Age-related changes in bone mineral content and density in intact male F344 rats

Bone strength and composition in spacefaring rodents: systematic review and meta-analysis

Studying the effects of space travel on bone of experimental animals provides unique advantages, including the ability to perform post-mortem analysis and mechanical testing. To synthesize the available data to assess how much and how consistently bone strength and composition parameters are affected by spaceflight, we systematically identified studies reporting bone health in spacefaring animals from Medline, Embase, Web of Science, BIOSIS, and NASA Technical reports. Previously, we reported the effect of spaceflight on bone architecture and turnover in rodents and primates. For this study, we selected 28 articles reporting bone strength and composition in 60 rats and 60 mice from 17 space missions ranging from 7 to 33 days in duration. Whole bone mechanical indices were significantly decreased in spaceflight rodents, with the percent difference between spaceflight and ground control animals for maximum load of −15.24% [Confidence interval: −22.32, −8.17]. Bone mineral density and calcium content were significantly decreased in spaceflight rodents by −3.13% [−4.96, −1.29] and −1.75% [−2.97, −0.52] respectively. Thus, large deficits in bone architecture (6% loss in cortical area identified in a previous study) as well as changes in bone mass and tissue composition likely lead to bone strength reduction in spaceflight animals.

Allicin Reversed the Process of Frailty in Aging Male Fischer 344 Rats With Osteoporosis

The research and development of pharmaceutical intervention is insufficient for the frail older adults, especially in preclinical stage for the frail individuals with osteoporosis. Garlic exerts an antiosteoporotic effect and its vital component allicin could protect organisms against aging. The present study aimed to investigate the effect of long-term intragastric administration of allicin (low dose of 4 mg·kg⁻¹·d⁻¹; middle dose of 8 mg·kg⁻¹·d⁻¹; high dose of 16 mg·kg⁻¹·d⁻¹) on frailty with osteoporosis in aging male Fischer 344 rats. Frailty was assessed with a 27-item frailty index based on quantifying health-related deficits in adult male rats varied from 13 to 21 months and in control rats from 6 to 9 months. Osteoporosis was appraised by bone mineral density detected by dual-energy X-ray absorptiometry, biomechanical properties measured by a three-point bending test, and bone metabolic analysis using ELISA. Allicin could attenuate frailty index scores by reducing the accumulation of health deficits in aging male Fischer 344 rats. Meanwhile, allicin could protect against senile osteoporosis, and the underlying mechanism may involve in increasing low bone turnover through elevation of both bone formation and bone resorption, and subsequently lead to increase of bone mineral density, contributing to reversing deleterious bone biomechanical features associated with aging. The present study reveals firstly that long-term oral administration with allicin attenuated frailty with osteoporosis during the process of aging, which provides a preclinical evidence for intervention of frailty.

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.

High Impact Exercise Improves Bone Microstructure and Strength in Growing Rats

Physical activity is beneficial for skeletal development. However, impact sports during adolescence, leading to bone growth retardation and/or bone quality improvement, remains unexplained. This study investigated the effects of in vivo low (LI), medium (MI), and high (HI) impact loadings applied during puberty on bone growth, morphometry and biomechanics using a rat model. 4-week old rats (n = 30) were divided into control, sham, LI, MI, and HI groups. The impact was applied on the right tibiae, 5 days/week for 8 weeks mimicking walking (450 µε), uphill running (850 µε) and jumping (1250 µε) conditions. Trabecular and cortical parameters were determined by micro-CT, bone growth rate by calcein labeling and toluidine blue staining followed by histomorphometry. Bio-mechanical properties were evaluated from bending tests. HI group reduced rat body weight and food consumption compared to shams. Bone growth rate also decreased in MI and HI groups despite developing thicker hypertrophic and proliferative zone heights. HI group showed significant increment in bone mineral density, trabecular thickness, cortical and total surface area. Ultimate load and stiffness were also increased in MI and HI groups. We conclude that impact loading during adolescence reduces bone growth moderately but improves bone quality and biomechanics at the end of the growing period.

Can repeated in vivo micro-CT irradiation during adolescence alter bone microstructure, histomorphometry and longitudinal growth in a rodent model?

