Bone loss detection in rats using a mouse densitometer

Small animal DXA instrument comparison and validation

Several new peripheral dual-energy X-ray absorptiometry (DXA) devices designed for assessment of bone and body composition in rodents have been developed. We compared the performance (accuracy and precision) of two of these devices, the InAlyzer and the iNSiGHT, to those of an established device, the PIXImus. We measured total body bone mineral content (BMC), bone mineral density (BMD), and body composition (lean and fat mass) on the three DXA devices in 18 male C57Bl/6 J mice (6 each of ages 8, 14, and 24 weeks, weighing 22 to 33 g). DXA body composition measures were compared to whole-body nuclear magnetic resonance (NMR) outcomes. BMC of the femur was also compared to ex vivo micro-computed tomography (microCT). Total body BMD from the InAlyzer and iNSiGHT devices was strongly correlated to that from PIXImus (R2 = 0.83 and 0.82, respectively), but was ~25 % higher than PIXImus. Total body BMC measures by InAlyzer were strongly associated with those from PIXImus (R2 = 0.86), whereas those from iNSiGHT were only weakly correlated (R2 = 0.29). Femur BMC from InAlyzer was strongly correlated with microCT outcomes, whereas iNSiGHT was only weakly correlated. InAlyzer and iNSiGHT fat mass measures were very strongly correlated with PIXImus and NMR outcomes (R2 = 0.91 to 0.97), with slightly weaker associations for lean mass (R2 = 0.81 to 0.76). Short-term precision of InAlyzer and iNSiGHT measurements were excellent, and akin to those from the PIXImus for both body composition and bone measures, ranging between 0.39 and 3.2 %. With faster scan times, closed X-ray source and excellent precision, the new devices are both satisfactory replacements for the now discontinued PIXImus system. However, given the accuracy of the bone and body composition measures, the InAlyzer may be preferable for studies where musculoskeletal changes are the main interest.

Zoledronic acid improves bone quality and muscle function in a high bone turnover state

SUMMARY

Zoledronic acid (ZA) prevents muscle weakness in mice with bone metastases; however, its role in muscle weakness in non-tumor-associated metabolic bone diseases and as an effective treatment modality for the prevention of muscle weakness associated with bone disorders, is unknown. We demonstrate the role of ZA-treatment on bone and muscle using a mouse model of accelerated bone remodeling, which represents the clinical manifestation of non-tumor associated metabolic bone disease. ZA increased bone mass and strength and rescued osteocyte lacunocanalicular organization. Short-term ZA treatment increased muscle mass, whereas prolonged, preventive treatment improved muscle mass and function. In these mice, muscle fiber-type shifted from oxidative to glycolytic and ZA restored normal muscle fiber distribution. By blocking TGFβ release from bone, ZA improved muscle function, promoted myoblast differentiation and stabilized Ryanodine Receptor-1 calcium channel. These data demonstrate the beneficial effects of ZA in maintaining bone health and preserving muscle mass and function in a model of metabolic bone disease.

Context and significance

TGFβ is a bone regulatory molecule which is stored in bone matrix, released during bone remodeling, and must be maintained at an optimal level for the good health of the bone. Excess TGFβ causes several bone disorders and skeletal muscle weakness. Reducing excess TGFβ release from bone using zoledronic acid in mice not only improved bone volume and strength but also increased muscle mass, and muscle function. Progressive muscle weakness coexists with bone disorders, decreasing quality of life and increasing morbidity and mortality. Currently, there is a critical need for treatments improving muscle mass and function in patients with debilitating weakness. Zoledronic acid's benefit extends beyond bone and could also be useful in treating muscle weakness associated with bone disorders.

Efficacy of Pulsed Electromagnetic Fields on Experimental Osteopenia in Rodents: A Systematic Review

