Accuracy and precision of lumbar bone mineral content by dual-energy X-ray absorptiometry in live female monkeys

Impairment of ovarian function and associated health-related abnormalities are attributable to low social status in premenopausal monkeys and not mitigated by a high-isoflavone soy diet

BACKGROUND

Psychological stress may impair premenopausal ovarian function and contribute to risk for chronic disease. Soy isoflavones may also influence ovarian function and affect health. Here, we report the effects of a psychological stressor (subordinate social status) and dietary soy on reproductive function and related health indices in female monkeys. We hypothesized that reproductive compromise and adverse health outcomes would be induced in subordinate when compared with dominant monkeys and be mitigated by exposure to soy.

METHODS

Subjects were 95 adult cynomolgus monkeys (Macaca fascicularis) housed in social groups of five or six. Animals consumed a soy-free, animal protein-based diet during an 8-month Baseline phase and then, during a 32-month Treatment phase, consumed either the baseline diet or an identical diet that substituted high-isoflavone soy protein for animal protein.

RESULTS

Across more than 1200 menstrual cycles, subordinate monkeys consistently exhibited ovarian impairment [increased cycle length (P < 0.02) and variability (P < 0.02) and reduced levels of progesterone (P < 0.04) and estradiol (P < 0.04)]. Subordinate status was confirmed behaviorally and was associated with elevated cortisol (P < 0.04) and relative osteopenia (P < 0.05). Consumption of the soy diet had no significant effects.

CONCLUSIONS

(i) Psychological stress adversely affects ovarian function and related health indices in a well-accepted animal model of women's health; (ii) Similar effects may extend to women experiencing reproductive impairment of psychogenic origin; (iii) soy protein and isoflavones neither exacerbate nor mitigate the effects of an adverse psychosocial environment; and (iv) this study was limited by an inability to investigate the genetic and developmental determinants of social status.

Bone mass and soy isoflavones in socially housed, premenopausal macaques

BACKGROUND

Soy consumption is associated with a lower incidence of hip fracture in Asian than in Western women, an effect often attributed to estrogen-like compounds (isoflavones) in soy. It is not known whether premenopausal soy exposure initiated in adulthood can increase bone mass and thereby reduce fracture risk.

OBJECTIVE

We aimed to determine whether a high-isoflavone soy diet influences bone mass in soy-naïve, premenopausal cynomolgus monkeys (Macaca fascicularis).

DESIGN

Ninety-four skeletally mature females were randomly assigned to consume diets whose protein content came from either high-isoflavone soy or casein and lactalbumin. Animals were socially housed. Bone mass and circulating isoflavone concentrations were measured at baseline and 19 and 31 mo after the start of treatment; bone biomarkers were measured at baseline and 31 mo.

RESULTS

There were no significant differences at any timepoint in whole-body bone mineral content between casein-fed (112.5 +/- 2.1, 119.2 +/- 1.9, and 120.7 +/- 2.1 g) and soy-fed (117.2 +/- 2.1, 122.4 +/- 2.0, and 125.4 +/- 2.3 g; P=0.12) monkeys. Similar results were seen for spinal bone mineral density (casein-fed: 0.46 +/- 0.01, 0.50 +/- 0.01, and 0.52 +/- 0.01 g/cm(2); soy-fed: 0.47 +/- 0.01, 0.51 +/- 0.01, and 0.52 +/- 0.01 g/cm(2); P=0.30) and bone biomarker measurements-bone-specific alkaline phosphatase (soy-fed: 82.3 +/- 4.1 and 63.2 +/- 3.4 ng/mL; casein-fed: 94.1 +/- 4.5 and 61.7 +/- 4.3 ng/mL; P=0.22) and C-terminal crosslink of type 1 collagen (soy-fed: 0.944 +/- 0.06 and 0.89 +/- 0.08 nmol/L; casein-fed: 0.97 +/- 0.07 and 0.78 +/- 0.06 nmol/L; P=0.20).

