Changes in bone macro- and microstructure in diabetic obese mice revealed by high resolution microfocus X-ray computed tomography

Computed tomography technologies to measure key structural features of polymeric biomedical implants from bench to bedside

Implanted polymeric devices, designed to encourage tissue regeneration, require porosity. However, characterizing porosity, which affects many functional device properties, is non-trivial. Computed tomography (CT) is a quick, versatile, and non-destructive way to gain 3D structural information, yet various CT technologies, such as benchtop, preclinical and clinical systems, all have different capabilities. As system capabilities determine the structural information that can be obtained, seamless monitoring of key device features through all stages of clinical translation must be engineered intentionally. Therefore, in this study we tested feasibility of obtaining structural information in pre-clinical systems and high-resolution micro-CT (μCT) under physiological conditions. To overcome the low CT contrast of polymers in hydrated environments, radiopaque nanoparticle contrast agent was incorporated into porous devices. The size of resolved features in porous structures is highly dependent on the resolution (voxel size) of the scan. As the voxel size of the CT scan increased (lower resolution) from 5 to 50 μm, the measured pore size was overestimated, and percentage porosity was underestimated by nearly 50%. With the homogeneous introduction of nanoparticles, changes to device structure could be quantified in the hydrated state, including at high-resolution. Biopolymers had significant structural changes post-hydration, including a mean increase of 130% in pore wall thickness that could potentially impact biological response. By incorporating imaging capabilities into polymeric devices, CT can be a facile way to monitor devices from initial design stages through to clinical translation.

Increased cancellous bone mass accompanies decreased cortical bone mineral density and higher axial deformation in femurs of leptin-deficient obese mice

INTRODUCTION

Leptin is a pleiotropic hormone that regulates food intake and energy homeostasis with enigmatic effects on bone development. It is unclear if leptin promotes or inhibits bone growth. The aim of this study was to characterize the micro-architecture and mechanical competence of femur bones of leptin-deficient mice.

MATERIALS AND METHODS

Right femur bones of 15-week old C57BL/6 (n = 9) and leptin-deficient (ob/ob, n = 9) mice were analyzed. Whole bones were scanned using micro-CT and morphometric parameters of the cortex and trabeculae were assessed. Elastic moduli were determined from microindentations in midshaft cross-sections. Mineral densities were determined using quantitative backscatter scanning electron microscopy. 3D models of the distal femur metaphysis, cleared from trabecular bone, were meshed and used for finite element simulations of axial loading to identify straining differences between ob/ob and C57BL/6 controls.

RESULTS

Compared with C57BL/6 controls, ob/ob mice had significantly shorter bones. ob/ob mice showed significantly increased cancellous bone volume and trabecular thickness. qBEI quantified a ∼7% lower mineral density in ob/ob mice in the distal femur metaphysis. Indentation demonstrated a significantly reduced Young's modulus of 12.14 [9.67, 16.56 IQR] GPa for ob/ob mice compared to 23.12 [20.70, 26.57 IQR] GPa in C57BL/6 mice. FEA revealed greater deformation of cortical bone in ob/ob as compared to C57BL/6 mice.

CONCLUSION

Leptin deficient ob/ob mice have a softer cortical bone in the distal femur metaphysis but an excessive amount of cancellous bone, possibly as a response to increased deformation of the bones during axial loading. Both FEA and direct X-ray and electron microscopy imaging suggest that the morphology and micro-architecture of ob/ob mice have inferior biomechanical properties suggestive of a reduced mechanical competence.

Impact of leptin deficiency on male tibia and vertebral body 3D bone architecture independent of changes in body weight

Leptin an adipokine with potent effects on energy balance and body weight plays an important role in defining bone architecture in growing mammals. However, major changes in body weight can also influence morphology of trabecular and cortical bone. Therefore, we examined the impact of leptin deficiency on tibia and vertebral body 3D bone architecture independent of changes in body weight. Furthermore, advances in computational 3D image analysis suggest that average morphological values may mask regional specific differences in trabecular bone thickness. The study utilized leptin-deficient Ob/Ob mice (n = 8) weight-paired to C57BL/6 (C57) control mice (n = 8) which were split into either lean or obese groups for 24 ± 2 weeks. Whole tibias and L3 vertebrae were fixed before high resolution microcomputed tomography (μCT) scanning was performed. Leptin deficiency independent of body weight reduced tibia cortical bone volume, trabecular bone volume/tissue volume, number, and mineral density. Mean tibia trabecular thickness showed no significant differences between all groups; however, significant changes in trabecular thickness were found when analyzed by region. This study demonstrates that leptin deficiency significantly impacts tibia and vertebral body trabecular and cortical bone 3D architecture independent of changes in body weight.

Increased tissue modulus and hardness in the TallyHO mouse model of early onset type 2 diabetes mellitus

Individuals with type 2 diabetes mellitus (T2DM) have a higher fracture risk compared to those without T2DM despite having higher bone mineral density (BMD). Thus, T2DM may alter other aspects of resistance to fracture beyond BMD such as bone geometry, microarchitecture, and tissue material properties. We characterized the skeletal phenotype and assessed the effects of hyperglycemia on bone tissue mechanical and compositional properties in the TallyHO mouse model of early-onset T2DM using nanoindentation and Raman spectroscopy. Femurs and tibias were harvested from male TallyHO and C57Bl/6J mice at 26 weeks of age. The minimum moment of inertia assessed by micro-computed tomography was smaller (-26%) and cortical porosity was greater (+490%) in TallyHO femora compared to controls. In three-point bending tests to failure, the femoral ultimate moment and stiffness did not differ but post-yield displacement was lower (-35%) in the TallyHO mice relative to that in C57Bl/6J age-matched controls after adjusting for body mass. The cortical bone in the tibia of TallyHO mice was stiffer and harder, as indicated by greater mean tissue nanoindentation modulus (+22%) and hardness (+22%) compared to controls. Raman spectroscopic mineral:matrix ratio and crystallinity were greater in TallyHO tibiae than in C57Bl/6J tibiae (mineral:matrix +10%, p < 0.05; crystallinity +0.41%, p < 0.10). Our regression model indicated that greater values of crystallinity and collagen maturity were associated with reduced ductility observed in the femora of the TallyHO mice. The maintenance of structural stiffness and strength of TallyHO mouse femora despite reduced geometric resistance to bending could potentially be explained by increased tissue modulus and hardness, as observed at the tibia. Finally, with worsening glycemic control, tissue hardness and crystallinity increased, and bone ductility decreased in TallyHO mice. Our study suggests that these material factors may be sentinels of bone embrittlement in adolescents with T2DM.