Osteoporosis leads to increased bone fragility and risk of fractures. Different strategies have been employed to reduce bone loss, including the use of a pulsed electromagnetic field (PEMF). Although many experimental studies have demonstrated the effect of PEMF on reduction of bone loss, the outcomes studied are varied and insufficient, and the quality of evidence is unknown. Therefore, the aim of this review was to assess the preclinical evidence on the effect of PEMF on bone loss. The existing challenges were also evaluated, and suggestions were provided to strengthen the quality of evidence in future studies. All original articles concerning the effect of PEMF on osteoporosis in animal models were included. Twenty-four studies met the inclusion criteria, 23 of which suggested that PEMF was effective in reducing bone loss, while one study failed to demonstrate any benefit. Risk of bias analysis suggested that information on key measures to reduce bias was frequently not reported. Animal models for osteoporosis, PEMF intervention regimens, outcomes, and specific bone detection sites seemed to influence the efficacy of PEMF in osteoporosis. Our results indicate the potential benefits of PEMF selection in animal models of osteoporosis. However, due to the heterogeneity of the parameters and the quality of the included literature, comprehensive studies using standardized protocols are warranted to confirm the results. © 2021 Bioelectromagnetics Society.

Determination of basal bone mineral density in the femur bones of male and female Wistar rats

Changes in bone mineral content of calcium (Ca), phosphorous (P), magnesium and potassium for male and female Wistar rats during their development from 3 weeks old to adulthood (27 weeks old) were measured. Bone mineral content was related to areal bone mineral density (BMD) which was measured in vivo at the femoral neck using a calibrated X-ray transmission system to obtain basal curves as a function of the age of the specimen. Diagnostic curves were built to determine low BMD (osteopaenia) and osteoporosis in female rats fed a Ca-depleted diet (50%) based on the obtained data and the criteria established by the World Health Organization. Bone mineral content is directly related to sex and age, but P did not change throughout the experimental period. P content did not exhibit significant changes with growing, while Ca was greatest in male rats, producing significant differences in the Ca:P ratio. Male rats reach the Ca:P ratio peak before female rats. However, areal BMD does not follow the same trend. On the other hand, osteoporosis produced a 45% decrease in this parameter for young and mature adults. These results make Z-score values available to diagnose bone-mass losses and hence the possibility of improving the conditions of non-contact measurement of BMD in vivo. This technique can be used for future experiments with Wistar rats.

NOTUM inhibition increases endocortical bone formation and bone strength

The disability, mortality and costs caused by non-vertebral osteoporotic fractures are enormous. Existing osteoporosis therapies are highly effective at reducing vertebral but not non-vertebral fractures. Cortical bone is a major determinant of non-vertebral bone strength. To identify novel osteoporosis drug targets, we phenotyped cortical bone of 3 366 viable mouse strains with global knockouts of druggable genes. Cortical bone thickness was substantially elevated in Notum^−/− mice. NOTUM is a secreted WNT lipase and we observed high NOTUM expression in cortical bone and osteoblasts but not osteoclasts. Three orally active small molecules and a neutralizing antibody inhibiting NOTUM lipase activity were developed. They increased cortical bone thickness and strength at multiple skeletal sites in both gonadal intact and ovariectomized rodents by stimulating endocortical bone formation. Thus, inhibition of NOTUM activity is a potential novel anabolic therapy for strengthening cortical bone and preventing non-vertebral fractures.

NOTUM is an enzyme that inactivates WNT proteins (which play a key role in early tissue development), and inhibiting NOTUM has been found to increase the formation of endocortical bone (within the cortex, the hard exterior of bone) and enhance bone strength. Existing therapies for osteoporosis (condition causing bone to become weak and brittle) are effective in reducing vertebral, but not non-vertebral, fractures. A team headed by Robert Brommage at Lexicon Pharmaceuticals, Texas aimed to identify novel osteoporosis drug targets in mice. Following inhibition of NOTUM activity, the authors observed increased cortical bone thickness and strength at multiple skeletal sites through stimulation of endocortical bone formation. The team concluded that inhibiting NOTUM activity has good potential as a new therapeutic strategy and could be beneficial in preventing non-vertebral osteoporotic fractures.

Synergistic Phytochemicals Fail to Protect Against Ovariectomy Induced Bone Loss in Rats

Menopause induces a loss of bone as a result of estrogen deficiency. Despite pharmaceutical options for the treatment of osteopenia and osteoporosis, many aging women use dietary supplements with estrogenic activity to prevent bone loss and other menopausal-related symptoms. Such supplements are yet to be tested for efficacy against a Food and Drug Administration (FDA) approved medication for menopausal bone loss such as zoledronic acid (ZA). The postmenopausal rat model was used to investigate the efficacy of various synergistic phytochemical blends mixed into the diet for 16 weeks. Retired-breeder, Fischer 344 rats were randomly assigned to sham or ovariectomy surgery and 4 treatment groups: ZA; genistein supplementation; and a low dose and high dose blend of genistein, resveratrol, and quercetin. Ovariectomy resulted in a loss of both trabecular and cortical bone which was prevented with ZA. The phytochemical blends tested were unable to reverse these losses. Despite the lack of effectiveness in preventing bone loss, a significant dose-response trend was observed in the phytochemical-rich diets in bone adipocyte number compared to ovariectomized control rats. Data from this study indicate that estrogenic phytochemicals are not as efficacious as ZA in preventing menopausal-related bone loss but may have beneficial effects on bone marrow adiposity in rats.

Dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and micro-computed tomography techniques are discordant for bone density and geometry measurements in the guinea pig

This study aims to examine agreement among bone mineral content (BMC) and density (BMD) estimates obtained using dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and micro-computed tomography (μCT) against high-resolution μCT and bone ash of the guinea pig femur. Middle-aged (n = 40, 86 weeks) male guinea pigs underwent in vivo followed by ex vivo DXA (Hologic QDR 4500A) scanning for intact and excised femur BMC and areal density. To assess bone architecture and strength, excised femurs were scanned on pQCT (Stratec XCT 2000L) as well as on two μCT scanners (LaTheta LCT-200; Skyscan 1174), followed by three-point bending test. Reproducibility was determined using triplicate scans; and agreement assessed using Bland-Altman plots with reference methods being high-resolution μCT (Skyscan) for BMD and bone ashing for BMC. All techniques showed satisfactory ex vivo precision (CV 0.05-4.3 %). However, bias compared to the reference method was highest (207.5 %) in trabecular bone volume fraction (BV/TV) measured by LaTheta, and unacceptable in most total femur and cortical bone measurements. Volumetric BMD (vBMD) and BV/TV derived by LaTheta and pQCT at the distal metaphysis were biased from the Skyscan by an average of 49.3 and 207.5 %, respectively. Variability of vBMD, BV/TV and cross-sectional area at the diaphysis ranged from -5.5 to 30.8 %. LaTheta best quantified total femur BMC with an upper bias of 3.3 %. The observed differences among imaging techniques can be attributable to inherent dissimilarity in construction design, calibration, segmentation and scanning resolution used. These bone imaging tools are precise but are not comparable, at least when assessing guinea pig bones.

Hyponatremia-induced osteoporosis

There is a high prevalence of chronic hyponatremia in the elderly, frequently owing to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Recent reports have shown that even mild hyponatremia is associated with impaired gait stability and increased falls. An increased risk of falls among elderly hyponatremic patients represents a risk factor for fractures, which would be further amplified if hyponatremia also contributed metabolically to bone loss. To evaluate this possibility, we studied a rat model of SIADH and analyzed data from the Third National Health and Nutrition Examination Survey (NHANES III). In rats, dual-energy X-ray absorptiometry (DXA) analysis of excised femurs established that hyponatremia for 3 months significantly reduced bone mineral density by approximately 30% compared with normonatremic control rats. Moreover, micro-computed tomography (microCT) and histomorphometric analyses indicated that hyponatremia markedly reduced both trabecular and cortical bone via increased bone resorption and decreased bone formation. Analysis of data from adults in NHANES III by linear regression models showed that mild hyponatremia is associated with increased odds of osteoporosis (T-score -2.5 or less) at the hip [odds ratio (OR) = 2.85; 95% confidence interval (CI) 1.03-7.86; p < .01]; all models were adjusted for age, sex, race, body mass index (BMI), physical activity, history of diuretic use, history of smoking, and serum 25-hydroxyvitamin D [25(OH)D] levels. Our results represent the first demonstration that chronic hyponatremia causes a substantial reduction of bone mass. Cross-sectional human data showing that hyponatremia is associated with significantly increased odds of osteoporosis are consistent with the experimental data in rodents. Our combined results suggest that bone quality should be assessed in all patients with chronic hyponatremia.