CONCLUSION

A soy diet high in isoflavones does not significantly affect bone characteristics in initially soy-naïve premenopausal monkeys.

Bone mineral measurements of subchondral and trabecular bone in healthy and osteoporotic rabbits

INTRODUCTION

Experimental models of osteoporosis in rabbits are useful to investigate anabolic agents because this animal has a fast bone turnover with predominant remodelling over the modelling processes. For that purpose, it is necessary to characterize the densitometric values of each type of bony tissue.

OBJECTIVE

To determine areal bone mass measurement in the spine and in trabecular, cortical and subchondral bone of the knee in healthy and osteoporotic rabbits.

DESIGN

Bone mineral content and bone mineral density were measured in lumbar spine, global knee, and subchondral and cortical bone of the knee with dual energy X-ray absorptiometry using a Hologic QDR-1000/W densitometer in 29 skeletally mature female healthy New Zealand rabbits. Ten rabbits underwent triplicate scans for evaluation of the effect of repositioning. Osteoporosis was experimentally induced in 15 rabbits by bilateral ovariectomy and postoperative corticosteroid treatment for 4 weeks. Identical dual energy X-ray absorptiometry (DXA) studies were performed thereafter.

RESULTS

Mean values of bone mineral content at the lumbar spine, global knee, subchondral bone and cortical tibial metaphysis were: 1934+/-217 mg, 878+/-83 mg, 149+/-14 mg and 29+/-7.0 mg, respectively. The mean values of bone mineral density at the same regions were: 298+/-24 mg/cm(2), 455+/-32 mg/cm(2), 617+/-60 mg/cm(2) and 678+/-163 mg/cm(2), respectively. Bone mineral content and bone density of healthy rabbits followed a normal distribution at the four skeletal regions studied. Precision after triplicate repositioning yielded a coefficient of variation ranging from 2.6% to 3.8%. The least significant change ranged between 7.3% and 10.7%. Bone mineral density measured at the four different skeletal regions correlated significantly. Bone mineral density in osteoporotic rabbits was significantly lower in the four regions studied than that in controls, rendering a T-score of, respectively, -2.0+/-1.1 in the lumbar spine, -2.2+/-2.1 in the global knee, -1.9+/-0.6 in the subchondral bone, and -5.7+/-3.1 in the cortical tibia (P<0.05).

CONCLUSIONS

DXA is a reliable and precise method to evaluate the bone mass in rabbits. Our results also suggest that subchondral bone is a bone of mixed densitometric characteristics with marked cortical bone predominance.

Social stress-associated depression in adult female cynomolgus monkeys (Macaca fascicularis)

This paper describes a behavior pattern in adult female cynomolgus monkeys that has several behavioral and physiological characteristics in common with human depression including reduced body fat, low levels of activity, high heart rate, hypothalamic-pituitary-adrenal (HPA) axis disturbances, and increased mortality. Under certain circumstances, this depressive behavior appears more common in socially stressed subordinate, than dominant, females. This is the first animal model of social stress-related depression in females and the first primate model of adult depression. It is important to have a female animal model of depression because women are more likely to experience a clinically significant depression than men, and depression in women is often associated with changes in reproductive system function. This model is particularly useful because these monkeys have menstrual cycles that are similar to those of women, and those that exhibit depressive behavior have relatively low levels of ovarian steroids. These monkeys may be a useful model of reproductive system-associated mood disorders in females.

