Pre-treatment bone turnover does not influence the level of the response to alendronate in postmenopausal osteoporosis at the bone tissue level

PURPOSE

The main effect of anti-resorptive agents such as bisphosphonates is a reduction of bone resorption, with a consequent marked decrease of bone turnover. This post-hoc analysis investigated the changes of histomorphometric parameters of bone turnover after alendronate (ALN), according to the baseline turnover.

METHODS

Ninety postmenopausal women underwent a transiliac bone biopsy before and after 6 (n = 44) or 12 (n = 46) months of treatment with ALN (70 mg/week). The dynamic parameters reflecting the bone formation and bone turnover were mineralizing surface (MS/BS; %), bone formation rate (BFR/BS; μm3/μm2/d), and activation frequency (Ac.f; /yr). Biochemical markers sPINP and the sCTX were assessed before treatment and after 3, 6, and 12 months. Subjects were divided into quartiles based on the baseline values of BFR/BS.

RESULTS

At baseline, MS/BS and Ac.f were significantly different (p < 0.0001) among the BFR quartiles. sCTX and sP1NP were not significantly different among quartiles. After ALN treatment, MS/BS was not significantly different among quartiles but Ac.f remained significantly lower in the first quartile compared to the third and fourth ones (p < 0.03). The absolute value of the difference between pre- and post-treatment significantly correlated with the baseline BFR/BS but when expressed in percent of the baseline value, the magnitude of the diminutions of MS/BS, Ac.f, sCTX, and sP1NP was similar in the four baseline BFR quartiles.

CONCLUSION

The percentage response to ALN appeared independent of the baseline level of bone turnover. After treatment, the bone turnover tended to be similar in all BFR quartiles. This analysis investigated the influence of baseline turnover measured by bone histomorphometry on the effect of alendronate. When expressed in percent of pre-treatment values, the decreases of histomorphometric parameters and biochemical markers of bone turnover were independent of the baseline turnover.

The relationship between bone strain index, bone mass, microarchitecture and mechanical behavior in human vertebrae: an ex vivo study

The aim of this study was to determine whether the Bone Strain Index (BSI), a recent DXA-based bone index, is related to bone mechanical behavior, microarchitecture and finally, to determine whether BSI improves the prediction of bone strength and the predictive role of BMD in clinical practice.

PURPOSE

Bone Strain Index (BSI) is a new DXA-based bone index that represents the finite element analysis of the bone deformation under load. The current study aimed to assess whether the BSI is associated with 3D microarchitecture and the mechanical behavior of human lumbar vertebrae.

METHODS

Lumbar vertebrae (L3) were harvested fresh from 31 human donors. The anteroposterior BMC (g) and aBMD (g/cm2) of the vertebral body were measured using DXA, and then the BSI was automatically derived. The trabecular bone volume (Tb.BV/TV), trabecular thickness (Tb.Th), degree of anisotropy (DA), and structure model index (SMI) were measured using µCT with a 35-µm isotropic voxel size. Quasi-static uniaxial compressive testing was performed on L3 vertebral bodies under displacement control to assess failure load and stiffness.

RESULTS

The BSI was significantly correlated with failure load and stiffness (r = -0.60 and -0.59; p < 0.0001), aBMD and BMC (r = -0.93 and -0.86; p < 0.0001); Tb.BV/TV and SMI (r = -0.58 and 0.51; p = 0.001 and 0.004 respectively). After adjustment for aBMD, the association between BSI and stiffness, BSI and SMI remained significant (r = -0.51; p = 0.004 and r = -0.39; p = 0.03 respectively, partial correlations) and the relation between BSI and failure load was close to significance (r = -0.35; p = 0.06).

CONCLUSION

The BSI was significantly correlated with the microarchitecture and mechanical behavior of L3 vertebrae, and these associations remained statistically significant regardless of aBMD.

Is Penguin Circovirus Circulating Only in the Antarctic Circle? Lack of Viral Detection in Namibia

The known host range of circoviruses is continuously expanding because of more intensive diagnostic activities and advanced sequencing tools. Recently, a new circovirus (penguin circovirus (PenCV)) was identified in the guano and cloacal samples collected from Adélie penguins (Pygoscelis adeliae) and chinstrap penguins (Pygoscelis antarcticus) in Antarctica. Although the virus was detected in several asymptomatic subjects, a potential association with feather disease was speculated. To investigate the occurrence and implications of PenCV in other penguin species located outside of Antarctica, a broad survey was undertaken in African penguins (Spheniscus demersus) on two islands off the southern Namibian coast. For this purpose, specific molecular biology assays were developed and validated. None of the 151 blood samples tested positive for PenCV. Several reasons could explain the lack of PenCV positive samples. African penguins and Pygoscelis species are separated by approximately 6000 km, so there is almost no opportunity for transmission. Similarly, host susceptibility to PenCV might be penguin genus-specific. Overall, the present study found no evidence of PenCV in African penguin colonies in Namibia. Further dedicated studies are required to assess the relevance of PenCV among different penguin species.

Murine models of posterolateral spinal fusion: A systematic review

BACKGROUND

Rodent models are commonly used experimentally to assess treatment effectiveness in spinal fusion. Certain factors are associated with better fusion rates. The objectives of the present study were to report the protocols most frequently used, to evaluate factors known to positively influence fusion rate, and to identify new factors.

METHOD

A systematic literature search of PubMed and Web of Science found 139 experimental studies of posterolateral lumbar spinal fusion in rodent models. Data for level and location of fusion, animal strain, sex, weight and age, graft, decortication, fusion assessment and fusion and mortality rates were collected and analyzed.

RESULTS

The standard murine model for spinal fusion was male Sprague Dawley rats of 295g weight and 13 weeks' age, using decortication, with L4-L5 as fusion level. The last two criteria were associated with significantly better fusion rates. On manual palpation, the overall mean fusion rate in rats was 58% and the autograft mean fusion rate was 61%. Most studies evaluated fusion as a binary on manual palpation, and only a few used CT and histology. Average mortality was 3.03% in rats and 1.56% in mice.

CONCLUSIONS

These results suggest using a rat model, younger than 10 weeks and weighing more than 300 grams on the day of surgery, to optimize fusion rates, with decortication before grafting and fusing the L4-L5 level.

Alendronate prolongs the reversal-resorption phase in human cortical bone remodeling

Despite their ability to reduce fracture-risk and increase Bone Mineral Density (BMD) in osteoporotic women, bisphosphonates are reported to reduce formation of new bone. Reduced bone formation has been suggested to lead to accumulation of microfractures and contribute to rare side effects in cortical bone such as atypical femur fractures. However, most studies are limited to trabecular bone. In this study, the cortical bone remodeling in human iliac bone specimens of 65 non-treated and 24 alendronate-treated osteoporotic women was investigated using a new histomorphometric classification of intracortical pores. The study showed that only 12.4 ± 11% of the cortical pore area reflected quiescent pores/osteons in alendronate-treated patients versus 8.5 ± 5% in placebo, highlighting that new cortical remodeling events remain to be activated. The percent and size of eroded pores (events in resorption-reversal phase) remained unchanged, but their contribution to total pore area was 1.4-fold higher in alendronate versus placebo treated patients (66 ± 22% vs 48 ± 22%, p < 0.001). On the other hand, the mixed eroded-formative pores (events with mixed resorption-reversal-formation phases) was 2-fold lower in alendronate versus placebo treated patients (19 ± 14% vs 39 ± 23% of total pore area, p < 0.001), and formative pores (event in formation phase) was 2.2-fold lower in alendronate versus placebo treated patients (2.1 ± 2.4% vs 4.6 ± 3.6%, p < 0.01), and their contribution to total pore area was 2.4-fold lower (1.3 ± 2.1% vs 3.1 ± 4.4%, p < 0.05). Importantly, these differences between alendronate and placebo treated patients were significant in patients after 3 years of treatment, not after 2 years of treatment. Collectively, the results support that cortical remodeling events activated during alendronate treatment has a prolonged reversal-resorption phase with a delayed transition to formation, becoming increasingly evident after 3-years of treatment. A potential contributor to atypical femur fractures associated with long-term bisphosphonate treatment.