Femoral bone mineral density and bone mineral content in bromocriptine-treated pregnant and lactating rats

Since hyperprolactinemia was found to induce osteopenia in the metaphysis of long bone in non-mated female rats, pregnant and lactating rats with sustainedly high plasma prolactin (PRL) levels might also exhibit some changes in their long bones. We performed a longitudinal study in pregnant, lactating and post-weaning rats, using dual-energy X-ray absorptiometry to demonstrate site-specific changes (i.e., metaphysis vs. diaphysis) in femoral bone mineral density (BMD) and content (BMC). The results showed that femoral metaphyseal BMD and BMC were higher when compared to their age-matched controls during pregnancy, before decreasing in late lactation and post-weaning. On the other hand, femoral diaphyseal BMC increased during pregnancy, early lactating and mid-lactating periods without change during late lactation and post-weaning. After 7 days of bromocriptine administration which inhibited endogenous PRL secretion, the lactation-induced increases in BMC during early and mid-lactating periods were abolished. Moreover, a decrease in metaphyseal BMD during late lactation was restored to the control levels by bromocriptine. However, bromocriptine did not antagonize the pregnancy-induced increases in BMD and BMC. It could be concluded that the effect of PRL on bone was variable during the reproductive periods. While having no effect on femoral BMD and BMC during pregnancy, PRL was responsible for bone gain in early and mid-lactating periods, but induced bone loss during late lactating period.

Energy restriction is associated with lower bone mineral density of the tibia and femur in lean but not obese female rats

Energy restriction decreases bone mineral density (BMD), and epidemiological studies suggest that the risk of weight loss-induced bone loss is greater in lean than in heavier individuals. Our goal in this study was to determine how bone density and geometry respond to energy restriction in mature obese rats compared with lean rats. At 6 mo of age, 36 diet-induced obese and lean female Sprague-Dawley rats were allocated to control (CTL; ad libitum; n = 18) and energy-restricted (EnR; 40% restriction; n = 18) diets. After 10 wk of dietary intervention, obese EnR rats lost more weight (-91 +/- 34 g) than lean EnR rats(-61 +/- 14 g) (P < 0.02), [corrected] whereas body weight did not change significantly in the 2 CTL groups (14 +/- 23 g). Only the lean EnR (and not obese EnR) rats showed lower BMD compared with CTL rats at the tibia, distal, and proximal femur and femoral neck, and trabecular bone volume (P < 0.05). Serum estradiol declined in lean EnR rats compared with baseline (P < 0.05) but not in the obese EnR rats. In addition, the final serum 25-hydroxyvitamin D (25OHD) concentration was higher (P < 0.05) in obese than in lean EnR rats. Serum parathyroid hormone decreased (P < 0.05) from baseline to final in lean and obese CTL, but not EnR rats. These data support the hypothesis that energy restriction in lean rats compared with obese rats is more detrimental to bone, and it is possible that the greater decline in estrogen and lower levels of 25OHD contribute to this effect.

Bone mineral density and content during weight cycling in female rats: effects of dietary amylase-resistant starch

BACKGROUND

Although there is considerable evidence for a loss of bone mass with weight loss, the few human studies on the relationship between weight cycling and bone mass or density have differing results. Further, very few studies assessed the role of dietary composition on bone mass during weight cycling. The primary objective of this study was to determine if a diet high in amylase-resistant starch (RS2), which has been shown to increase absorption and balance of dietary minerals, can prevent or reduce loss of bone mass during weight cycling.

METHODS

Female Sprague-Dawley (SD) rats (n = 84, age = 20 weeks) were randomly assigned to one of 6 treatment groups with 14 rats per group using a 2 x 3 experimental design with 2 diets and 3 weight cycling protocols. Rats were fed calcium-deficient diets without RS2 (controls) or diets high in RS2 (18% by weight) throughout the 21-week study. The weight cycling protocols were weight maintenance/gain with no weight cycling, 1 round of weight cycling, or 2 rounds of weight cycling. After the rats were euthanized bone mineral density (BMD) and bone mineral content (BMC) of femur were measured by dual energy X-ray absorptiometry, and concentrations of calcium, copper, iron, magnesium, manganese, and zinc in femur and lumbar vertebrae were determined by atomic absorption spectrophotometry.

RESULTS

Rats undergoing weight cycling had lower femur BMC (p < 0.05) and marginally lower BMD (p = 0.09) than rats not undergoing weight cycling. In comparison to controls, rats fed RS2 had higher femur BMD (p < 0.01) and BMC (p < 0.05), as well as higher values for BMD and BMC measured at the distal end (p < 0.001 and p < 0.01) and femoral neck (p < 0.01 and p < 0.05). Consistent with these findings, RS2-fed rats also had higher femur calcium (p < 0.05) and magnesium (p < 0.0001) concentrations. They also had higher lumbar vertebrae calcium (p < 0.05) and magnesium (p < 0.05) concentrations.

