Vertebral Bone Strength Research Articles

Flaxseed Does Not Enhance the Estrogenic Effect of Low-Dose Estrogen Therapy on Markers of Uterine Health in Ovariectomized Rats

Flaxseed (FS) is an oilseed rich in phytoestrogens and n-3 polyunsaturated fatty acids, compounds that may attenuate bone loss during aging. We previously demonstrated using the ovariectomized (OVX) rat model of postmenopausal osteoporosis that 10% dietary FS combined with low-dose estrogen therapy (LD) preserves vertebral bone mass and strength more so than either treatment alone. However, it was prudent to also consider the effect of this intervention on uterine tissue as LD, and possibly FS, may have estrogenic, and thus negative, effects on uterine tissue. The present study investigated if FS enhances the estrogenic effect of LD on markers of uterine health in OVX rats. Three-month-old rats were randomized to groups: (1) SHAM, (2) OVX, (3) OVX+FS, (4) OVX+LD, or (5) OVX+FS+LD. Ground FS was added to the AIN-93M diet (100 g/kg of diet), and LD was delivered by subcutaneous implant (0.42 μg of 17β-estradiol/kg of body weight/day) to mimic LD in postmenopausal women. After 12 weeks, histological analyses of uterine tissue demonstrated flattened or cuboidal luminal epithelia organized in a single layer in the OVX group, while FS, LD, and FS+LD induced a single layer of elongated luminal epithelia, columnar in shape. The SHAM group had the greatest epithelial mass. Cell proliferation was similar among all OVX groups. Therefore FS and FS+LD similarly induce estrogen-like effects on the morphology of luminal epithelia that are weaker than in the SHAM group without inducing cell proliferation in OVX rats. Thus, FS does not enhance the estrogenic effect of LD on markers of uterine health in OVX rats.

Spinal fractures in recreational bobsledders: an unexpected mechanism of injury

Study design: Retrospective case series and literature review.Objective: To report and discuss spinal fractures occurring in recreational bobsledders.Summary of background data: Spinal fractures have been commonly described following traumatic injury during a number of recreational sports. Reports have focused on younger patients and typically involved high-impact sports or significant injuries. With an aging population and a wider array of recreational sports, spinal injuries may be seen after seemingly benign activities and without a high-impact injury.Methods: A retrospective review of two patients and review of the literature was performed.Results: Two patients with spinal fractures after recreational bobsledding were identified. Both patients, aged 57 and 54 years, noticed a simultaneous onset of severe back pain during a routine turn on a bobsled track. Neither was involved in a high-impact injury during the event. Both patients were treated conservatively with resolution of symptoms. An analysis of the bobsled track revealed that potential forces imparted to the rider may be greater than the yield strength of vertebral bone.Conclusions: Older athletes may be at greater risk for spinal fracture associated with routine recreational activities. Bobsledding imparts large amounts of force during routine events and may result in spinal trauma. Older patients, notably those with osteoporosis or metabolic bone disease, should be educated about the risks associated with seemingly benign recreational sports.

Chlorthalidone improves vertebral bone quality in genetic hypercalciuric stone-forming rats

We have bred a strain of rats to maximize urine (u) calcium (Ca) excretion and model hypercalciuric nephrolithiasis. These genetic hypercalciuric stone-forming (GHS) rats excrete more uCa than control Sprague-Dawley rats, uniformly form kidney stones, and similar to patients, demonstrate lower bone mineral density. Clinically, thiazide diuretics reduce uCa and prevent stone formation; however, whether they benefit bone is not clear. We used GHS rats to test the hypothesis that the thiazide diuretic chlorthalidone (CTD) would have a favorable effect on bone density and quality. Twenty GHS rats received a fixed amount of a 1.2% Ca diet, and half also were fed CTD (4 to 5 mg/kg/d). Rats fed CTD had a marked reduction in uCa. The axial and appendicular skeletons were studied. An increase in trabecular mineralization was observed with CTD compared with controls. CTD also improved the architecture of trabecular bone. Using micro-computed tomography (µCT), trabecular bone volume (BV/TV), trabecular thickness, and trabecular number were increased with CTD. A significant increase in trabecular thickness with CTD was confirmed by static histomorphometry. CTD also improved the connectivity of trabecular bone. Significant improvements in vertebral strength and stiffness were measured by vertebral compression. Conversely, a slight loss of bending strength was detected in the femoral diaphysis with CTD. Thus results obtained in hypercalciuric rats suggest that CTD can favorably influence vertebral fracture risk. CTD did not alter formation parameters, suggesting that the improved vertebral bone strength was due to decreased bone resorption and retention of bone structure.