Dual-energy CT hybridation and kernel processing effects on the estimation of bone mineral mass and density: a calcination study on ex vivo human femur

INTRODUCTION

Recent technological advances with dual-energy quantitative computed tomography (DEQCT) allow to combine two images of different level of energy to obtain simulated mono-energetic images at 60 keV (_SIM60KeV-QCT) with improved image contrast in clinical practice. This study includes three topics: (1) compare bone mineral content (BMC), areal and volumetric bone mineral density (aBMD, vBMD) obtained with _SIM60KeV-QCT, single-energy QCT (SEQCT), and dual X-ray absorptiometry (DXA); (2) compare ash density and weight with respective vBMD and BMC assessed on _SIM60KeV-QCT, SEQCT, and DXA; and (3) compare the influence of reconstruction kernels on the accuracy of vBMD and BMC using ash density and ash weight as the reference values.

METHODS

DXA, SEQCT, and DEQCT acquisitions were performed ex vivo on 42 human femurs. Standard kernel (SK) and bone kernel (BK) were applied to each stack of images. Ten diaphyses and 10 femoral necks were cut, scanned, and reconstructed using the techniques described above. Finally, the bone specimens were calcined to obtain the ash weight.

RESULTS

QCT analysis (SEQCT, _SIM60KeV-QCT) underestimated BMC value compared to DXA. For femoral necks, all QCT analyses provided an unbiased estimate of ash weight but underestimated ash density regardless of the kernel used. For femoral diaphysis, SEQCT BK, _SIM60KeV-QCT BK, and SK underestimated ash weight but not ash density.

CONCLUSION

BMC and vBMD quantifications with the _SIM60KeV-QCT gave similar results as the SEQCT. Further studies are needed to optimize the use of _SIM60KeV-QCT in clinical situations. SK should be used given the effect of kernels on QCT assessment.

Bisphosphonates impair the onset of bone formation at remodeling sites

Bisphosphonates are widely used anti-osteoporotic drugs targeting osteoclasts. They strongly inhibit bone resorption, but also strongly reduce bone formation. This reduced formation is commonly ascribed to the mechanism maintaining the resorption/formation balance during remodeling. The present study provides evidence for an additional mechanism where bisphosphonates actually impair the onset of bone formation after resorption. The evidence is based on morphometric parameters recently developed to assess the activities reversing resorption to formation. Herein, we compare these parameters in cancellous bone of alendronate- and placebo-treated postmenopausal osteoporotic patients. Alendronate increases the prevalence of eroded surfaces characterized by reversal cells/osteoprogenitors at low cell density and remote from active bone surfaces. This indicates deficient cell expansion on eroded surfaces - an event that is indispensable to start formation. Furthermore, alendronate decreases the coverage of these eroded surfaces by remodeling compartment canopies, a putative source of reversal cells/osteoprogenitors. Finally, alendronate strongly decreases the activation frequency of bone formation, and decreases more the formative compared to the eroded surfaces. All these parameters correlate with each other. These observations lead to a model where bisphosphonates hamper the osteoprogenitor recruitment required to initiate bone formation. This effect results in a larger eroded surface, thereby explaining the well-known paradox that bisphosphonates strongly inhibit bone resorption without strongly decreasing eroded surfaces. The possible mechanism for hampered osteoprogenitor recruitment is discussed: bisphosphonates may decrease the release of osteogenic factors by the osteoclasts, and/or bisphosphonates released by osteoclasts may act directly on neighboring osteoprogenitor cells as reported in preclinical studies.

DXA body composition corrective factors between Hologic Discovery models to conduct multicenter studies

BACKGROUND

Dual X-ray absorptiometry body composition measurements are widely used for clinical and research settings. It is well known that measurements vary across instruments, needing caution for longitudinal monitoring or multicentric studies. This study was to quantify intra- and inter-center variability of bone mineral content, bone mineral density, fat and lean body composition measurements between Hologic Discovery models in order to calculate the corrective factors to be applied for multicenter research projects.

MATERIALS AND METHODS

A whole body phantom composed of materials representing the thickness and percentage of bone, lean and fat mass in the human physiological range was analyzed ten times in three different centers using dual energy X-ray absorptiometry scanners (Two Hologic Discovery QDR A and one QDR W). In addition, we used a morphometric vertebral phantom to monitor stability and a three steps block phantom to check accuracy.

RESULTS

We found a good long-term stability and accuracy for the three devices. Intra-center coefficients of variation were within the range of the manufacturer acceptable values (bone mineral density: 1.40%, bone mineral content: 1%, area: 1.50%, fat mass: 0.89%, lean mass: 0.76%, total mass: 0.12%). Whereas the inter-center coefficient of variation exceeded 8% (bone mineral density: 8.18%, bone mineral content: 3.03%, area: 8.63%: fat mass: 3,92%, lean mass: 7.89%, total mass: 2.85%).

CONCLUSION

Our study showed that the discrepancies across centers remain a major concern, particularly with regard to body composition results. Our study highlight the need of cross calibration between densitometers and proposes corrective factors evaluated from a whole body phantom to lead multicentric studies adjustment.

Quantitative histomorphometric analysis of halved iliac crest bone biopsies yield comparable ROD diagnosis as full 7.5mm wide samples

BACKGROUND AND OBJECTIVES

Histomorphometric analysis of a transiliac bone biopsy is the gold standard for the diagnosis of renal osteodystrophy (ROD). This procedure is costly, invasive and usually performed with a trephine with an internal diameter of 7.5 mm. Our objective was to evaluate the accuracy of ROD diagnosis on halved histological bone sections to determine if they are comparable to the standard 7.5 mm samples.

DESIGN

We included 68 bone biopsies performed in CKD patients for diagnostic purposes with a 7.5 mm diameter trephine. Quantitative histomorphometric analysis of the whole bone samples was performed including assessment of bone mineralization, turnover and volume. Each histological section (representing the whole 7.5 mm diameter biopsy) was then divided lengthwise in two hemisections (representing the 3.5 mm diameter biopsy). Histomorphometric analysis was repeated this time on the two hemibiopsies for each sample, blinded from initial results. Diagnoses were classified as osteitis fibrosa, adynamic bone disease, mixed uremic bone disease, osteomalacia or other. Correlations between the whole sample and the hemibiopsies for each parameter were studied. Concordance between the various bone parameters and final ROD diagnosis obtained from the whole section versus the two hemi sections was evaluated.

RESULTS

Highly significant correlations were found between parameters measured on the whole section and the corresponding hemisections, with r coefficient of 0.98 for osteoid surface and thickness and bone formation rate, 0.97 for osteoclast surface, and 0.96 for bone volume (p < 0.001). Final diagnosis was in full accordance between the whole biopsy and the two corresponding hemi-biopsies in 91% of cases.

CONCLUSIONS

Accurate diagnosis of ROD type was obtained by evaluation of bone surface areas of 3 mm diameter. These data suggest that small invasive bone biopsies might provide accurate ROD diagnostics while decreasing both invasiveness and cost of the procedure.

Avian Influenza H5N8 Outbreak in African Penguins (Spheniscus demersus), Namibia, 2019

In January 2019, high mortalities were reported among African Penguins (Spheniscus demersus) in a breeding colony on Halifax Island, Namibia, Africa. Analysis of samples by reverse transcription quantitative PCR indicated the presence of highly pathogenic avian influenza (HPAI) subtype H5N8. Sequence analysis of the hemagglutinin and neuraminidase genes confirmed the presence of the virus in the birds and its high similarity to HPAI subtype H5N8 identified in South Africa in 2017. There have been no previous reports of HPAI H5N8 in Namibia.

