Quantitative analysis of three-dimensional complexity and connectivity changes in trabecular microarchitecture in relation to aging, menopause, and inflammation

The Hematopoietic Bone Marrow Niche Ecosystem

The bone marrow (BM) microenvironment, also called the BM niche, is essential for the maintenance of fully functional blood cell formation (hematopoiesis) throughout life. Under physiologic conditions the niche protects hematopoietic stem cells (HSCs) from sustained or overstimulation. Acute or chronic stress deregulates hematopoiesis and some of these alterations occur indirectly via the niche. Effects on niche cells include skewing of its cellular composition, specific localization and molecular signals that differentially regulate the function of HSCs and their progeny. Importantly, while acute insults display only transient effects, repeated or chronic insults lead to sustained alterations of the niche, resulting in HSC deregulation. We here describe how changes in BM niche composition (ecosystem) and structure (remodeling) modulate activation of HSCs in situ. Current knowledge has revealed that upon chronic stimulation, BM remodeling is more extensive and otherwise quiescent HSCs may be lost due to diminished cellular maintenance processes, such as autophagy, ER stress response, and DNA repair. Features of aging in the BM ecology may be the consequence of intermittent stress responses, ultimately resulting in the degeneration of the supportive stem cell microenvironment. Both chronic stress and aging impair the functionality of HSCs and increase the overall susceptibility to development of diseases, including malignant transformation. To understand functional degeneration, an important prerequisite is to define distinguishing features of unperturbed niche homeostasis in different settings. A unique setting in this respect is xenotransplantation, in which human cells depend on niche factors produced by other species, some of which we will review. These insights should help to assess deviations from the steady state to actively protect and improve recovery of the niche ecosystem in situ to optimally sustain healthy hematopoiesis in experimental and clinical settings.

A healthy dose of chaos: Using fractal frameworks for engineering higher-fidelity biomedical systems

Optimal levels of chaos and fractality are distinctly associated with physiological health and function in natural systems. Chaos is a type of nonlinear dynamics that tends to exhibit seemingly random structures, whereas fractality is a measure of the extent of organization underlying such structures. Growing bodies of work are demonstrating both the importance of chaotic dynamics for proper function of natural systems, as well as the suitability of fractal mathematics for characterizing these systems. Here, we review how measures of fractality that quantify the dose of chaos may reflect the state of health across various biological systems, including: brain, skeletal muscle, eyes and vision, lungs, kidneys, tumours, cell regulation, skin and wound repair, bone, vasculature, and the heart. We compare how reports of either too little or too much chaos and fractal complexity can be damaging to normal biological function, and suggest that aiming for the healthy dose of chaos may be an effective strategy for various biomedical applications. We also discuss rising examples of the implementation of fractal theory in designing novel materials, biomedical devices, diagnostics, and clinical therapies. Finally, we explain important mathematical concepts of fractals and chaos, such as fractal dimension, criticality, bifurcation, and iteration, and how they are related to biology. Overall, we promote the effectiveness of fractals in characterizing natural systems, and suggest moving towards using fractal frameworks as a basis for the research and development of better tools for the future of biomedical engineering.

Fractal Dimension Analysis of High-Resolution X-Ray Phase Contrast Micro-Tomography Images at Different Threshold Levels in a Mouse Spinal Cord

Fractal analysis is a powerful method for the morphological study of complex systems that is increasingly applied to biomedical images. Spatial resolution and image segmentation are crucial for the discrimination of tissue structures at the multiscale level. In this work, we have applied fractal analysis to high-resolution X-ray phase contrast micro-tomography (XrPCμT) images in both uninjured and injured tissue of a mouse spinal cord. We estimated the fractal dimension (FD) using the box-counting method on tomographic slices segmented at different threshold levels. We observed an increased FD in the ipsilateral injured hemicord compared with the contralateral uninjured tissue, which was almost independent of the chosen threshold. Moreover, we found that images exhibited the highest fractality close to the global histogram threshold level. Finally, we showed that the FD estimate largely depends on the image histogram regardless of tissue appearance. Our results demonstrate that the pre-processing of XrPCμT images is critical to fractal analysis and the estimation of FD.