Calcitropic Hormones and IGF-I Are Influenced by Dietary Protein

Elderly men and women with protein deficiencies have low levels of circulating IGF-I, and it is likely this contributes to reduced bone formation and increased bone resorption. We hypothesized that calcitropic hormones are involved in this effect and are affected by dietary protein. We therefore investigated the influence of a low-protein diet on the PTH-1,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] axis and IGF-I in rats, using pamidronate to block resorption that normally contributes to mineral homeostasis. We fed 6-month-old Sprague Dawley female rats isocaloric diets containing 2.5% or 15% casein for 2 wk. Pamidronate was then administered sc (0.6 mg/kg/) for 5 d. Blood samples were collected at different time points. Serum 1,25(OH)₂D₃, IGF-I, PTH, calcium, and phosphorus were determined in all rats; vertebral bone strength and histomorphometric analysis were performed in rats subject to the longest low-protein diets. We found 2 wk of low protein increased PTH levels, decreased 1,25(OH)₂D₃, calcium, and IGF-I, suggesting that increased PTH compensates for low-protein-induced decreases in 1,25(OH)₂D₃. Pamidronate augmented the increased PTH after 8 wk of low protein and prevented the 1,25(OH)₂D₃ decrease. IGF-I remained low. Protein malnutrition induced decreases in relative bone volume and trabecular thickness, which was prevented by pamidronate. Maximal load was reduced by protein restriction, but rescued by pamidronate. In summary, the low protein diet resulted in hyperparathyroidism, a reduction in circulating levels of IGF-I, and reduced 1,25(OH)₂D₃ despite hyperparathyroidism. Blocking resorption resulted in further increases in PTH and improved microarchitecture and biomechanical properties, irrespective of vitamin D status or protein intake.

Eldecalcitol (ED-71)

ED-71 is a new vitamin D receptor ligand, bearing a hydroxypropoxy substituent at the 2β-position of 1α, 25 (OH) (2)D(3). In ovariectomized rats, ED-71 increased vertebral bone mass and bone strength by inhibiting bone resorption and maintaining bone formation. In randomized, placebo-controlled, double-blinded clinical trial for osteoporotic subjects, ED-71 increased lumber vertebral and hip bone mineral density independently vitamin D status. Furthermore, ED-71 may have a better osteoprotective effect than alfacalcidol and suggest that ED-71 may serve as a new generation of active vitamin D with anti-fracture efficacy in osteiporotic subjects.

Genetic analysis of vertebral trabecular bone density and cross-sectional area in older men

