate model. At the nanoscale level, the 3D HFGMC method is applied to obtain the effective elastic properties of a representative unit cell (RUC) representing the mineral collagen fibrils composite. Next at the submicron scale level, the 3D sublaminate model is used to generate the effective elastic properties of a repeated stack of multilayered lamellae demonstrating the nature of the trabeculae (bone-wall). Thirdly, at the micron scale level, the 3D HFGMC method is used again on a RUC of the highly porous VTB microstructure. The VTB-RUC geometries are taken from microcomputed tomography scans of VTB samples harvested from different vertebrae of human cadavers [Formula: see text]. The predicted anisotropic overall elastic properties for native VTBs are, then, examined as a function of age and sex. The predicted results of the VTBs longitudinal Young's modulus are compared to reported values found in the literature. The proposed 3D nested modeling analysis framework provides a good agreement with reported values of Young's modulus of single trabeculae as well as for VTB-RUC in the literature.

RANK-RANKL Mediated Bone Destruction in B-Cell Acute Lymphoblastic Leukemia

Survival rates for pediatric B-Cell Acute Lymphoblastic Leukemia (B-ALL) have improved dramatically over the past 40 years approaching a current long-term survival rate of 85%. However childhood B-ALL patients continue to confront co-morbidities and their long-term consequences. For example, osteopenia and osteoporosis associated fractures are a common complication of pediatric leukemia at diagnosis, during treatment and in long-term B-ALL survivors. The STeroid-associated Osteoporosis in the Pediatric Population (STOPP) study reported that at ALL diagnosis, 16% of children and adolescents present with bone pain, vertebral compression and low vertebral Bone Mineral Density (BMD) scores, with the greatest incidence of vertebral fractures (VF) seen in the first year following diagnosis (J Clin Endocrinol Metab. 2015, 100:3408-17). Glucocorticoid treatment further elevated fracture risk in this population. These data underscore the need to identify molecular mechanism by which leukemic cells contribute to bone loss, and provide targeted therapies to limit these effects.Our laboratory previously showed that Rag2-/- p53-/- Prkdcscid/scid triple mutant (TM) and p53-/- Prkdcscid/scid double mutant (DM) mice develop spontaneous B-ALL, but only TM animals exhibit dissemination of leukemic blasts to the leptomeninges of the CNS, a poor prognosis feature observed in pediatric and adult ALL patients. We observed that TM leukemic mice also displayed fragile vertebral bones. Using comparative transcriptome analysis, we found that RANKL (Receptor Activator of the Nuclear factor-kB Ligand), a Tumor Necrosis Factor (TNF) superfamily member ligand and a key regulator of B cell and osteoclast differentiation, was expressed at greater levels in TM compared to the DM leukemia cells. RANKL binds to its receptor RANK, which is expressed in osteoclast precursor cells. RANK-RANKL interaction induces signaling in the osteoclast precursors and drives their differentiation into mature bone resorbing osteoclasts (Proc. Natl. Acad. Sci. 1999, 96:3540-3545). Upon adoptive leukemia cell transfer into immune deficient mice, RANKL+ TM but not DM cells caused decreased vertebral trabecular bone density in the recipients. Treatment with the recombinant RANKL antagonist protein Osteoprotegerin (OPG-Fc) inhibited the growth and dissemination of RANKL+TM leukemic cells and attenuated bone destruction in the recipient mice. These data suggested that TM mouse leukemia cells cause bone loss in the absence of glucocorticoid or other chemotherapy agents.We then examined the potential role of RANKL in osteoporosis associated with human B-ALL. RANKL mRNA was expressed by a majority of primary human adult and pediatric B-ALL. To determine whether primary patient B-ALL can cause bone loss, we transplanted RANKL+ human B-ALL samples of multiple cytogenetic high-risk subgroups (Complex, hypo-diploid and Mixed Lineage Leukemia (MLL) rearranged) into NOD.SCID.gC-/-(NSG) recipient mice. Micro-CT imaging and bone density measures in the xenotransplant recipients revealed extensive vertebral trabecular bone destruction. Immuno-histological analysis of the human B-ALL recipient mice demonstrated extensive osteoporotic damage of the long bones and marked RANKL protein expression in the long bones of mice harboring extensive human B-ALL cell burden compared to NSG control mice. To determine whether RANKL-RANK interaction was required for the B-ALL mediated bone destruction, cohorts of NSG mice engrafted with human B-ALL were treated with recombinant OPG-Fc compared to a matched Fc control protein. OPG-Fc treatment did not attenuate leukemia cell expansion and bone marrow burden, but despite bulky disease, the treatment conferred robust protection from bone destruction suggesting that RANKL was a critical mediator of this clinical complication.Our data demonstrate a central role of the RANK-RANKL axis in B-ALL-mediated bone disease and identify an actionable therapeutic target to reduce acute and long-term morbidity. Denosumab, an anti-RANKL antibody has been approved for the treatment of bone metastasis by solid tumors and for post-menopausal osteoporosis. Our pre-clinical studies suggest that Denosumab and other agents that inhibit the RANK-RANKL pathway may be efficacious in patients with B-ALL associated bone degeneration. DisclosuresNo relevant conflicts of interest to declare.