The effect of type 2 diabetes mellitus on the prognosis of osteoporotic vertebral compression fracture with osteoporotic fracture classification after vertebroplasty

BACKGROUND

To analyze the clinical and radiological effects of type 2 diabetes mellitus on the prognosis of osteoporotic vertebral compression fracture after percutaneous vertebroplasty, and explore the prognostic value of osteoporotic fracture classification.

METHODS

Osteoporotic vertebral compression fracture patients who received vertebroplasty from January 1, 2016 to June 30, 2021 were divided into type 2 diabetes mellitus group and control group in this retrospective cohort study. Visual analogue scale, Oswestry Disability Index, bone cement leakage, new compression fracture, anterior, middle, and posterior portion heights of vertebral body and local Cobb angle on X-ray before surgery, 2 days after surgery, 6 months, and 12 months after surgery were recorded, and the osteoporotic fracture classification was performed. P < 0.05 was set as statistical significance.

RESULTS

A total of 261 vertebral bodies were included, containing 68 in the type 2 diabetes mellitus group and 193 in the control group. There were no differences in baseline characteristics between the two groups. At 6 months after vertebroplasty, the local Cobb angle of the type 2 diabetes mellitus group was 8.29 ± 4.90° greater than that of the control group 6.05 ± 5.18° (P = 0.002). At 12 months, compared with pre-operation, the anterior portion height recovered 8.13 ± 12.90%, which was less than 12.51 ± 14.92% of the control group (P = 0.032), and 19.07 ± 16.47% of the middle portion height recovery was less than the control group's 24.63 ± 17.67% (P = 0.024). Compared with the control group, osteoporotic fracture 2 vertebral bodies of the type 2 diabetes mellitus group at 12 months postoperatively in middle portion height (14.82 ± 14.71% vs 24.78 ± 18.16%, P = 0.023) and local Cobb angle (5.65 ± 4.06° vs 3.26 ± 4.86°, P = 0.043) restored significantly worse. Besides, osteoporotic fracture 3 with type 2 diabetes mellitus restored worse in anterior portion height (5.40 ± 11.02% vs 13.57 ± 12.79%, P = 0.008), middle portion height (11.22 ± 15.53% vs 17.84 ± 12.36%, P = 0.041) and local Cobb angle (10.85 ± 3.79 vs 7.97 ± 3.83°, P = 0.002) at 12 months postoperatively. There was no difference in radiological outcomes of osteoporotic fracture 4 between the two groups.

CONCLUSIONS

The degree of fractured vertebral compression, the recovery of the height and angle obtained immediately after surgery and the clinical symptoms in type 2 diabetes mellitus patients were not different from those in the control. However, vertebral body morphology of type 2 diabetes mellitus patients was worse since the sixth month after surgery. Osteoporotic fracture classification has a good prognostic reference value for both the control and the type 2 diabetes mellitus population.

The miRNA-144-5p/IRS1/AKT axis regulates the migration, proliferation, and mineralization of osteoblasts: A mechanism of bone repair in diabetic osteoporosis

Diabetic osteoporosis (DOP) is a disorder of bone metabolism induced by multiple mechanisms. Previous studies have revealed that microRNAs (miRNAs) play crucial roles in bone metabolism. MiRNA-144-5p has been proven to participate in the regulation of osteoblast activities; however, its specific mechanism in DOP has not been elucidated. This study investigated whether high glucose (HG) inhibited osteoblasts by regulating miRNA-144-5p. Our results showed that HG inhibited bone formation not only in vivo but also in vitro. We observed that HG severely hindered the migration, proliferation and mineralization of osteoblasts, while miRNA-144-5p was upregulated by way of the cell counting kit-8 assay, wound healing assay, alkaline phosphatase (ALP) activity assay and alizarin red staining. Double luciferase reporter experiments showed that miRNA-144-5p directly targeted insulin receptor substrate 1 (IRS1). The IRS1/AKT signaling pathway is closely related to osteoblasts' migration, proliferation, and mineralization. Silencing miRNA-144-5p promoted the mRNA, and protein expression of IRS1, thereby letting the expression of total AKT down, and then preventing phosphorylation of AKT into the nucleus to regulate migration, proliferation, and mineralization genes of osteoblasts. In conclusion, this study indicated that HG regulated the migration, proliferation, and mineralization of osteoblasts via the miRNA-144-5p/IRS1/AKT axis, which suggested a possible mechanism for DOP pathology.

Improved fatigue properties, bone microstructure and blood glucose in type 2 diabetic rats with verapamil treatment

BACKGROUND

Type 2 diabetes mellitus is a global epidemic disease, which leads to a severe complication named increased bone fracture risk. This study aimed to explore if verapamil treatment could improve bone quality of type 2 diabetes mellitus.

METHODS

Rat models of control, diabetes and verapamil treatment with 4/12/24/48 mg/kg/d were established, respectively. Blood glucose was monitored during 12-week treatment, and bilateral tibiae were collected. Microstructural images of bilateral metaphyseal cancellous bone and high-resolution images of cortical bone of left tibial shafts were obtained by micro-computed tomography. Fatigue properties of bone were evaluated via cyclic compressive tests of right tibial shafts.