Systematic analysis of lncRNAs, miRNAs and mRNAs for the identification of biomarkers for osteoporosis in the mandible of ovariectomized mice

Osteoporosis is a complex and multifactorial disease caused by an imbalance between bone formation and resorption. Post-menopausal women with endogenous estrogen deficiency suffer from systemic bone loss and osteoporosis, and are at high risk of this affecting the jaw bones. MicroRNAs (miRNAs or miRs) have been implicated in the mechanisms of metabolic bone diseases and are expressed at differential levels in alveolar bone following ovariectomy. In the present study, we systematically analyzed the expression profiles of miRNAs, mRNAs and long non-coding RNA (lncRNAs) in the mandible of ovariectomized (OVX) mice. A complex miRNA-mRNA-lncRNA regulatory network was constructed based on differentially expressed RNAs. Two core differentially expressed genes (DEGs), namely, LRP2 binding protein (Lrp2bp) and perilipin 4 (Plin4), significantly influenced the network targeted by differentially expressed miRNAs. Moreover, peroxisome proliferator-activated receptor (PPAR) and insulin signaling pathways were significantly dysregulated in the mandible of OVX mice. Several differentially expressed lncRNAs were also implicated in the two signaling pathways, which influenced mandible development by forming competing endogenous RNA. On the whole, our data indicate that the comprehensive analysis of miRNAs, mRNAs and lncRNAs provides insight into the pathogenesis of estrogen deficiency-induced osteoporosis in the mandible. This study proposes potential biomarkers for diagnosis or therapeutic targets for osteoporosis which may aid in the development of novel drugs for the treatment of osteoporosis.

The Cooccurrence of Obesity, Osteoporosis, and Sarcopenia in the Ovariectomized Rat: A Study for Modeling Osteosarcopenic Obesity in Rodents

Background

Obesity, osteoporosis, and sarcopenia may individually occur due to age-related gradual alterations in body composition. This study investigates the cooccurrence of these age-related diseases in female animals with low levels of ovarian hormone in the absence of complex multifactorial process of chronological aging.

Methods

Thirty-six 5- and 10-month-old female rats were chosen to model pre- and postmenopausal women, respectively. Rats were divided into three treatment groups in each age category—sham, ovariectomized (ovx), and ovx + E₂ (17β-estradiol, 10 μg/kg)—and were pair-fed. Volunteer wheel running activity, body composition, bone microstructure, serum C-telopeptides of type I collagen, bone specific alkaline phosphatase, E₂, and gastrocnemius and soleus muscles were analyzed.

Results

The cooccurrence of osteoporosis, sarcopenia, and obesity was observed in the older ovx rats associated with a significant (p < 0.05) increased fat mass (30%), bone loss (9.6%), decreased normalized muscle mass-to-body-weight ratio (10.5%), and a significant decrease in physical activity (57%). The ratio of tibial bone mineral density to combined muscle mass was significantly decreased in both ovx age categories.

Conclusion

Ovariectomized rat could be used as an experimental model to examine the effect of loss of ovarian hormones, while controlling for energy intake and expenditure, to conduct obesity and body composition translational research in females without the confounding effect of genetic background.

Effects of Astragalus membranaceus with supplemental calcium on bone mineral density and bone metabolism in calcium-deficient ovariectomized rats

It has been reported that Astragalus membranaceus, an Asian traditional herb, has an estrogenic effect in vitro. To examine the possible role of A. membranaceus extract with supplemental calcium (Ca) on bone status in calcium-deficient (LCa) ovariectomized (OVX) rats, a total of 48 female rats were divided into six groups: (1) normal control, (2) sham operation with LCa (sham-LCa), (3) OVX with LCa (OVX-LCa), (4) A. membranaceus supplementation with OVX-LCa (OVX-MLCa), (5) Ca supplementation with OVX (OVX-Ca), and (6) A. membranaceus and Ca supplementation with OVX (OVX-MCa). A. membranaceus ethanol extract (500 mg/kg BW) and/or Ca (800 mg/kg BW) were administered orally for 8 weeks along with a Ca-deficient diet. Results revealed that Ca supplementation with or without A. membranaceus extract significantly improved bone mineral density, biomechanical strength, and ash weight of the femur and tibia in OVX rats. High Ca with A. membranaceus combination supplementation significantly increased the ash weight of the femur and tibia and decreased urinary Ca excretion compared with supplementation of Ca alone. Uterine weight was not changed by A. membranaceus administration in OVX rats. These results suggest that A. membranaceus extract combined with supplemental Ca may be more protective against the Ca loss of bone than A. membranaceus or supplementation of Ca alone in calcium-insufficient postmenopausal women.