Construction of the effective plastic yield surfaces of vertebral trabecular bone under twisting and bending moments stresses using a 3D microstructural model

Trabecular bone experiences complex multiaxial loads which can lead to entire bone fracture. The available knowledge of the failure properties of trabecular under multiaxial states of stress is quite limited, especially under bending and twisting moment stresses. Analytical models of the mechanical response of trabecular bone based on microstructural models can significantly enhance our understanding of multiaxial failure behavior under such loadings. For this purpose, plastic yield surfaces are derived for lattice‐like models of the trabecular bone structure with a relatively high effective density, such that failure occurs by full plastic flow. The asymptotic discrete homogenization approach is involved to construct the plastic collapse surfaces of the periodic 3D rod‐like architecture of vertebral bone in micropolar couple stress space incorporating natural anisotropy of bone. Both in‐plane and out‐of‐plane bending couple stress states are considered in addition to torsional couple stresses. A plastic yield criterion is adopted to address general bending and torsional couple loadings, accounting for combined cell wall bone microstructure bending and torsion. The criterion for full plastic yielding is micromechanically motivated and relies on the calculation of the microscopic couple stresses (or micromoments) that are linked to the homogenized curvatures. The plastic yield surface is associated to a complete plasticization of the trabecular strut section. Additionally, since the effective bone density is the most important factor affecting the failure behavior of bone, the plastic strengths of vertebral bone are obtained in terms of the relative density to provide insights about the impact of bone relative density on the plastic collapse conditions. The vertebral plastic failure domains due to torsional and bending couple stresses are related to the relative density, expressed in terms of the micro‐architecture parameters, itself changing with age.

Variation in Attenuation in L1 Trabecular Bone at Different Tube Voltages: Caution Is Warranted When Screening for Osteoporosis With the Use of Opportunistic CT.

The purpose of this study is to investigate the variation in attenuation values (expressed as Hounsfield units) for L1 vertebral body trabecular bone at different tube voltages used in dual-energy CT (DECT) and to remind physicians to consider changes in attenuation values when they approach opportunistic screening for osteoporosis. Consecutive patients who underwent DECT examination of the abdomen and pelvis for suspected urolithiasis were included in the study. Attenuation noted on CT of the L1 trabecular bone performed with the use of tube voltages of 80, 100, and 140 kV was recorded. The correlation between the attenuation noted when the tube voltage was 140 kV and the attenuation noted when the tube voltage was either 80 or 100 kV was calculated, and differences in the mean CT attenuation values were compared. The mean attenuation values from L1 trabecular bone measurement performed for 191 patients were analyzed. As expected, the mean attenuation values decreased as the tube voltage increased. There was a strong correlation between the attenuation values noted when tube voltages of 80 and 140 kV were used (r2 = 0.97) and those noted when 100 and 140 kV were used (r2 = 0.96). The mean attenuation value noted at 80 kV was 76.4 HU (65%) higher than that noted at 140 kV (p < 0.001). The mean attenuation value at 100 kV was 45.5 HU (39.9%) higher than that noted at 140 kV (p < 0.001). We confirmed that attenuation values of L1 trabecular bone, unlike attenuation values of fat, fluid, or soft tissue, vary at different CT x-ray tube voltages. Therefore, standard reference attenuation values for trabecular bone seen at 120 kV cannot be applied to other single-energy settings, DECT, or CT examinations where dose modulation software automatically raises or lowers the tube voltage from 120 kV. Knowledge of the specific energy spectra used is essential before performing opportunistic CT evaluation for osteoporosis.