Bone-Forming and Antiresorptive Effects of Romosozumab in Postmenopausal Women With Osteoporosis: Bone Histomorphometry and Microcomputed Tomography Analysis After 2 and 12 Months of Treatment

Sclerostin, a protein produced by osteocytes, inhibits bone formation. Administration of sclerostin antibody results in increased bone formation in multiple animal models. Romosozumab, a humanized sclerostin antibody, has a dual effect on bone, transiently increasing serum biochemical markers of bone formation and decreasing serum markers of bone resorption, leading to increased BMD and reduction in fracture risk in humans. We aimed to evaluate the effects of romosozumab on bone tissue. In a subset of 107 postmenopausal women with osteoporosis in the multicenter, international, randomized, double-blind, placebo-controlled Fracture Study in Postmenopausal Women with Osteoporosis (FRAME), transiliac bone biopsies were performed either after 2 (n = 34) or 12 (n = 73) months of treatment with 210 mg once monthly of romosozumab or placebo to evaluate histomorphometry and microcomputed tomography-based microarchitectural endpoints. After 2 months, compared with either baseline values assessed after a quadruple fluorochrome labeling or placebo, significant increases (P < 0.05 to P < 0.001) in dynamic parameters of formation (median MS/BS: romosozumab 1.51% and 5.64%; placebo 1.60% and 2.31% at baseline and month 2, respectively) were associated with a significant decrease compared with placebo in parameters of resorption in cancellous (median ES/BS: placebo 3.4%, romosozumab 1.8%; P = 0.022) and endocortical (median ES/BS: placebo 6.3%, romosozumab 1.6%; P = 0.003) bone. At 12 months, cancellous bone formation was significantly lower (P < 0.05 to P < 0.001) in romosozumab versus placebo and the lower values for resorption endpoints seen at month 2 persisted (P < 0.001), signaling a decrease in bone turnover (P = 0.006). No significant change was observed in periosteal and endocortical bone. This resulted in an increase in bone mass and trabecular thickness with improved trabecular connectivity, without significant modification of cortical porosity at month 12. In conclusion, romosozumab produced an early and transient increase in bone formation, but a persistent decrease in bone resorption. Antiresorptive action eventually resulted in decreased bone turnover. This effect resulted in significant increases in bone mass and improved microarchitecture. © 2019 American Society for Bone and Mineral Research.

Spatial Distribution of Microcracks in Osteoarthritic Femoral Neck: Influence of Osteophytes on Microcrack Formation

Osteophytes have been suggested to influence the bone mechanical properties. The aim of this study was to compare the microcrack density in osteophytes with that in the other parts of the osteoarthritic femoral neck (FN). The presence of microcracks was investigated in the ultra-distal FN and in the osteophytes in samples obtained during hip arthroplasty in 24 postmenopausal women aged 67 ± 10 years. Furthermore, the 3D microarchitecture and the collagen crosslinks contents were assessed by high-resolution peripheral quantitative computed tomography and high-performance liquid chromatography, respectively. Osteophytes were present in the 24 FN, mainly at the level of the inferior quadrant. Microcracks were present in all FN with an average of 2.8 per sample. All observed microcracks were linear. The microcrack density (Cr.N/BV; #/mm²) was significantly higher in cancellous than in cortical bone (p = 0.004), whereas the microcrack length (Cr.Le, µm) was significantly greater in cortical bone (p = 0.04). The collagen crosslinks ratio pyridinoline/deoxypyridinoline was significantly and negatively correlated with Cr.N/BV in the posterior (r' = - 0.68, p = 0.01) and inferior (r' = - 0.53, p = 0.05) quadrants. Microcracks were observed in seven osteophytes in seven patients. When microcracks were present in the osteophyte area, Cr.N/BV was also significantly higher in the whole FN and in the quadrant of the osteophyte compared to the cases without microcrack in the osteophyte (p < 0.03). In conclusion, in FN from hip osteoarthritis microcracks are present in all FNs but in only 23% of the osteophytes. The microcrack formation was greater and their progression was smaller in the cancellous bone than in the cortex. The spatial distribution of microcracks varied according to the proximity of the osteophyte, and suggests that osteophyte may influence microcrack formation related to changes in local bone quality.

Cortical Fractal Analysis and Collagen Crosslinks Content in Femoral Neck After Osteoporotic Fracture in Postmenopausal Women: Comparison with Osteoarthritis

The femoral neck (FN) has been previously characterized by thinner cortices in osteoporotic fracture (HF) when compared to hip osteoarthritis (HOA). The purposes of this study were to complete the previous investigations on FNs from HF and HOA by analyzing the complexity of the cortical structure and to approach the intrinsic properties of cortical bone by assessing the collagen crosslink contents. FN samples were obtained during arthroplasty in 35 postmenopausal women (HF; n = 17; mean age 79 ± 2 years; HOA; n = 18; mean age 66 ± 2 years). The cortical fractal dimension (Ct.FD) and lacunarity (Ct.Lac) derived from high-resolution peripheral quantitative tomography (isotropic voxel size: 82 μm) images of FN by using Ctan software and Fraclac running in ImageJ were analyzed. The collagen crosslinks content [pyridinoline, deoxypyridinoline, pentosidine (PEN)] were assessed in cortical bone. Ct.FD was significantly lower (p < 0.0001) in HF than HOA reflecting a decreased complexity and was correlated to the age and BMD. In two sub-groups, BMD- and age-matched, respectively, Ct.FD remained significantly lower in HF than HOA (p < 0.001). Ct.Lac was not different between HF and HOA. PEN content was two times higher in HF than HOA (p < 0.0001) independently of age. In conclusion, FN with HF was characterized by a less complex cortical texture and higher PEN content than HOA. In addition to the decreased bone mass and BMD previously reported, these modifications contribute to the lower bone quality in HF than HOA in postmenopausal women.

Metapopulation Tracking Juvenile Penguins Reveals an Ecosystem-wide Ecological Trap

Climate change and fisheries are transforming the oceans, but we lack a complete understanding of their ecological impact [1-3]. Environmental degradation can cause maladaptive habitat selection, inducing ecological traps with profound consequences for biodiversity [4-6]. However, whether ecological traps operate in marine systems is unclear [7]. Large marine vertebrates may be vulnerable to ecological traps [6], but their broad-scale movements and complex life histories obscure the population-level consequences of habitat selection [8, 9]. We satellite tracked postnatal dispersal in African penguins (Spheniscus demersus) from eight sites across their breeding range to test whether they have become ecologically trapped in the degraded Benguela ecosystem. Bayesian state-space and habitat models show that penguins traversed thousands of square kilometers to areas of low sea surface temperatures (14.5°C-17.5°C) and high chlorophyll-a (∼11 mg m^-3). These were once reliable cues for prey-rich waters, but climate change and industrial fishing have depleted forage fish stocks in this system [10, 11]. Juvenile penguin survival is low in populations selecting degraded areas, and Bayesian projection models suggest that breeding numbers are ∼50% lower than if non-impacted habitats were used, revealing the extent and effect of a marine ecological trap for the first time. These cascading impacts of localized forage fish depletion-unobserved in studies on adults-were only elucidated via broad-scale movement and demographic data on juveniles. Our results support suspending fishing when prey biomass drops below critical thresholds [12, 13] and suggest that mitigation of marine ecological traps will require matching conservation action to the scale of ecological processes [14].

Exenatide Improves Bone Quality in a Murine Model of Genetically Inherited Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is associated with skeletal complications, including an increased risk of fractures. Reduced blood supply and bone strength may contribute to this skeletal fragility. We hypothesized that long-term administration of Exenatide, a glucagon-like peptide-1 receptor agonist, would improve bone architecture and strength of T2DM mice by increasing blood flow to bone, thereby stimulating bone formation. In this study, we used a model of obesity and severe T2DM, the leptin receptor-deficient db/db mouse to assess alterations in bone quality and hindlimb blood flow and to examine the beneficial effects of 4 weeks administration of Exenatide. As expected, diabetic mice showed marked alterations in bone structure, remodeling and strength, and basal vascular tone compared with lean mice. Exenatide treatment improved trabecular bone mass and architecture by increasing bone formation rate, but only in diabetic mice. Although there was no effect on hindlimb perfusion at the end of this treatment, Exenatide administration acutely increased tibial blood flow. While Exenatide treatment did not restore the impaired bone strength, intrinsic properties of the matrix, such as collagen maturity, were improved. The effects of Exenatide on in vitro bone formation were further investigated in primary osteoblasts cultured under high-glucose conditions, showing that Exenatide reversed the impairment in bone formation induced by glucose. In conclusion, Exenatide improves trabecular bone mass by increasing bone formation and could protect against the development of skeletal complications associated with T2DM.