Relationship between age, skeletal site, and time post-ovariectomy on bone mineral and trabecular microarchitecture in rats

The ovariectomized (OVX) rat is widely used in osteoporosis research, but no standard model exists. The individual effects of rat age, skeletal site, and time post-ovariectomy (post-OVX) on bone have been examined. However, the relationship between them is not yet fully explored. This study examined how various combinations of rat age, skeletal site, and time post-OVX affect bone mineral and microarchitecture. The rats used were 12 (n = 28), 24 (n = 28), and 44 (n = 31) weeks old. In each age group, approximately half underwent OVX and other half underwent Sham surgeries. Bone mineral (content and density) and trabecular morphology was assessed at 2, 5, 10, 15, 20, 25, and 30 weeks post-surgery. Sites examined included the proximal tibia, spine, distal femur, and proximal femur. Overall, the proximal tibia showed the earliest and greatest differences between OVX and Sham groups. The 24-week-old group showed the best osteoporotic response. The 12-week-old group showed growth effects, whilst the 44-week-old group showed aging effects. The response of certain sites to OVX was also found to depend on the rat age used. These findings may aid in explaining discrepancies reported in the literature as well as synergistic combinations that may signify advanced conditions. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:189-196, 2011.

Micro-computed tomography and histologic evaluation of the interface of hydrogel expander and underlying bone: influence of pressure distributors on bone resorption

PURPOSE

Tissue expanders lead to changes in the underlying bone and can cause bone resorption. We investigated whether the insertion of mechanical devices that distribute the load on the bone can influence these effects.

MATERIALS AND METHODS

A total of 28 Lewis rats were assigned to 1 of 4 groups. Hydrogel expanders were placed subcutaneously either directly on the calvaria, on titanium mesh, or on a titanium plate. The fourth group of rats served as the controls. The bone quality and thickness were assessed beneath, and at the periphery of, the expanders using micro-computed tomography and histologic examination.

RESULTS

Micro-computed tomography images were obtained before and 21 days after insertion. The images revealed a significant decrease in hydroxyapatite density beneath the expanders in the group with only expanders. This decrease was reduced with the use of titanium mesh and completely prevented with the use of titanium plates. Histologic examination revealed a significant decrease in bone density and marked lacunae beneath the hydrogel expanders in the group with only expanders. In contrast, the titanium mesh decreased the size of the lacunae, and the titanium plates completely prevented both the formation of lacunae and the decrease in bone thickness.

CONCLUSION

The bone resorption caused by hydrogel expanders can be diminished using titanium mesh and completely prevented by the insertion of a titanium plate.

Micro computed tomography for vascular exploration

Vascular exploration of small animals requires imaging hardware with a very high spatial resolution, capable of differentiating large as well as small vessels, in both in vivo and ex vivo studies. Micro Computed Tomography (micro-CT) has emerged in recent years as the preferred modality for this purpose, providing high resolution 3D volumetric data suitable for analysis, quantification, validation, and visualization of results. The usefulness of micro-CT, however, can be adversely affected by a range of factors including physical animal preparation, numerical quantification, visualization of results, and quantification software with limited possibilities. Exacerbating these inherent difficulties is the lack of a unified standard for micro-CT imaging. Most micro-CT today is aimed at particular applications and the software tools needed for quantification, developed mainly by imaging hardware manufacturers, lack the level of detail needed to address more specific aims. This review highlights the capabilities of micro-CT for vascular exploration, describes the current state of imaging protocols, and offers guidelines and suggestions aimed at making micro-CT more accurate, replicable, and robust.

Changes of microstructure and mineralized tissue in the middle and late phase of osteoporotic fracture healing in rats

BACKGROUND

With osteoporosis emerged as one of the most important health issues, more and more investigations are focusing on osteoporotic fracture healing. However, there are few studies on the changes of microstructure and mineralized tissue of newly formed callus.

OBJECTIVE

We established an osteoporotic fracture rat model to evaluate the changes of microstructure and mineralized tissue during osteoporotic fracture healing.

