Age-related changes in bone mineral density, cross-sectional area and strength at different skeletal sites in male rats

Chronic Iodine Intake Excess Damages the Structure of Articular Cartilage and Epiphyseal Growth Plate

This study aimed to explore the influence of excess iodine on the articular cartilage and epiphyseal growth plate in rats. Wistar rats (n = 200) were randomly divided into five groups with 40 rats in each: normal iodine (NI), 5-fold high iodine group (5HI), 10-fold high iodine group (10HI), 50-fold high iodine group (50HI), and 100-fold high iodine group (100HI). The rats were executed in 6 and 12 months. 24-h urinary iodine concentration (UIC) was monitored by arsenic-cerium catalytic spectrophotometry. The chemiluminescence method was used to determine the thyroid function. The pathological changes in the epiphyseal plate, articular cartilage, and thickness of the epiphyseal plate were observed. The mRNA expression of collagen II (ColII), collagen X, matrix metalloproteinase-13 (MMP-13), and fibroblast growth factor receptor 1 in articular chondrocytes was detected by RT-PCR. 24-h UIC increased as iodine intake increased. In the 12th month, there was a significant increase in serum sTSH and a decrease in serum FT4 in HI groups, compared to the NI group. There was a decrease in the number of proliferating cells in the epiphyseal plate and an increase in the number of mast cell layers. The chondrocytes appeared disorganized, and the tidal lines were disturbed or even broken. Growth plate thickness decreased with increasing iodine intake. Compared with the NI group, ColII and MMP-13 mRNA expression in chondrocytes in all HI groups significantly increased. Chronic iodine overdose increases the risk of hypothyroidism. Chronic iodine overdose leads to abnormal morphology of epiphyseal growth plates and articular cartilage, increasing the risk of osteoarthritis.

Surgical Classification for Preclinical Rat Femoral Bone Defect Model: Standardization Based on Systematic Review, Anatomical Analysis and Virtual Surgery

Though surgical techniques profoundly influence in vivo experiments, significant heterogeneity exists in current surgeries for inducing rat femoral bone defects. Such variations reduce the reproducibility and comparability of preclinical studies, and are detrimental to clinical translation. The purposes of this study were: (1) to conduct a systematic review of rat femoral defect models, summarizing and analyzing the surgical techniques; (2) to analyze surgical design and potential pitfalls via 3D anatomy and virtual surgeries for fostering future precision research; and (3) to establish a surgical classification system, for improving the reproducibility and comparability among studies, avoiding unnecessary repetitive experiments. The online database PubMed was searched to identify studies from January 2000 to June 2022 using keywords, including rat, femur, bone defect. Eligible publications were included for a review of surgical methods. Anatomical analysis and virtual surgeries were conducted based on micro-CT reconstruction of the rat femur for further investigation and establishment of a classification system. A total of 545 publications were included, revealing marked heterogeneity in surgical methods. Four major surgical designs were reported for inducing defects from the proximal to distal femur: bone tunnel, cortical window, segmental defect, and wedge-shaped defect. Anatomical analysis revealed potential pitfalls hindering efficient clinical translation. A classification system was established according to the anatomical region, surgical design, and fixation devices. This systematic review in combination with 3D analysis and virtual surgery provides a general overview of current surgical approaches to inducing femoral defects in rats, and establishes a surgical classification facilitating preclinical research of quality and translational value.

Cetaceans Humerus Radiodensity by CT: A Useful Technique Differentiating between Species, Ecophysiology, and Age

Cetaceans are mammals that underwent a series of evolutionary adaptations to live in the aquatic environment, including morphological modifications of various anatomical structures of the skeleton and their bone mineral density (BMD); there are few studies on the latter. BMD is related to the radiodensity measured through computed tomography (CT) in Hounsfield units (HU). This work aimed to test and validate the usefulness of studying humeral bone radiodensity by CT of two cetacean species (the Atlantic spotted dolphin and the pygmy sperm whale) with different swimming and diving habits. The radiodensity was analysed at certain levels following a new protocol based on a review of previous studies. Humeral radiodensity values were related to four aspects: species, diving behaviour, swimming activity level, and age. We observed that the consistent differences in the radiodensity of the cortical bone of the distal epiphysis between animals of different life-history categories suggest that this bone portion could be particularly useful for future ontogenetic studies. Hence, this technique may be helpful in studying and comparing species with different ecophysiologies, particularly distinguishing between swimming and diving habits.

Combination treatment with ibandronate and eldecalcitol prevents osteoporotic bone loss and deterioration of bone quality characterized by nano-arrangement of the collagen/apatite in an ovariectomized aged rat model

Combination therapy with bisphosphonates and vitamin D₃ analogs has been frequently used for the treatment of osteoporosis. However, its effects on bone anisotropies, such as orientations of collagen and apatite at the nanometer-scale, which is a promising bone quality index, and its trabecular architecture at the micrometer scale, are not well understood despite its important mechanical properties and its role in fracture risk. In the present study, we analyzed the effects of ibandronate (IBN), eldecalcitol (ELD), and their combination on the collagen/apatite orientation and trabecular architectural anisotropy using an estrogen-deficiency-induced osteoporotic rat model. Estrogen deficiency caused by ovariectomy (OVX) excessively increased the degree of collagen/apatite orientation or trabecular architectural anisotropy along the craniocaudal axis in the lumbar vertebra compared to that of the sham-operated group. The craniocaudal axis corresponds to the direction of principal stress in the spine. The excessive material anisotropy in the craniocaudal axis contributed to the enhanced Young's modulus, which may compensate for the reduced mechanical resistance by bone loss to some extent. The solo administration of IBN and ELD prevented the reduction of bone fraction (BV/TV) determined by μ-CT, and combination therapy showed the highest efficacy in BV/TV gain. Furthermore, the solo administration and combination treatment significantly decreased the degree of collagen/apatite orientation to the sham level. Based on the results of bone mass and collagen/apatite orientation, combination treatment is an effective strategy. This is the first report to demonstrate the efficacy of IBN, ELD, and combination treatment with IBN and ELD relative to the bone micro-architectural anisotropy characterized by collagen/apatite orientation.

