Three-dimensional cortical bone microstructure in a rat model of hypoxia-induced growth retardation

Gestational intermittent hypoxia reduces mandibular growth with decreased Sox9 expression and increased Hif1a expression in male offspring rats

Introduction

Maternal obstructive sleep apnea (OSA) during pregnancy is the risk factor for impaired fetal growth with low birth weight in the offspring. However, it is unclear whether gestational intermittent hypoxia (IH, a hallmark of maternal OSA) has long-term detrimental consequences on the skeletal development of offspring. This study aimed to investigate postnatal maxillofacial bone growth and cartilage metabolism in male and female offspring that were exposed to gestational IH.

Methods

Mother rats underwent IH at 20 cycles/h (nadir, 4% O2; peak, 21% O2; 0% CO2) for 8 h per day during gestational days (GD) 7-20, and their male and female offspring were analyzed postnatally at 5 and 10 weeks of age. All male and female offspring were born and raised under normoxic conditions.

Results

There was no significant difference in whole-body weight and tibial length between the IH male/female offspring and their control counterparts. In contrast, the mandibular condylar length was significantly shorter in the IH male offspring than in the control male offspring at 5 and 10 weeks of age, while there was no significant difference in the female offspring. Real-time polymerase chain reaction (PCR) showed that gestational IH significantly downregulated the mRNA level of SOX9 (a chondrogenesis marker) and upregulated the mRNA level of HIF-1α (a hypoxia-inducible factor marker) in the mandibular condylar cartilage of male offspring, but not in female offspring.

Conclusion

Gestational IH induced underdeveloped mandibular ramus/condyles and reduced mRNA expression of SOX9, while enhancing mRNA expression of HIF-1α in a sex-dependent manner.

Type 2 diabetes and bone fragility in children and adults

Type 2 diabetes (T2D) is a global epidemic disease. The prevalence of T2D in adolescents and young adults is increasing alarmingly. The mechanisms leading to T2D in young people are similar to those in older patients. However, the severity of onset, reduced insulin sensitivity and defective insulin secretion can be different in subjects who develop the disease at a younger age. T2D is associated with different complications, including bone fragility with consequent susceptibility to fractures. The purpose of this systematic review was to describe T2D bone fragility together with all the possible involved pathways. Numerous studies have reported that patients with T2D show preserved, or even increased, bone mineral density compared with controls. This apparent paradox can be explained by the altered bone quality with increased cortical bone porosity and compr-omised mechanical properties. Furthermore, reduced bone turnover has been described in T2D with reduced markers of bone formation and resorption. These findings prompted different researchers to highlight the mechanisms leading to bone fragility, and numerous critical altered pathways have been identified and studied. In detail, we focused our attention on the role of microvascular disease, advanced glycation end products, the senescence pathway, the Wnt/β-catenin pathway, the osteoprotegerin/receptor-activator of nuclear factor kappa B ligand, osteonectin and fibroblast growth factor 23. The understanding of type 2 myeloid bone fragility is an important issue as it could suggest possible interventions for the prevention of poor bone quality in T2D and/or how to target these pathways when bone disease is clearly evident.

Bone fragility in diabetes: novel concepts and clinical implications

Increased fracture risk represents an emerging and severe complication of diabetes. The resulting prolonged immobility and hospitalisations can lead to substantial morbidity and mortality. In type 1 diabetes, bone mass and bone strength are reduced, resulting in up to a five-times greater risk of fractures throughout life. In type 2 diabetes, fracture risk is increased despite a normal bone mass. Conventional dual-energy x-ray absorptiometry might underestimate fracture risk, but can be improved by applying specific adjustments. Bone fragility in diabetes can result from cellular abnormalities, matrix interactions, immune and vascular changes, and musculoskeletal maladaptation to chronic hyperglycaemia. This Review summarises how the bone microenvironment responds to type 1 and type 2 diabetes, and the mechanisms underlying fragility fractures. We describe the value of novel imaging technologies and the clinical utility of biomarkers, and discuss current and future therapeutic approaches that protect bone health in people with diabetes.