MATERIALS AND METHODS

A mid-shaft femur fracture model was established 12 weeks after ovariectomy as an osteoporotic fracture group (OPF group). Femurs were then harvested at 4 weeks, 8 weeks and 12 weeks after fracture for peripheral quantitative computed tomography (pQCT), micro-computed tomography (MicroCT), histology and biomechanical test. A sham-operated group was used for comparison, i.e. the normal fracture group (NF group).

RESULTS

The pQCT-derived total external callus area in the OPF group was smaller than that in the NF group at 4 weeks after fracture (P<0.05), whereas it was 21% larger in the OPF group than that in the NF group at 12 weeks after fracture (P<0.01). The pQCT-derived bone mineral density in the OPF group was significantly inferior to the NF group at all the time points (P<0.05 for all the time points, respectively). MicroCT data, at 12 weeks after fracture, showed the total callus, bony callus, and newly formed bone was approximately 20% lower in the OPF group than that in the NP group, and the total connectivity was 56% lower in the OPF group as compared to the NF group. Biomechanical test data, at 12 weeks after fracture, showed that the failure load of the left femur of OPF group was 17% less compared to that of the NF group (P<0.01), and 15% lower bending stiffness (P<0.05), 20% lower bending stress (P<0.01), and 28% lower energy at failure (P<0.01) were observed in the OPF group as compared to the NF group.

CONCLUSION

The decrease in mineralized tissue and the not well connected microstructure in newly formed callus may explain the decline of mechanical impairment of fracture healing in the ovariectomized rats.

Monitoring individual morphological changes over time in ovariectomized rats by in vivo micro-computed tomography

The ovariectomized (OVX) rat is a well established model for osteoporosis research. The recent development of in vivo micro-computed tomography (micro-CT) provides new possibilities to monitor individual bone changes over time. The purpose of this study was to establish the normal time course of bone loss in the OVX rat model, and to determine the ability to detect morphological changes in vivo compared to cross-sectional study designs where animals are sacrificed at each time point. Eight-month-old female Wistar rats were randomly assigned to one of two groups: OVX (N = 10) or sham-operated (N = 10). In vivo micro-CT scanning of the right proximal tibial metaphyses occurred at 1-month intervals for 6 months. Morphological analyses were performed at each time step for every animal, and a two-way ANOVA with repeated measures was used to analyze the data. A second statistical analysis was performed without repeated measures for analysis as a cross-sectional study design. The repeated measures analysis was more sensitive to early changes than the cross-sectional study analysis. Changes were detected by longitudinal analysis in the sham-operated and OVX animals over time (P < 0.001) with the exception of trabecular separation in the sham animals. The OVX animals had decreases of bone volume ratio of 33% after 1 month, and 72% after 3 months relative to baseline measurements. Significant changes in bone volume ratio, trabecular number and separation were detected early using a longitudinal analysis, thus in vivo assessment is well poised to enable the study of early treatment protocols on the effects of bone architecture. The in vivo analysis found significant changes in the sham animals which were not detected by the cross-sectional analysis, and the changes to the OVX animal morphology was detected sooner. A substantial variation of baseline morphometry within the homogenous group of rats and response to OVX was observed, thus emphasizing the advantage of performing in vivo analysis where each animal acts as its own control. These data provide new insight into individual bone changes following OVX, and can be used as baseline information upon which future in vivo studies can be designed.

Soy moderately improves microstructural properties without affecting bone mass in an ovariectomized rat model of osteoporosis