Sclerostin does not play a major role in the pathogenesis of skeletal complications in type 2 diabetes mellitus

In contrast to previously reported elevations in serum sclerostin levels in diabetic patients, the present study shows that the impaired bone microarchitecture and cellular turnover associated with type 2 diabetes mellitus (T2DM)-like conditions in ZDF rats are not correlated with changes in serum and bone sclerostin expression.

INTRODUCTION

T2DM is associated with impaired skeletal structure and a higher prevalence of bone fractures. Sclerostin, a negative regulator of bone formation, is elevated in serum of diabetic patients. We aimed to relate changes in bone architecture and cellular activities to sclerostin production in the Zucker diabetic fatty (ZDF) rat.

METHODS

Bone density and architecture were measured by micro-CT and bone remodelling by histomorphometry in tibiae and femurs of 14-week-old male ZDF rats and lean Zucker controls (n = 6/group).

RESULTS

ZDF rats showed lower trabecular bone mineral density and bone mass compared to controls, due to decreases in bone volume and thickness, along with impaired bone connectivity and cortical bone geometry. Bone remodelling was impaired in diabetic rats, demonstrated by decreased bone formation rate and increased percentage of tartrate-resistant acid phosphatase-positive osteoclastic surfaces. Serum sclerostin levels (ELISA) were higher in ZDF compared to lean rats at 9 weeks (+40 %, p < 0.01), but this difference disappeared as their glucose control deteriorated and by week 14, ZDF rats had lower sclerostin levels than control rats (-44 %, p < 0.0001). Bone sclerostin mRNA (qPCR) and protein (immunohistochemistry) were similar in ZDF, and lean rats at 14 weeks and genotype did not affect the number of empty osteocytic lacunae in cortical and trabecular bone.

CONCLUSION

T2DM results in impaired skeletal architecture through altered remodelling pathways, but despite altered serum levels, it does not appear that sclerostin contributes to the deleterious effect of T2DM in rat bone.

Highly crosslinked polyethylene: a safe alternative to conventional polyethylene for dual mobility cup mobile component. A biomechanical validation

PURPOSE

Dual mobility cup (DMC) consists of a cobalt-chromium (CoCr) alloy cup articulated with a polyethylene (PE) mobile component capturing the femoral head in force using a snap-fit technique. This biomechanical study was the first to evaluate and compare the generation of cracks in the retentive area of DMC mobile components made of highly crosslinked PE (XLPE) or conventional ultra-high molecular weight PE (UHMWPE).

METHODS

Eighty mobile components designed for a 52-mm diameter Symbol® DMC (Dedienne Santé, Mauguio, France) and a 28-mm diameter femoral head were analyzed. Four groups of 20 mobile components were constituted according to the PE material: raw UHMWPE, sterilized UHMWPE, annealed XLPE and remelted XLPE. Ten mobile components in each group were impacted with a 28-mm diameter CoCr femoral head using a snap-fit technique. The occurrence, location and area of the cracks in the retentive area were investigated using micro-CT (Skyscan 1176®, Bruker, Aarsellar, Belgium) with a 35 μm nominal isotropic voxel size by two observers blinded to the PE material and impaction or not of the mobile components.

RESULTS

Compared to conventional UHMWPE, the femoral head snap-fit did not generate more or wider cracks in the retentive area of annealed or remelted XLPE mobile components.

CONCLUSION

This biomechanical study suggests that XLPE in DMC could be a safe alternative to conventional UHMWPE regarding the generation of cracks in the retentive area related to the femoral head snap-fit.

Vertebral body morphology is associated with incident lumbar vertebral fracture in postmenopausal women. The OFELY study

We investigate the predictive role of vertebral anterior cortical curvature and height heterogeneity in the occurrence of vertebral fractures in postmenopausal women. Women who will fracture had shorter vertebral height, greater heterogeneity of height than those who will not fracture, and their anterior vertebral body edge was less concave.

INTRODUCTION

Vertebral morphology has been demonstrated to be associated with further risk of fracture. The aim of this study was to analyze vertebral anterior cortical curvature (Ct.curv) and vertebral height heterogeneity in postmenopausal women before the occurrence of a vertebral fracture.

METHODS

This case-control study included 29 postmenopausal women who have underwent incident lumbar vertebral fractures (mean age 71 ± 9 years, mean time to fractures 9 ± 4 years), age-matched with 57 controls. From lateral X-rays of lumbar spine radiographs (T12 to L4), the following parameters were measured: (1) the posterior, middle, and anterior vertebral heights; (2) the heterogeneity of heights evaluated by the coefficient of variation of these three variables; (3) antero-posterior width, a 2D estimator of cross-sectional area; and (4) Ct.curv.

RESULTS

Mean vertebral heights were significantly lower among women who fractured than in controls (p < 0.05). The anterior and middle heights were significantly lower at L4 and L3 levels in fracture group (p = 0.02). The heterogeneity of vertebral height was significantly greater in the fracture group (p = 0.003). In addition, fractured patients had a significantly higher Ct.curv on L3 (p = 0.04). After adjustment for bone mineral density (BMD), only the heterogeneity of vertebral height remained significant (p = 0.005).

CONCLUSION

The current case-control study confirmed the association between vertebral height and occurrence of future vertebral fracture in postmenopausal women. The vertebrae with the smallest Ct.curv tended to fracture less often, and the heterogeneity of vertebral heights was associated with future fracture independently of BMD. An additional validation in a prospective study would be needed to confirm these initial results.

Are Biochemical Markers of Bone Turnover Representative of Bone Histomorphometry in 370 Postmenopausal Women?

CONTEXT

The levels of bone formation and resorption can be assessed at the tissue level by bone histomorphometry on transiliac bone biopsies. Systemic biochemical markers of bone turnover reflect the overall bone formation and resorption at the level of the entire skeleton but cannot discriminate the different skeletal compartments.

OBJECTIVE

Our aim was to investigate the correlations between the serum biochemical markers of formation and resorption with histomorphometric parameters.

DESIGN

We performed post hoc analysis of a previous clinical study.

SETTING

Patients were selected from the general population.

PATIENTS

A total of 371 untreated postmenopausal osteoporotic women aged 50 to 84 years with a lumbar T-score ≤ -2.5 SD or ≤ -1 SD with at least one osteoporotic fracture.

INTERVENTIONS

Transiliac bone biopsies were obtained after a double tetracycline labeling, and blood samples were collected.

MAIN OUTCOME MEASURES

The static and dynamic parameters of formation and bone resorption were measured by histomorphometry. Serum biochemical markers of formation (bone alkaline phosphatase [ALP]; procollagen type I N-terminal propeptide [PINP]) and resorption (C-terminal crosslinking telopeptide of collagen type 1 [sCTX]) were assessed.

RESULTS

The mean values of biochemical markers were: bone ALP, 15.0 ± 5.2 ng/mL; PINP, 56.2 ± 21.9 μg/mL; and sCTX, 0.58 ± 0.26 ng/mL. Bone ALP and PINP were significantly correlated with both the static and dynamic parameters of formation (0.21 ≤ r' ≤ 0.36; 0.01 ≥ P ≥ .0001). sCTX was significantly correlated with all resorption parameters (0.18 ≤ r' ≤ 0.24; 0.02 ≥ P ≥ .0001).

CONCLUSION

Bone turnover markers were significantly but modestly associated with bone turnover parameters measured in iliac cancellous bone. The iliac crest bone may not represent perfectly the whole bone turnover.