A toxicity profile of osteoprotegerin in the cynomolgus monkey

Osteoprotegerin (OPG) is a novel secreted glycoprotein of the tumor necrosis factor (TNF) receptor superfamily that acts as an antiresorptive agent inhibiting osteoclast maturation. OPG acts by competitively inhibiting the association of the OPG ligand with the RANK receptor on osteoclasts and osteoclast precursors. This inhibition of osteoclasts can lead to excess accumulation of newly synthesized bone and cartilage in vivo. The purpose of this study was to investigate the potential toxicity of a human recombinant form of OPG in the young cynomolgus monkey. OPG was administered by intravenous (i.v.) or subcutaneous (s.c.) injection three times per week for either 4 or 13 weeks. There were no deaths during the study, no clinical signs related to treatment, no effect on body weight, appetence, or ophthalmology. No toxicologically relevant changes in routine laboratory investigations, organ weights, or gross or histopathological findings were observed. Serum ionized calcium and phosphorus were decreased at all dose levels. Evaluations were performed to monitor biochemical markers of bone resorption (N-telopeptide [NTx], deoxypyridinoline [DPD]), bone formation (skeletal alkaline phosphatase [sALP], osteocalcin [OC]), parathyroid hormone [PTH], and bone density of the proximal tibia and distal radius in vivo. Dose-related decreases in NTx and/or DPD were observed at each dose level, with up to a 90% decrease in NTx noted for animals treated i.v. or s.c. at 15 mg/kg. Similar decreases were observed for sALP and OC. PTH was increased for animals treated at 5 and 15 mg/kg (i.v. or s.c.). Trabecular bone density was increased for the majority of males and females treated i.v. or s.c. at 15 mg/kg and males treated i.v. at 5 mg/kg. Microscopic examination of the sternebrae revealed corresponding increases in bone. Decreases in markers of bone turnover, and corresponding increases in bone density, were consistent with the pharmacological action of OPG as an osteoclast inhibitor. The no-observable-adverse-effect level (NOAEL) of OPG was 15 mg/kg.

Use of biochemical markers to monitor changes in bone turnover in cynomolgus monkeys

The ovariectomized old cynomolgus monkey is a recognized model of human osteoporosis, and the same species can be used for the assessment of the efficacy and potential toxicity of agents intended to prevent or treat osteoporosis. Several assays have been developed that can measure the same biochemical markers of bone turnover as are used in human patients for the diagnosis and treatment follow-up of bone-related diseases, including osteoporosis. The aim of the present study was to describe the results obtained with these assays in normal control monkeys, their variations with age and sex, and their sensitivity in monitoring the bone turnover induced by ovariectomy in old skeletally mature cynomolgus monkeys. Seven old cynomolgus monkeys were bilaterally ovariectomized and 13 age-matched monkeys were sham-operated. Bone mineral density and biochemical markers were measured before and at regular intervals after surgery for up to 20 months. Total alkaline phosphatase (total ALP), bone-specific alkaline phosphatase isoenzyme (bone ALP) and osteocalcin (OC) were highly correlated to the decrease in bone mineral density (BMD) induced by ovariectomy. Deoxypyridinoline (DPD) measured by enzyme-linked immunoassay was insensitive to the bone resorption induced by ovariectomy, but cross-linked N-telopeptide (NTX-I) was higher in ovariectomized monkeys than in control monkeys. These results demonstrate that reliable biochemical parameters are available to adequately monitor and provide insight into osteoclastic bone resorption and osteoblastic bone formation, the two components of bone turnover in this animal model, and can thus be used to assess the efficacy and toxicity of potential therapeutic agents.

Seasonal interaction of serum vitamin D concentration and bone density in alpacas

OBJECTIVE

To evaluate temporal changes in bone mineral density associated with seasonal variation in serum vitamin D, calcium, and phosphorus concentrations in alpacas.

ANIMALS

5 healthy mature neutered male alpacas.

PROCEDURE

Metacarpal bone mineral density was measured at 4 times during a year. Each time alpacas were weighed, blood was collected for determination of serum calcium, phosphorus, and vitamin D concentrations, and samples of feed were analyzed for nutrient content. Vitamin D status was determined by use of an assay that measured serum 25-hydroxycalciferol concentration. Effects of changes in serum vitamin D, calcium, and phosphorus concentration and body weight with season on bone mineral density were determined.

RESULTS

Bone mineral density, body weight, and serum vitamin D and phosphorus concentrations varied with season. Bone mineral density, serum vitamin D concentration, and body weight also varied among individual alpacas. Serum vitamin D concentration was lower in January than the previous October and increased from May to the following September. The decrease in bone mineral density lagged behind the decrease in serum vitamin D concentration and was lower in May, compared with the previous October. Body weight was lower in May than the previous October or following September. Solar radiation was highest in July and lowest in December.