We investigated 383 bone candidate genes for associations between single nucleotide polymorphisms and vertebral trabecular volumetric bone mineral density (vBMD) and cross-sectional area (CSA) in 2,018 Caucasian men aged ≥ 65 years. SNPs in TGFBR3, SOST, KL, CALCR, LEP, CSF1R, PTN, GNRH2, FGFR2, and MEPE were associated with vBMD and SNPs in CYP11B1, DVL2, DLX5, WNT4, and PAX7 were associated with CSA in independent study samples (p < 0.005). Vertebral bone mineral density and cross-sectional area are important determinants of vertebral bone strength. Little is known about the specific genetic variants that influence these phenotypes in humans. We investigated the potential genetic variants associated with vertebral trabecular volumetric BMD and CSA measured by quantitative computed tomography. We initially tested for association between these phenotypes and 4608 tagging and potentially functional single nucleotide polymorphisms (SNPs) in 383 candidate genes in 862 community-dwelling Caucasian men aged ≥ 65 years in the Osteoporotic Fractures in Men Study. SNP associations were then validated by genotyping an additional 1,156 randomly sampled men from the same cohort. We identified 11 SNPs in 10 genes (TGFBR3, SOST, KL, CALCR, LEP, CSF1R, PTN, GNRH2, FGFR2, and MEPE) that were consistently associated with trabecular vBMD and five SNPs in five genes (CYP11B1, DVL2, DLX5, WNT4, and PAX7) that were consistently associated with CSA in both samples (p < 0.005). None of the SNPs associated with trabecular vBMD were associated with CSA. Our findings raise the possibility that at least some of the loci for vertebral trabecular BMD and bone size may be distinct.

Changes in the contents of enzymatic immature, mature, and non-enzymatic senescent cross-links of collagen after once-weekly treatment with human parathyroid hormone (1–34) for 18 months contribute to improvement of bone strength in ovariectomized monkeys

Improvements in total content of enzymatic cross-linking, the ratio of hydroxylysine-derived enzymatic cross-links, and non-enzymatic advanced glycation end product cross-link formation from once-weekly administration of hPTH(1-34) for 18months in OVX cynomolgus monkeys contributed to the improvement of bone strength. Parathyroid hormone (PTH) is used for the treatment of osteoporosis. To elucidate the contribution of material properties to bone strength after once-weekly treatment with hPTH(1-34) in an ovariectomized (OVX) primate model, the content of collagen and enzymatic immature, mature, and non-enzymatic cross-links, collagen maturity, trabecular architecture, and mineralization in vertebrae were simultaneously estimated. Adult female cynomolgus monkeys were divided into four groups (n = 18-20 each) as follows: SHAM group, OVX group, and OVX monkeys given once-weekly subcutaneous injections of hPTH(1-34) either at 1.2 or 6.0μg/kg (low- or high-PTH groups) for 18months. The content of collagen, enzymatic and non-enzymatic cross-linking pentosidine, collagen maturity, trabecular architecture, mineralization, and cancellous bone strength of vertebrae were analyzed. Low-PTH and high-hPTH treatments increased the content of enzymatic immature and mature cross-links, bone volume (BV/TV), and trabecular thickness, and decreased pentosidine, compared with the OVX group. Stepwise logistic regression analysis revealed that BV/TV, the content of total enzymatic cross-links, and calcium content independently affected ultimate load (model R (2) = 0.748, p < 0.001) and breaking energy (model R (2) = 0.702, p < 0.001). BV/TV was the most powerful and enzymatic cross-link content was the second powerful determinant of both ultimate load and breaking energy. The most powerful determinant of stiffness was the enzymatic cross-link content (model R (2) = 0.270, p < 0.001). Once-weekly preventive administration of hPTH(1-34) increased the total contents of immature and mature enzymatic cross-links, which contributed significantly to vertebral cancellous bone strength.

Effects of preexisting microdamage, collagen cross‐links, degree of mineralization, age, and architecture on compressive mechanical properties of elderly human vertebral trabecular bone

Previous studies have shown that the mechanical properties of trabecular bone are determined by bone volume fraction (BV/TV) and microarchitecture. The purpose of this study was to explore other possible determinants of the mechanical properties of vertebral trabecular bone, namely collagen cross-link content, microdamage, and mineralization. Trabecular bone cores were collected from human L2 vertebrae (n = 49) from recently deceased donors 54-95 years of age (21 men and 27 women). Two trabecular cores were obtained from each vertebra, one for preexisting microdamage and mineralization measurements, and one for BV/TV and quasi-static compression tests. Collagen cross-link content (PYD, DPD, and PEN) was measured on surrounding trabecular bone. Advancing age was associated with impaired mechanical properties, and with increased microdamage, even after adjustment by BV/TV. BV/TV was the strongest determinant of elastic modulus and ultimate strength (r² = 0.44 and 0.55, respectively). Microdamage, mineralization parameters, and collagen cross-link content were not associated with mechanical properties. These data indicate that the compressive strength of human vertebral trabecular bone is primarily determined by the amount of trabecular bone, and notably unaffected by normal variation in other factors, such as cross-link profile, microdamage and mineralization.