In vivo micro-computed tomography (micro-CT) can monitor longitudinal changes in bone mass and microstructure in small rodents but imposing high doses of radiation can damage the bone tissue. However, the effect of weekly micro-CT scanning during the adolescence on bone growth and architecture is still unknown. The right proximal tibia of male Sprague-Dawley rats randomized into three dose groups of 0.83, 1.65 and 2.47 Gy (n = 11/group) were CT scanned at weekly intervals from 4th to 12th week of age. The left tibia was used as a control and scanned only at the last time point. Bone marrow cells were investigated, bone growth rates and histomorphometric analyses were performed, and bone structural parameters were determined for both left and right tibiae. Radiation doses of 1.65 and 2.47 Gy affected bone marrow cells, heights of the proliferative and hypertrophic zones, and bone growth rates in the irradiated tibiae. For the 1.65 Gy group, irradiated tibiae resulted in lower BMD, Tb.Th, Tb.N and a higher Tb.Sp compared with the control tibiae. A decrease in BMD, BV/TV, Tb.Th, Tb.N and an increase in Tb.Sp were observed between the irradiated and control tibiae for the 2.47 Gy group. For cortical bone parameters, no effects were noticed for 1.65 and 0.83 Gy groups, but a lower Ct.Th was observed for 2.47 Gy group. Tibial bone development was adversely impacted and trabecular bone, together with bone marrow cells, were negatively affected by the 1.65 and 2.47 Gy radiation doses. Cortical bone microstructure was affected for 2.47 Gy group. However, bone development and morphometry were not affected for 0.83 Gy group. These findings can be used as a proof of concept for using the reasonable high-quality image acquisition under 0.83 Gy radiation doses during the adolescent period of rats without interfering with the bone development process.

High-fat/high-sucrose diet results in higher bone mass in aged rats

Intake of high-fat/high-sucrose (HFS) diet or high fat diet influences bone metabolism in young rodents, but its effects on bone properties of aged rodents still remain unclear. This study aimed to examine the effects of HFS diet intake on trabecular bone architecture (TBA) and cortical bone geometry (CBG) in aged rats. Fifteen male Wistar rats over 1 year were randomly divided into two groups. One group was fed a standard laboratory diet (SLD) and the other group was fed a HFS diet for six months. The femur/tibia, obtained from both groups at the end of experimental period, were scanned by micro-computed tomography for TBA/CBG analyses. Serum biochemical analyses were also conducted. Body weight was significantly higher in the HFS group than in the SLD group. In both femur and tibia, the HFS group showed higher trabecular/cortical bone mass in reference to bone mineral content, volume bone mineral density and TBA/CBG parameters compared with the SLD group. In addition, serum calcium, inorganic phosphorus, total protein, triacylglycerol, HDL and TRACP-5b levels were significantly higher in the HFS group than in the SLD group. There were good correlations between body weight and bone parameters in the femur and tibia. These results suggest that HFS diet intake results in higher bone mass in aged rats. Such effects of HFS diet intake might have been induced by increased body weight.

PIXE study on the effects of parathyroid hormone on elemental content in rat bones

Parathyroid hormone (PTH) has attracted considerable interest as a bone anabolic agent. PTH plays a central role in regulating calcium phosphate metabolism and its increases in production in response to low serum calcium levels. A continuous hypersecretion of PTH, as occurs in primary hyperparathyroidism, leads to bone resorption. In this study, the effect of different doses of parathyroid hormone (PTH) on bone mineral content (BMC) in rats was investigated by particle-induced X-ray emission (PIXE). This study will help in investigating further the toxicity of extremely high doses of PTH on BMC. For this study, PTH at doses of 15, 45, or 135μg/kg/day were applied to 9-month-old male and female Sprague Dawley (SD) rats. The concentrations of calcium (Ca), phosphorus (P), strontium (Sr), and zinc (Zn) were measured for bone treatment of PTH. From the results of the research, it was revealed that the biomechanical characteristics of the bone as well as the bone mass were enhanced after the treatment. It was further found that the concentrations of other elements also increased, excluding Zn. This research proved that PTH assists in the treatment of osteoporosis as revealed by the characteristics of different elements. PIXE can be used to determine the concentrations of bone mineral content.