Soy protein is reported to prevent bone loss in both women and rat models of osteoporosis. However, the role of soy isoflavones on the trabecular microarchitectural properties needs to be explored. In the present study, we examined whether soy protein with graded doses of isoflavones reverses loss of bone mineral density (BMD), bone mineral content (BMC), and trabecular microstructure in an ovariectomized (Ovx) osteopenic rat model. Seventy-eight 9-m old female Sprague-Dawley rats were either sham-operated (Sham; 1 group) or Ovx (5 groups) and fed a semi-purified casein-based diet. After 90 days, the occurrence of bone loss was confirmed using dual energy X-ray absorptiometry. Thereafter, rats were assigned to the following treatments: Sham, Ovx (control), Ovx + 17beta-estradiol (E(2); 10 microg/kg body wt. twice per week), Ovx + soy protein depleted of isoflavones (Soy-; 0.06 mg isoflavones/g protein), Ovx + soy protein with normal isoflavone content (Soy; 3.55 mg isoflavones/g protein), and Ovx + isoflavone-enriched soy protein (Soy+; 7.10 mg isoflavones/g protein). After 125 days of treatment, rats were euthanized, and tibia and lumbar bones were collected for the assessment of BMD, BMC, and trabecular microarchitectural properties using X-ray microcomputed tomography. None of the treatments had an effect on BMD or microarchitectural properties of the lumbar vertebra. However, Soy treatment significantly increased tibial BMC and BMD by 10% and 4.5% compared with Ovx control, but the increase in BMD was not enough to reach the BMD levels of the Sham control group. The Soy+ diet positively affected the tibial architectural properties including trabecular thickness, separation, and number. In summary, our findings suggest that soy protein does not restore bone loss in osteopenic rats; however, higher doses of isoflavones may be required to reverse the loss of tibial microstructural properties.

Loss of chaotic trabecular structure in OPG-deficient juvenile Paget's disease patients indicates a chaogenic role for OPG in nonlinear pattern formation of trabecular bone

The RANK-RANKL-OPG system of osteoclast regulation may play a key role in determining chaotic structure in trabecular bone. Iliac trabecular bone from juvenile Paget's disease patients deficient in functional OPG shows parallel, anisotropic structure instead of normal chaotic structure. Evidence from experimental systems suggests that RANK-RANKL-OPG controls key nonlinear "chaogenic" parameters, such as friction, forcing frequency, feedback, and boundary forcing. The RANK-RANKL-osteoprotegerin (OPG) system of osteoclast regulation may play a key role in determining chaotic structure in trabecular bone. Iliac trabecular bone from juvenile Paget's disease (JPD) patients deficient in functional OPG shows parallel, anisotropic structure instead of normal chaotic structure. Evidence from experimental systems suggests that RANK-RANKL-OPG controls key nonlinear "chaogenic" parameters, such as friction, forcing frequency, feedback, and boundary forcing. The Belousov-Zhabotinsky reaction-diffusion system, the catalytic oxidation of CO on platinum surfaces, and thermal diffusion in liquid helium allow visualization of nonlinear emergent patterns such as labyrinthine structures, turbulence, and cellular structures, all of which bear some resemblance to trabecular bone. In JPD, the gene for OPG (TNFRSF11B) is subject to an inactivating mutation, leading to increased resorption and accelerated remodeling. Histomorphometric images of iliac crest trabecular bone from teenagers suffering from JPD show a highly unusual array of parallel, regular trabecular plates, instead of the typical chaotic, fractal patterns of normal trabecular bone. Loss of OPG function is associated with a change from chaotic to regular structure, suggesting that the RANK-RANKL-OPG system is controlling key nonlinear "chaogenic" parameters. Looking at trabecular bone from the perspective of nonlinear pattern formation may help understand other phenomena, such as the marked dependence of trabecular bone's architectural and mechanical quality on remodeling rate independent of the trabecular bone mass.

High-resolution Micro-CT evaluation of mid- to long-term effects of estrogen deficiency on rat trabecular bone

RATIONALE AND OBJECTIVES

Previous studies have shown dramatic short-term bone loss following ovariectomy. The purpose of this study was to evaluate mid- to long-term effects of estrogen deficiency on microarchitecture of tibial trabecular bone using a high-resolution microcomputed tomography (Micro-CT).

MATERIALS AND METHODS

Twenty-eight female rats were divided into two equal groups: ovariectomized (OVX, n = 14) and sham-operated (SOVX, n = 14), which in turn were divided into two equal subgroups (euthanized either 6 or 16 weeks after surgery). The left tibia of each animal was scanned with a high-resolution micro-CT (Skyscan 1072 micro-CT system; SkyScan, Aartselaar, Belgium). The Micro-CT system used an X-ray CCD-camera with a cooled 1024 x 1024-pixel 12-bit sensor.

RESULTS

Ovariectomy significantly decreased the ratio of bone volume:tissue volume (-42% at 6 weeks and -69% at 16 weeks) and trabecular thickness (-13% at 6 weeks and -30% at 16 weeks), while significantly increasing trabecular separation (+73% at 6 weeks and +100% at 16 weeks) and structure model index (+15% at 6 weeks and +48% at 16 weeks), when compared with SOVX, from 6 to 16 weeks.