A bisphosphonate that does not affect osteoclasts prevents osteoblast and osteocyte apoptosis and the loss of bone strength induced by glucocorticoids in mice

Although a major effect of bisphosphonates on bone is inhibition of resorption resulting from their ability to interfere with osteoclast function, these agents also prevent osteoblast and osteocyte apoptosis in vitro and in vivo. However, the contribution of the latter property to the overall beneficial effects of the drugs on bone remains unknown. We compared herein the action on glucocorticoid-induced bone disease of the classical bisphosphonate alendronate with that of IG9402, a bisphosphonate analog that preserves osteoblast and osteocyte viability but does not induce osteoclast apoptosis in vitro. The bisphosphonates were injected daily (2.3 μmol/kg) to 5-month-old Swiss Webster mice (6-11 per group), starting 3 days before implantation of pellets releasing the glucocorticoid prednisolone (2.1 mg/kg/day). IG9402 did not affect levels of circulating C-telopeptide or osteocalcin, markers of resorption and formation, respectively, nor did it decrease mRNA levels of osteocalcin or collagen 1a1 in bone. On the other hand, alendronate decreased all these parameters. Moreover, IG9402 did not reduce cancellous mineralizing surface, mineral apposition rate, or bone formation rate, whereas alendronate induced a decrease in each of these bone formation measures. These findings demonstrate that, in contrast to alendronate, IG9402 does not inhibit bone turnover. Both alendronate and IG9402, on the other hand, activated survival kinase signaling in vivo, as evidenced by induction of ERK phosphorylation in bone. Furthermore, both bisphosphonates prevented the increase in osteoblast and osteocyte apoptosis as well as the decrease in vertebral bone mass and strength induced by glucocorticoids. We conclude that a bisphosphonate that does not affect osteoclasts prevents osteoblast and osteocyte apoptosis and the loss of bone strength induced by glucocorticoids in mice.

Captopril improves osteopenia in ovariectomized rats and promotes bone formation in osteoblasts

The present study was designed to investigate the effects of captopril, an angiotensin-converting enzyme inhibitor (ACEI), on bone loss in aged ovariectomized (OVX) rats and its impact on the differentiation of cultured primary osteoblasts. Ten-month-old female Sprague-Dawley rats were used for the study. After 2 months post ovariectomy (OVX), the rats were treated with captopril (1 or 5 mg/kg/day, respectively) for another 2 months. At endpoint, trabecular bone of the fourth lumbar vertebrae (L4) was undecalcified and examined by bone histomorphometry; the fifth lumbar vertebrae (L5) were examined by compression test. Primary osteoblasts were isolated from the calvaria of newborn rats and treated with different concentrations of captopril in a different durations. The content of secreted alkaline phosphatase (ALP) and mRNA expression of collagen I in osteoblasts were determined to demonstrate osteoblast bone formation. In aged rats with estrogen deficiency-induced osteopenia, captopril increased the trabecular area (%BV/TV) of L4 up to 33% and improved biomechanical properties by increasing L5 break stress and elastic modulus when compared to those in the OVX group (P < 0.01). Captopril showed dose-dependent effects on promoting the secretion of ALP and increased mRNA expression of collagen I in the cultured rat osteoblasts. In summary, captopril, one of the most widely used ACEIs, has the potential effects of improving lumbar vertebral bone strength in aged OVX rats and promoting osteoblast bone formation in vitro.