Role of trace elements (Zn, Sr, Fe) in bone development: energy dispersive X-ray fluorescence study of rat bone and tooth tissue

Osteoporosis is one of the most common debilitating disease around the world and it is more and more established among young people. There are well known recommendations for nutrition of newborns and children concerning adequate calcium and vitamin D intake in order to maintain proper bone density. Nevertheless, important role in structure and function of a healthy bone tissue is played by an integration between all constituents including elements other than Ca, like trace elements, which control vital processes in bone tissue. It is important from scientific point of view as well as prevention of bone diseases, to monitor the mineralization process considering changes of the concentration of minerals during first stage of bone formation. This work presents studies of trace element (zinc, strontium, and iron) concentration in bones and teeth of Wistar rats at the age of 7, 14, and 28 days. Energy dispersive X-ray fluorescence (EDXRF) was used to examine mandibles, skulls, femurs, tibiae, and incisors. The quantitative analysis was performed using fundamental parameters method (FP). Zn and Sr concentrations were highest for the youngest individuals and decreased with age of rats, while Fe content was stable in bone matrix for most studied bones. Our results reveal the necessity of monitoring concentration of not only major, but also minor elements, because the trace elements play special role in the first period of bone development.

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.

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.

Characterization of skeletal alterations in a model of prematurely aging mice

An age-related bone loss occurs, apparently associated with the concomitant increase in an oxidative stress situation. However, the underlying mechanisms of age-related osteopenia are ill defined since these studies are time consuming and require the use of many animals (mainly rodents). Here, we aimed to characterize for the first time the bone status of prematurely aging mice (PAM), which exhibit an increased oxidative stress. Tibiae from adult (6 months) PAM show an increase in bone mineral density (BMD) and bone mineral content (assessed by bone densitometry) versus those in their normal counterparts (non-prematurely aging mice, NPAM) and similarly decreased in both kinds of mouse with age. However, at this bone site, trabecular BMD (determined by μ-computerized tomography) was similar in both adult PAM and old (18 months) NPAM. Femurs from these groups of mice present an increase in oxidative stress, inflammation, osteoclastogenic, and adipogenic markers, but a decrease in the gene expression of osteoblastic differentiation markers and of the Wnt/β-catenin pathway. Our findings show that adult PAM recapitulate various age-related bone features, and thus are a suitable model for premature bone senescence studies.

[Pathophysiology of aging bone]

Deterioration of organ and systems function are the principal signs of aging. Aging is also believed to be a major factor in the loss of bone mass and quality, which in turn leads to an increase in the risk of fractures. Several factors seem to contribute to this scenario, with metabolic changes related to aging in the bone tissue itself being among them. Most of the current knowledge on the mechanisms associated with osteopenia/osteoporosis during aging has been generated from research in animal models (mainly rats and mice) and cell cultures derived from subjects of different ages. In this work, we have reviewed and summarised these studies, which have begun to establish the physiological and molecular basis of the bone alterations related to aging.

PARALLEL CHANGES IN EXTRACELLULAR MATRIX PROTEIN GENE EXPRESSION, BONE FORMATION AND BIOMECHANICAL PROPERTIES IN AGING RAT BONE

The effect of aging on long bone mechanical properties and bone formative capacity was characterized in the male Fisher 344 rat. The femurs of rats from three age groups (4 mo., 12 mo. and 28 mo.) were tested in three-point bending to determine their structural properties. The apparent material properties were then calculated by adjusting for bone geometry. Bone formation was assessed by dynamic histomorphometry of both cortical and cancellous bone as well as by Northern blot analysis for the expression of the osteoblast phenotypic proteins osteopontin (OP), osteocalcin (OC), type I collagen (COL) and alkaline phosphatase (AP). Aging resulted in a decline in the apparent material properties that was associated with a compensatory alteration of bone geometry that preserved structural strength and stiffness. Histomorphometric analysis revealed significant age-related decreases in cancellous bone volume, trabecular number and increased trabecular separation suggesting the existence of senile osteopenia in the proximal tibia of the male Fisher 344 rat. A significant decline in bone formation rate (BFR), but not mineral apposition rate, suggests that a reduction in osteoblast number, but not osteoblast activity, contributes to age-related bone loss. The decline in BFR with aging was reflected in a decreased mRNA expression for OP, OC and COL but not AP. Further, the pattern of mRNA expression was consistent with reduced osteoblast differentiation with aging. The present study indicates the age-related decline in material properties of long bones is paralleled by a decrease in osteogenesis.

Interaction between exercise, dietary restriction and age-related bone loss in a rodent model of male senile osteoporosis

BACKGROUND

The pathophysiology of age-related bone loss and whether age-related bone loss can be prevented by exercise are still a matter of debate.