Chronic administration of Glucagon-like peptide-1 receptor agonists improves trabecular bone mass and architecture in ovariectomised mice

Some anti-diabetic therapies can have adverse effects on bone health and increase fracture risk. In this study, we tested the skeletal effects of chronic administration of two Glucagon-like peptide-1 receptor agonists (GLP-1RA), increasingly used for type 2 diabetes treatment, in a model of osteoporosis associated bone loss and examined the expression and activation of GLP-1R in bone cells. Mice were ovariectomised (OVX) to induce bone loss and four weeks later they were treated with Liraglutide (LIR) 0.3mg/kg/day, Exenatide (Ex-4) 10 μg/kg/day or saline for four weeks. Mice were injected with calcein and alizarin red prior to euthanasia, to label bone-mineralising surfaces. Tibial micro-architecture was determined by micro-CT and bone formation and resorption parameters measured by histomorphometric analysis. Serum was collected to measure calcitonin and sclerostin levels, inhibitors of bone resorption and formation, respectively. GLP-1R mRNA and protein expression were evaluated in the bone, bone marrow and bone cells using RT-PCR and immunohistochemistry. Primary osteoclasts and osteoblasts were cultured to evaluate the effect of GLP-1RA on bone resorption and formation in vitro. GLP-1RA significantly increased trabecular bone mass, connectivity and structure parameters but had no effect on cortical bone. There was no effect of GLP-1RA on bone formation in vivo but an increase in osteoclast number and osteoclast surfaces was observed with Ex-4. GLP-1R was expressed in bone marrow cells, primary osteoclasts and osteoblasts and in late osteocytic cell line. Both Ex-4 and LIR stimulated osteoclastic differentiation in vitro but slightly reduced the area resorbed per osteoclast. They had no effect on bone nodule formation in vitro. Serum calcitonin levels were increased and sclerostin levels decreased by Ex-4 but not by LIR. Thus, GLP-1RA can have beneficial effects on bone and the expression of GLP-1R in bone cells may imply that these effects are exerted directly on the tissue.

Differential Effects of IL-17A and TNF-α on Osteoblastic Differentiation of Isolated Synoviocytes and on Bone Explants from Arthritis Patients

Objective

TNF-α and IL-17A act on fibroblast-like synoviocytes (FLS) and contribute to cytokine production, inflammation, and tissue destruction in rheumatoid arthritis (RA). The aim of this study was to compare their effects on osteogenic differentiation of isolated FLS and on whole bone explants from RA and osteoarthritis (OA) patients.

Methods

Fibroblast-like synoviocytes and bone explants were cultured in the presence or absence of TNF-α and/or IL-17A. Mineralization of extracellular matrix of FLS was measured by alizarin red and alkaline phosphatase activity (ALP). mRNA expression was analyzed by qRT-PCR for Wnt5a, BMP2, and RUNX2, key genes associated with osteogenesis. IL-6 and IL-8 levels were measured by enzyme-linked immunosorbent assays. Bone explant structure was quantified by histomorphometry.

Results

In isolated OA and RA FLS, the combination of TNF-α and IL-17A induced matrix mineralization, increased ALP activity and expression of the osteogenesis-associated genes Wnt5a, BMP2, and Runx2, indicating an osteogenic differentiation. Wnt5a levels increased with TNF-α alone and in combination with IL-17A. BMP2 expression decreased with IL-17A and TNF-α after 12 h with OA FLS and 24 h with RA FLS. Runx2 expression decreased only with combination of TNF-α and IL-17A in OA FLS and with cytokines alone and combined in RA FLS. IL-6 and IL-8 production increased with IL-17A and/or TNF-α in both FLS and bone samples, especially from RA. Treatment of bone explants with cytokine combination increased ALP in OA but not RA samples. A decrease in bone volume was seen with cytokine combination, especially with RA explants.

Conclusion

Differences were observed for the effects of IL-17A and TNF-α on osteogenic differentiation. In isolated FLS, increased osteoblastogenesis was observed, contrasting with the inhibitory effect in whole bone, specifically in RA. The net effect of IL-17A and TNF-α appears to depend on the disease state and the presence of other cells.

Fracture discrimination by combined bone mineral density (BMD) and microarchitectural texture analysis

The use of bone mineral density (BMD) for fracture discrimination may be improved by considering bone microarchitecture. Texture parameters such as trabecular bone score (TBS) or mean Hurst parameter (H) could help to find women who are at high risk of fracture in the non-osteoporotic group. The purpose of this study was to combine BMD and microarchitectural texture parameters (spine TBS and calcaneus H) for the detection of osteoporotic fractures. Two hundred and fifty five women had a lumbar spine (LS), total hip (TH), and femoral neck (FN) DXA. Additionally, texture analyses were performed with TBS on spine DXA and with H on calcaneus radiographs. Seventy-nine women had prevalent fragility fractures. The association with fracture was evaluated by multivariate logistic regressions. The diagnostic value of each parameter alone and together was evaluated by odds ratios (OR). The area under curve (AUC) of the receiver operating characteristics (ROC) were assessed in models including BMD, H, and TBS. Women were also classified above and under the lowest tertile of H or TBS according to their BMD status. Women with prevalent fracture were older and had lower TBS, H, LS-BMD, and TH-BMD than women without fracture. Age-adjusted ORs were 1.66, 1.70, and 1.93 for LS, FN, and TH-BMD, respectively. Both TBS and H remained significantly associated with fracture after adjustment for age and TH-BMD: OR 2.07 [1.43; 3.05] and 1.47 [1.04; 2.11], respectively. The addition of texture parameters in the multivariate models didn't show a significant improvement of the ROC-AUC. However, women with normal or osteopenic BMD in the lowest range of TBS or H had significantly more fractures than women above the TBS or the H threshold. We have shown the potential interest of texture parameters such as TBS and H in addition to BMD to discriminate patients with or without osteoporotic fractures. However, their clinical added values should be evaluated relative to other risk factors.

Excessive growth hormone expression in male GH transgenic mice adversely alters bone architecture and mechanical strength

Patients with acromegaly have a higher prevalence of vertebral fractures despite normal bone mineral density (BMD), suggesting that GH overexpression has adverse effects on skeletal architecture and strength. We used giant bovine GH (bGH) transgenic mice to analyze the effects of high serum GH levels on BMD, architecture, and mechanical strength. Five-month-old hemizygous male bGH mice were compared with age- and sex-matched nontransgenic littermates controls (NT; n=16/group). Bone architecture and BMD were analyzed in tibia and lumbar vertebrae using microcomputed tomography. Femora were tested to failure using three-point bending and bone cellular activity determined by bone histomorphometry. bGH transgenic mice displayed significant increases in body weight and bone lengths. bGH tibia showed decreases in trabecular bone volume fraction, thickness, and number compared with NT ones, whereas trabecular pattern factor and structure model index were significantly increased, indicating deterioration in bone structure. Although cortical tissue perimeter was increased in transgenic mice, cortical thickness was reduced. bGH mice showed similar trabecular BMD but reduced trabecular thickness in lumbar vertebra relative to controls. Cortical BMD and thickness were significantly reduced in bGH lumbar vertebra. Mechanical testing of femora confirmed that bGH femora have decreased intrinsic mechanical properties compared with NT ones. Bone turnover is increased in favor of bone resorption in bGH tibia and vertebra compared with controls, and serum PTH levels is also enhanced in bGH mice. These data collectively suggest that high serum GH levels negatively affect bone architecture and quality at multiple skeletal sites.

The role of bone intrinsic properties measured by infrared spectroscopy in whole lumbar vertebra mechanics: organic rather than inorganic bone matrix?

Whole bone strength is determined by bone mass, microarchitecture and intrinsic properties of the bone matrix. However, few studies have directly investigated the contribution of bone tissue material properties to whole bone strength in humans. This study assessed the role of bone matrix composition on whole lumbar vertebra mechanics. We obtained 17 fresh frozen human lumbar spines (8 W, 9 M, aged 76±11years). L3 bone mass was measured by DXA and microarchitecture by μ-CT with a 35 μm-isotropic resolution. Microarchitectural parameters were directly measured: Tb.BV/TV, SMI, Tb.Th, DA, Ct.Th, Ct.Po and radius of anterior cortical curvature. Failure load (N), stiffness (N/mm) and work to failure (N.mm) were extracted from quasi-static uniaxial compressive testing performed on L3 vertebral bodies. FTIRM analysis was performed on 2 μm-thick sections from L2 trabecular cores, with a Perkin-Elmer GXII Auto-image Microscope equipped with a wide band detector. Twenty measurements per sample were performed at 30∗100 μm of spatial resolution. Each spectrum was collected at 4 cm(-1) resolution and 50 scans in transmission mode. Mineral and collagen maturity, and mineralization and crystallinity index were measured. There was no association between the bone matrix characteristics and bone mass or microarchitecture. Mineral maturity, mineralization and crystallinity index were not related to whole vertebra mechanics. However, collagen maturity was positively correlated with whole vertebra failure load and stiffness (r=0.64, p=0.005 and r=0.54, p=0.025, respectively). The collagen maturity (3rd step) in combination with bone mass (i.e., BMC, 1st step) and microarchitecture (i.e., Tb.Th, 2nd step) improved the prediction of whole vertebra mechanical properties in forward stepwise multiple regression models, together explaining 71% of the variability in whole vertebra stiffness (p=0.001). In conclusion, we demonstrated a substantial contribution of collagen maturity, but not mineralization parameters, to whole bone strength of human lumbar vertebrae that was independent of bone mass and microarchitecture.