Bone Structural, Biomechanical and Histomorphometric Characteristics of the Hindlimb Skeleton in the Marsh Rice Rat (Oryzomys palustris)

INTRODUCTION

The rice rat (Oryzomys palustris) is a non-conventional laboratory rodent species used to model some human bone disorders. However, no studies have been conducted to characterize the postcranial skeleton. Therefore, we aimed to investigate age- and gender-related features of the hindlimb skeleton of this species.

METHODS

We used femurs and tibiae from 94 rats of both genders aged 4-28 wks. Bone mineral content (BMC), volumetric bone mineral density (vBMD), and biomechanical properties were determined in femurs. In addition, bone histomorphometry of tibiae was conducted to assess bone cell activities and bone turnover over time.

RESULTS

Bone length, total metaphysis BMC and vBMD, mid-diaphyseal BMC and vBMD, cortical thickness, and cortical area progressively augmented with age. Whereas the increase in these parameters plateaued at age 16-22 wks in female rats, they continued to rise to age 28 wks in male rats. Furthermore, bone strength parameters increased with age, with few differences between genders. We also observed a rapid decrease in longitudinal growth between ages 4-16 wks. Whereas young rats had a greater bone formation rate and bone turnover, older rice rats had greater bone volume and trabecular thickness, with no differences between genders.

CONCLUSIONS

1) Sexual dimorphism in the rice rat becomes grossly evident at age 16 wks; 2) the age-related increases in bone mass, structural cortical parameters, and in some biomechanical property parameters plateau at an older age in male than in female rats; and 3) bone growth and remodeling significantly decreased with age irrespective of the gender.

Changes in bone mass associated with obesity and weight loss in humans: Applicability of animal models

The implications of obesity and weight loss for human bone health are not well understood. Although the bone changes associated with weight loss are similar in humans and rodents, that is not the case for obesity. In humans, obesity is generally associated with increased bone mass, an outcome which is exacerbated by advanced age and menopause. In rodents, by contrast, bone mass decreases in proportion to severity and duration of obesity, and is influenced by sex, age and mechanical load. Despite these discrepancies, rodents are frequently used to model the situation in humans. In this review, we summarise the existing knowledge of the effects of obesity and weight loss on bone mass in humans and rodents, focusing on the translatability of findings from animal models. We then describe how animal models should be used to broaden the understanding of the relationship between obesity, weight loss, and skeletal health in humans. Specifically, we highlight the aspects of study design that should be considered to optimise translatability of the rodent models of obesity and weight loss. Notably, the sex, age, and nutritional status of the animals should ideally match those of interest in humans. With these caveats in mind, and depending on the research question asked, our review underscores that animal models can provide valuable information for obesity and weight-management research.

Age-Related Increases in Marrow Fat Volumes have Regional Impacts on Bone Cell Numbers and Structure

The increasing levels of bone marrow fat evident in aging and osteoporosis are associated with low bone mass and attributed to reduced osteoblastogenesis. Local lipotoxicity has been proposed as the primary mechanism driving this reduction in bone formation. However, no studies have examined the correlation between high levels of marrow fat volumes and changes in local cellularity. In this study, we hypothesize that areas of bone marrow with high fat volumes are associated with significant changes in cell number within a similar region of interest (ROI). Inbred albino Louvain (LOU) rats, originating from the Wistar strain, have been described as a model of healthy aging with the absence of obesity but expressing the typical features of age-related bone loss. We compared local changes in distal femur cellularity and structure in specific ROI of undecalcified bone sections from 4- and 20-month-old male and female LOU rats and Wistar controls. Our results confirmed that older LOU rats exhibited significantly higher fat volumes than Wistar rats (p < 0.001). These higher fat volume/total volume were associated with lower trabecular number (p < 0.05) and thickness (p < 0.05) and higher trabecular separation (p < 0.05). In addition, osteoblast and osteocyte numbers were reduced in the similar ROI containing high levels of adiposity, while osteoclast number was higher compared to control (p < 0.03). In summary, marrow ROIs with a high level of adiposity were associated with a lower bone mass and changes in cellularity explaining associated bone loss. Further studies assessing the levels of lipotoxicity in areas of high local marrow adiposity and identifying molecular actors involved in this phenomenon are still required.

Aging and low-intensity exercise change oxidative biomarkers in brain regions and radiographic measures of femur of Wistar rats

We investigated changes in oxidative biomarkers in brain regions such as brainstem, cerebellum, and cerebral cortex of 3-, 6-, 18-, 24-, and 30-month-old rats. We also assessed the effects of low-intensity exercise on these biomarkers in these regions of 6-, 18-, and 24-month-old rats that started exercise on a treadmill at 3, 15, and 21 months of age, respectively. Radiographic images of the femur were taken for all rats. A total of 25 rats (age: twelve 6-, ten 18-, ten 24-, and three 30-month-old rats) were used. Lipid hydroperoxide levels increased in cerebellum at 18 months. Total antioxidant activity exhibited lowest values in brainstem at 3 months. Superoxide dismutase activity did not exhibit significant changes during aging. Total thiol content exhibited lowest values in brain regions of 24- and 30-month-old rats. Exercise reduced total thiol content in brainstem at 6 months, but no change occurred in other regions and other ages. Femur increased its length and width and cortical thickness with advancing age. No change occurred in medullary width. Radiolucency increased and sclerosis was found in cortical and medullary bone with advancing age. Exercise reduced radiolucency and medullary sclerosis. Therefore, aging differentially changed oxidative biomarkers in different brain regions and radiographic measures of the femur. Low-intensity exercise only ameliorated some radiographic measurements of femur. Since the present study possessed limitations (small number of rats per group), a beneficial effect of regular low-intensity exercise on oxidative markers in brain cannot be ruled out.