OBJECTIVE

It was the aim of this study to investigate the long-term effects of exercise and mild food restriction on bone mineral density (BMD) and bone geometry in the appendicular skeleton of aging male rats.

METHODS

Male Sprague-Dawley rats were studied from 5 to 23 months of age. The rats were divided into 4 groups: baseline, free access to food and running wheels (RW), fed to pair weight with the RW group (PW) and sedentary control animals with free access to food (SED). All rats were housed individually. Volumetric BMD and geometry of femurs and tibiae were assessed by peripheral quantitative computed tomography (pQCT). In addition, the tibial shafts were analyzed by cortical bone histomorphometry.

RESULTS

At the end of the experiment, RW and PW rats had similar body weight. The body weight of SED rats was 31% greater than that of RW rats. pQCT analysis of femurs and tibiae as well as histomorphometric analysis of the tibial shafts showed that dietary restriction resulted in an enlargement of the marrow cavity and cortical thinning at the femoral and tibial shafts relative to the RW and SED groups. Voluntary running exercise provided no additional protection against age-related bone loss when compared with the 31% heavier SED control rats. Neither exercise nor increased body weight in SED animals could completely prevent age-related bone loss between 19 and 23 months of age.

CONCLUSION

We conclude that dietary restriction had clear negative effects on BMD and bone geometry and that running wheel exercise provided partial protection but could not prevent age-related bone loss.

Insufficient DNA methylation affects healthy aging and promotes age-related health problems

DNA methylation plays an integral role in development and aging through epigenetic regulation of genome function. DNA methyltransferase 1 (Dnmt1) is the most prevalent DNA methyltransferase that maintains genomic methylation stability. To further elucidate the function of Dnmt1 in aging and age-related diseases, we exploited the Dnmt1+/− mouse model to investigate how Dnmt1 haploinsufficiency impacts the aging process by assessing the changes of several major aging phenotypes. We confirmed that Dnmt1 haploinsufficiency indeed decreases DNA methylation as a result of reduced Dnmt1 expression. To assess the effect of Dnmt1 haploinsufficiency on general body composition, we performed dual-energy X-ray absorptiometry analysis and showed that reduced Dnmt1 activity decreased bone mineral density and body weight, but with no significant impact on mortality or body fat content. Using behavioral tests, we demonstrated that Dnmt1 haploinsufficiency impairs learning and memory functions in an age-dependent manner. Taken together, our findings point to the interesting likelihood that reduced genomic methylation activity adversely affects the healthy aging process without altering survival and mortality. Our studies demonstrated that cognitive functions of the central nervous system are modulated by Dnmt1 activity and genomic methylation, highlighting the significance of the original epigenetic hypothesis underlying memory coding and function.

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.

Cortical bone loss in androgen-deficient aged male rats is mainly caused by increased endocortical bone remodeling

INTRODUCTION

Hypogonadism is considered to be one of the major risk factors for osteoporosis in men. Here, we sequentially studied the effects of androgen deficiency on cortical bone in aged orchiectomy (ORX) rats.

MATERIALS AND METHODS

One hundred seventy 13-mo-old male Fischer-344 rats were either ORX or sham-operated. After in vivo fluorochrome labeling, groups of 8-15 SHAM and ORX rats each were killed at 2 wk and 1, 2, 3, 4, 6, and 9 mo after surgery. To examine the effects of testosterone replacement therapy, 9-mo-old ORX rats were supplemented with testosterone undecanoate at a weekly dose of 6 mg/kg for 4 mo. Cortical bone changes in the tibial shaft were monitored by pQCT analysis and by bone histomorphometry.

RESULTS

SHAM rats did not show age-related bone loss at the tibial diaphysis. pQCT analysis and bone histomorphometry showed cortical bone osteopenia in ORX rats, beginning from 2 mo after surgery until the end of the study. Androgen deficiency induced a sustained decrease in periosteal bone formation during the first 4 mo after ORX. However, although periosteal expansion of the tibial shaft tended to be slower in ORX rats compared with SHAM controls, the reduction in total cross-sectional area in ORX animals reached statistical significance only at 4 mo after surgery. The major mechanism for cortical bone loss in aged ORX rats was a progressive expansion of the marrow cavity, which was associated with an initial increase in endocortical eroded perimeter at 1 and 2 mo after surgery, followed by a sustained increase in endocortical bone formation until the end of the study. All these changes were prevented in aged ORX rats receiving testosterone supplementation in an insulin-like growth factor system-independent fashion.