CONCLUSIONS AND CLINICAL RELEVANCE

Seasonal changes in bone mineral density are associated with changes in serum vitamin D concentrations in alpacas. Changes in bone mineral density associated with a decline in serum vitamin D concentration may predispose some alpacas to developing fractures minimal trauma.

Evidence for common controls over inheritance of bone quantity and body size from segregation analysis in a pedigreed colony of nonhuman primates (Macaca nemestrina)

The genetic determinants of bone mineral quantity and body size and their postulated interaction are just beginning to be elucidated. The heritability of bone quantity and its relationship to components of body size were therefore investigated using segregation analysis applied to a large pedigreed nonhuman primate (Macaca nemestrina) breeding colony. The colony consisted of 216 females and 16 males with uniform dietary histories, environmental conditions, and rearing of offspring apart from the mother to minimize familial aggregation. Bone quantity (bone mineral content and spinal areal density) was measured by dual-energy X-ray absorptiometry (DXA). Size included measures of body mass, length, breadth, and a composite index. Body mass was determined from both body weight and lean body mass by DXA. Length was assessed by measuring trunk and thigh lengths, and breadth by measuring chest circumference and bitrochanteric width. A composite index of size was also calculated from a linear function of trunk and thigh lengths, chest circumference and bitrochanteric width, and lean body mass. Traits of bone quantity and size were highly correlated (r = 0.56-0.96, p < 0.001). Significant (p < or = 0.03) univariate heritabilities were found for spine bone mineral density (SPBMD; h(2) = 0.66) and whole body bone mineral content (WBBMC; h(2) = 0.40) and size measures of length (trunk h(2) = 0.71, thigh h(2) = 0.65), breadth (bitrochanteric width h(2) = 0.31), lean body mass (LEAN; h(2) = 0.37), and the composite index of size (SIZE-PC, h(2) = 0.49) adjusted for demographic variables. The data were also subjected to an analysis of bivariate genetic correlations and factor analysis, both of which suggested a robust interaction between body size and bone quantity. Bivariate genetic correlations between body size and the bone quantities WBBMC, SBMD, and spine bone mineral content (SPBMC) were high (e.g., using LEAN as a measure of size, r = 0.57, 0.41, and 0.57, respectively). Factor analysis showed that 80% of the phenotypic and 72% of the genetic variances of all traits were accounted for by a single factor, suggesting common genetic controls operative over bone quantity and size.

Bone mineral density, osteopenia, and osteoporosis in the rhesus macaques of Cayo Santiago

This cross-sectional study investigates metabolic bone disease and the relationship between age and bone mineral density (BMD) in males and females of a large, well-documented skeletal population of free-ranging rhesus monkeys (Macaca mulatta), from the Caribbean Primate Research Center Museum collection from Cayo Santiago, Puerto Rico. The sample consists of 254 individuals aged 1.0-20+ years. The data consist of measurements of bone mineral content and bone mineral density, obtained from dual-energy X-ray absorptiometry (DEXA), of the last lumbar vertebra from each monkey. The pattern of BMD differs between male and female rhesus macaques. Females exhibit an initial increase in BMD with age, with peak bone density occurring around age 9.5 years, and remaining constant until 17.2 years, after which there is a steady decline in BMD. Males acquire bone mass at a faster rate, and attain a higher peak BMD at an earlier age than do females, at around 7 years of age, and BMD remains relatively constant between ages 7-18.5 years. After age 7 there is no apparent effect of age on BMD in the males of this sample; males older than 18.5 years were excluded due to the presence of vertebral osteophytosis, which interferes with DEXA. The combined frequency of osteopenia and osteoporosis in this population is 12.4%. BMD values of monkeys with vertebral wedge fractures are generally higher than those of virtually all of the nonfractured osteopenic/osteoporotic individuals, thus supporting the view that BMD as measured by DEXA is a useful but imperfect predictor of fracture risk, and that low BMD may not always precede fractures in vertebral bones. Other factors such as bone quality (i.e., trabecular connectivity) should also be considered. The skeletal integrity of a vertebra may be compromised by the loss of key trabeculae, resulting in structural failure, but the spine may still show a BMD value within normal limits, or within the range of osteopenia.