Management of Osteoporotic Fractures of the Thoracolumbar Spine

Approximately 2 million people sustain an osteoporotic fracture in the United States each year; 25% of those are vertebral compression fractures. Most fractures can be treated nonoperatively, using a combination of bracing, physical therapy, and pain medications. Surgical treatment may be considered for patients with severe pain or who have failed nonoperative options. Surgical treatment options include vertebroplasty and kyphoplasty, which involve the injection of bone cement (polymethylmethacrylate) to augment vertebral bone strength; kyphoplasty adds the inflation of a balloon tamp to help reduce the fracture and create a space for the cement. The risk of cement extravasation is relatively high, especially during vertebroplasty; however, the incidence of symptomatic leaks is relatively low. Overall, both procedures offer low complication rates, excellent pain relief, and improved function after vertebral compression fractures.

RANKL inhibition as a targeted approach in the management of osteoporosis

Cortical and trabecular bone undergo a continuous and balanced remodeling process, consisting of an osteoclast-mediated boneresorption phase and an osteoblast-mediated bone-formation phase. An imbalance in this process, which favours bone resorption, results in bone loss and in damage to the skeletal microarchitecture, as seen in clinical conditions such as osteoporosis, rheumatoid arthritis and bone metastases. Currently, treatments are available for preventing or reversing excessive bone resorption through osteoclast inhibition. Among anti-resorptive treatments, nitrogen-containing bisphosphonates bind to hydroxyapatite with high affinity, are internalized by osteoclasts during the resorptionphase and inhibit osteoclast function, suppressing the mevalonate pathway. A more targeted anti-resorptive approach might be achieved through inhibition of RANK ligand (RANKL), which is one of the primary mediators of osteoclast activity, essential for osteoclast differentiation, function and survival. RANKL exerts direct catabolic effects on cortical and trabecular bone, leading to decreases in bone volume, mineral density and strength. Understanding the role of RANKL in the pathogenesis of bone disease has led to investigation of RANKL inhibition in conditions characterized by excessive bone resorption. In many preclinical models of postmenopausal osteoporosis, RANKL inhibition has prevented bone loss and microarchitecture damage, and has been associated with increased vertebral and femoral bone strength. A variety of innovative therapeutic approaches targeting RANKL inhibition are currently under investigation in humans. In randomized, controlled clinical trials, 6monthly subcutaneous administration of an experimental, fully human, monoclonal antibody against RANKL to womenwith osteopenia or postmenopausal osteoporosis significantly increased bone mineral density (BMD) at all skeletal sites (including the lumbar spine, femoral neck and distal radius) and decreased markers of bone turnover in a rapid, pronounced and sustained manner. Moreover, in two clinical studies, this therapeutic approach produced significantly greater increases in BMD than alendronate at all measured skeletal sites after 12 months of treatment. RANKL inhibition with this monoclonal antibody has recently been demonstrated to significantly reduce the risk of vertebral, non-vertebral and hip fractures inwomen with postmenopausal osteoporosis after 3 years of treatment. The frequency and pattern of reported adverse events have been similar to placebo or bisphosphonate treatment, suggesting a good tolerability profile. These data suggest that RANKL inhibition offers an additional and innovative therapeutic approach for the treatment of postmenopausal osteoporosis and, on the basis of comparative BMD results, may provide an incremental clinical benefit compared with currently available antiresorptive treatments.

One Year of Transgenic Overexpression of Osteoprotegerin in Rats Suppressed Bone Resorption and Increased Vertebral Bone Volume, Density, and Strength