CONCLUSION

Weight cycling reduces bone mass. A diet high in RS2 can minimize loss of bone mass during weight cycling and may increase bone mass in the absence of weight cycling.

Modeling corticosteroid effects in a rat model of rheumatoid arthritis I: mechanistic disease progression model for the time course of collagen-induced arthritis in Lewis rats

A mechanism-based model was developed to describe the time course of arthritis progression in the rat. Arthritis was induced in male Lewis rats with type II porcine collagen into the base of the tail. Disease progression was monitored by paw swelling, bone mineral density (BMD), body weights, plasma corticosterone (CST) concentrations, and tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, and glucocorticoid receptor (GR) mRNA expression in paw tissue. Bone mineral density was determined by PIXImus II dual energy X-ray densitometry. Plasma CST was assayed by high-performance liquid chromatography. Cytokine and GR mRNA were determined by quantitative real-time polymerase chain reaction. Disease progression models were constructed from transduction and indirect response models and applied using S-ADAPT software. A delay in the onset of increased paw TNF-alpha and IL-6 mRNA concentrations was successfully characterized by simple transduction. This rise was closely followed by an up-regulation of GR mRNA and CST concentrations. Paw swelling and body weight responses peaked approximately 21 days after induction, whereas bone mineral density changes were greatest at 23 days after induction. After peak response, the time course in IL-1beta, IL-6 mRNA, and paw edema slowly declined toward a disease steady state. Model parameters indicate TNF-alpha and IL-1beta mRNA most significantly induce paw edema, whereas IL-6 mRNA exerted the most influence on BMD. The model for bone mineral density captures rates of turnover of cancellous and cortical bone and the fraction of each in the different regions analyzed. This small systems model integrates and quantitates multiple factors contributing to arthritis in rats.

High physiological prolactin induced by pituitary transplantation decreases BMD and BMC in the femoral metaphysis, but not in the diaphysis of adult female rats

High physiological prolactin (PRL) stimulated intestinal calcium absorption and renal calcium uptake in mammals. Previous histomorphometric study revealed a significant increase in bone turnover in the trabecular part of the PRL-exposed long (cortical) bone; however, whole-bone densitometric analysis was unable to demonstrate such effect. We therefore studied differential changes in bone mineral density (BMD) and contents (BMC) of the femoral diaphysis and metaphysis in adult female rats exposed to high PRL induced by anterior pituitary (AP) transplantation. The estrogen-dependent effects of PRL on the femur were also investigated. We found that chronic exposure to PRL had no effect on BMD or BMC of the femoral diaphysis, which represented the cortical part of the long bone. It is interesting that 7 weeks after an AP transplantation, BMD and BMC of the femoral metaphysis were significantly decreased by 8% and 14%, respectively. Ovariectomy (Ovx) for 2, 5, and 7 weeks also decreased BMD and BMC in the femoral metaphysis, but not in the diaphysis. However, the AP transplantation plus Ovx (AP+Ovx) produced no additive effects. Nevertheless, 2.5 microg/kg 17beta-estradiol (E2) supplementation abolished the osteopenic effects of both Ovx and AP+Ovx on the femur. As for the L5-6 vertebrae, BMD and BMC were not affected by PRL exposure, but were significantly decreased by Ovx and AP+Ovx, and such decreases were completely prevented by E2 supplementation. It could be concluded that high physiological PRL induced a significant osteopenia in the trabecular part, i.e., the metaphysis, of the femora of adult female rats in an estrogen-dependent manner. Since PRL had no detectable effect on the vertebrae, the effects of PRL on bone appeared to be site-specific.