The Effect of TSH Suppression on Vertebral Trabecular Bone Scores in Patients With Differentiated Thyroid Carcinoma.

The effect of thyrotropin (TSH) suppressive therapy on trabecular bone scores (TBSs) is unclear. The aim of this study was to investigate the effect of TSH suppression on vertebral TBSs of postmenopausal women with differentiated thyroid carcinoma (DTC). We conducted a retrospective cohort study including 273 postmenopausal women with DTC who had received TSH suppressive therapy. Bone mineral density (BMD) and TBSs at the lumbar spine were analyzed using dual-energy X-ray absorptiometry (DXA). The association between the parameters of TSH suppressive therapy and bone parameters was investigated. Study subjects showed upper-normal free thyroxine levels and suppressed TSH at DXA evaluation. The mean duration of TSH suppression was 4.4 ± 2.9 years. Serum free T4 and TSH were not independently associated with lumbar spine BMD or TBS levels. Duration of TSH suppression was negatively correlated with lumbar spine TBS levels, but not with BMD. Longer duration of TSH suppression was independently associated with lower lumbar spine TBSs after adjusting for age, body mass index (BMI), and BMD. Lumbar spine TBSs were significantly lower in patients whose duration of TSH suppression was ≥5 years compared with those whose duration was <3 years after adjusting for age, BMI, and BMD. Longer duration of TSH suppression in postmenopausal DTC patients was associated with decreased vertebral bone strength by altering TBSs rather than BMD. TBSs should be considered when estimating vertebral bone fragility in postmenopausal DTC patients receiving long-term TSH suppressive therapy.

50 - Variations in Density and Shear Strength within the Human Thoracic Vertebral Endplate and Trabecular Bone

50 - Variations in Density and Shear Strength within the Human Thoracic Vertebral Endplate and Trabecular Bone

Discoidin Receptor 2 Controls Bone Formation and Marrow Adipogenesis.

Cell-extracellular matrix (ECM) interactions play major roles in controlling progenitor cell fate and differentiation. The receptor tyrosine kinase, discoidin domain receptor 2 (DDR2), is an important mediator of interactions between cells and fibrillar collagens. DDR2 signals through both ERK1/2 and p38 MAP kinase, which stimulate osteoblast differentiation and bone formation. Here we show that DDR2 is critical for skeletal development and differentiation of marrow progenitor cells to osteoblasts while suppressing marrow adipogenesis. Smallie mice (Ddr2slie/slie ), which contain a nonfunctional Ddr2 allele, have multiple skeletal defects. A progressive decrease in tibial trabecular bone volume/total volume (BV/TV) was observed when wild-type (WT), Ddr2wt/slie , and Ddr2slie/slie mice were compared. These changes were associated with reduced trabecular number (Tb.N) and trabecular thickness (Tb.Th) and increased trabecular spacing (Tb.Sp) in both males and females, but reduced cortical thickness only in Ddr2slie/slie females. Bone changes were attributed to decreased bone formation rather than increased osteoclast activity. Significantly, marrow fat and adipocyte-specific mRNA expression were significantly elevated in Ddr2slie/slie animals. Additional skeletal defects include widened calvarial sutures and reduced vertebral trabecular bone. To examine the role of DDR2 signaling in cell differentiation, bone marrow stromal cells (BMSCs) were grown under osteogenic and adipogenic conditions. Ddr2slie/slie cells exhibited defective osteoblast differentiation and accelerated adipogenesis. Changes in differentiation were related to activity of runt-related transcription factor 2 (RUNX2) and PPARγ, transcription factors that are both controlled by MAPK-dependent phosphorylation. Specifically, the defective osteoblast differentiation in calvarial cells from Ddr2slie/slie mice was associated with reduced ERK/MAP kinase and RUNX2-S319 phosphorylation and could be rescued with a constitutively active phosphomimetic RUNX2 mutant. Also, DDR2 was shown to increase RUNX2-S319 phosphorylation and transcriptional activity while also increasing PPARγ-S112 phosphorylation, but reducing its activity. DDR2 is, therefore, important for maintenance of osteoblast activity and suppression of marrow adipogenesis in vivo and these actions are related to changes in MAPK-dependent RUNX2 and PPARγ phosphorylation. © 2016 American Society for Bone and Mineral Research.