Isolated Cyclic Loading During Adolescence Improves Tibial Bone Microstructure and Strength at Adulthood

Bone is a unique living tissue, which responds to the mechanical stimuli regularly imposed on it. Adolescence facilitates a favorable condition for the skeleton that enables the exercise to positively influence bone architecture and overall strength. However, it is still dubious for how long the skeletal benefits gained in adolescence is preserved at adulthood. The current study aims to use a rat model to investigate the effects of in vivo low- (LI), medium- (MI), and high- (HI) intensity cyclic loadings applied during puberty on longitudinal bone development, morphometry, and biomechanics during adolescence as well as at adulthood. Forty-two young (4-week-old) male rats were randomized into control, sham, LI, MI, and HI groups. After a 5 day/week for 8 weeks cyclic loading regime applied on the right tibia, loaded rats underwent a subsequent 41-week, normal cage activity period. Right tibias were removed at 52 weeks of age, and a comprehensive assessment was performed using μCT, mechanical testing, and finite element analysis. HI and MI groups exhibited reduced body weight and food intake at the end of the loading period compared with shams, but these effects disappeared afterward. HI cyclic loading increased BMD, bone volume fraction, trabecular thickness, trabecular number, and decreased trabecular spacing after loading. All loading-induced benefits, except BMD, persisted until the end of the normal cage activity period. Moreover, HI loading induced enhanced bone area, periosteal perimeter, and moment of inertia, which remained up to the 52nd week. After the normal cage activity at adulthood, the HI group showed increased ultimate force and stress, stiffness, postyield displacement and energy, and toughness compared with the sham group. Overall, our findings suggest that even though both trabecular and cortical bone drifted through age-related changes during aging, HI cyclic loading performed during adolescence can render lifelong benefits in bone microstructure and biomechanics. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

N-Acetyl Cysteine Treatment Restores Early Phase Fracture Healing in Ethanol-Fed Rats

BACKGROUND

Fracture healing in alcoholics is delayed and often associated with infections resulting in prolonged rehabilitation. It has been reported that binge drinking of alcohol increases oxidative stress and delays fracture healing in rats, which is prevented by treatment with the antioxidant n-acetyl cysteine (NAC). Oxidative stress is a significant factor in pathologies of various organs resulting from chronic alcoholism. Therefore, we hypothesize that treatment with NAC reduces oxidative stress and restores fracture healing in chronic alcoholics.

METHODS

Rats (10 months old) were pair-fed the Lieber-DeCarli ethanol (EtOH) diet or control diet for 16 weeks. A closed fracture was performed and rats allowed to recover for 72 hours. Rats were divided into 4 groups-control, control + NAC, EtOH, and EtOH + NAC-and injected intraperitoneally with 200 mg/kg of NAC daily for 3 days. Serum and bone fracture callus homogenates were collected and assayed for traditional markers of inflammation, oxidative stress, and bone regeneration.

RESULTS

The oxidative stress marker malondialdehyde (MDA) was increased in both serum and bone tissue in EtOH-fed animals compared to controls. NAC treatment significantly (p < 0.01) reduced MDA to near normal levels and dramatically increased the index of antioxidant efficacy (catalase/MDA ratio) (p < 0.01). Inflammatory markers tumor necrosis factor-α, interferon-γ, and interleukin-6 were significantly decreased in serum and callus following NAC treatment. NAC treatment reduced EtOH-induced bone resorption as evidenced by significant decreases in C-telopeptide of type-I-collagen levels (p < 0.05) and band-5 tartrate-resistant acid phosphatase levels in the tissue (p < 0.001).

CONCLUSIONS

Oxidative stress and excessive inflammation are involved in the inhibition of fracture healing by EtOH. In this study, early short-term treatment of EtOH-fed animals with the antioxidant NAC reduced oxidative stress and normalized the innate immune response to fracture in the early phase of fracture healing, thereby restoring the normal onset of bone regeneration.

Organ and tissue level properties are more sensitive to age than osteocyte lacunar characteristics in rat cortical bone

Modeling and remodeling induce significant changes of bone structure and mechanical properties with age. Therefore, it is important to gain knowledge of the processes taking place in bone over time. The rat is a widely used animal model, where much data has been accumulated on age-related changes of bone on the organ and tissue level, whereas features on the nano- and micrometer scale are much less explored. We investigated the age-related development of organ and tissue level bone properties such as bone volume, bone mineral density, and load to fracture and correlated these with osteocyte lacunar properties in rat cortical bone. Femora of 14 to 42-week-old female Wistar rats were investigated using multiple complementary techniques including X-ray micro-computed tomography and biomechanical testing. The body weight, femoral length, aBMD, load to fracture, tissue volume, bone volume, and tissue density were found to increase rapidly with age at 14–30 weeks. At the age of 30–42 weeks, the growth rate appeared to decrease. However, no accompanying changes were found in osteocyte lacunar properties such as lacunar volume, ellipsoidal radii, lacunar stretch, lacunar oblateness, or lacunar orientation with animal age. Hence, the evolution of organ and tissue level properties with age in rat cortical bone is not accompanied by related changes in osteocyte lacunar properties. This suggests that bone microstructure and bone matrix material properties and not the geometric properties of the osteocyte lacunar network are main determinants of the properties of the bone on larger length scales.