Energy restriction-induced changes in body composition are age specific in mice

Restricting energy intake while supplying adequate micronutrients slows aging and extends maximal lifespan, whereas loss of body weight with exercise training does not. Our goal was to test the hypothesis that weight loss via energy restriction (ER) alters body composition in a way that is: 1) distinct from exercise-induced weight loss; and 2) conserved regardless of the age at which ER is initiated. An experimental model was developed where matched losses in weight could be induced with 6 mo of ER (approximately 55% of ad libitum energy intake) or voluntary exercise on a running wheel in adult (12 mo) male C57BL/6 mice and a similar amount of ER-induced weight loss could be induced in aged mice (24 mo). Using dual-energy X-ray absorptiometry, we determined that ER and exercise in the 12-mo-old mice caused nearly identical changes in the amount and distribution of adipose tissue in the 12-mo group, with 70-75% of overall weight loss due to fat loss. Decreased prostate and epididymal fat weights were similar with ER and exercise, and heart weight was unaffected by either intervention. In contrast to the adult mice, in aged mice, ER caused primarily a loss of lean body mass including the heart, with no decreased prostate or fat pad weight. Bone mineral density was decreased by ER but not exercise in the adult mice, an effect not seen in the aged mice. Our data refute the hypothesis that ER causes a unique change in body composition that is conserved across age and suggest that fat loss may not be an essential component of the anti-aging effects of ER.

Biochemical markers in preclinical models of osteoporosis

Although several treatments for osteoporosis exist, further understanding of the mode of action of current treatments, as well as development of novel treatments, are of interest. Thus, preclinical models of osteoporosis are very useful, as they provide the possibility for gaining knowledge about the cellular mechanisms underlying the disease and for studying pharmaceutical prevention or intervention of the disease in simple and strictly controlled systems. In this review, we present a comprehensive collection of studies using biochemical markers of bone turnover for investigation of preclinical models of osteoporosis. These range from pure and simple in vitro systems, such as osteoclast cultures, to ex vivo models, such as cultures of embryonic murine tibiae and, finally, to in vivo models, such as ovariectomy and orchidectomy of rats. We discuss the relevance of the markers in the individual models, and compare their responses to those observed using 'golden standard' methods.

High-calcium diet modulates effects of long-term prolactin exposure on the cortical bone calcium content in ovariectomized rats

High physiological prolactin induced positive calcium balance by stimulating intestinal calcium absorption, reducing renal calcium excretion, and increasing bone calcium deposition in female rats. Although prolactin-induced increase in trabecular bone calcium deposition was absent after ovariectomy, its effects on cortical bones were still controversial. The present investigation, therefore, aimed to study the effect of in vivo long-term high physiological prolactin induced by either anterior pituitary (AP) transplantation or 2.5 mg/kg prolactin injection on cortical bones in ovariectomized rats. Since the presence of prolactin receptors (PRLR) in different bones of normal adult rats has not been reported, we first determined mRNA expression of both short- and long-form PRLRs at the cortical sites (tibia and femur) and trabecular sites (calvaria and vertebrae) by using the RT-PCR. Our results showed the mRNA expression of both PRLR isoforms with predominant long form at all sites. However, high prolactin levels induced by AP transplantation in normal rats did not have any effect on the femoral bone mineral density or bone mineral content. By using (45)Ca kinetic study, 2.5 mg/kg prolactin did not alter bone formation, bone resorption, calcium deposition, and total calcium content in tibia and femur of adult ovariectomized rats. AP transplantation also had no effect on the cortical total calcium content in adult ovariectomized rats. Because previous work showed that the effects of prolactin were age dependent and could be modulated by high-calcium diet, interactions between prolactin and these two parameters were investigated. The results demonstrated that 2.0% wt/wt high-calcium diet significantly increased the tibial total calcium content in 9-wk-old young AP-grafted ovariectomized rats but decreased the tibial total calcium content in 22-wk-old adult rats. As for the vertebrae, the total calcium contents in both young and adult rats were not changed by high-calcium diet. The present results thus indicated that the adult cortical bones were potentially direct targets of prolactin. Moreover, the effects of high physiological prolactin on cortical bones were age dependent and were observed only under the modulation of high-calcium diet condition.