Effect of micro-computed tomography voxel size and segmentation method on trabecular bone microstructure measures in mice

Micro-computed tomography (μCT) is currently the gold standard for determining trabecular bone microstructure in small animal models. Numerous parameters associated with scanning and evaluation of μCT scans can strongly affect morphologic results obtained from bone samples. However, the effect of these parameters on specific trabecular bone outcomes is not well understood. This study investigated the effect of μCT scanning with nominal voxel sizes between 6–30μm on trabecular bone outcomes quantified in mouse vertebral body trabecular bone. Additionally, two methods for determining a global segmentation threshold were compared: based on qualitative assessment of 2D images, or based on quantitative assessment of image histograms. It was found that nominal voxel size had a strong effect on several commonly reported trabecular bone parameters, in particular connectivity density, trabecular thickness, and bone tissue mineral density. Additionally, the two segmentation methods provided similar trabecular bone outcomes for scans with small nominal voxel sizes, but considerably different outcomes for scans with larger voxel sizes. The Qualitatively Selected segmentation method more consistently estimated trabecular bone volume fraction (BV/TV) and trabecular thickness across different voxel sizes, but the Histogram segmentation method more consistently estimated trabecular number, trabecular separation, and structure model index. Altogether, these results suggest that high-resolution scans be used whenever possible to provide the most accurate estimation of trabecular bone microstructure, and that the limitations of accurately determining trabecular bone outcomes should be considered when selecting scan parameters and making conclusions about inter-group variance or between-group differences in studies of trabecular bone microstructure in small animals.

High‐fat diet exacerbates bone loss in mice implanted with low‐dose slow‐release lipopolysaccharide pellets

Obesity is associated with chronic up‐regulation of inflammatory cytokines which stimulate osteoclast activity and bone resorption. Osteopenia or low bone mass is observed in a variety of physiological conditions with chronic inflammation including aging and post‐menopause with estrogen deficiency. This study investigated whether obesity induced by a high‐fat diet alters bone loss in an animal model of chronic inflammation with low‐dose, slow‐release of lipopolysaccharide (LPS). Forty‐eight 6‐wk‐old female C57BL/6 mice were randomly assigned to four treatment groups (n=12/group) in a 2×2 factorial design: control (placebo) or LPS treatment and fed either a normal‐fat (NF, 10% energy as fat) or a high‐fat (HF, 45% energy as fat) diet ad libitum for 3 mon. LPS (E‐coli serotype 0127:B8) was incorporated into time‐release pellets designed to provide a consistent dose (1.3μg/day) for 3 months The LPS and placebo (containing just biodegradable carrier binder) pellets were implanted subcutaneously in the dorsal region of the neck. Mice implanted with LPS had similar body weight, fat mass and lean mass to those in the placebo (NF + HF) groups. LPS treatment increased serum concentration of tartrate‐resistant acid phosphatase (TRAP, a bone resorption marker), expression of proinflammatory cytokines (TNF‐α and IL‐6) in abdominal adipose tissue, and bone marrow osteoclast differentiation, while decreasing tibial and vertebral trabecular bone volume, trabecular thickness, connectivity density, and bone mineral density (P &lt; 0.05). Mice fed the HF diet had higher body weight (P &lt; 0.05) mainly due to increased fat mass (P &lt; 0.05) than animals fed the NF diet. Obesity induced by the HF diet increased serum TRAP concentration, bone marrow osteoclast differentiation, and expression of TNF‐α and IL‐6 in adipose tissue (P &lt; 0.05). Compared to the NF groups, mice in the HF groups had decreased bone volume, connectivity density, trabecular number while had increased trabecular separation, and structure model index (P &lt; 0.05). Mice implanted with LPS pellets and fed the high‐fat diet had the lowest bone mineral density compared to all other groups. These results show that obesity exacerbates bone loss in mice with chronic inflammation induced by low‐dose slow‐release LPS administration.Support or Funding Informationthe USDA Agricultural Research Service program “Bone Metabolism in Obesity,” Current Research Information System no. 5450‐51000‐046‐00D