FINDINGS

Verapamil treatment had no significant effect on blood glucose, but blood glucose tended to decline with the increase of verapamil-treated time and dose. Compared with controls, osteocyte lacunar and canal porosities in diabetes and verapamil-treated groups were significantly decreased (P < 0.05), trabecular separation and degree of anisotropy were significantly increased (P < 0.05), while trabecular tissue mineral density, trabecular bone volume fraction and trabecular number in verapamil-treated (48 mg/kg/d) group were significantly higher than those in diabetes (P < 0.05). Compared with diabetes, initial compressive elastic moduli in verapamil-treated (12/24/48 mg/kg/d) groups were significantly increased (P < 0.05), while secant modulus degradations in verapamil-treated (24/48 mg/kg/d) groups were significantly decreased (P < 0.05).

INTERPRETATION

Verapamil could improve bone microstructure and fatigue properties in type 2 diabetic rats; and high-dose verapamil presented a significant effect on improving bone quality. These findings provided a new possibility for preventing the high bone fracture risk of type 2 diabetes mellitus in clinics.

The pathophysiology of osteoporosis in obesity and type 2 diabetes in aging women and men: The mechanisms and roles of increased bone marrow adiposity

Osteoporosis is defined as a systemic skeletal disease characterized by decreased bone mass and micro-architectural deterioration leading to increased fracture risk. Osteoporosis incidence increases with age in both post-menopausal women and aging men. Among other important contributing factors to bone fragility observed in osteoporosis, that also affect the elderly population, are metabolic disturbances observed in obesity and Type 2 Diabetes (T2D). These metabolic complications are associated with impaired bone homeostasis and a higher fracture risk. Expansion of the Bone Marrow Adipose Tissue (BMAT), at the expense of decreased bone formation, is thought to be one of the key pathogenic mechanisms underlying osteoporosis and bone fragility in obesity and T2D. Our review provides a summary of mechanisms behind increased Bone Marrow Adiposity (BMA) during aging and highlights the pre-clinical and clinical studies connecting obesity and T2D, to BMA and bone fragility in aging osteoporotic women and men.

Anatomical variation in intracortical canal network microarchitecture and its influence on bone fracture risk

Intracortical canals are a major contributor to cortical bone porosity and influence its mechanical response. Canal networks act as stress concentrators and the magnitude of which depends on the size and spatial distribution of canals. In the present study, we investigated site-dependent variation in intracortical canal network morphological indices and their effect on the mechanical response of bone. For this, mid-diaphysis of rat tibia bones were scanned using high-resolution micro-CT and morphological indices were measured for four main anatomical sites-anterior, posterior, medial and lateral. Further, a micro-finite element (μFE) model was developed to quantify the stress concentration regions in different cortices. The fracture risk was assessed using an effective strain approach. Results show that canal porosity, canal orientation and canal length are site-dependent whereas canal diameter and canal number density are independent of the site. The lateral cortex has significantly higher porosity compared to the posterior cortex (p < 0.05). The orientation of canals is found significantly different between endosteal and periosteal regions for anterior and medial quadrants. Canals are inclined at higher angles with bone axis in the endosteal region as compare to the periosteal region. The μ-FE results show that the regions with higher effective strain are concentrated around the canals. Further, failed element volume per unit bone volume is found highest for medial cortex whereas lowest for posterior cortex. The higher failed volume is associated with more radial canals in the medial cortex as compare to other cortices. The linear regression analysis shows that the volume of overstrained elements strongly depends on canal orientation (R² = 0.73, p < 0.0001) and canal porosity (R² = 0.61, p < 0.0001). The findings from this study suggest that along with vascular canal porosity, canal orientation and canal diameter can further improve the bone fracture risk assessment.

A Potential Participant in Type 2 Diabetes Bone Fragility: TIMP-1 at Sites of Osteocyte Lacunar-Canalicular System

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of bone fracture, but the bone mineral density (BMD) is typically normal or higher in such patients. Because the fracture risk is independent of reduced BMD, bone fragility in T2DM may be partially due to poor bone quality. The mechanisms triggering bone quality abnormalities in T2DM are complex, and include the accumulation of advanced glycation end-products, the increased inflammation, and low bone turnover. Matrix metalloproteinases (MMPs) in bone can hydrolyze the bone matrix. Tissue inhibitors of MMPs (TIMPs) can inhibit the activity of MMPs. Both MMPs and TIMPs participate in mediating bone quality. Among all types of TIMPs, TIMP-1 is mostly reportedly increased in the serum of T2DM patients. Because osteocytes can express TIMP-1, and osteocyte pericellular matrix influences bone quality partially regulated by perilacunar/canalicular remodeling, we hypothesized that TIMP-1 at sites of osteocyte lacunar-canalicular system is involved in T2DM bone fragility.

Bone regeneration in a mouse model of type 1 diabetes: Influence of sex, vitamin D3, and insulin

AIM

This study set forth a question: are there any differences in bone responses to insulin and/or vitamin D3 treatment in female and male type 1 diabetic (T1D) mice?

MAIN METHODS

To address this issue, a non-critical sized femur defect was created in streptozotocin (STZ)-T1D mice. Control non-diabetic and T1D female and male mice received: saline; vitamin D3; insulin; or vitamin D3 plus insulin, for 21 days.

KEY FINDINGS

Female and male T1D mice showed impaired bone healing, as indicated by histological and micro-computed tomography (micro-CT) analysis. Vitamin D3 or insulin improved the bone regeneration in T1D mice, irrespective of sex. Vitamin D3 plus insulin did not exhibit any additional effects. There were no differences regarding the numbers of TRAP-stained osteoclasts in either evaluated groups. The osteoblast-related gene osterix was upregulated in vitamin D3-treated male T1D mice, as revealed by RT-qPCR. Female T1D mice treated with vitamin D3, insulin, or vitamin D3 plus insulin presented an increased expression of insulin growth factor-1 (IGF-1) mRNA. Conversely, IGF-1 mRNA levels were reduced by the same treatments in male TD1 mice.