PIXImus bone densitometer and associated technical measurement issues of skeletal growth in the young rat

The PIXImus dual-energy X-ray absorptiometer (DXA) is designed to measure body composition, bone mineral content (BMC), area (BA), and density (BMD) in mice and rats. The aims of this study were to longitudinally measure BMC, BA, and BMD in growing rats and to identify potential technical problems associated with the PIXImus. Total femur and lumbar DXA measurements, body weight, and length of initially 3-week-old rats (n = 10) were taken at weeks 5, 9, and 14. BMC and BMD of femoral metaphyseal and diaphyseal regions rich in trabecular and cortical bone, respectively, were obtained. Results showed significant increases in body weight, total femur BMC and BMD, lumbar area, length, BMC, and BMD at each time point. There was a significant positive correlation between body weight and total femur BMD (r = 0.97, P < 0.001) as well as lumbar BMD (r = 0.99, P < 0.001). BMD values for the femoral metaphyseal region and the lumbar spine were also positively correlated (r = 0.96, P < 0.01). Several technical issues (e.g., positioning of animals), difficulties (e.g., in analysis of images), and limitations (e.g., inability to detect underdeveloped calcified bone in growing animals and bone edge detection) of the software pertinent to the PIXImus were evident. In conclusion, despite limitations in the software, the PIXImus is a valuable tool for studying skeletal development of growing rats.

Two-week longitudinal survey of bone architecture alteration in the hindlimb-unloaded rat model of bone loss: sex differences

The goal of this study was to determine, through a longitudinal follow-up, whether sex influences bone adaptation during simulated weightlessness. Twelve-week-old male and female Wistar rats were hindlimb unweighted for 2 wk, and the time course of bone alteration was monitored in vivo by means of densitometry and unbiased three-dimensional quantitative microcomputed tomography at 7 and 14 days. Compared with male rats, female rats had twice more cancellous bone volume at the proximal tibia at baseline, and this bone volume continued to increase, whereas in males it stabilized. Conversely, cortical area was greater in males than in females, and in both sexes cortical bone was still expanding. Hindlimb unloading resulted in larger reductions in males than in females in both cortical and cancellous compartments. In females, trabecular thickness and number decreased mildly, whereas in males trabecular number was dramatically reduced. In both sexes, the trabecular network became less connected and more rod-like shaped. Bone cellular activities evaluated by histomorphometry showed decreased bone formation rate in both sexes and increased resorption activity only in males. In conclusion, in female rats unloaded-related cancellous alterations reversed the growing process, whereas in males, which show lower growth process, it induced an accentuation of age-related cancellous bone changes for most of the parameters.

In Vitro, Ex Vivo, andIn VivoMethodological Approaches for Studying Therapeutic Targets of Osteoporosis and Degenerative Joint Diseases: How Biomarkers Can Assist?

Although our approach to the clinical management of osteoporosis (OP) and degenerative joint diseases (DJD)-major causes of disability and morbidity in the elderly-has greatly advanced in the past decades, curative treatments that could bring ultimate solutions have yet to be found or developed. Effective and timely development of candidate drugs is a critical function of the availability of sensitive and accurate methodological arsenal enabling the recognition and quantification of pharmacodynamic effects. The established concept that both OP and DJD arise from an imbalance in processes of tissue formation and degradation draws attention to need of establishing in vitro, ex vivo, and in vivo experimental settings, which allow obtaining insights into the mechanisms driving increased bone and cartilage degradation at cellular, organ, and organism levels. When addressing changes in bone or cartilage turnover at the organ or organism level, monitoring tools adequately reflecting the outcome of tissue homeostasis become particularly critical. In this context, bioassays targeting the quantification of various degradation and formation products of bone and cartilage matrix elements represent a useful approach. In this review, a comprehensive overview of widely used and recently established in vitro, ex vivo, and in vivo set-ups is provided, which in many cases effectively take advantage of the potentials of biomarkers. In addition to describing and discussing the advantages and limitations of each assay and their methods of evaluation, we added experimental and clinical data illustrating the utility of biomarkers for these methodological approaches.

Human stanniocalcin-2 exhibits potent growth-suppressive properties in transgenic mice independently of growth hormone and IGFs