CONCLUSION

Based on the experimental results, there are alterations of trabecular microarcihtecture in the tibia following mid- and long-term estrogen deficiency. More rod-shaped trabeculae are formed with increasing duration of estrogen deficiency. The high-resolution micro-CT imaging system is useful to evaluate the mid- to long-term trabecular changes seen with estrogen deficiency or osteoporosis.

Quantitative analysis of interconnectivity of porous biodegradable scaffolds with micro-computed tomography

Pore interconnectivity within scaffolds is an important parameter influencing cell migration and tissue ingrowth needed to promote tissue regeneration. Methods for assessment of interconnectivity are usually qualitative, restricted to two-dimensional images, or are destructive. Microcomputed tomography nondestructively provides three-dimensional (3D) images of intact specimens at high spatial resolutions. We describe an image analysis technique for quantitative assessment of scaffold interconnectivity. Scaffolds were made via a particulate leaching process with 75%, 80%, 85%, and 88% volumetric porogen fractions. Specimens were scanned and resulting 3D, digital images were analyzed with a custom algorithm. A series of virtual, idealized scaffolds were also created for illustration of the algorithm's analysis approach and for its validation. The program calculated accessible void fractions over a range of minimum connection sizes. In real specimens, nearly 100% of the porous volume was connected with outside air for connections greater than or equal to 20 microm in their smallest dimension. In scaffolds made with 75% porogen, the accessible void fraction decreased to 78% if only those connections greater than or equal to 260 microm were considered. The relationship between accessible void fraction and connection size varied as a function of porogen content. The interconnectivity parameter described here may have implications for cell migration and tissue growth into scaffolds.

Detecting and tracking local changes in the tibiae of individual rats: a novel method to analyse longitudinal in vivo micro-CT data

In this study we present the analysis of in vivo micro-CT scans using a new method based on image registration that accurately evaluates longitudinal micro-CT studies. We tested if detailed changes in the bone architecture could be detected and tracked in individual animals. A prototype in vivo micro-CT scanner (Skyscan 1076) was developed in which tibiae of rats that are lying on a bed under gas anaesthesia were scanned. For this study, three female Wistar rats were used: a sham-operated rat, an ovariectomised (OVX) rat and one rat that served as a reproducibility control. The reproducibility control rat was scanned twice in 1 day. The other animals were scanned at week 0, just before surgery, at week 4 and at week 14 after surgery. Architectural changes over time were detected by overlaying two data sets made at different time points using an algorithm that uses mutual information for optimal registration. The scans were segmented into binary data sets using a local thresholding algorithm. The reproducibility test showed small errors of less than 3% in bone volume measurements and errors less than 0.5% in measurements of trabecular thickness. The sham-operated rat showed no changes in total bone volume, though thinning and eventual loss of some small trabeculae could be detected, which could be related to the age of the animal. The OVX rat lost much trabecular bone volume, especially in the metaphysis (60% at week 4, 75% at week 14). The remaining trabeculae slowly increased in thickness. Following the different scans in time showed the forming of new trabecular structures. Additionally, small longitudinal growth at the growth plate could be detected after the first 4 weeks. Further, the OVX rat showed extensive modelling at the proximal endosteal lateral cortex. We have shown a new method that can detect and track changes in the local bone architecture and individual trabeculae in time, in an individual living animal. This method enables longitudinal in vivo micro-CT studies and has the potential to greatly contribute to experimental rat or mouse studies on pharmacological intervention and transgenic models.

Isoflavones with supplemental calcium provide greater protection against the loss of bone mass and strength after ovariectomy compared to isoflavones alone