SIGNIFICANCE

Altogether, the results suggested that T1D similarly delayed the osseous healing in female and male mice, with beneficial effects for either vitamin D3 or insulin in T1D mice of both sexes. However, data indicated marked sex differences regarding the expression of genes implicated in bone formation, in T1D mice treated with vitamin D3 and/or insulin.

Development of HFD-Fed/Low-Dose STZ-Treated Female Sprague-Dawley Rat Model to Investigate Diabetic Bone Fragility at Different Organization Levels

Type 2 diabetes (T2D) adversely affects the normal functioning, intrinsic material properties, and structural integrity of many tissues, and bone fragility is one of them. To simulate human T2D and to investigate diabetic bone fragility, many rodent diabetic models have been developed. Still, an outbred genetically normal nonobese diabetic rat model is not available that can better simulate the disease characteristics of nonobese T2D patients, who have a high prevalence in Asia. In this study, we used a combination treatment of high-fat diet (4 weeks, 58% kcal as fat) and low-dose streptozotocin (STZ; 35 mg/kg i.p. at the end of the fourth week) to develop T2D in female Sprague-Dawley (SD) rats. After 8 weeks of the establishment of the T2D model, the femoral bones were excised after euthanizing rats (animal age approximately 21 to 22 weeks; n = 10 with T2D, n = 10 without diabetes). The bone microstructure (μCT), mechanical, and material properties (three-point bending, cyclic reference point indentation, nanoindentation), mean mineral crystallite size (XRD), bone composition (mineral-to-matrix ratio, nonenzymatic cross-link ratio [NE-xLR], Fourier transform-infrared microspectroscopy), and total fluorescent advanced glycation end products were analyzed. We found that diabetic bone had reduced whole-bone strength and compromised structural properties (μCT). The NE-xLRs were elevated in the T2D group, and strongly and negatively correlated with postyield displacement, which suggests bone fragility was caused by a lack of glycation control. Along with that, the decreased mineral-to-matrix ratio and modulus, increased indentation distance increase, and wider mineral crystallite size in the T2D group were evidence that the diabetic bone composition and material properties had changed, and bone became weaker with a tendency to easily fracture. Altogether, this model simulates the natural history and metabolic characteristics of late-stage T2D (insulin resistance and as disease progress develops, hypoinsulinemia) for nonobese young (and/or adolescent) T2D patients (Asians) and provides potential evidence of diabetic bone fragility at various organization levels. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Evaluating the Activity of Sodium Butyrate to Prevent Osteoporosis in Rats by Promoting Osteal GSK-3β/Nrf2 Signaling and Mitochondrial Function

Oxidative stress (OS) and mitochondrial dysfunction are key pathophysiological features of osteoporosis and obesity. Sodium butyrate (NaB), produced by fermentation by the gut microbiota of the large intestine, has been demonstrated to protect against OS by improving specific antioxidant enzymes and to regulate mitochondria redox homeostasis in vivo. Here, in an unblinded study, we identified femur mitochondria as the main target of the beneficial effects of NaB, consisting of reversion of bone loss and body-weight gain in obesity-prone rats. In particular, NaB promoted the activity of mitochondrial antioxidant enzymes and energy metabolism, preserved the bone microstructure and calcium homeostasis, and activated bone metabolism, as shown by increased Nrf2/GSK-3β signaling and the upregulation of PGC-1α and TFAM. In vitro experiments showed that moderate NaB treatment prevented H₂O₂-induced oxidative damage in MC3T3-E1 cells, improved osteoblast mineralization and differentiation, and maintained the balance in bone metabolism by enhancing intracellular antioxidant enzyme activity and ATP production and decreasing the ROS level. In conclusion, NaB promoted the Nrf2/GSK-3β signaling pathway and mitochondrial function and is a potential new therapeutic strategy for obesity and osteoporosis.

Exploring polyoxometalates as non-destructive staining agents for contrast-enhanced microfocus computed tomography of biological tissues

To advance clinical translation of regenerative medicine, there is, amongst others, still need for better insights in tissue development and disease. For this purpose, more precise imaging of the 3D microstructure and spatial interrelationships of the different tissues within organs is crucial. Despite being destructive towards the sample, conventional histology still is the gold standard for structural analysis of biological tissues. It is, however, limited by 2D sections of a 3D object, prohibiting full 3D structural analysis. MicroCT has proven to provide full 3D structural information of mineralized tissues and dense biomaterials. However, the intrinsic low X-ray absorption of soft tissues requires contrast-enhancing staining agents (CESAs). In a previous study, we showed that hafnium-substituted Wells-Dawson polyoxometalate (Hf-WD POM) allows simultaneous contrast-enhanced microCT (CE-CT) visualization of bone and its marrow vascularization and adiposity. In this study, other POM species have been examined for their potential as soft tissue CESAs. Four Wells-Dawson POMs, differing in structure and overall charge, were used to stain murine long bones and kidneys. Their staining potential and diffusion rate were compared to those of Hf-WD POM and phosphotungstic acid (PTA), a frequently used but destructive CESA. Monolacunary Wells-Dawson POM (Mono-WD POM) showed similar soft tissue enhancement as Hf-WD POM and PTA. Moreover, Mono-WD POM is less destructive, shows a better diffusion than PTA, and its synthesis requires less time and cost than Hf-WD POM. Finally, the solubility of Mono-WD POM was improved by addition of lithium chloride (LiCl) to the staining solution, enhancing further the soft tissue contrast. STATEMENT OF SIGNIFICANCE: To advance clinical translation of regenerative medicine, there is, amongst others, still need for better insights in tissue development and disease. For this purpose, more precise imaging of the 3D microstructure and spatial interrelationships of the different tissues within organs is crucial. Current standard structural analysis techniques (e.g. 2D histomorphometry), however, do not allow full 3D assessment. Contrast-enhanced X-ray computed tomography has emerged as a powerful 3D structural characterization tool of soft biological tissues. In this study, from a library of Wells Dawson polyoxometalates (WD POMs), we identified monolacunary WD POM together with lithium chloride, dissolved in phosphate buffered saline, as the most suitable contrast-enhancing staining agent solution for different biological tissues without tissue shrinkage.