Circadian factors BMAL1 and RORα control HIF-1α transcriptional activity in nucleus pulposus cells: implications in maintenance of intervertebral disc health.

BMAL1 and RORα are major regulators of the circadian molecular oscillator. Since previous work in other cell types has shown cross talk between circadian rhythm genes and hypoxic signaling, we investigated the role of BMAL1 and RORα in controlling HIF-1-dependent transcriptional responses in NP cells that exist in the physiologically hypoxic intervertebral disc. HIF-1-dependent HRE reporter activity was further promoted by co-transfection with either BMAL1 or RORα. In addition, stable silencing of BMAL1 or inhibition of RORα activity resulted in decreased HRE activation. Inhibition of RORα also modulated HIF1α-TAD activity. Interestingly, immunoprecipitation studies showed no evidence of BMAL1, CLOCK or RORα binding to HIF-1α in NP cells. Noteworthy, stable silencing of BMAL1 as well as inhibition of RORα decreased expression of select HIF-1 target genes including VEGF, PFKFB3 and Eno1. To delineate if BMAL1 plays a role in maintenance of disc health, we studied the spinal phenotype of BMAL1-null mice. The lumbar discs of null mice evidenced decreased height, and several parameters associated with vertebral trabecular bone quality were also affected in nulls. In addition, null animals showed a higher ratio of cells to matrix in NP tissue and hyperplasia of the annulus fibrosus. Taken together, our results indicate that BMAL1 and RORα form a regulatory loop in the NP and control HIF-1 activity without direct interaction. Importantly, activities of these circadian rhythm molecules may play a role in the adaptation of NP cells to their unique niche.

Relationship between sample volumes and modulus of human vertebral trabecular bone in micro-finite element analysis

Micro-finite element (μFE) models have been widely used to assess the biomechanical properties of trabecular bone. How to choose a proper sample volume of trabecular bone, which could predict the real bone biomechanical properties and reduce the calculation time, was an interesting problem. Therefore, the purpose of this study was to investigate the relationship between different sample volumes and apparent elastic modulus (E) calculated from μFE model. 5 Human lumbar vertebral bodies (L1–L5) were scanned by micro-CT. Cubic concentric samples of different lengths were constructed as the experimental groups and the largest possible volumes of interest (VOI) were constructed as the control group. A direct voxel-to-element approach was used to generate μFE models and steel layers were added to the superior and inferior surface to mimic axial compression tests. A 1% axial strain was prescribed to the top surface of the model to obtain the E values. ANOVA tests were performed to compare the E values from the different VOIs against that of the control group. Nonlinear function curve fitting was performed to study the relationship between volumes and E values. The larger cubic VOI included more nodes and elements, and more CPU times were needed for calculations. E values showed a descending tendency as the length of cubic VOI decreased. When the volume of VOI was smaller than (7.34mm3), E values were significantly different from the control group. The fit function showed that E values approached an asymptotic values with increasing length of VOI. Our study demonstrated that apparent elastic modulus calculated from μFE models were affected by the sample volumes. There was a descending tendency of E values as the length of cubic VOI decreased. Sample volume which was not smaller than (7.34mm3) was efficient enough and timesaving for the calculation of E.