CONCLUSIONS

We conclude that androgen deficiency-induced cortical bone loss in aged, nongrowing rats is mainly caused by augmented endocortical bone remodeling.

Relationships between density and Young's modulus with microporosity and physico-chemical properties of Wistar rat cortical bone from growth to senescence

The aim of this study is to assess density and elastic properties of Wistar rat cortical bone from growth to senescence and to correlate them with morphological and physico-chemical properties of bone. During growth (from 1 to 9 months), bone density and Young's modulus were found to increase from 1659+/-85 to 2083+/-13 kg m(-3) and from 8+/-0.8 to 19.6+/-0.7 GPa respectively. Bone microporosity was found to decrease from 8.1+/-0.7% to 3.3+/-0.7%. Physico-chemical investigations exhibited a mineralization of bone matrix and a maturation of apatite crystals, as protein content decreased from 21.4+/-0.2% to 17.6+/-0.6% and apatite crystal size and carbonate content increased (c-axis length: from 151 to 173 A and CO(3)W%: from 4.1+/-0.3% to 6.1+/-0.2%). At adult age, all properties stabilized. During senescence, a slow decrease of mechanical properties was first observed (from 12 to 18 months, rho=2089+/-14 to 2042+/-30 kg m(-3) and E(3)=19.8 +/-1.3 to 14.8+/-1.5 GPa), followed by a stabilization. Physico-chemical properties stabilized while microporosity increased slightly (from 3.3% to 4%) but not significantly (p>0.05). A multiple regression analysis showed that morphological and physico-chemical properties had significant effects on density regression model. Microporosity had a greater effect on Young's modulus regression model than physico-chemical properties. This study showed that bone structure, mineralization and apatite maturation should be considered to improve the understanding of bone mechanical behaviour.

Aging reduces skeletal blood flow, endothelium-dependent vasodilation, and NO bioavailability in rats

We determined whether aging diminishes bone blood flow and impairs endothelium-dependent vasodilation. Femoral perfusion was lower in old animals, as well as endothelium-dependent vasodilation and NO bioavailability. These effects could contribute to old age-related bone loss and the increased risk of fracture.

INTRODUCTION

Aging has been shown to diminish bone blood flow in rats and humans. The purpose of this study was to determine whether blood flow to regions of the femur perfused primarily through the principal nutrient artery (PNA) are diminished with aging and whether this putative reduction in flow is associated with impaired endothelium-dependent vasodilation.

MATERIALS AND METHODS

Blood flow was measured in conscious young adult (4-6 mo old) and aged (24-26 mo old) male Fischer-344 rats using radiolabeled microspheres. Endothelium-dependent vasodilation of the PNA was assessed in vitro using acetylcholine (ACh), whereas the contribution of the NO synthase (NOS) and cyclooxygenase (COX) signaling pathways to endothelium-dependent vasodilation was determined using the NOS and COX inhibitors L-NAME and indomethacin, respectively.

RESULTS

Femoral blood flow in the aged rats was 21% and 28% lower in the proximal and distal metaphyses, respectively, and 45% lower in the diaphyseal marrow. Endothelium-dependent vasodilation was reduced with old age (young: 83 +/- 6% maximal relaxation; aged: 62 +/- 5% maximal relaxation), whereas endothelium-independent vasodilation (sodium nitroprusside) was unaffected by age. The reduction in endothelium-dependent vasodilation was mediated through impairment of the NOS signaling pathway, which resulted in lower NO bioavailability (young: 168 +/- 56 nM; aged: 50 +/- 7 nM).

CONCLUSIONS

These data show that reductions in metaphyseal bone and diaphyseal marrow perfusion with old age are associated with diminished endothelium-dependent vasodilation through an impairment of the NOS mechanism. Such age-related changes in bone perfusion and vascular NO signaling could impact clinical bone loss, increase risk of fracture, and impair fracture healing in the elderly.