Resveratrol as anti-aging therapy for age-related bone loss

INTRODUCTION

Previous studies have indicated that resveratrol, a natural phytoestrogen, can act as an anti-aging therapy to resist age-related changes of several body tissues. However, the anti-aging effects of resveratrol on bone have been poorly investigated in this natural aging population. Accordingly, this study was design to evaluate the effects of resveratrol on bone mass and biomechanical properties in old rat femora.

METHODS

Twenty 22-month-old male Wistar rats were divided into two randomly assigned groups (n=10). The first group was treated for 10 weeks with resveratrol (10 mg/kg per day) and the second group was left untreated (control). Rat femora were collected. Bone mass and bone microestructure were investigated by microcomputed tomography and histomorphometry. Biomechanical properties were determined by a three-point bending test. Plasma levels of CTX (carboxy-terminal telopeptide of type I collagen) and osteocalcin were also determined. Statistical analyses were performed by a Student two-tailed unpaired t-test. In all experiments, a value of p<0.05 was considered significant.

RESULTS

Microcomputed tomography analyses demonstrated that resveratrol-treated rats had significant higher bone volume, bone trabecular number, and cortical thickness and lower spacing between trabeculae in comparison to the control group. Histomorphometric analyses confirmed the increase of bone volume in resveratrol-treated rats compared to controls. Resveratrol-treated rats had significant higher bone flexural modulus, stiffness, and ultimate load compared to control group. Treatment was not associated with changes in plasma CTX or osteocalcin.

CONCLUSION

These findings demonstrate that resveratrol increases bone microstructure and bone mechanical properties in old male rats, suggesting that resveratrol might be used as anti-aging therapy to resist age-induced bone loss.

Impact of orange juice consumption on bone health of the U.S. population in the national health and nutrition examination survey 2003-2006

Orange juice (OJ) fortified with calcium (Ca) and vitamin D has turned OJ into a readily available source of these nutrients for children and adults. However, the impact of OJ consumption on Ca and vitamin D adequacy and bone health has not been documented. The aim of this study was the evaluation of the contribution of 100% OJ consumption to dietary and serum Ca and vitamin D status, and bone health parameters in the U.S. population aged 4 years and older (n=13,971) using the National Health and Nutrition Examination Survey (NHANES) 2003-2004 and 2005-2006. Food consumption data were coded to produce micronutrient intake values using the USDA Food and Nutrient Database for Dietary Studies 3.0. Serum concentrations of bone-related micronutrients and biomarkers, bone mineral density (BMD), and bone mineral content (BMC) were measured. Analysis of data was conducted using SAS software 9.2 and SUDAAN. OJ consumers showed higher intakes of bone-related micronutrients, compared with nonconsumers (P<.05). In addition, OJ consumers had higher serum Ca levels in adults (P<.01) and had a lower odds ratio for serum 25-hydroxyvitamin D3 <20 ng/mL in children (P<.05). OJ consumption was positively associated with femur BMD in children (P<.05) and with femur BMC in both children and adults (P<.05). In conclusion, OJ may be recommended as an effective dietary means of improving the status of Ca and vitamin D, acid-base balance, and of promoting bone health in children and adults.

Resveratrol supplementation preserves long bone mass, microstructure, and strength in hindlimb-suspended old male rats

Resveratrol has gained popularity as an "anti-aging" compound due to its antioxidant and anti-inflammatory properties. Few studies have investigated the role of resveratrol supplementation in the prevention of age-related bone loss and skeletal disuse despite increased inactivity and age-related bone loss in the elderly. The objective of the study was to investigate the effect of resveratrol supplementation on disuse and age-related bone loss. Old (age 33 months) Fischer 344 × Brown Norway male rats were provided either trans-resveratrol (12.5 mg/kg bw/day) or deionized distilled water by oral gavage for 21 days. Rats were hindlimb-suspended (HLS) or kept ambulatory (AMB) for 14 days. Both femora and tibiae were collected. Bone mass was measured by dual-energy X-ray absorptiometry and bone microstructure was determined by micro-computed tomography. HLS of old male rats accelerated loss of bone mineral content, decreased trabecular bone volume per unit of total volume, and increased trabecular separation. Resveratrol supplementation ameliorated bone demineralization and loss of bone microarchitecture in HLS old male rats. The peak force measured by the three-point bending test was reduced (P = 0.007) in HLS/control compared to AMB/control rats. Resveratrol supplementation ameliorated HLS-induced loss of femur strength. Plasma osteocalcin and alkaline phosphatase was higher (P < 0.04) and C-reactive protein was lower (P = 0.04) in old male rats given resveratrol. The bone protective effects of resveratrol appeared to be mediated through increased osteoblast bone formation, possibly due to reduced inflammation. Based on the results, resveratrol supplementation appeared to provide a feasible dietary therapy for preserving the skeletal system during disuse and age-related bone loss.

Basic biology of skeletal aging: role of stress response pathways

Although a decline in bone formation and loss of bone mass are common features of human aging, the molecular mechanisms mediating these effects have remained unclear. Evidence from pharmacological and genetic studies in mice has provided support for a deleterious effect of oxidative stress in bone and has strengthened the idea that an increase in reactive oxygen species (ROS) with advancing age represents a pathophysiological mechanism underlying age-related bone loss. Mesenchymal stem cells and osteocytes are long-lived cells and, therefore, are more susceptible than other types of bone cells to the molecular changes caused by aging, including increased levels of ROS and decreased autophagy. However, short-lived cells like osteoblast progenitors and mature osteoblasts and osteoclasts are also affected by the altered aged environment characterized by lower levels of sex steroids, increased endogenous glucocorticoids, and higher oxidized lipids. This article reviews current knowledge on the effects of the aging process on bone, with particular emphasis on the role of ROS and autophagy in cells of the osteoblast lineage in mice.