Zebrafish as an Emerging Model for Osteoporosis: A Primary Testing Platform for Screening New Osteo-Active Compounds

Osteoporosis is metabolic bone disease caused by an altered balance between bone anabolism and catabolism. This dysregulated balance is responsible for fragile bones that fracture easily after minor falls. With an aging population, the incidence is rising and as yet pharmaceutical options to restore this imbalance is limited, especially stimulating osteoblast bone-building activity. Excitingly, output from large genetic studies on people with high bone mass (HBM) cases and genome wide association studies (GWAS) on the population, yielded new insights into pathways containing osteo-anabolic players that have potential for drug target development. However, a bottleneck in development of new treatments targeting these putative osteo-anabolic genes is the lack of animal models for rapid and affordable testing to generate functional data and that simultaneously can be used as a compound testing platform. Zebrafish, a small teleost fish, are increasingly used in functional genomics and drug screening assays which resulted in new treatments in the clinic for other diseases. In this review we outline the zebrafish as a powerful model for osteoporosis research to validate potential therapeutic candidates, describe the tools and assays that can be used to study bone homeostasis, and affordable (semi-)high-throughput compound testing.

Is Diabetic Skeletal Fragility Associated with Microvascular Complications in Bone?

PURPOSE OF REVIEW

The objective of this literature review is to determine whether there are indications that microvascular complications occur in diabetic bone. Evidence definitively linking diabetic skeletal fragility with microvascular complications in bone remains elusive.

RECENT FINDINGS

Circumstantial evidence, some recent and some lost to time, suggests that atherosclerotic vascular diseases such as peripheral arterial disease cause poor blood perfusion of bone and subsequent hypoxia and contribute to low bone density and high cortical porosity, patterns similar to some recently observed in diabetic subjects. Evidence also exists to suggest that potentially anti-angiogenic conditions, such as impaired vascular endothelial growth factor (VEGF) signaling, predominate in diabetic bone. Microvascular complications may contribute, in part, to diabetic skeletal fragility but data supporting this interpretation are primarily circumstantial at this time. This review highlights gaps in our knowledge and hopefully spurs further discussions and research on this topic.

Deciduous teeth structure changes in congenital heart disease: Ultrastructure and microanalysis

OBJECTIVES

Oral manifestations recorded for congenital heart disease (CHD) patients include teeth hypoplasia and high caries incidence. These observations suggested that the enamel and dentin of the teeth may be altered, increasing the risk for caries incidence. This study was designed to investigate the effect of CHD on the ultrastructure and composition of deciduous sound teeth.

METHODS

Thirty sound exfoliated human deciduous incisor teeth were selected for this study. They were divided into three groups, Group I (control) from healthy children (n = 6), Group II from acyanotic CHD children (n = 12) and Group III from cyanotic CHD children (n = 12). Each tooth was longitudinally sectioned, providing enough specimens for ultrastructure and chemical analysis using ESEM/EDAX. The results of ESEM/EDAX and dentin image analysis were statistically analyzed using one-way ANOVA test followed by Tukey's test.

RESULTS

Enamel of groups II and III showed increased dissolution and irregular orientation of enamel prisms. Orifices of dentinal tubules demonstrated widening and irregular outlines, also lateral branching increased markedly. Image analysis of dentin ESEM photomicrographs showed a highly significant increase in surface area of dentinal tubules. Decrease in calcium (Ca) and phosphorus (P) levels was statistically significant (P < 0.05).

CONCLUSION

CHDs affect the structure and chemical composition of deciduous teeth.

Subtraction micro-computed tomography of angiogenesis and osteogenesis during bone repair using synchrotron radiation with a novel contrast agent

Quantitative three-dimensional (3D) imaging of angiogenesis during bone repair remains an experimental challenge. We developed a novel contrast agent containing 0.07- to 0.1-μm particles of zirconium dioxide (ZrCA) and established subtraction μCT using synchrotron radiation (sSRCT) for quantitative imaging of angiogenesis and bone repair. This method was applied to a rat model of tibial bone repair 3 days (DAY3; n = 2), 5 days (DAY5; n = 8), or 10 days (DAY10; n = 8) after drill-hole injury. Using the same drill-hole defect model, its potential use was illustrated by comparison of bone repair between hindlimbs subjected to mechanical unloading (n = 6) and normal weight bearing (n = 6) for 10 days. Following vascular casting with ZrCA, the defect site was scanned with 17.9- and 18.1-keV X-rays. In the latter, image contrast between ZrCA-filled vasculature and bone was enhanced owing to the sharp absorption jump of zirconium dioxide at 18.0 keV (k-edge). The two scan data sets were reconstructed with 2.74-μm voxel resolution, registered by mutual information, and digitally subtracted to extract the contrast-enhanced vascular image. K2HPO4 phantom solutions were scanned at 17.9 keV for quantitative evaluation of bone mineral. Angiogenesis had already started, but new bone formation was not found on DAY3. New bone emerged near the defect boundary on DAY5 and took the form of trabecular-like structure invaded by microvessels on DAY10. Vascular and bone volume fractions, blood vessel and bone thicknesses, and mineralization were higher on DAY10 than on DAY5. All these parameters were found to be decreased after 10 days of hindlimb unloading, indicating the possible involvement of angiogenesis in bone repair impairment caused by reduced mechanical stimuli. In conclusion, the combined technique of sSRCT and ZrCA vascular casting is suitable for quantitative 3D imaging of angiogenesis and its surrounding bone regeneration. This method will be useful for better understanding the linkage between angiogenesis and bone repair.