RANKL is an essential mediator of bone resorption, and its activity is inhibited by osteoprotegerin (OPG). Transgenic (Tg) rats were engineered to continuously overexpress OPG to study the effects of continuous long-term RANKL inhibition on bone volume, density, and strength. Lumbar vertebrae, femurs, and blood were obtained from 1-yr-old female OPG-Tg rats (n = 32) and from age-matched wildtype (WT) controls (n = 23). OPG-Tg rats had significantly greater serum OPG (up to 260-fold) and significantly lower serum TRACP5b and osteocalcin compared with WT controls. Vertebral histomorphometry showed significant reductions in osteoclasts and bone turnover parameters in OPG-Tg rats versus WT controls, and these reductions were associated with significantly greater peak load in vertebrae tested through compression. No apparent differences in bone material properties were observed in OPG-Tg rat vertebrae, based on their unchanged intrinsic strength parameters and their normal linear relationship between vertebral bone mass and strength. Femurs from OPG-Tg rats were of normal length but showed mild osteopetrotic changes, including reduced periosteal perimeter (-6%) and an associated reduction in bending strength. Serum OPG levels in WT rats showed no correlations with any measured parameter of bone turnover, mass, or strength, whereas the supraphysiological serum OPG levels in OPG-Tg rats correlated negatively with bone turnover parameters and positively with vertebral bone mass and strength parameters. In summary, low bone turnover after 1 yr of OPG overexpression in rats was associated with increased vertebral bone mass and proportional increases in bone strength, with no evidence for deleterious effects on vertebral material properties.

Trabecular Microarchitecture of Hominoid Thoracic Vertebrae

Spontaneous vertebral fractures are a common occurrence in modern humans, yet these fractures are not documented in other hominoids. Differences in vertebral bone strength between humans and apes associated with trabecular bone microarchitecture may contribute to differences in fracture incidence. We used microcomputed tomography to examine trabecular bone microarchitecture in the T8 vertebra of extant young adult hominoids. Scaled volumes of interest from the anterior vertebral body were analyzed at a resolution of 46 microm, and bone volume fraction, trabecular thickness, trabecular number, trabecular separation, structure model index, and degree of anisotropy were compared among species. As body mass increased, so did trabecular thickness, but bone volume fraction, structure model index, and degree of anisotropy were independent of body mass. Bone volume fraction was not significantly different between the species. Degree of anisotropy was not significantly different among the species, suggesting similarity of loading patterns in the T8 vertebra due to similar anatomical and postural relationships within each species' spine. Degree of anisotropy was negatively correlated with bone volume fraction (r(2) = 0.85, P < 0.05) in humans, whereas the apes demonstrated no such relationship. This suggested that less dense human trabecular bone was more preferentially aligned to habitual loading. Furthermore, we theorize that trabeculae in ape thoracic vertebrae would not be expected to become preferentially aligned if bone volume fraction was decreased. The differing relationship between bone volume fraction and degree of anisotropy in humans and apes may cause less dense human bone to be more fragile than less dense ape bone.

Biomechanical allometry in hominoid thoracic vertebrae

Considerable differences in spinal morphology have been noted between humans and other hominoids. Although comparative analyses of the external morphology of vertebrae have been performed, much less is known regarding variations in internal morphology (density) and biomechanical performance among humans and closely related non-human primates. In the current study we utilize density calibrated computed tomography images of thoracic vertebral bodies from hominoids ( n = 8–15 per species, human specimens 20–40 years of age) to obtain estimates of vertebral bone strength in axial compression and anteroposterior bending and to determine how estimates of strength scale with animal body mass. Our biomechanical analysis suggests that the strength of thoracic vertebral bodies is related to body mass (M) through power law relationships (y ∝ M b) in which the exponent b is 0.89 (reduced major axis) for prediction of axial compressive strength and is equal to 1.89 (reduced major axis) for prediction of bending strength. No differences in the relationship between body mass and strength were observed among hominoids. However, thoracic vertebrae from humans were found to be disproportionately larger in terms of vertebral length (distance between cranial and caudal endplates) and overall vertebral body volume (p < 0.05). Additionally, vertebral bodies from humans were significantly less dense than in other hominoids (p < 0.05). We suggest that reduced density in human vertebral bodies is a result of a systemic increase in porosity of cancellous bone in humans, while increased vertebral body volume and length are a result of functional adaptation during growth resulting in a vertebral bone structure that is just as strong, relative to body mass, as in other hominoids.