Reference point indentation study of age-related changes in porcine femoral cortical bone

The reference point indentation (RPI) method is a microindentation technique involving successive indentation cycles. We employed RPI to measure average stiffness (Ave US), indentation distance increase (IDI), total indentation distance (TID), average energy dissipated (Ave ED), and creep indentation distance (CID) of swine femoral cortical bone (mid-diaphysis) as a function of age (1, 3.5, 6, 14.5, 24, and 48 months) and loading directions (longitudinal and transverse). The Ave US increases with animal age, while the IDI, TID, Ave ED, and CID decrease with age, for both longitudinal (transverse surface) and transverse (periosteal surface) loading directions. Longitudinal measurements generally give higher Ave US and lower IDI and TID values compared to transverse measurements. The RPI measurements show similar trends to those obtained using nanoindentation test, and ash and water content tests.

Aging mechanisms in bone

Advancing age and loss of bone mass and strength are closely linked. Elevated osteoblast and osteocyte apoptosis and decreased osteoblast number characterize the age-related skeletal changes in humans and rodents. Similar to other tissues, oxidative stress increases in bone with age. This article reviews current knowledge on the effects of the aging process on bone and its cellular constituents, with particular emphasis on the role of reactive oxygen species (ROS). FoxOs, sirtuins and the p53/p66^shc signaling cascade alter osteoblast number and bone formation via ROS-dependent and -independent mechanisms. Specifically, activation of the p53/p66^shc signaling increases osteoblast/osteocyte apoptosis in the aged skeleton and decreases bone mass. FoxO activation in osteoblasts prevents oxidative stress to preserve skeletal homeostasis. However, while defending against stress FoxOs bind to β-catenin and attenuate Wnt/T-cell cell factor transcriptional activity and osteoblast generation. Thus, pathways that impact longevity and several diseases of ageing might also contribute to age-related osteoporosis.

Unraveling the role of FoxOs in bone--insights from mouse models

The FoxO subfamily of forkhead transcription factors plays a critical role in a variety of physiological processes including metabolism, differentiation, proliferation, apoptosis and protection from stress. FoxO activity is inhibited by growth factors and the insulin signaling pathways and stimulated by nutrient depletion and a plethora of reactive oxygen species (ROS)-induced post-translational modifications. Recent studies have uncovered a fundamental role for FoxOs in skeletal homeostasis. In cells of the osteoblast lineage, FoxOs modulate redox balance, protein synthesis, and differentiation through the activation of specific gene programs and interaction with other transcription factors and co-factors such as β-catenin, ATF-4, and Runx2. FoxO activation also attenuates osteoclastogenesis through both cell autonomous and indirect mechanisms. In this review I discuss recent advances in the understanding of FoxO specific actions in osteoblast progenitors, osteoblasts, and osteoclast, as well as the implications of FoxO activation for age-related skeletal involution.

Perinatal exposure to environmental contaminants detected in Canadian Arctic human populations changes bone geometry and biomechanical properties in rat offspring

Arctic inhabitants consume large proportions of fish and marine mammals, and are therefore continuously exposed to levels of environmental toxicants, which may produce adverse health effects. Fetuses and newborns are the most vulnerable groups. The aim of this study was to evaluate changes in bone geometry, mineral density, and biomechanical properties during development following perinatal exposure to a mixture of environmental contaminants corresponding to maternal blood levels in Canadian Arctic human populations. Sprague-Dawley rat dams were dosed with a Northern Contaminant Mixture (NCM) from gestational day 1 to postnatal day (PND) 23. NCM contains 27 contaminants comprising polychlorinated biphenyls, organochlorine pesticides, and methylmercury. Femurs were collected on PND 35, 77 and 350, and diaphysis was analyzed by peripheral quantitative computed tomography and three-point bending test, while femoral neck was assessed in an axial loading experiment. Dose-response modeling was performed to establish the benchmark dose (BMD) for the analyzed bone parameters. Exposure to the high dose of NMC resulted in short and thin femur with reduced mechanical strength in offspring at PND35. BMD of femur length, cortical area, and stiffness were 3.2, 1.6, and 0.8 mg/kg bw/d, respectively. At PND77 femur was still thin, but at PND350 no treatment-related bone differences were detected. This study provides new insights on environmental contaminants present in the maternal blood of Canadian Arctic populations, showing that perinatal exposure induces bone alterations in the young offspring. These findings could be significant from a health risk assessment point of view.

Integrative physiology of the aging bone: insights from animal and cellular models

Age-related bone loss is a common worldwide phenomenon in the aging population, placing them at an increased risk of fractures. Fortunately, basic and translational studies have been pivotal in providing us with a mechanistic understanding of the cellular and molecular pathophysiology of this condition. This review focuses on the current concepts and paradigms of age-related bone loss and how various animal and cellular models have broadened our understanding in this fascinating but complex area. Changes in hormonal, neuronal, and biochemical cues with age and their effect on bone have been discussed. This review also outlines recent studies on the relationship between bone and fat in the marrow, as well as the fate of the marrow mesenchymal stromal cell population, which can give rise to either bone-forming osteoblasts or fat-forming adipocytic cells as a function of age.