Hyperglycemia compromises Rat Cortical Bone by Increasing Osteocyte Lacunar Density and Decreasing Vascular Canal Volume

Uncontrolled diabetes is associated with increased risk of bony fractures. However, the mechanisms have yet to be understood. Using high-resolution synchrotron micro-CT, we calculated the changes in the microstructure of femoral cortices of streptozotocin-induced hyperglycemic (STZ) Wistar Albino rats and tested the mechanical properties of the mineralized matrix by nanoindentation. Total lacunar volume of femoral cortices increased in STZ group due to a 9% increase in lacunar density. However, total vascular canal volume decreased in STZ group due to a remarkable decrease in vascular canal diameter (7 ± 0.3 vs. 8.5 ± 0.4 µm). Osteocytic territorial matrix volume was less in the STZ group (14,908 ± 689 µm³) compared with healthy controls (16,367 ± 391 µm³). In conclusion, hyperglycemia increased cellularity and lacunar density, decreased osteocyte territorial matrix, and reduced vascular girth, in addition to decreasing matrix mechanical properties in the STZ group when compared with euglycemic controls.

Birol Ay et al. use high-resolution synchrotron radiation micro-CT to calculate the changes in the microstructure of femoral cortices in STZ-induced hyperglycemic rats. They show that hyperglycemia increases lacunar density due to a reduction in osteocytic territorial matrix volume but decreases total vascular canal volume due to a decrease in canal diameter.

Reporting Guidelines, Review of Methodological Standards, and Challenges Toward Harmonization in Bone Marrow Adiposity Research. Report of the Methodologies Working Group of the International Bone Marrow Adiposity Society

The interest in bone marrow adiposity (BMA) has increased over the last decade due to its association with, and potential role, in a range of diseases (osteoporosis, diabetes, anorexia, cancer) as well as treatments (corticosteroid, radiation, chemotherapy, thiazolidinediones). However, to advance the field of BMA research, standardization of methods is desirable to increase comparability of study outcomes and foster collaboration. Therefore, at the 2017 annual BMA meeting, the International Bone Marrow Adiposity Society (BMAS) founded a working group to evaluate methodologies in BMA research. All BMAS members could volunteer to participate. The working group members, who are all active preclinical or clinical BMA researchers, searched the literature for articles investigating BMA and discussed the results during personal and telephone conferences. According to the consensus opinion, both based on the review of the literature and on expert opinion, we describe existing methodologies and discuss the challenges and future directions for (1) histomorphometry of bone marrow adipocytes, (2) ex vivo BMA imaging, (3) in vivo BMA imaging, (4) cell isolation, culture, differentiation and in vitro modulation of primary bone marrow adipocytes and bone marrow stromal cell precursors, (5) lineage tracing and in vivo BMA modulation, and (6) BMA biobanking. We identify as accepted standards in BMA research: manual histomorphometry and osmium tetroxide 3D contrast-enhanced μCT for ex vivo quantification, specific MRI sequences (WFI and H-MRS) for in vivo studies, and RT-qPCR with a minimal four gene panel or lipid-based assays for in vitro quantification of bone marrow adipogenesis. Emerging techniques are described which may soon come to complement or substitute these gold standards. Known confounding factors and minimal reporting standards are presented, and their use is encouraged to facilitate comparison across studies. In conclusion, specific BMA methodologies have been developed. However, important challenges remain. In particular, we advocate for the harmonization of methodologies, the precise reporting of known confounding factors, and the identification of methods to modulate BMA independently from other tissues. Wider use of existing animal models with impaired BMA production (e.g., Pfrt^-/-, Kit^W/W-v) and development of specific BMA deletion models would be highly desirable for this purpose.

High Glucose Downregulates Connexin 43 Expression and Its Gap Junction and Hemichannel Function in Osteocyte-like MLO-Y4 Cells Through Activation of the p38MAPK/ERK Signal Pathway

PURPOSE

Osteocyte network structure correlates with bone material quality. This network is profoundly altered in diabetic mice; however, the underlying mechanisms are unknown. The gap junction protein connexin 43 (Cx43) is necessary for normal osteocyte function and osteocyte network formation. Here, we evaluated Cx43 expression in patients with diabetes, the effect of high glucose on Cx43 expression, and the function of Cx43 gap junctions and hemichannels in osteocyte-like MLO-Y4 (MLO-Y4) cells.

PATIENTS AND METHODS

Human cortical bone samples were obtained from patients with or without type II diabetes mellitus (T2DM) who underwent arthroplasty surgery to treat osteoporosis-induced femoral neck fracture.

Cx43 expression was quantified in human cortical bone samples from both groups of patients and MLO-Y4 cells. The functions of Cx43 gap junctions and hemichannels in MLO-Y4 cells were evaluated using dye transfer and dye uptake assays, respectively. Furthermore, we evaluated levels of membrane Cx43 (mCx43), the functional form, and p38MAPK/ERK1/2 signaling, which is involved in mCx43 internalization, to characterize the mechanism of decreased Cx43 expression and gap junctions and hemichannels function.

RESULTS

Osteocyte Cx43 expression was decreased in femoral neck cortical bone samples of patients with T2DM patients compared with the non-diabetic control group. In addition, Cx43 expression was decreased in MLO-Y4 cells treated with high glucose. The functions of Cx43 gap junctions and hemichannels were inhibited in MLO-Y4 cells treated with high glucose. mCx43 expression was decreased in response to activation of p38-MAPK/ERK signaling. Inhibition of the p38-MAPK/ERK pathway partially reversed the decreases in Cx43 hemichannels and gap-junctions function.