Although hormone replacement therapy (HRT) and calcium (Ca) supplementation preserve bone mass more when combined, there is a growing concern over the safety of HRT that necessitates thorough investigation of effective, alternative treatments for bone loss. While plant-derived estrogen-like compounds such as isoflavones preserve bone, it is not known whether isoflavones and Ca supplementation attenuate losses in bone mass and strength to a greater extent when combined. This study compared the effects of an isoflavone extract + high Ca to isoflavone extract or high Ca alone on preservation of bone mineral density (BMD) and biomechanical strength in ovariectomized (ovx) rats. Rats were sham-operated (n = 10) or ovx (n = 40). Shams were fed a 0.2% Ca diet. Ovx rats were randomized to a 0.2% Ca diet alone (OVX) or with isoflavone extract (IE; 1.6 g/kg diet) or to a high Ca diet (Ca; 2.5%) alone or a high Ca diet with the isoflavone extract (IE + Ca) for 8 weeks. BMD of femur and lumbar spine were measured by dual-energy X-ray absorptiometry. The biomechanical strength of femurs and individual vertebra was measured by three-point bending and compression testing, respectively. The average food intake was lowest (P < 0.05) among sham and IE groups and greatest (P < 0.05) among the OVX group. Final body weight was lowest (P < 0.05) among shams and highest (P < 0.05) among the OVX group while IE + Ca were lighter (P < 0.05) than all ovx groups. Femur and vertebra BMD was greater (P < 0.05) among IE + Ca and sham rats compared to IE, Ca, or OVX rats. Although there were differences in femur BMD among groups, biomechanical properties at the femur midpoint did not differ among groups, possibly due to the lack of cortical bone loss at this site. Conversely, vertebra biomechanical strength was greater (P < 0.05) among IE + Ca and Ca alone groups compared to IE alone. Uterine weight was higher (P < 0.05) among shams than OVX and IE with no difference among shams, Ca, or IE + Ca rats, suggesting that the isoflavones did not have an uterotrophic effect. In conclusion, isoflavones combined with high Ca are more protective against the loss of femur and vertebra BMD than isoflavones or high Ca diet alone.

The effects of ovariectomy on the mechanical properties of skin in rats

OBJECTIVE

After menopause, observable changes occur in the physical characteristics of the human skin. These changes and their responses to various treatments can be assessed with non-invasive in-vivo mechanical tests. However, tests measuring breaking strength and tensile strengths can only be done ex-vivo, they require relatively higher quantities of skin and thus have generally been performed on animals. Mechanical changes in the skin of ovariectomized rats, an appropriate model for the study of postmenopausal period, have not been dealt with in the literature. In this study mechanical characteristics of the skin, such as breaking strength and tensile strength have been tested and studied histologically in ovariectomized rats.

METHODS

Sixteen rats were divided into two groups, one undergoing ovariectomy and one control group undergoing a sham operation. Three months later, the rats were sacrificed and tensile properties of their back skins were tested with a tensometer and evaluated histologically.

RESULTS AND CONCLUSION

Breaking strength, tensile strength and the Young's modulus have increased and the thickness of the subcutis has decreased in ovariectomized rats. This study should be tested by others, because of existence of some conflicts between available knowledge and the results, relating to postmenopausal skin changes.

Effect of vitamin K2 on three-dimensional trabecular microarchitecture in ovariectomized rats

Menatetrenone, a vitamin K2 with four isoprene units, has been reported to improve osteoporotic bone loss. The purpose of this investigation was to clarify the effect of menatetrenone on the three-dimensional (3D) trabecular microarchitecture in ovariectomized (OVX) rats by using microcomputed tomography (MCT). Forty-two 13-week-old female rats were used and divided into four groups: the OVX (OVX + MK-4) group treated with menatetrenone, the (OVX untreated) group, the sham-operated (Sham + MK-4) group treated with menatetrenone, and the sham-operated group not treated with menatetrenone (Sham untreated) group. OVX rats were fed a calcium-deficient diet. Menatetrenone treatment was begun just after the ovariectomy, and the mean menatetrenone oral intake over the 8-week period was adjusted to 30 mg/kg BW per day. The proximal metaphyseal region of the right tibia was evaluated by dual X-ray absorptiometry (DXA) and MCT. A parametric analysis of the reconstructed trabecular volume was carried out using bone volume fractions, the fractal dimension calculated by the 3D box-counting method, and the connectivity density as determined by topological analysis. Menatetrenone significantly increased the trabecular bone volume, fractal dimension, and connectivity in the OVX + MK-4 group compared with the OVX-untreated group (p < 0.01). Our results suggest that an 8-week administration of menatetrenone protects against the loss of trabecular bone volume and its connectivity when treatment is begun just after the ovariectomy. Despite this apparent protection, it remains unknown whether it is possible to reestablish trabecular connectivity if therapeutic intervention occurs after the trabecular connectivity has been lost.