Stanniocalcin (STC)-2 was discovered by its primary amino acid sequence identity to the hormone STC-1. The function of STC-2 has not been examined; thus we generated two lines of transgenic mice overexpressing human (h)STC-2 to gain insight into its potential functions through identification of overt phenotypes. Analysis of mouse Stc2 gene expression indicates that, unlike Stc1, it is not highly expressed during development but exhibits overlapping expression with Stc1 in adult mice, with heart and skeletal muscle exhibiting highest steady-state levels of Stc2 mRNA. Constitutive overexpression of hSTC-2 resulted in pre- and postnatal growth restriction as early as embryonic day 12.5, progressing such that mature hSTC-2-transgenic mice are approximately 45% smaller than wild-type littermates. hSTC-2 overexpression is sometimes lethal; we observed 26-34% neonatal morbidity without obvious dysmorphology. hSTC-2-induced growth retardation is associated with developmental delay, most notably cranial suture formation. Organ allometry studies show that hSTC-2-induced dwarfism is associated with testicular organomegaly and a significant reduction in skeletal muscle mass likely contributing to the dwarf phenotype. hSTC-2-transgenic mice are also hyperphagic, but this does not result in obesity. Serum Ca2+ and PO4 were unchanged in hSTC-2-transgenic mice, although STC-1 can regulate intra- and extracellular Ca2+ in mammals. Interestingly, severe growth retardation induced by hSTC-2 is not associated with a decrease in GH or IGF expression. Consequently, similar to STC-1, STC-2 can act as a potent growth inhibitor and reduce intramembranous and endochondral bone development and skeletal muscle growth, implying that these tissues are specific physiological targets of stanniocalcins.

Combined intervention of soy isoflavone and moderate exercise prevents body fat elevation and bone loss in ovariectomized mice

Body fat accumulation and bone loss are both often associated with estrogen deficiency following menopause. In this study, we examined whether soy isoflavone, one of the phytoestrogens, and moderate exercise interventions exhibit cooperative effects on body composition and bone mass in ovariectomized (OVX) mice. Eight-week-old female mice were assigned to 6 groups: (1) sham-operated (sham); (2) OVX; (3) OVX with received a soy isoflavone diet (OVX+ISO); (4) OVX with exercised on a treadmill (OVX+EX); (5) OVX with given both isoflavone and exercise (OVX+ISO&EX ); and (6) OVX with treated with 17 beta-estradiol subcutaneously (OVX+E2). Body composition and bone mineral density (BMD) were estimated by dual-energy x-ray absorptiometry (DXA). After the 6-week intervention, whole body fat (%) in the OVX group showed significantly higher than that in the sham group. Intervention of exercise and isoflavone alone partially inhibited OVX-induced body fat gain, and the combined intervention as well as E2 treatment completely restored fat mass to the sham level. Lean body mass in the whole body was not different in OVX group compared with that in OVX+ISO, OVX+EX, and OVX+E2 groups, but it was significantly higher in OVX+ISO&EX than in other groups. BMD of the whole body, lumbar spine, or femur showed significantly reduced by OVX, and the bone loss was partially inhibited by intervention of exercise or isoflavone alone. However, the combined intervention completely restored the bone mass to the level of sham, as did E2. Serum total cholesterol was significantly increased by OVX, which was normalized by the combined intervention or E2 treatment. These results demonstrate that combined intervention of soybean isoflavone and exercise prevented body fat accumulation in the whole body with an increase in lean body mass and restoration of bone mass, and reduced high serum cholesterol in OVX mice.

Bone mineral measurements in mice: comparison of two devices

Animal models are widely used to explore the pathogenesis and management of osteoporosis. Mice are increasingly being used in animal models. We have evaluated the precision, accuracy, and ability to monitor changes in bone mineral measurements of mice with the Piximus and Hologic QDR 2000 devices. One hundred and twenty-two C57/BL6 mice were used in this study; 70 of them were put on a low calcium diet and followed prospectively for 14 wk. They were measured using both devices at baseline and at wk 14. Using the Piximus, we measured the whole body, the tibia, and two caudal vertebrae. Using the Hologic, we measured the tibia, which we divided into three equal parts. The remaining mice were used to evaluate the precision and accuracy of the measurement. The accuracy, which was determined only for the Hologic device, revealed a mean difference between the in vivo bone mineral content (BMC) and the ash weight of 0.1 mg. The precision, evaluated from the coefficient of variation (%) and the Smallest Detectable Difference (SDD, in absolute values) was good for both devices, confirming their ability to detect small differences in longitudinal studies: as little as 0.004 g for the BMC of the total tibia on both devices, and 0.003 g/cm2 for whole body bone mineral density (BMD) on the Piximus. The BMC found using the two devices was comparable, whereas the BMD obtained on the Hologic device was nearly double that found using the Piximus. The comparison of the results by Bland and Altman's method showed that the difference between the results was not dependent on the magnitude of the measurement. We concluded that bone density and bone-density changes in mice can be measured precisely in vivo using the Hologic and Piximus devices; the latter being able to measure the whole body BMD with good precision.