CONCLUSION

High glucose dampened Cx43 gap junction and hemichannel function in MLO-Y4 cells by activating the p38MAPK/ERK pathway leading to subsequent mCx43 internalization.

T1-weighted MRI images accurately represent the volume and surface of architectural mineral damage of osteonecrosis of the femoral head: Comparison with high-resolution computed tomography

The potency of magnetic resonance imaging (MRI) to measure the exact extent of osteonecrosis of the femoral head (ONFH) remains uncertain. The objective of this study was to determine if the volume of necrosis assessed with MRI accurately reflects the volume of architectural mineral alterations in osteonecrosis of the femoral head by comparison with high-resolution microfocus X-ray computed tomography (HR-μCT). Fourteen male patients aged 53 years [46.2;59.0] suffering from ONFH were prospectively enrolled to undergo preoperative MRI and ex vivo analysis using HR-μCT. The necrotic zone on T1-weighted MRI scans was defined as total necrosis (delimited by the low-signal peripheral band) or dark necrosis (low-signal lesions only). The HR-μCT scans delimited outer necrosis and inner necrosis by including or excluding the sclerotic zone. The intra-class correlation coefficient (ICC) was calculated to compare the agreement of surface areas and volumes of necrosis measurements with the two techniques. There was an overall excellent agreement between MRI dark necrosis volume and HR-μCT outer necrosis volume (ICC=0.91[0.54;0.98]) while the MRI total necrosis volume showed poor agreement with both HR-μCT delimitations of necrosis volume. For surface area, agreement between MRI dark necrosis and HR-μCT delimitations was good for inner necrosis (ICC=0.70[0.21;0.9]) and moderate for outer necrosis (ICC=0.58[0.07;0.85]). This study demonstrates that measurement of the MRI lesions provides a reliable assessment of the extent of ONFH-related architectural damage.

Effects of Diabetes on Bone Material Properties

PURPOSE OF REVIEW

Individuals with type 1 and type 2 diabetes mellitus (T1DM, T2DM) have an increased risk of bone fracture compared to non-diabetic controls that is not explained by differences in BMD, BMI, or falls. Thus, bone tissue fracture resistance may be reduced in individuals with DM. The purpose of this review is to summarize work that analyzes the effects of T1DM and T2DM on bone tissue compositional and mechanical properties.

RECENT FINDINGS

Studies of clinical T2DM specimens revealed increased mineralization and advanced glycation endproduct (AGE) concentrations and significant relationships between mechanical performance and composition of cancellous bone. Specifically, in femoral cancellous tissue, compressive stiffness and strength increased with mineral content; and post-yield properties decreased with AGE concentration. In addition, cortical resistance to in vivo indentation (bone material strength index) was lower in patients with T2DM vs. age-matched non-diabetic controls, and this resistance decreased with worsening glycemic control. Recent studies on patients with T1DM and history of a prior fragility fracture found greater mineral content and concentrations of AGEs in iliac trabecular bone and correspondingly stiffer, harder bone at the nanosacle. Recent observational data showed greater AGE and mineral content in surgically retrieved bone from patients with T2DM vs. non-DM controls, consistent with reduced bone remodeling. Limited data on human T1DM bone tissue also showed higher mineral and AGE content in patients with prior fragility fractures compared to non-DM and non-fracture controls.

Glucocorticoid aggravates bone micro-architecture deterioration and skeletal muscle atrophy in mice fed on high-fat diet

High fat diet (HFD) induced obesity has deleterious effect on bone micro-architecture and is associated with low-grade chronic inflammation. Exogenous glucocorticoids (GC) are used to treat inflammatory conditions but with concomitant adverse effect on musculoskeletal system. This study aims to highlight the effect of exogenous GCs on musculoskeletal system in mice fed on HFD. Adult BALB/c mice were fed either normal chow or high fat diet and were exogenously administered with GC for 10 weeks. At the end of the study, animals were autopsied and bone, muscle, serum samples were collected for micro-CT, gene expression and histological study. HFD induced obesity resulted in deterioration in bone micro-architecture predominant in trabecular region of long bones and was significantly amplified with GC administration. Approximately, 37% and 25% loss in femoral and tibial bone volume was observed in obese animals with exogenous GC. Further, deteriorating bone pathology was apparent from reduced bone mineral density (BMD) and bone strength parameter which was correlated to alteration in osteoblast and adipocytes pool of cells in bone marrow. Transcriptional analysis of osteoblast marker genes, bone morphogenetic protein 2 (BMP-2), osteocalcin (OCN) exhibited decreased formation. Moreover, similar degeneration was observed in skeletal muscle physiology with stimulation in muscle atrophy genes atrogin-1, muscle ring finger motif-1 (MuRF-1) and inflammatory markers accompanied with intra-myocellular lipid accumulation. Thus, our results showed that detrimental effect of GC on bone and skeletal muscle is aggravated with HFD, attributed to alteration in bone marrow cell population and skeletal muscle atrophy.

High-resolution contrast-enhanced microCT reveals the true three-dimensional morphology of the murine placenta

Genetic engineering of the mouse genome identified many genes that are essential for embryogenesis. Remarkably, the prevalence of concomitant placental defects in embryonic lethal mutants is highly underestimated and indicates the importance of detailed placental analysis when phenotyping new individual gene knockouts. Here we introduce high-resolution contrast-enhanced microfocus computed tomography (CE-CT) as a nondestructive, high-throughput technique to evaluate the 3D placental morphology. Using a contrast agent, zirconium-substituted Keggin polyoxometalate (Zr-POM), the soft tissue of the placenta (i.e., different layers and cell types and its vasculature) was imaged with a resolution of 3.5 µm voxel size. This approach allowed us to visualize and study early and late stages of placental development. Moreover, CE-CT provides a method to precisely quantify placental parameters (i.e., volumes, volume fraction, ratio of different placental layers, and volumes of specific cell populations) that are crucial for statistical comparison studies. The CE-CT assessment of the 3D morphology of the placentas was validated (i) by comparison with standard histological studies; (ii) by evaluating placentas from 2 different mouse strains, 129S6 and C57BL/6J mice; and (iii) by confirming the placental phenotype of mice lacking phosphoinositol 3-kinase (PI3K)-p110α. Finally, the Zr-POM-based CE-CT allowed for inspection of the vasculature structure in the entire placenta, as well as detecting placental defects in pathologies characterized by embryonic resorption and placental fusion. Taken together, Zr-POM-based CE-CT offers a quantitative 3D methodology to investigate placental development or pathologies.