A comparison of dual-energy X-ray absorptiometry and somatometrics for determining body fat in rhesus macaques

OBJECTIVE

Various approaches have been used to assess fat and fat distribution in nonhuman primates, including measurements of body weight, body dimensions, and estimates derived from these, such as body mass index. Methods such as tritiated water dilution and dual-energy X-ray absorptiometry (DXA) have also been used. The aim of the present study was to evaluate and compare DXA measurements and somatometrics.

RESEARCH METHODS AND PROCEDURES

Body composition of 15 adult male rhesus macaques was measured by DXA and somatometrics at four time-points over a 4-year period. Additionally, DXA precision and somatometric variability were analyzed by repeated measurements of the same subjects.

RESULTS

DXA estimates of body fat were positively correlated with body weight, body mass index, body circumferences, and abdominal skinfold thicknesses. DXA assessments of soft tissue composition were precise, with coefficients of variation below 3.3% for all compartments analyzed. The majority of the observed variability in somatometrics was explained by subject variance, rather than by inter- or intraobserver variability, or by observer experience level.

DISCUSSION

We conclude that noninvasive DXA technology provides precise estimates of nonhuman primate body composition that correlate well with the traditional somatometric measures used in primate studies.

Effects on bone of oral hormone replacement therapy initiated 2 years after ovariectomy in young adult monkeys

The purpose of this study was to determine the effects of oral estrogen replacement therapy with conjugated equine estrogens (CEE), alone or in combination with continuous medroxyprogesterone acetate (MPA), on lumbar spine bone mineral content (BMC) and density (BMD) and on serum chemistries in ovariectomized cynomolgus monkeys when therapy is initiated following a 2 year hypoestrogenic period. Study design was done in the form of a randomized, placebo-controlled, nonhuman primate paraclinical trial. Monkeys were subjects in an experiment designed to study the effects of a lipid-lowering diet combined with hormone replacement therapy on atherosclerosis. Initially, they were ovariectomized and fed a high-fat diet for 24 months. They were then were allocated to three treatment groups by stratified randomization and were fed a diet containing reduced dietary fat for an additional 28 months. Treatment groups consisted of: (1) an untreated group (ovx, n = 24); (2) a CEE-treated group (CEE, n = 19); and (3) a CEE plus continuous MPA group (CEE + MPA, n = 20). Lumbar spine BMC and BMD values were measured by dual-energy x-ray absorptiometry at baseline and 4, 10, 16, 22, and 28 months of treatment. Serum chemistries were relevant to bone metabolism at 22 and 28 months. Rates of gain in BMC and BMD were greater (p < 0.05) in hormone-supplemented animals (groups 2 and 3) than in untreated ovx animals during the first 16 months of treatment, resulting in increased BMC and BMD measurements in these groups. Serum markers of bone metabolism were significantly lower (p < 0.05) in the hormone-treated groups (groups 2 and 3) compared with ovx animals after 22 and 28 months of treatment, indicating reductions in bone turnover rate. Oral estrogen replacement with CEE at doses similar to those taken by women leads to significantly increased BMC and BMD in monkeys, even when therapy is begun 2 years after ovariectomy. Most of the increase occurred during the first 16 months of treatment. The addition of MPA to the CEE regimen provided no additional benefit.