Skeletal inflammation and attenuation of Wnt signaling, Wnt ligand expression, and bone formation in atherosclerotic ApoE-null mice.

ApoE-null (ApoE-KO) mice fed a high-fat diet (HFD) develop atherosclerosis, due in part to activation of vascular inflammation by oxidized low-density lipoprotein. Since bone loss also occurs in these mice, we used them to investigate the impact of oxidized lipids on bone homeostasis and to search for underlying pathogenic pathways. Four-month-old female ApoE-KO mice fed a HFD for three months exhibited increased levels of oxidized lipids in bone, as well as decreased femoral and vertebral trabecular and cortical bone mass, compared with ApoE-KO mice on normal diet. Despite HFD-induced increase in expression of Alox15, a lipoxygenase that oxidizes LDL and promotes atherogenesis, global deletion of this gene failed to ameliorate the skeletal impact of HFD. Osteoblast number and function were dramatically reduced in trabecular and cortical bone of HFD-fed mice, whereas osteoclast number was modestly reduced only in trabecular bone, indicating that an imbalance in favor of osteoclasts was responsible for HFD-induced bone loss. These changes were associated with decreased osteoblast progenitors and increased monocyte/macrophages in the bone marrow as well as increased expression of IL-1β, IL-6, and TNF. HFD also attenuated Wnt signaling as evidenced by reduced expression of Wnt target genes, and it decreased expression of pro-osteoblastogenic Wnt ligands. These results suggest that oxidized lipids decrease bone mass by increasing anti-osteoblastogenic inflammatory cytokines and decreasing pro-osteoblastogenic Wnt ligands.

Morphological models of trabecular bone suitable for high-porosity regions and vertebrae

The complex microarchitecture of trabecular bone makes it difficult to perform computational analyses on the real structure. Researchers have often resorted to using morphological idealizations employing simplified geometries. One such idealized structure, based on the gyroid, was found to mimic trabecular bone well. However, structures generated using the basic gyroid equation manifested discontinuities at high porosities. Another disadvantage of the gyroid is that it cannot model vertebral trabecular bone, which generally resembles cubic cells. To address these two shortcomings, we describe: (i) a modified structure based on the skeletal gyroid, which remains connected even at extremely high porosities, (ii) a cubic grid-like structure, based on the primitive minimal surface, for studying vertebrae.

Prevalence of Poor Bone Quality in Women Undergoing Spinal Fusion Using Biomechanical-CT Analysis.

Retrospective, cross-sectional analysis of vertebral bone quality in spine-fusion patients at a single medical center. To characterize the prevalence of osteoporosis and fragile bone strength in a spine-fusion population of women with an age range of 50 years to 70 years. Fragile bone strength is defined as the level of vertebral strength below which a patient is at as high a risk of future vertebral fracture as a patient having bone density-defined osteoporosis. Poor bone quality--defined here as the presence of either osteoporosis or fragile bone strength--is a risk factor for spine-fusion patients that often goes undetected but can now be assessed preoperatively by additional postprocessing of computed tomography (CT) scans originally ordered for perioperative clinical assessment. Utilizing such perioperative CT scans for a cohort of 98 women (age range: 51-70 yr) about to undergo spine fusion, we retrospectively used a phantomless calibration technique and biomechanical-CT postprocessing analysis to measure vertebral trabecular bone mineral density (BMD) (in mg/cm³) and by nonlinear finite element analysis, vertebral compressive strength (in Newtons, N) in the L1 or L2 vertebra. Preestablished validated threshold values were used to define the presence of osteoporosis (trabecular BMD of 80 mg/cm³ or lower) and fragile bone strength (vertebral strength of 4500 N or lower). Fourteen percent of the women tested positive for osteoporosis, 27% tested positive for fragile bone strength, and 29% were classified as having poor bone quality (either osteoporosis or fragile bone strength). Over this narrow age range, neither BMD nor vertebral strength were significantly correlated with age, weight, height, or body mass index (P values 0.14-0.97 for BMD; 0.13-0.51 for strength). Poor bone quality appears to be common in women between ages 50 years and 70 years undergoing spinal fusion surgery. 3.