Age-related changes in the 3D hierarchical structure of rat tibia cortical bone characterized by high-resolution micro-CT

Three-dimensional hierarchical structure of female Sprague-Dawley rat tibia cortical bone was characterized as a function of age (3, 12, 32, 42, 60, and 72 wk) using a high-resolution micro-computed tomography. At the whole bone level, 3-wk samples exhibited statistically significant differences in a mean total tissue volume, mean cortical bone volume, mean cortical bone volume density, mean periosteal perimeter, and mean cortical thickness (P < 0.05) compared with all other ages. At the tissue level, there was a statistically significant increase in a mean canal number density and a decrease in a mean canal volume and diameter between 3-wk and 12-wk samples. While no significant variations were found between mean canal lengths, there was a dependence of mean canal orientation on age. At the cell level, there were no statistically significant differences in a lacuna number density and a lacuna volume density, and all lacunae element-based parameters displayed no dependence on age across age. In addition, at the microstructural level, the cannular indexes were reported separately for anterior, posterior, medial, and lateral anatomic regions. From 3 to 32 wk of age, there existed significantly fewer canals per volume of bone in the medial region of the tibia vs. other cross-sectional quadrants. Although there were changes with age, there were no statistically significant differences in the mean canal volume, mean canal diameter, and mean canal length between the four anatomic regions.

Effects of vitamin K on the morphometric and material properties of bone in the tibiae of growing rats

Suboptimal vitamin K nutriture is evident during rapid growth. We aimed to determine whether vitamin K(2) (menaquinone-4 [MK-4]) supplementation is beneficial to bone structure and intrinsic bone tissue properties in growing rats. Male Wistar rats (5 weeks old) were assigned to either a control diet (n = 8) or an MK-4-supplemented diet (22 mg d(-1) kg(-1) body weight, n = 8). After a 9-week feeding period, we determined the serum concentration ratio of undercarboxylated osteocalcin to γ-carboxylated osteocalcin and the urinary deoxypyridinoline level. All rats were then euthanized, and their tibiae were analyzed by micro-computed tomography for trabecular architecture and synchrotron radiation micro-computed tomography for cortical pore structure and mineralization. Fourier transform infrared microspectroscopy and a nanoindentation test were performed on the cortical midlayers of the anterior and posterior cortices to assess bone tissue properties. Neither body weight nor tibia length differed significantly between the 2 groups. Dietary MK-4 supplementation decreased the ratio of undercarboxylated osteocalcin to γ-carboxylated osteocalcin but did not affect deoxypyridinoline, indicating a positive effect on bone formation but not bone resorption. Trabecular volume fraction and thickness were increased by MK-4 (P < .05). Neither the cortical pore structure nor mineralization was affected by MK-4. On the other hand, MK-4 increased mineral crystallinity, collagen maturity, and hardness in both the anterior and posterior cortices (P < .05). These data indicate the potential benefit of MK-4 supplementation during growth in terms of enhancing bone quality.

Quantitative second-harmonic generation microscopy for imaging porcine cortical bone: comparison to SEM and its potential to investigate age-related changes

We propose the use of second-harmonic generation (SHG) microscopy for imaging collagen fibers in porcine femoral cortical bone. The technique is compared with scanning electron microscopy (SEM). SHG microscopy is shown to have excellent potential for bone imaging primarily due its intrinsic specificity to collagen fibers, which results in high contrast images without the need for specimen staining. Furthermore, this technique's ability to quantitatively assess collagen fiber organization is evaluated through an exploratory examination of bone structure as a function of age, from very young to mature bone. In particular, four different age groups: 1 month, 3.5 months, 6 months, and 30 months, were studied. Specifically, we employ the recently developed Fourier transform-second harmonic generation (FT-SHG) imaging technique for the quantification of the structural changes, and observe that as the bone develops, there is an overall reduction in porosity, the number of osteons increases, and the collagen fibers become comparatively more organized. It is also observed that the variations in structure across the whole cross-section of the bone increase with age. The results of this work show that quantitative SHG microscopy can serve as a valuable tool for evaluating the structural organization of collagen fibers in ex vivo bone studies.