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

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

Effects of ageing on the biomechanical properties of rat articular cartilage

Previous studies have demonstrated that male Sprague Dawley (SD) rats experience age-related bone loss with the same characteristics as that in ageing men. As articular cartilage, like bone, is a critical component of the health and function of the musculoskeletal system, the authors hypothesized that articular cartilage in the untreated male SD rats could be a suitable model for studying the age-related deterioration of articular cartilage in men. To test this hypothesis, male SD rats were killed at between 6 and 27 months. The right femur of each rat was removed. The effects of ageing on the structural integrity of the distal femoral articular cartilage were studied by biomechanical testing with a creep indentation apparatus. The aggregate modulus, Poisson's ratio, permeability, thickness, and percentage recovery of articular cartilage were determined using finite element/non-linear optimization modelling. No significant differences were observed in these biomechanical properties of the distal femoral articular cartilage as a function of age. Therefore, untreated male SD rats appear to be unsuitable for studying the age-related changes of articular cartilage as they occur in men. However, and more intriguingly, it is also possible that ageing does not affect the biomechanical properties of articular cartilage in the absence of cartilage pathology.

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.

Soy isoflavones may protect against orchidectomy-induced bone loss in aged male rats

Evidence from several studies suggests that soy protein and/or its isoflavones may have beneficial effects on bone in postmenopausal women and animal models who have osteoporosis. The present study examined the dose-dependent effects of soy isoflavones in the context of soy protein or casein on the male skeleton. Thirteen-month-old male Fisher 344 rats were orchidectomized (ORX; 5 groups) or sham-operated (Sham; 1 group) and immediately placed on dietary treatments for 180 days. Diets were semi-purified and the protein source was either casein (Sham and ORX; controls), casein with two added doses of isoflavones (Iso1; 600 mg/kg diet and Iso2; 1200 mg/kg diet), soy protein with normal isoflavones content (Soy; 600 mg/kg diet), or soy protein with added isoflavones (Soy+; 1200 mg/kg diet). A 7% loss of whole body bone mineral density (BMD) was observed due to orchidectomy; however, the ORX induced BMD loss was significantly reduced to 4.3 and 4.7 % with the Soy and Soy+, respectively. Both doses of isoflavones in conjunction with casein also reduced the loss of whole body BMD, albeit not significantly different from ORX control animals. Trabecular bone histomorphometric analysis of the proximal tibia further supported the bone-sparing role of soy isoflavones as indicated by higher percent bone volume and trabecular number, and lower trabecular separation. We conclude that isoflavones exert modest beneficial effects on the male skeleton whether provided with casein or a soy protein.

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.

Bone development and age-related bone loss in male C57BL/6J mice

The objective of this study was to examine changes in the long bones of male C57BL/6J mice with growth and aging, and to consider the applicability of this animal for use in studying Type II osteoporosis. Male C57BL/6J mice were aged in our colony between 4 and 104 weeks (n=9-15/group). The right femur and humeri were measured for length and subjected to mechanical testing (3-point flexure) and compositional analysis. The left femurs were embedded and thick slices at the mid-diaphysis were assessed for morphology, formation indices, and bone structure. In young mice, rapid growth was marked by substantial increases in bone size, mineral mass, and mechanical properties. Maturity occurred between 12 and 42 weeks of age with the maintenance of bone mass and mechanical properties. From peak levels, mice aged for 104 weeks experienced decreased whole femur mass (12.1 and 18.6% for dry and ash mass, respectively), percentage mineralization (7.4%), diminished whole bone stiffness (29.2%), energy to fracture (51.8%), and decreased cortical thickness (20.1%). Indices of surface-based formation decreased rapidly from the onset of the study. However, the periosteal perimeter and, consequently, the cross-sectional moments of inertia continued to increase through 104 weeks, thus maintaining structural properties. This compensated for cortical thinning and increased brittleness due to decreased mineralization and stiffness. The shape of the mid-diaphysis became increasingly less elliptical in aged mice, and endocortical resorption and evidence of subsequent formation were present in 20-50% of femurs aged > or =78 weeks. This, combined with the appearance of excessive endocortical resorption after 52 weeks, indicated a shift in normal mechanisms regulating bone shape and location, and was suggestive of remodeling. The pattern of bone loss at the femoral mid-diaphysis in this study is markedly similar to that seen in cortical bone in the human femoral neck in Type II osteoporosis. This study has thus demonstrated that the male C57BL/6J mouse is a novel and appropriate model for use in studying endogenous, aging-related osteopenia and may be a useful model for the study of Type II osteoporosis.