The predictive value of trabecular bone score (TBS) on whole lumbar vertebrae mechanics: an ex vivo study

We investigated the association of trabecular bone score (TBS) with microarchitecture and mechanical behavior of human lumbar vertebrae. We found that TBS reflects vertebral trabecular microarchitecture and is an independent predictor of vertebral mechanics. However, the addition of TBS to areal BMD (aBMD) did not significantly improve prediction of vertebral strength.

INTRODUCTION

The trabecular bone score (TBS) is a gray-level measure of texture using a modified experimental variogram which can be extracted from dual-energy X-ray absorptiometry (DXA) images. The current study aimed to confirm whether TBS is associated with trabecular microarchitecture and mechanics of human lumbar vertebrae, and if its combination with BMD improves prediction of fracture risk.

METHODS

Lumbar vertebrae (L3) were harvested fresh from 16 donors. The anteroposterior and lateral bone mineral content (BMC) and areal BMD (aBMD) of the vertebral body were measured using DXA; then, the TBS was extracted using TBS iNsight software (Medimaps SA, France). The trabecular bone volume (Tb.BV/tissue volume, TV), trabecular thickness (Tb.Th), degree of anisotropy, and structure model index (SMI) were measured using microcomputed tomography. Quasi-static uniaxial compressive testing was performed on L3 vertebral bodies to assess failure load and stiffness.

RESULTS

The TBS was significantly correlated to Tb.BV/TV and SMI (r = 0.58 and -0.62; p = 0.02, 0.01), but not related to BMC and BMD. TBS was significantly correlated with stiffness (r = 0.64; p = 0.007), independently of bone mass. Using stepwise multiple regression models, we failed to demonstrate that the combination of BMD and TBS was better at explaining mechanical behavior than either variable alone. However, the combination TBS, Tb.Th, and BMC did perform better than each parameter alone, explaining 79% of the variability in stiffness.

CONCLUSIONS

In our study, TBS was associated with microarchitecture parameters and with vertebral mechanical behavior, but TBS did not improve prediction of vertebral biomechanical properties in addition to aBMD.

Mice lacking AMP-activated protein kinase α1 catalytic subunit have increased bone remodelling and modified skeletal responses to hormonal challenges induced by ovariectomy and intermittent PTH treatment

AMP-activated protein kinase (AMPK) is a key regulator of cellular and body energy homeostasis. We previously demonstrated that AMPK activation in osteoblasts increases in vitro bone formation while deletion of the Ampkα1 (Prkaa1) subunit, the dominant catalytic subunit expressed in bone, leads to decreased bone mass in vivo. To investigate the cause of low bone mass in the Ampkα1(-/-) mice, we analysed bone formation and resorption in the tibia of these mice by dynamic histomorphometry and determined whether bone turnover can be stimulated in the absence of the Ampkα1 subunit. We subjected 12-week-old Ampkα1(+)(/)(+) and Ampkα1(-/-) mice to ovariectomy (OVX), intermittent PTH (iPTH) administration (80 μg/kg per day, 5 days/week) or both OVX and iPTH hormonal challenges. Tibiae were harvested from these mice and bone micro-architecture was determined by micro-computed tomography. We show for the first time that Ampkα1(-/-) mice have a high bone turnover at the basal level in favour of bone resorption. While both Ampkα1(+)(/)(+) and Ampkα1(-/-) mice lost bone mass after OVX, the bone loss in Ampkα1(-/-) mice was lower compared with controls. iPTH increased trabecular and cortical bone indexes in both ovariectomised Ampkα1(+)(/)(+) and Ampkα1(-/-) mice. However, ovariectomised Ampkα1(-/-) mice showed a smaller increase in bone parameters in response to iPTH compared with Ampkα1(+)(/)(+) mice. By contrast, non-ovariectomised Ampkα1(-/-) mice responded better to iPTH treatment than non-ovariectomised Ampkα1(+)(/)(+) mice. Overall, these data demonstrate that Ampkα1(-/-) mice are less affected by changes in bone turnover induced by OVX but respond better to the anabolic challenge induced by iPTH. These results suggest that AMPKα1 activation may play a role in the hormonal regulation of bone remodelling.

Comparison of 2D and 3D bone microarchitecture evaluation at the femoral neck, among postmenopausal women with hip fracture or hip osteoarthritis

OBJECTIVES

High resolution peripheral quantitative tomography (HR-pQCT) is used more widely to assess microarchitecture, but we are lacking comparisons between HR-pQCT and histomorphometry, which is considered the gold standard. They have only been assessed on different anatomical regions. The purpose of our study was to assess the microarchitecture and the relative contribution of cortical and trabecular bone in hip fracture with this 3D imaging technique, compared with the 2D histomorphometry.

MATERIAL AND METHODS

We compared the distribution of cortical and trabecular bone in the ultradistal femoral neck samples (~3mm thick) obtained after total hip replacement in 21 hip osteoarthritis (HOA, 66±8yrs) and 20 hip fracture (HF, 79±8yrs) menopausal women by a direct 3D evaluation method (HR-pQCT: XtremeCT, Scanco Medical AG) and by histomorphometry, performed and averaged on three 10μm-thick sections 800μm apart.

RESULTS

Significant correlations were found between both techniques for trabecular bone volume, number, thickness, separation and cortical thickness (0.51<r'<0.81, p<0.01). The connectivity was also significantly correlated (r'=0.58, p<0.001) between both techniques, as well as the trabecular bone pattern factor measured in 2D with the structural model index (SMI) measured in 3D (r'=0.62, p<0.001). However HR-pQCT overestimated the absolute value of most parameters, with higher values being even more overestimated. The agreement between the two techniques was weak for cortical porosity. With the 3D measurements we found that trabecular bone volume was 43% lower in HF than HOA (p<0.01), associated with loss of trabecular connectivity (-50%, p<0.01) and a more rod-like structure (SMI, 22%, p<0.01), mainly at the inferior (34%, p<0.01) and posterior (22%, p<0.05) quadrants. Cortical thickness was found to be lower in the posterior quadrants (-22%, p<0.05) and tended to be lower in HF than in HOA at the inferior quadrant (-14%, p=0.08), but it was still the highest at the inferior quadrant in both groups. In conclusion, 3D methods confirmed the alteration of trabecular and cortical bone found by histomorphometry in HF compared with HOA and the frequency of the rod-like structure in HF.

Determinants of the mechanical behavior of human lumbar vertebrae after simulated mild fracture

The ability of a vertebra to carry load after an initial deformation and the determinants of this postfracture load-bearing capacity are critical but poorly understood. This study aimed to determine the mechanical behavior of vertebrae after simulated mild fracture and to identify the determinants of this postfracture behavior. Twenty-one human L(3) vertebrae were analyzed for bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) and for microarchitecture by micro-computed tomography (µCT). Mechanical testing was performed in two phases: initial compression of vertebra to 25% deformity, followed, after 30 minutes of relaxation, by a similar test to failure to determine postfracture behavior. We assessed (1) initial and postfracture mechanical parameters, (2) changes in mechanical parameters, (3) postfracture elastic behavior by recovery of vertebral height after relaxation, and (4) postfracture plastic behavior by residual strength and stiffness. Postfracture failure load and stiffness were 11% ± 19% and 53% ± 18% lower than initial values (p = .021 and p < .0001, respectively), with 29% to 69% of the variation in the postfracture mechanical behavior explained by the initial values. Both initial and postfracture mechanical behaviors were significantly correlated with bone mass and microarchitecture. Vertebral deformation recovery averaged 31% ± 7% and was associated with trabecular and cortical thickness (r = 0.47 and r = 0.64; p = .03 and p = .002, respectively). Residual strength and stiffness were independent of bone mass and initial mechanical behavior but were related to trabecular and cortical microarchitecture (|r| = 0.50 to 0.58; p = .02 to .006). In summary, we found marked variation in the postfracture load-bearing capacity following simulated mild vertebral fractures. Bone microarchitecture, but not bone mass, was associated with postfracture mechanical behavior of vertebrae.