Low-Frequency Electrical Stimulation of Denervated Skeletal Muscle Retards Muscle and Trabecular Bone Loss in Aged Rats

Electrical stimulation (ES)-induced muscle contraction has multiple effects; however, mechano-responsiveness of bone tissue declines with age. Here, we investigated whether daily low-frequency ES-induced muscle contraction treatment reduces muscle and bone loss and ameliorates bone fragility in early-stage disuse musculoskeletal atrophy in aged rats. Twenty-seven-month-old male rats were assigned to age-matched groups comprising the control (CON), sciatic nerve denervation (DN), or DN with direct low-frequency ES (DN+ES) groups. The structural and mechanical properties of the trabecular and cortical bone of the tibiae, and the morphological and functional properties of the tibialis anterior (TA) muscles were assessed one week after DN. ES-induced muscle contraction force mitigated denervation-induced muscle and trabecular bone loss and deterioration of the mechanical properties of the tibia mid-diaphysis, such as the stiffness, but not the maximal load, in aged rats. The TA muscle in the DN+ES group showed significant improvement in the myofiber cross-sectional area and muscle force relative to the DN group. These results suggest that low-frequency ES-induced muscle contraction treatment retards trabecular bone and muscle loss in aged rats in early-stage disuse musculoskeletal atrophy, and has beneficial effects on the functional properties of denervated skeletal muscle.

Type 2 Diabetes Mellitus Increases the Risk to Hip Fracture in Postmenopausal Osteoporosis by Deteriorating the Trabecular Bone Microarchitecture and Bone Mass

T2DM is linked to an increase in the fracture rate as compared to the nondiabetic population even with normal or raised bone mineral density (BMD). Hence, bone quality plays an important role in the pathogenesis of skeletal fragility due to T2DM. This study analyzed the changes in the trabecular bone microstructure due to T2DM at various time points in ovariectomized and nonovariectomized rats. Animals were divided into four groups: (I) control (sham), (II) diabetic (sham), (III) ovariectomized, and (IV) ovariectomized with diabetes. The trabecular microarchitecture of the femoral head was characterized using a micro-CT. The differences between the groups were analyzed at 8, 10, and 14 weeks of the onset of T2DM using a two-way analysis of variance and by post hoc multiple comparisons. The diabetic group with and without ovariectomies demonstrated a significant increase in trabecular separation and a decrease in bone volume fraction, trabecular number, and thickness. BMD decreased in ovariectomized diabetic animals at 14 weeks of the onset of T2DM. No significant change was found in connectivity density and degree of anisotropy among groups. The structural model index suggested a change towards a weaker rod-like microstructure in diabetic animals. The data obtained suggested that T2DM affects the trabecular structure within a rat's femoral heads negatively and changes are most significant at a longer duration of T2DM, increasing the risk to hip fractures.

Relationship between the Second to Fourth Finger Length Ratio and Calcaneus Quantitative Ultrasound

This study aimed to characterize the relationship between the ratio of the length of the second and fourth fingers (2D:4D value) and the speed of sound of the calcaneus by quantitative ultrasound (QUS-SOS) in undergraduate female students. We recruited 138 young women with a mean age of 19.6 ± 1.4 years. The participants' calcaneus QUS-SOS was measured using an ultrasound bone densitometer. We also measured the participants' weight, height, and grip strength. A self-reported questionnaire was used to obtain information on participants' secondary sexual characteristics, and exercise habits. The present study showed that the 2D:4D value of both hands was significantly correlated with the calcaneus QUS-SOS. The 2D:4D value of the left hand was also positively associated with the calcaneus QUS-SOS results in several respects. These findings suggest that the 2D:4D value may be useful for the screening of risk for a low bone quality in undergraduate female students.

Unraveling the compromised biomechanical performance of type 2 diabetes- and Roux-en-Y gastric bypass bone by linking mechanical-structural and physico-chemical properties

Type 2 diabetes mellitus (T2DM) is a metabolic disorder associated with obesity and hyperglycemia. Roux-en-Y gastric bypass (RYGB) surgery is a common treatment for severely obese patients and T2DM. Both RYGB and T2DM are linked to increased skeletal fragility, though the exact mechanisms are poorly understood. Our aim was to characterize the structural, mechanical and compositional properties of bones from diet-induced obese and RYGB-treated obese (bypass) mice to elucidate which the exact factors are contributing to the increased skeletal fragility. To achieve this, a combinatory approach including microfocus X-ray computed tomography, 3-point bending, finite element modeling and Raman spectroscopy, was used. Compared to aged-matched lean controls, the obese mice displayed decreased cortical thickness, trabecular bone loss, decreased stiffness and increased Young’s modulus. For the bypass mice, these alterations were even more pronounced, and additionally they showed low mineral-to-matrix ratio in the cortical endosteal area. Accumulation of the advanced glycation end-product (AGE) pentosidine was found in the cortex of obese and bypass groups and this accumulation was correlated with an increased Young’s modulus. In conclusion, we found that the increased fracture risk in T2DM- and post-RYGB bones is mainly driven by accumulation of AGEs and macro-structural alterations, generating biomechanical dysfunctionality.