Age-related differences in thoracic and lumbar vertebral bone density and strength assessed using QCT-based finite element analysis

Age-related differences in thoracic and lumbar vertebral bone density and strength assessed using QCT-based finite element analysis

Effects of low-magnitude, high-frequency mechanical stimulation in the rat osteopenia model

SummaryIn this study, short-term, whole-body vertical vibration at 90 Hz improved trabecular bone quality. There was an improvement of bone quality and density in both osteoporotic and control rats. This treatment may therefore be an attractive option for the treatment of osteoporosis.IntroductionAside from pharmacological treatment options, physical exercise is known to augment bone mass. In this study, the effects of whole-body vertical vibration (WBVV) on bone quality and density were evaluated using an osteoporotic rat model.MethodsSixty female Sprague Dawley rats were ovariectomized (C) or sham (SHAM) operated at the age of 3 months. After 3 months, both groups were divided into two subgroups that received either WBVV at 90 Hz for 35 days or no treatment. After sacrificing the rats, we evaluated vertebral bone strength, histomorphometric parameters, and bone mineral density (BMD).ResultsTreatment with WBVV resulted in improved biomechanical properties. The yield load after WBVV was significantly enhanced. According to yield load and Young’s modulus, the treated OVX rats reached the level of the untreated SHAM animals. In all measured histomorphometric parameters, WBVV significantly improved bone density. Treatment with WBVV demonstrated greater effects on the trabecular bone compared to the cortical bone. The ash-BMD index showed significant differences between treated and untreated rats.ConclusionUsing WBVV as a non-pharmacological supportive treatment option for osteoporosis demonstrated an enhancement of bone strength and bone mass. This procedure may be an attractive option for the treatment of osteoporosis.

High resolution computed tomography of the vertebrae yields accurate information on trabecular distances if processed by 3D fuzzy segmentation approaches

Introduction The structure of trabecular bone represents an aspect of bone properties that affects vertebral bone strength independently of bone mineral density [M. Kleerekoper, A. Villanueva, J. Stanciu, D. Rao, and A. Parfitt. The role of three-dimensional trabecular microstructure in the pathogenesis of vertebral compression fractures. Calcif. Tissue Int., 37:594–597, Dec 1985; E. Seeman and P. Delmas. Bone quality—the material and structural basis of bone strength and fragility. N. Engl. J. Med., 354:2250–2261, May 2006.]. Using the mathematical concept of fuzzy distance transformation (FDT), we evaluated the accuracy of measurements of trabecular distance (Tb.Di f ) which can be determined for vertebrae in vivo using high resolution computed tomography (HRCT). Methods In a first step extrema voxels with a very high likelihood of representing bone or marrow are identified. A probability level of being a bone voxel is assigned to all other voxel. This probability is based on the FDT of the voxel's gray-level, preprint submitted to Elsevier June 10, 2008; revised July 15, 2008 i.e. the shortest gray-value weighted distance to the marrow background. Next, the resulting bone structure is skeletonized. The space between the ridges of the skeleton is filled with the largest possible spheres. The average over the radii of the spheres defines Tb.Di f , a measure of trabecular distance. 14 whole vertebrae embedded in polymethyl methylacrylate were scanned by HRCT (voxel size 156 × 156 × 400 μm 3) inside an anthropomorphic abdomen phantom. Scans obtained on Scanco Xtreme CT (XCT, voxel size 82 3 μm 3) without the phantom were used as reference. Results Tb.Di f calculated on XCT data were almost identical to trabecular distance values (1/Tb.N⁎) determined with the manufacturer's standard software ( r 2 = 0.98). Tb.Di f values obtained with HRCT correlated strongly with Tb.Di f values obtained by XCT ( r 2 = 0.89). Over the range from 400 to 1400 μm trabecular distance could be estimated with a residual error of 78 μm. Conclusions The FDT based variable Tb.Di f provides 3D estimates of trabecular distances with residual errors of less than 100 μm using a HRCT protocol which also can be employed in vivo for assessing vertebral microarchitecture.