Workplace bullying and psychotropic drug use: the mediating role of physical and mental health status

OBJECTIVES

The association between workplace bullying and psychotropic drug use is not well established. This study was aimed at exploring the association between workplace bullying, and its characteristics, and psychotropic drug use and studying the mediating role of physical and mental health.

METHODS

The study population consisted of a random sample of 3132 men and 4562 women of the working population in the south-east of France. Workplace bullying, evaluated using the validated instrument elaborated by Leymann, and psychotropic drug use, as well as covariates, were measured using a self-administered questionnaire. Covariates included age, marital status, presence of children, education, occupation, working hours, night work, physico-chemical exposures at work, self-reported health, and depressive symptoms. Statistical analysis was performed using logistic regression analysis and was carried out separately for men and women.

RESULTS

Workplace bullying was strongly associated with psychotropic drug use. Past exposure to bullying increased the risk for this use. The more frequent and the longer the exposure to bullying, the stronger the association with psychotropic drug use. Observing bullying on someone else at the workplace was associated with psychotropic drug use. Adjustment for covariates did not modify the results. Additional adjustment for self-reported health and depressive symptoms reduced the magnitude of the associations, especially for men.

CONCLUSIONS

The association between bullying and psychotropic drug use was found to be significant and strong and was partially mediated by physical and mental health.

Role of trabecular microarchitecture and its heterogeneity parameters in the mechanical behavior of ex vivo human L3 vertebrae

Low bone mineral density (BMD) is a strong risk factor for vertebral fracture risk in osteoporosis. However, many fractures occur in people with moderately decreased or normal BMD. Our aim was to assess the contributions of trabecular microarchitecture and its heterogeneity to the mechanical behavior of human lumbar vertebrae. Twenty-one human L(3) vertebrae were analyzed for BMD by dual-energy X-ray absorptiometry (DXA) and microarchitecture by high-resolution peripheral quantitative computed tomography (HR-pQCT) and then tested in axial compression. Microarchitecture heterogeneity was assessed using two vertically oriented virtual biopsies--one anterior (Ant) and one posterior (Post)--each divided into three zones (superior, middle, and inferior) and using the whole vertebral trabecular volume for the intraindividual distribution of trabecular separation (Tb.Sp*SD). Heterogeneity parameters were defined as (1) ratios of anterior to posterior microarchitectural parameters and (2) the coefficient of variation of microarchitectural parameters from the superior, middle, and inferior zones. BMD alone explained up to 44% of the variability in vertebral mechanical behavior, bone volume fraction (BV/TV) up to 53%, and trabecular architecture up to 66%. Importantly, bone mass (BMD or BV/TV) in combination with microarchitecture and its heterogeneity improved the prediction of vertebral mechanical behavior, together explaining up to 86% of the variability in vertebral failure load. In conclusion, our data indicate that regional variation of microarchitecture assessment expressed by heterogeneity parameters may enhance prediction of vertebral fracture risk.

Association between collagen cross-links and trabecular microarchitecture properties of human vertebral bone

It has been suggested that age-related deterioration in trabecular microarchitecture and changes in collagen cross-link concentrations may contribute to skeletal fragility. To further explore this hypothesis, we determined the relationships among trabecular bone volume fraction (BV/TV), microarchitecture, collagen cross-link content, and bone turnover in human vertebral trabecular bone. Trabecular bone specimens from L2 vertebrae were collected from 51 recently deceased donors (54-95 years of age; 20 men and 30 women). Trabecular bone volume and microarchitecture was assessed by microCT and bone formation, reflected by osteoid surface (OS/BS, %), was measured by 2D histomorphometry. Pyridinoline (PYD), deoxypyridinoline (DPD), pentosidine (PEN) and collagen content in the cancellous bone were analysed by high-performance liquid chromatography. Associations between variables were investigated by Pearson correlations and multiple regression models, which were constructed with BV/TV and collagen cross-links as explanatory variables and microarchitecture parameters as the dependent variables.

RESULTS

Microarchitecture parameters were modestly to strongly correlated with BV/TV (r(2)=0.10-0.71). The amount of mature enzymatic PYD and DPD cross-links were not associated with the microarchitecture, either before or after adjustment for BV/TV. However, there was a positive correlation between PEN content and trabecular number (r=0.45, p=0.001) and connectivity density (r=0.40, p=0.004), and a negative correlation between PEN content and trabecular separation (r=-0.29, p=0.04). In the multiple regression models including BV/TV, age and PEN content was still significantly associated with several of the microarchitecture variables. In summary, this study suggests a link between trabecular microarchitecture and the collagen cross-link profile. As PEN reflects non-enzymatic glycation of collagen and generally increases with bone age, the association between PEN and trabecular architecture suggests that the preserved trabeculae may contain mainly old bone and have undergone little remodeling. Thus, vertebral fragility may not only be due to alterations in bone architecture but also to modification of collagen cross-link patterns thereby influencing bone's mechanical behavior.

Workplace bullying and sleep disturbances: findings from a large scale cross-sectional survey in the French working population

STUDY OBJECTIVES

The purpose of this study was to explore the associations between workplace bullying, the characteristics of workplace bullying, and sleep disturbances in a large sample of employees of the French working population.

DESIGN

Workplace bullying, evaluated using the validated instrument developed by Leymann, and sleep disturbances, as well as covariates, were measured using a self-administered questionnaire. Covariates included age, marital status, presence of children, education, occupation, working hours, night work, physical and chemical exposures at work, self-reported health, and depressive symptoms. Statistical analysis was performed using logistic regression analysis and was carried out separately for men and women.

SETTING

General working population.

PARTICIPANTS

The study population consisted of a random sample of 3132 men and 4562 women of the working population in the southeast of France.

RESULTS

Workplace bullying was strongly associated with sleep disturbances. Past exposure to bullying also increased the risk for this outcome. The more frequent the exposure to bullying, the higher the risk of experiencing sleep disturbances. Observing someone else being bullied in the workplace was also associated with the outcome. Adjustment for covariates did not modify the results. Additional adjustment for self-reported health and depressive symptoms diminished the magnitude of the associations that remained significant.

CONCLUSIONS

The prevalence of workplace bullying (around 10%) was found to be high in this study as well was the impact of this major job-related stressor on sleep disturbances. Although no conclusion about causality could be drawn from this cross-sectional study, the findings suggest that the contribution of workplace bullying to the burden of sleep disturbances may be substantial.

Microarchitecture influences microdamage accumulation in human vertebral trabecular bone

It has been suggested that accumulation of microdamage with age contributes to skeletal fragility. However, data on the age-related increase in microdamage and the association between microdamage and trabecular microarchitecture in human vertebral cancellous bone are limited. We quantified microdamage in cancellous bone from human lumbar (L(2)) vertebral bodies obtained from 23 donors 54-93 yr of age (8 men and 15 women). Damage was measured using histologic techniques of sequential labeling with chelating agents and was related to 3D microarchitecture, as assessed by high-resolution microCT. There were no significant differences between sexes, although women tended to have a higher microcrack density (Cr.Dn) than men. Cr.Dn increased exponentially with age (r = 0.65, p < 0.001) and was correlated with bone volume fraction (BV/TV; r = -0.55; p < 0.01), trabecular number (Tb.N; r = -0.56 p = 0.008), structure model index (SMI; r = 0.59; p = 0.005), and trabecular separation (Tb.Sp; r = 0.59; p < 0.009). All architecture parameters were strongly correlated with each other and with BV/TV. Stepwise regression showed that SMI was the best predictor of microdamage, explaining 35% of the variance in Cr.Dn and 20% of the variance in diffuse damage accumulation. In addition, microcrack length was significantly greater in the highest versus lowest tertiles of SMI. In conclusion, in human vertebral cancellous bone, microdamage increases with age and is associated with low BV/TV and a rod-like trabecular architecture.