Evaluation of vertebral volumetric vs. areal bone mineral density during growth

Bone mineral "density" (BMD) measured by dual-energy X-ray absorptiometry (DEXA) does not represent the volumetric density (grams per cubic centimeter), but rather the areal density (grams per square centimeter). This distinction is important during growth. The purpose of this study was to measure vertebral dimensions in cadavers of young pigtail macaques (Macaca nemestrina), and to derive equations to predict the volumetric bone density from noninvasive measurements. We measured the areal bone density by DEXA, vertebral volume by underwater weighing, mineral content by ashing, dimensions of lumbar vertebrae by calipers, and dimensions of vertebrae by radiography. Somatometric measurements of the female lumbar vertebral bodies showed that the shape changed during growth. The bone mineral content from the densitometer correlated significantly with the ash weight (r = 0.99, error 8.7%). The correlation coefficient between the volumetric bone mineral density and areal BMD measurement was significant (r = 0.68, p < 0.0001) with a 9.5% error; this improved significantly to 0.82 (7.2% error) when the BMD was divided by the vertebral depth from the radiograph. A real BMD showed a strong correlation with age (r = 0.82, p < 0.0001), with an average increase of 7.4%/year. In contrast, volumetric mineral density showed a weak relationship with age (r = 0.43, p < 0.01), for an average increase of 1.5%/year. When studying bone mineral density during growth, the differences between volumetric and areal bone mineral density should be taken into consideration.

Oral contraceptive treatment inhibits the normal acquisition of bone mineral in skeletally immature young adult female monkeys

The purpose of the present study was to determine the effects of oral contraceptive therapy on bone density and serum markers of bone metabolism in a prospective, longitudinal study of young adult female cynomolgus monkeys. Two hundred and seven intact cynomolgus monkeys were randomized to two groups, and fed an atherogenic diet containing either no drug (Control) or a triphasic oral contraceptive regimen (Contraceptive). Measurements of bone density were carried out by dual-energy X-ray absorptiometry at 10-month intervals (0, 10, and 20 months) and serum bone biomarkers were determined at 5-month intervals over the 20-month time course. No significant differences in these variables were observed prior to treatment. Both groups of animals gained bone mineral during the study, indicating that peak bone mass had not been reached at baseline. Contraceptive-treated animals gained less spinal (lumbar vertebrae 2-4) bone mineral content and density and less whole-body bone mineral content than Controls over the course of the study. Significant depressive effects of contraceptive treatment on gains in BMC and BMD were observed during each 10-month interval of the study. Bone metabolism was inhibited in the Contraceptive group, as reflected by marked reductions (approximately 40%) in serum osteocalcin and alkaline phosphatase levels along with moderate reductions in serum acid phosphatase and calcium. The results suggest that triphasic oral contraceptive treatment of young adult female monkeys that have not reached peak bone mass inhibits net bone accretion and/or growth by reducing bone metabolism. Thus, prolonged continuous oral contraceptive use in skeletally immature females may lead to a lower peak bone mass--an effect which could increase the risk of fractures in later life.

The effect of advancing age on bone mineral content of female rhesus monkeys

Dual-energy X-ray absorptiometry (DXA) can be used to assess bone mass in nonhuman primates; however, the changes in bone mineral across the lifespan have not been well described. The purpose of this cross-sectional study was to evaluate the effect of maturation and subsequent aging on bone mineral content (BMC) and bone size (two dimensional bone area) in female rhesus monkeys at sites analogous to those commonly evaluated in humans. Total body (n = 178) and lumbar spine (n = 167) DXA scans were performed on female rhesus monkeys aged 2.8 to 34.6 years. Radius scans (n = 86) were performed on monkeys aged 9.7 to 34.6 years. Measurement precision was comparable to that reported for humans. At all sites, BMC was highly correlated with bone area (p = 0.0001), which was positively correlated with both body weight (p < or = 0.002) and age (p < or = 0.08). Total body and lumbar spine BMC and bone area increased with maturation (p < 0.0001) until age 11 and then remained stable with further advancing age. There was little change in total body and lumbar spine area-adjusted BMC across the lifespan. At the radial sites, there were no significant changes in BMC or bone area with age, but the area-adjusted BMC and the weight- and area-adjusted BMC declined in older animals (p < 0.05). In conclusion, the female rhesus monkey does not attain peak bone mass until age 11. Significant bone loss at later ages was observed only at radial sites.