Effects of tissue age on bone tissue material composition and nanomechanical properties in the rat cortex

Although osteoporosis is known to alter bone tissue composition, the effects of such compositional changes on tissue material properties have not yet been examined. The natural gradient in tissue mineral content arising from skeletal appositional growth provides a basic model for investigation of relationships between tissue composition and mechanical properties. The purpose of this study was to examine the effects of tissue age on bone tissue composition and nanomechanical properties. The nanomechanical properties and composition of regions of differing tissue age were characterized in the femoral cortices of growing rats using nanoindentation and Raman spectroscopy. In addition, spatial maps of the properties of periosteal tissue were examined to investigate in detail the spatial gradients in the properties of newly formed tissue. Newly formed tissue (0-4 days) was 84% less stiff and had 79% lower mineral:matrix ratio than older intracortical (15-70 days) tissue. Tissue modulus, hardness, mineral:matrix ratio, and carbonate:phosphate ratio increased sharply with distance from the periosteum and attained the properties of intracortical tissue within 4 days of formation. The mineral: matrix ratio explained 54% and 62% of the variation in tissue indentation modulus and hardness, respectively. Our data demonstrate significant variations in tissue mechanical properties with tissue age and relate mechanical properties to composition at the microscale.

An in vivo magnetic resonance imaging technique for measurement of rat lumbar vertebral body blood perfusion

The technical feasibility of dynamic contrast-enhanced magnetic resonance imaging (MRI) measurement of rat vertebral blood perfusion using a 1.5 T clinical scanner and a small surface coil was investigated in this study. Nine male 7-month-old Wistar-Kyoto rats were used. Computed tomographic assessment of lumbar vertebral bone mineral density (BMD) and MRI assessment of lumbar vertebral blood perfusion were performed twice with 8 weeks' interval. A 4.7 cm surface coil was used for receiving radiofrequency signal. Gadolinium-DOTA (0.3 mmol/kg) was injected through the tail vein of the rat as a quick bolus and dynamic MRI scan was carried out on the central sagittal plane of the lumbar spine for 8 min with a temporal resolution of 0.6 s. Blood perfusion parameters of wash-in rate, maximum enhancement and wash-out rate were derived from the dynamic MR images. No vertebral body size and vertebral BMD difference was detected between the two time points ( P = 0.222 and 0.123, respectively). Wash-in rate was 0.105 (±0.016)% and 0.111 (±0.018)%, maximum enhancement 126.5 (±10.6)% and 129.2 (±13.4)%, and wash-out rate 0.788 (±0.182)% and 0.792 (±0.182)% for the two time points. With these parameters, no difference was found between the two time points with a P value of 0.575, 0.889 and 0.754, respectively. We conclude that dynamic contrast-enhanced MRI measurement of rat vertebral blood perfusion using a 1.5 T clinical scanner and a small surface coil is feasible and reliable. This technique offers a non-invasive means to probe vertebral blood perfusion changes associated with rat disease models.

Age-related bone loss in the LOU/c rat model of healthy ageing

Inbred albino Louvain (LOU) rats are considered a model of healthy aging due to their increased longevity in the absence of obesity and with a low incidence of common age-related diseases. In this study, we characterized the bone phenotype of male and female LOU rats at 4, 20 and 27 months of age using quantitative micro computed tomographic (mCT) imaging, histology and biochemical analysis of circulating bone biomarkers. Bone quality and morphometry of the distal femora, assessed by mCT, was similar in male and female rats at 4 months of age and deteriorated over time. Histochemical staining of undecalcified bone showed a significant reduction in cortical and trabecular bone by 20 months of age. The reduction in mineralized tissue was accompanied by reduced numbers of osteoblasts and osteoclasts and a significant increase in marrow adiposity. Biochemical markers of bone turnover, C-telopeptide and osteocalcin, correlated with the age-related bone loss whereas the calciotropic hormones PTH and vitamin D remained unchanged over time. In summary, aged LOU rats exhibit low-turnover bone loss and marrow fat infiltration, which are the hallmarks of senile osteoporosis, and thus represent a novel model in which to study the molecular mechanisms leading to this disorder.

Three-dimensional microstructure of the bone in a hamster model of senile osteoporosis

Age-related bone loss, which is poorly characterized, is a major underlying cause of osteoporotic fractures in the elderly. In order to identify the morphological feature of age-related bone loss, we investigated sex and site (tibia, femur and vertebra) dependence of bone microstructure in aging hamsters from 3 to 24 months of age using micro-CT. In the proximal tibia and distal femur, trabecular bone volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th) and bone mineral density (BMD) increased to a maximum at 6 or 12 months and then declined progressively from 12 to 24 months of age. Trabecular separation (Tb.Sp), trabecular bone pattern factor (TBPf) and structure model index (SMI) increased with age. As compared with male hamsters, BV/TV and Tb.N were significantly lower in females at 18 and 24 months of age. Age-related decrease of trabecular BV/TV in the vertebral body was less than that of the femoral and tibial metaphyses. In the mid-femoral diaphysis, cortical bone area remained constant from 3 to 24 months of age. Cortical thickness decreased from 12 to 24 months and cortical BMD declined significantly from 18 to 24 months of age. These findings indicate that skeletal site and sex differences exist in hamster bone structure. Age-related bone changes in hamsters resemble those in humans. We conclude that hamster may be a useful model to study at least some aspects of bone loss during human aging.