Influence of Early and Late Zoledronic Acid Administration on Vertebral Structure and Strength in Ovariectomized Rats

An annual infusion of zoledronic acid (ZOL) reduces fracture risk in osteoporotic patients. Previously, we showed that a single ZOL injection inhibited changes in bone microstructure and strength in rat tibiae after ovariectomy. Here, we determined the effects of a single ZOL injection as preventive and restorative treatment on the bone microstructure and strength in lumbar and caudal vertebrae of ovariectomized (OVX) rats. Twenty-nine female 35-week-old Wistar rats were divided into four groups: SHAM-OVX (n = 9), OVX (n = 5), OVX and early ZOL (n = 8), and OVX and late ZOL (n = 7). ZOL was given once (20 microg/kg body weight s.c.) at OVX in the early ZOL group and 8 weeks later in the late ZOL group; rats were killed 16 weeks after OVX. Trabecular and cortical bone microarchitecture were measured in lumbar (L3) and caudal (Cd6) vertebrae using micro-computed tomography, and compressive mechanical properties were determined in L3 vertebrae. Compared to SHAM-OVX, OVX rats had significantly lower BV/TV; SMI, Tb.N, Tb.Sp, and Conn.D tended to be deteriorated in lumbar vertebrae, while both ZOL groups did not differ from the SHAM-OVX group. Both ZOL groups had significantly higher BV/TV than OVX; the early ZOL group also had significantly lower SMI and higher Tb.Th. OVX tended to decrease mechanical properties, while early and late ZOL treatment inhibited OVX-induced degeneration. Neither OVX nor ZOL induced changes in the trabecular microarchitecture of caudal vertebrae. In summary, in adult rats a single ZOL injection inhibited OVX-induced changes in lumbar vertebral bone microarchitecture and strength.

Ubiquitin Ligase Smurf1 Mediates Tumor Necrosis Factor-induced Systemic Bone Loss by Promoting Proteasomal Degradation of Bone Morphogenetic Signaling Proteins

Chronic inflammatory disorders, such as rheumatoid arthritis, are often accompanied by systemic bone loss, which is thought to occur through inflammatory cytokine-mediated stimulation of osteoclast resorption and inhibition of osteoblast function. However, the mechanisms involved in osteoblast inhibition remain poorly understood. Here we test the hypothesis that increased Smad ubiquitin regulatory factor 1 (Smurf1)-mediated degradation of the bone morphogenetic protein pathway signaling proteins mediates reduced bone formation in inflammatory disorders. Osteoblasts derived from bone marrow or long bone samples of adult tumor necrosis factor (TNF) transgenic (TNF-Tg) mice were used in this study. TNF decreased the steady-state levels of Smad1 and Runx2 protein similarly to those in long bones of TNF-Tg mice. In the presence of the proteasome inhibitor MG132, TNF increased accumulation of ubiquitinated Smad1 protein. TNF administration over calvarial bones caused decreases in Smad1 and Runx2 protein levels and mRNA expression of osteoblast marker genes in wild-type, but not in Smurf1(-/-) mice. Vertebral bone volume and strength of TNF-Tg/Smurf1(-/-) mice were examined by a combination of micro-CT, bone histomorphometry, and biomechanical testing and compared with those from TNF-Tg littermates. TNF-Tg mice had significantly decreased bone volume and biomechanical properties, which were partially rescued in TNF-Tg/Smurf1(-/-) mice. We conclude that in chronic inflammatory disorders where TNF is increased, TNF induces the expression of ubiquitin ligase Smurf1 and promotes ubiquitination and proteasomal degradation of Smad1 and Runx2, leading to systemic bone loss. Inhibition of ubiquitin-mediated Smad1 and Runx2 degradation in osteoblasts could help to treat inflammation-induced osteoporosis.