The Impact of Type 2 Diabetes on Bone Fracture Healing

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease known by the presence of elevated blood glucose levels. Nowadays, it is perceived as a worldwide epidemic, with a very high socioeconomic impact on public health. Many are the complications caused by this chronic disorder, including a negative impact on the cardiovascular system, kidneys, eyes, muscle, blood vessels, and nervous system. Recently, there has been increasing evidence suggesting that T2DM also adversely affects the skeletal system, causing detrimental bone effects such as bone quality deterioration, loss of bone strength, increased fracture risk, and impaired bone healing. Nevertheless, the precise mechanisms by which T2DM causes detrimental effects on bone tissue are still elusive and remain poorly studied. The aim of this review was to synthesize current knowledge on the different factors influencing the impairment of bone fracture healing under T2DM conditions. Here, we discuss new approaches used in recent studies to unveil the mechanisms and fill the existing gaps in the scientific understanding of the relationship between T2DM, bone tissue, and bone fracture healing.

Sost Deficiency does not Alter Bone's Lacunar or Vascular Porosity in Mice

SCLEROSTIN (Sost) is expressed predominantly in osteocytes acting as a negative regulator of bone formation. In humans, mutations in the SOST gene lead to skeletal overgrowth and increased bone mineral density, suggesting that SCLEROSTIN is a key regulator of bone mass. The function of SCLEROSTIN as an inhibitor of bone formation is further supported by Sost knockout (KO) mice which display a high bone mass with elevated bone formation. Previous studies have indicated that Sost exerts its effect on bone formation through Wnt-mediated regulation of osteoblast differentiation, proliferation, and activity. Recent in vitro studies have also suggested that SCLEROSTIN regulates angiogenesis and osteoblast-to-osteocyte transition. Despite this wealth of knowledge of the mechanisms responsible for SCLEROSTIN action, no previous studies have examined whether SCLEROSTIN regulates osteocyte and vascular configuration in cortices of mouse tibia. Herein, we image tibiae from Sost KO mice and their wild-type (WT) counterparts with high-resolution CT to examine whether lack of SCLEROSTIN influences the morphometric properties of lacunae and vascular canal porosity relating to osteocytes and vessels within cortical bone. Male Sost KO and WT mice (n = 6/group) were sacrificed at 12 weeks of age. Fixed tibiae were analyzed using microCT to examine cortical bone mass and architecture. Then, samples were imaged by using benchtop and synchrotron nano-computed tomography at the tibiofibular junction. Our data, consistent with previous studies show that, Sost deficiency leads to significant enhancement of bone mass by cortical thickening and bigger cross-sectional area and we find that this occurs without modifications of tibial ellipticity, a measure of bone shape. In addition, our data show that there are no significant differences in any lacunar or vascular morphometric or geometric parameters between Sost KO mouse tibia and WT counterparts. We, therefore, conclude that the significant increases in bone mass induced by Sost deficiency are not accompanied by any significant modification in the density, organization, or shape of osteocyte lacunae or vascular content within the cortical bone. These data may imply that SCLEROSTIN does not modify the frequency of osteocytogenic recruitment of osteoblasts to initiate terminal osteocytic differentiation in mice.

Chronic Hyperglycemia Modulates Rat Osteoporotic Cortical Bone Microarchitecture into Less Fragile Structures

There is controversy concerning the diabetes impact on bone quality, notorious in type 2 diabetic postmenopausal women. One pointed cause might be uncontrolled glycemia. In this study, the effect of chronic hyperglycemia in bone turnover, morphology, and biomechanics was evaluated in female Wistar rats in the presence/absence of estrogens (ovariectomy). Animals (n = 28) were divided into sham, ovariectomized (OVX), hyperglycemic (streptozotocin 40 mg/kg, single-dose i.p.-STZ), and hyperglycemic-ovariectomized (STZ + OVX) animals. Blood biomarkers were estimated 60 days postovariectomy. Body weight, vertebral microarchitecture (L4-histomorphometry), femur biomechanical properties (bending tests), tibia ultrastructure (scanning electron microscopy), and femur and urinary calcium (atomic absorption) were also evaluated. The increased PINP/CTX ratio of hyperglycemic animals and the similar ratio between STZ + OVX and healthy animals contrasting with the lower ratio of OVX (in line with its histomorphometric data) suggest a tendency for improved bone formation in hyperglycemic-ovariectomized animals. The increased tibia medullar canal, which contrasts with the unaffected cortical thickness of both hyperglycemic groups while that of OVX decreased, was associated to the increased stiffness and strength of STZ + OVX bones compared to those of OVX, in line with the observed ultrastructure. Concluding, chronic hyperglycemia in ovariectomized female rats causes bone morphological changes that translate positively in the ultrastructure and mechanical properties of cortical bones.

Electrical Stimulation of Denervated Rat Skeletal Muscle Retards Capillary and Muscle Loss in Early Stages of Disuse Atrophy

The purpose of the present study is to investigate the effects of low-frequency electrical muscle stimulation (ES) on the decrease in muscle mass, fiber size, capillary supply, and matrix metalloproteinase (MMP) immunoreactivity in the early stages of denervation-induced limb disuse. Direct ES was performed on the tibialis anterior muscle following denervation in seven-week-old male rats. The rats were divided into the following groups: control (CON), denervation (DN), and denervation with direct ES (DN + ES). Direct ES was performed at an intensity of 16 mA and a frequency of 10 Hz for 30 min per day, six days a week, for one week. We performed immunohistochemical staining to determine the expression of dystrophin, CD34, and MMP-2 in transverse sections of TA muscles. The weight, myofiber cross-sectional area (FCSA), and capillary-to-fiber (C/F) ratio of the tibialis anterior (TA) muscle were significantly reduced in the DN group compared to the control and DN + ES groups. The MMP-2 positive area was significantly greater in DN and DN + ES groups compared to the control group. These findings suggest beneficial effects of direct ES in reducing muscle atrophy and capillary regression without increasing MMP-2 immunoreactivity in the early stages of DN-induced muscle disuse in rat hind limbs.