Ovariectomy sensitizes rat cortical bone to whole-body vibration

This study was designed to determine the modulatory effect of estrogen on mechanical stimulation in bone. Trabecular and cortical bone compartments of ovariectomized rats exposed to whole-body vibration of different amplitudes were evaluated by peripheral quantitative computed tomographic (pQCT) analysis and histomorphometry and compared to controls not exposed to vibration. Rats underwent whole-body vibration (20 minutes/day, 5 days/week) on a vibration platform for 2 months. The control rats were placed on the platform without vibration for the same time. We divided rats into six groups: a sham control (SHAM); a sham vibrated (SHAM-V) at 30 Hz, 0.6 g; a SHAM-V at 30 Hz, 3g; an ovariectomized control (OVX); an ovariectomized vibrated (OVX-V) at 30 Hz, 0.6 g; and an OVX-V at 30 Hz, 3g. In vivo, pQCT analyses of the tibiae were performed at the start of the experiment and after 4 and 8 weeks. After 8 weeks the tibiae were excised for histomorphometric and for in vitro pQCT analyses. In the SHAM-V group, vibration had no effect upon the different bone parameters. In the OVX-V group, vibration induced a significant increase compared to the OVX group of the cortical and medullary areas (P < 0.01) and of the periosteal (P < 0.01) and endosteal (P < 0.05) perimeters at the 3 g vibration. The strain strength index increased in the OVX-V group significantly (P < 0.01) at the higher vibration. The results showed that low-amplitude, high-frequency whole-body vibration is anabolic to bone in OVX animals. The osteogenic potential is limited to the modeling of the bone cortex and depends on the amplitude of the vibration.

Influence of physical exercise and food restriction on the biomechanical properties of the femur of ageing male rats

BACKGROUND

Voluntary running in wheels as well as food reduction increase the life spans of rats. Disparate parameters such as the collagen biomarker of ageing and the development of kidney pathologies are decreased by voluntary exercise. There are few reports on the influence of physical exercise and food restriction on the skeleton of male rats. Most investigations initiated rather short-term interventions in 4- to 5-week-old animals and thus studied more the influence of growth than the influence of ageing on the skeleton.

OBJECTIVE

To compare the effects of physical exercise and food restriction on the biomechanical properties of bone tissue of ageing male rats with the interventions starting at the age of 5 months with the end point at 23 months. This enables the study of the influence of these interventions on the ageing of the skeleton.

METHODS

Five groups of male Sprague-Dawley rats were used: baseline (BL), voluntarily running in wheels (RW), food restriction to attain pair weight with RW animals (PW), forced running in treadmills (TM), and sedentary controls (SE). The biomechanical properties of femoral neck, diaphysis, and distal metaphysis were measured.

RESULTS

While the body weights and fat-free mass increased from BL to SE group, the occiput-sacrum length did not increase and the length of the femur increased marginally. These lengths were slightly retarded in RW and PW groups compared to the SE group. The strength of the distal femoral metaphysis decreased from BL to SE group. This decrease was counteracted by physical exercise (RW and TM groups) as well as by food restriction (PW group). In contrast, the strength of the femoral mid-diaphysis did not differ between BL and SE groups.

CONCLUSIONS

The distal metaphysis in the male rat femur is more prone to decreasing biomechanical strength than the diaphysis during ageing. Physical exercise, when started at the age of 5 months, when the skeleton has reached its adult size, is somewhat effective in counteracting these changes. There is also some retarding effect of food restriction.

Bone loss dynamics result in trabecular alignment in aging and ovariectomized rats

Because of the destructive nature of techniques used to measure bone morphometry, studies of architectural changes and bone loss have utilized cross-sectional study designs, with all its inherent limitations in nuances. Here, the results of a longitudinal study using in vivo micro-CT are presented elucidating the dynamics of bone loss and architectural adaptation in rat models of aging and postmenopausal bone loss. Using 3-D methodology, we observed the changes in bone architecture in the proximal tibia of normally aging and ovariectomized rats for 54 weeks. Spatial patterns in bone resorption were observed that were similar for both groups. Remaining trabeculae increased in thickness or were remodeled into new trabecular structures, especially in the ovariectomized animals. The combination of bone loss and bone formation resulted in alignment of trabeculae across the growth plate. Cortical modeling that was associated with growth continued after cessation of longitudinal growth in the ovariectomized animals, resulting in shape changes of the proximal tibia. The organized nature of the changes in bone architecture that occurred after ovariectomy and the high similarity with the changes observed in the normally aging animals, suggest that estrogen depletion resulted in an acceleration of a normal bone adaptation process. The observed aligning of trabeculae suggests regulation through mechanical loading.

Hyperbilirubinemia is not a major contributing factor to altered bone mineral density in patients with chronic liver disease

Reduced bone density is commonly encountered in patients with chronic liver disease. Prior studies have shown that unconjugated bilirubin inhibits osteoblast activity and function in vitro and in animal models of bone mineralization. To determine whether hyperbilirubinemia promotes the development of hepatic osteodystrophy, bone mineral density (BMD) was measured by dual energy X-ray absorptiometry in a cohort of 86 consecutive patients with chronic liver disease referred for liver transplant evaluation. The mean age of the study population was 52 years (range, 22-73), in which 52% were female and 90% were white. Average bone density values were significantly lower than expected for age, race, and sex, with Z-scores for the femoral neck and spine of -0.50 (95% confidence interval [CI] -0.63 to -0.37; p=0.0003) and -0.69 (95% CI -0.85 to -0.52; p=0.0001), respectively. Sixty-one subjects (71%) exhibited reduced BMD (T-score of femoral neck or spine<or=-1 standard deviation [SD] below the young-adult mean), and 18 subjects (21%) met criteria for osteoporosis (T-score<-2.5 SD). Stepwise logistic regression analyses identified significant associations between BMD and serum creatinine, alkaline phosphatase, age, and gender. On the other hand, neither unconjugated, nor conjugated, nor total serum bilirubin levels were found to predict diminished BMD. The lack of association between serum unconjugated bilirubin levels and bone mineralization was validated in hyperbilirubinemic Gunn rats, in which BMD and serum osteocalcin levels were no different than in wild-type rodents. In conclusion, the finding that serum bilirubin levels do not correlate with reduced BMD in patients with end-stage liver disease, and that chronic unconjugated hyperbilirubinemia does not lead to alterations in bone mineralization in Gunn rats, suggests that bilirubin is not a major contributing factor to hepatic osteodystrophy.