Dietary Restriction-Induced Alterations in Bone Phenotype: Effects of Lifelong Versus Short-Term Caloric Restriction on Femoral and Vertebral Bone in C57BL/6 Mice.

Caloric restriction (CR) is a well-described dietary intervention that delays the onset of aging-associated biochemical and physiological changes, thereby extending the life span of rodents. The influence of CR on metabolism, strength, and morphology of bone has been controversially discussed in literature. Thus, the present study evaluated whether lifelong CR versus short-term late-onset dietary intervention differentially affects the development of senile osteoporosis in C57BL/6 mice. Two different dietary regimens with 40% food restriction were performed: lifelong CR starting in 4-week-old mice was maintained for 4, 20, or 74 weeks. In contrast, short-term late-onset CR lasting a period of 12 weeks was commenced at 48 or 68 weeks of age. Control mice were fed ad libitum (AL). Bone specimens were assessed using microcomputed tomography (μCT, femur and lumbar vertebral body) and biomechanical testing (femur). Adverse effects of CR, including reduced cortical bone mineral density (Ct.BMD) and thickness (Ct.Th), were detected to some extent in senile mice (68+12w) but in particular in cortical bone of young growing mice (4+4w), associated with reduced femoral failure force (F). However, we observed a profound capacity of bone to compensate these deleterious changes of minor nutrition with increasing age presumably via reorganization of trabecular bone. Especially in lumbar vertebrae, lifelong CR lasting 20 or 74 weeks had beneficial effects on trabecular bone mineral density (Tb.BMD), bone volume fraction (BV/TV), and trabecular number (Tb.N). In parallel, lifelong CR groups showed reduced structure model index values compared to age-matched controls indicating a transformation of vertebral trabecular bone microarchitecture toward a platelike geometry. This effect was not visible in senile mice after short-term 12-week CR. In summary, CR has differential effects on cortical and trabecular bone dependent on bone localization and starting age. Our study underlines that bone compartments possess a lifelong capability to cope with changing nutritional influences.

Neoflavonoid dalbergiphenol from heartwood of Dalbergia sissoo acts as bone savior in an estrogen withdrawal model for osteoporosis.

Dalbergiphenol (DGP) is a neoflavonoid isolated from heartwood of Dalbergia sissoo. Effects of DGP on skeletal health remain to be elucidated. The objective of the present study was to investigate the biological effects of DGP on bone loss in ovariectomized mice. Adult BALB/c mice were ovariectomized and administered DGP (1 and 5 mg/kg/d) or 17β-estradiol (E2) orally for 6 weeks. The sham group and the ovariectomy (OVX) + vehicle group served as controls. Eight female BALB/c mice were taken for each group. Uterine estrogenicity, bone microarchitecture, biomechanical strength, new bone formation (based on bone formation rate and mineral apposition rate), and skeletal expression of osteogenic and resorptive gene markers were studied. OVX resulted in a marked increase in body weight and a decrease in femoral and vertebral trabecular bone volume that were prevented by DGP or E2 treatment. DGP treatment increased bone biomechanical strength and new bone formation rate in ovariectomized mice, comparable with E2 treatment. However, increase in uterine weight and estrogenicity were observed in E2-treated ovariectomized mice, but not in response to DGP treatment. Treatment with DGP increased messenger RNA expression of runt-related transcription factor 2, osterix, and collagen type I, and decreased messenger RNA expression of tartrate-resistant acid phosphatase and the osteoprotegerin-to-receptor activator of nuclear factor-κB ligand ratio in the femur of ovariectomized mice. Overall findings suggest that DGP treatment can effectively prevent OVX-induced increase in bone loss and decrease in bone strength possibly by increasing osteoblastic activities and by decreasing osteoclastic activities.