Bone sialoprotein plays a functional role in bone formation and osteoclastogenesis

Bone sialoprotein (BSP) and osteopontin (OPN) are both highly expressed in bone, but their functional specificities are unknown. OPN knockout (^−/−) mice do not lose bone in a model of hindlimb disuse (tail suspension), showing the importance of OPN in bone remodeling. We report that BSP^−/− mice are viable and breed normally, but their weight and size are lower than wild-type (WT) mice. Bone is undermineralized in fetuses and young adults, but not in older (≥12 mo) BSP^−/− mice. At 4 mo, BSP^−/− mice display thinner cortical bones than WT, but greater trabecular bone volume with very low bone formation rate, which indicates reduced resorption, as confirmed by lower osteoclast surfaces. Although the frequency of total colonies and committed osteoblast colonies is the same, fewer mineralized colonies expressing decreased levels of osteoblast markers form in BSP^−/− versus WT bone marrow stromal cultures. BSP^−/− hematopoietic progenitors form fewer osteoclasts, but their resorptive activity on dentin is normal. Tail-suspended BSP^−/− mice lose bone in hindlimbs, as expected. In conclusion, BSP deficiency impairs bone growth and mineralization, concomitant with dramatically reduced bone formation. It does not, however, prevent the bone loss resulting from loss of mechanical stimulation, a phenotype that is clearly different from OPN^−/− mice.

Thyroid Hormone Excess Rather Than Thyrotropin Deficiency Induces Osteoporosis in Hyperthyroidism

Thyrotoxicosis is an important but under recognized cause of osteoporosis. Recently, TSH deficiency, rather than thyroid hormone excess, has been suggested as the underlying cause. To investigate the molecular mechanism of osteoporosis in thyroid disease, we characterized the skeleton in mice lacking either thyroid hormone receptor alpha or beta (TRalpha(0/0), TRbeta-/-). Remarkably, in the presence of normal circulating thyroid hormone and TSH concentrations, adult TRalpha(0/0) mice had osteosclerosis accompanied by reduced osteoclastic bone resorption, whereas juveniles had delayed endochondral ossification with reduced bone mineral deposition. By contrast, adult TRbeta-/- mice with elevated TSH and thyroid hormone levels were osteoporotic with evidence of increased bone resorption, whereas juveniles had advanced ossification with increased bone mineral deposition. Analysis of T3 target gene expression revealed skeletal hypothyroidism in TRalpha(0/0) mice, but skeletal thyrotoxicosis in TRbeta-/- mice. These studies demonstrate that bone loss in thyrotoxicosis is independent of circulating TSH levels and mediated predominantly by TRalpha, thus identifying TRalpha as a novel drug target in the prevention and treatment of osteoporosis.

Contribution of the advanced glycation end product pentosidine and of maturation of type I collagen to compressive biomechanical properties of human lumbar vertebrae

Collagen characteristics contribute to bone biomechanical properties. Yet, few studies have analyzed the independent contributions of bone mineral density (BMD) and post-translational modifications of type I collagen to whole bone strength. Thus, the aim of this study was to determine the relative contributions of BMD and both enzymatic and non-enzymatic collagen crosslink concentration to the biomechanical properties of human vertebrae. Nineteen L3 vertebrae were collected after necropsy (age 26-93; 10 males, 9 females). BMD of the vertebral body was measured by DXA, and the vertebrae were compressed to failure to assess the stiffness, failure load and work to fracture. After mechanical testing, the concentration of both enzymatic crosslinks pyridinoline (PYD), and deoxypyridinoline (DPD) as well as, and the non-enzymatic crosslinks pentosidine (PEN) were analyzed in trabecular and cortical bone by reversed-phase HPLC. The extent of aspartic acid isomerization of type I collagen C telopeptide (CTX) was evaluated by ELISA of native (alpha CTX) and isomerized (beta CTX) forms. BMD was significantly positively related with stiffness (R(2) = 0.74; P < 0.0001), failure load (R(2) = 0.69; P < 0.0001) and work to fracture (R(2) = 0.44; P = 0.002). Bivariate regression analysis showed no association between collagen traits and biomechanical properties. However, in a multiple regression model, BMD and trabecular PEN were both significantly associated with failure load and work to fracture (multiple R(2) = 0.83, P = 0.001 and R(2) = 0.67, P = 0.001, respectively). Similarly, BMD and trabecular alpha/beta CTX ratio were both associated with stiffness (multiple R(2) = 0.83, P = 0.015). These findings indicate that post-translational modifications of type I collagen have an impact on skeletal fragility.

Evaluation and development of automatic two-dimensional measurements of histomorphometric parameters reflecting trabecular bone connectivity: correlations with dual-energy x-ray absorptiometry and quantitative ultrasound in human calcaneum

In osteoporosis, bone fragility results from both bone loss and changes in trabecular microarchitecture, which can be quantified by bone histomorphometric parameters. Twenty human calcaneum were collected after necropsy. All measurements were performed at the same anatomical location. Bone histomorphometric parameters were measured on histological slides with an automatic image analyzer. The aims of our study were (1) to develop automatic measurements of four additional parameters reflecting trabecular network connectivity and complexity, i.e., trabecular bone pattern factor (TBPf), Euler number/tissue volume (Euler) according to the three definitions previously reported and to a fourth one established in the laboratory (Euler(strut.cavity)), marrow star volume, and interconnectivity index, and to determine their usefulness in microarchitecture characterization; and (2) to validate these parameters by evaluating their relationship with dual-energy X-ray absorptiometry and quantitative ultrasound (QUS) measurements performed on the same samples. The statistical analysis showed that TBPf and Euler(strut.cavity) appeared to be the most significant connectivity parameters, independently of bone quantity (bone mineral density, apparent density, cancellous bone volume). For QUS, after adjustment for bone quantity, only speed of sound (SOS) was significantly and negatively correlated to Euler(strut.cavity). Broadband ultrasound attenuation depends only on bone quantity. In conclusion, TBPf (a strut analysis parameter extrapolable in three dimensions) and Euler(strut.cavity) (the only bone connectivity parameter reflecting SOS) are two valid bone microarchitecture parameters. These new parameters were significantly correlated to the established trabecular structure parameters: trabecular thickness or trabecular spacing, being weakly correlated with SOS.

Relationship between compressive properties of human os calcis cancellous bone and microarchitecture assessed from 2D and 3D synchrotron microtomography

The aim of this study was to determine the contribution of 2D and 3D microarchitectural characteristics in the assessment of the mechanical strength of os calcis cancellous bone. A sample of cancellous bone was removed in a medio-lateral direction from the posterior body of calcaneus, taken at autopsy in 17 subjects aged 61-91 years. The sample was first used for the assessment of morphological parameters from 2D morphometry and 3D synchrotron microtomography (microCT) (spatial resolution=10 microm). The 2D morphometry was obtained from three slices extracted from the 3D microCT images. Very good concordance was shown between 3D microCT slices and the corresponding physical histologic slices. In 2D, the standard histomorphometric parameters, fractal dimension, mean intercept length, and connectivity were computed. In 3D, histomorphometric parameters were computed using both the 3D mean intercept length method and model-independent techniques. The 3D fractal dimension and the 3D connectivity, assessed by Euler density, were also evaluated. The cubic samples were subjected to elastic compressive tests in three orthogonal directions (X, Y, Z) close to the main natural trabecular network directions. A test was performed until collapse of trabecular network in the main direction (Z). The mechanical properties were significantly correlated to most morphological parameters resulting from 2D and 3D analysis. In 2D, the correlation between the mechanical strength and bone volume/tissue volume was not significantly improved by adding structural parameters or connectivity parameter (nodes number/tissue volume). In 3D, one architectural parameter (the trabecular thickness, Tb.Th) permitted to improve the estimation of the compressive strength from the bone volume/tissue volume alone. However, this improvement was minor since the correlation with the BV/TV alone was high (r=0.96). In conclusion, which is in agreement with the statistic's rules, we found, in this study, that the determination of the os calcis bone compressive strength using the 3D bone volume fraction cannot be improved by adding 3D architectural parameters.