Analyses of hind leg skeletons in human growth hormone transgenic rats

Growth hormone (GH) is essential in the development and growth of the skeleton and for the maintenance of bone mass and density, and its secretion is known to decline with aging. We have previously produced transgenic rats with low circulating GH that represent several age-associated phenotypes such as obesity, insulin-resistance and leptin-resistance. In the present study, the cross-sectional area, bone mineral density, and strength indexes of the hind leg skeletons of the transgenic rats were examined by an X-ray computed tomography scanning. The mean cross-sectional area of the transgenic rats showed no increase after 2 months old up to 8 months old and the strength indexes were significantly lower than their non-transgenic siblings at all ages examined. The trabecular bone mineral density in the transgenic rats drastically decreased at 8 months old, while the cortical bone mineral density was comparable to the non-transgenic rats, suggesting the onset of osteoporosis at this period. The results obtained in this study indicate that the transgenic rats could be useful model to gain insight into the complex mechanism leading to osteoporosis with aging.

Age-Related Changes in Bone Mineral Density, Cross-Sectional Area and the Strength of Long Bones in the Hind Limbs and First Lumbar Vertebra in Female Wistar Rats

Age-related changes in bone mineral density (BMD) and cross-sectional area and bone strength index (SSI) of the femur, tibia, humerus, and first lumbar vertebra in female Wistar (WM/MsNrs) rats were examined by a quantitative computed tomography (pQCT) method. One hundred and sixteen virgin female Wistar (WM/MsNrs) rats aged 2-33 months were used. The data indicate that the total BMD values of metaphyses and diaphyses of long bones increased until 12 months, then decreased to a varying degree depending on the bone after 15-24 months, but the values of cortical and trabecular BMD with age were not always similar to the total BMD value. Nevertheless, the values for cross-sectional area and SSI in the long bones increased regardless of the total BMD decrease with age, indicating that this increase might have been due to a characteristic of the modeling pattern in rats. The total and cortical BMD values in the first lumbar vertebra decreased after 18 months, and SSI did after 15 months. The data obtained in this study were compared with those obtained from males in a previous study. In conclusion, it was indicated that in this strain the rats over 12 months with the highest total BMD values in the femur and tibia, and before the onset of various tumors, are useful as a model animal for osteoporosis experiments and observation of senile bone change.

A comparison of bone geometry and cortical density at the mid-femur between prepuberty and young adulthood using magnetic resonance imaging

In upper extremity bones, a sexual dimorphism exists in the development of periosteal and endocortical bone surfaces during growth. Little is known about developmental patterns of bone geometry at weight-bearing bones like the femur. Using MRI and dual energy X-ray absorptiometry (DXA), this study assessed the differences in mid-femoral total (TA), cortical (CA) and medullary areas (MA), cortical thickness, and cortical density (BMD(compartment)) between prepuberty and young adulthood in 145 healthy subjects (94 females) 6 to 25 years old. Additionally, agreement between mid-femoral total bone volume (TV) measurements by DXA and MRI were investigated. In both sexes, TA, CA, MA, and cortical thickness were significantly larger in adults compared to prepubertal subjects (P < 0.001), and males had greater values than females. This sex difference persisted for TA, CA, and cortical thickness (P < 0.05), but not MA, after adjusting for femur length and weight. Mean (SD) cortical BMD increased from 1.05 (0.07) and 1.09 (0.10) g/cm(3) in prepubertal children to 1.46 (0.14) and 1.42 (0.1) g/cm(3) in young adults, females and males, respectively (P < 0.001). TV measurements by DXA were significantly greater than by MRI (P < 0.001) in young adults. In conclusion, periosteal and endocortical expansion and increasing cortical BMD are the growth processes found at the mid-femur in both sexes. Our findings contrast to that in upper extremity bones, where MA is constant in females during growth. The difference in femoral bone development may be due to higher strains caused by weight bearing and genetic factors. DXA, in contrast to MRI, is inaccurate in the determination of mid-femoral TV measures.

Life span and spontaneous tumors incidence of the Wistar Mishima (WM/MsNrs) rat

The life spans and spontaneous tumors in a total of 1960 Wistar Mishima (WM/MsNrs) rats, inbred strain, from the 80-130th generations were examined. The average life span (mean +/- SD) was 731 +/- 173 days (n = 1053) in the males and 813 +/- 214 days (n = 907) in the females (p < 0.0001). The average life span of tumor-afflicted females was significantly longer than that of the non-tumor group (p < 0.0001), while no such difference was observed in males. Tumors were observed in 33 males (3.1%) and 246 females (27.1%). In the males, tumors were often observed under the skin (2.2%). Frequencies of tumors in lung and liver, bones and intestine were less than 0.5%. In the females, incidence of mammary tumor was 20.1%, and various organs such as ovaries, uterus, bones, lung, and liver had tumor incidence frequencies of less than 3.5%. It was concluded that WM/MsNrs rats might be suitable for life span and age-related studies because of their characteristics of length of longevity and the low incidence of spontaneous tumors in both sexes.