The effects of hormone replacement therapy on carbohydrate metabolism and cardiovascular risk factors in surgically postmenopausal cynomolgus monkeys

Controversy exists regarding the effects of estrogen and estrogen/progestin replacement therapies on glucose tolerance and insulin resistance. Also unknown are whether changes in glucose tolerance and insulin resistance with hormone therapy affect arterial glycation and atherosclerosis. We studied ovariectomized female monkeys fed a lipid-lowering diet and given either no hormone replacement therapy (n = 25) or conjugated equine estrogens (CEE) alone (n = 22) or combined with medroxyprogesterone acetate ([MPA] n = 21) for 30 months. Monkeys receiving combined hormone replacement had significantly higher fasting glucose and insulin levels and higher insulin responses to a glucose challenge compared with controls or those given estrogen alone. Monkeys given estrogen-only therapy had lower body weights, lower measures of abdominal adiposity, and decreased serum androgen concentrations. However, due to the effective dietary lipid decrease, there was no additional effect of hormone treatment on atherosclerosis. Also, there was no correlation between either arterial glycation or insulin levels and atherosclerosis extent. Thus, although there were adverse effects of combined hormone replacement therapy on carbohydrate metabolism, we were unable to determine whether these effects altered the extent of atherosclerosis.

The use of dual-energy x-ray absorptiometry in animals

The use of dual-energy absorptiometry (DXA) to measure bone mineral content (BMC) and bone mineral density (BMD) is widespread in humans and has been adapted to animals because of the need to examine bone and body composition in longitudinal studies. In this review, the indications and techniques for DXA in small-sized animals (rodents, cats, and rabbits) and large-sized animals (dogs, swine, nonhuman primates, sheep, and horses) are discussed. Now that software has been developed for measuring BMD in small laboratory animals, the most frequent use of DXA in animals is in rats. An ultrahigh-resolution mode of acquisition is used for their small bones but also is necessary for other small-sized animals such as rabbits and cats. In larger-sized animals such as dogs, pigs, and sheep, software used in humans has been adapted successfully to measure BMC/BMD and body composition. The human spine and left and right hip protocols are adapted easily to animals of this size, and the software for body composition has been adapted to dogs. Measurement of bone mass around metallic implants is possible in animals and most studies have involved dogs. To ensure precision of DXA in the noninvasive measurement of BMD in animals, attention to positioning and ability of the operator to define the same region of interest using clearly defined anatomical landmarks on the scan image cannot be overemphasized. This is one of the essential requirements for successful densitometry in animals.

Development of osteopenia in ovariectomized cynomolgus monkeys (Macaca fascicularis)

Spinal osteopenia that is due in part to failure to gain bone has previously been reported in ovariectomized nonhuman primates. In these studies, development of osteopenia over one year was followed by dual-energy x-ray absorptiometry in both domestically-reared and feral ovariectomized (OVX) and sham-ovariectomized (SHAM) cynomolgus monkeys. To promote development of absolute osteopenia, the domestically-reared animals were all older than nine years and were fed a diet containing 0.14% calcium for most of the experimental period. Both SHAM and OVX feral animals fed 0.6% calcium gained bone mass, with significantly lower rates of gain in SHAM monkeys. OVX domestically-reared monkeys lost bone during one year, while SHAM domestically-reared animals showed no significant change from baseline. Thus, relative osteopenia developed in both experiments, but only the domestically-reared animals developed absolute osteopenia. Nonhuman primates are the only animal model shown to develop absolute osteopenia after ovariectomy. These data suggest that absolute osteopenia develops after ovariectomy in monkeys with stable pre-ovariectomy bone mass which are fed a level of calcium comparable to that consumed by American women.

Dual-energy X-ray absorptiometry in sheep: experiences with in vivo and ex vivo studies

As different large animal models of osteopenia and osteoporosis are explored, the use of DXA to rapidly, non-invasively and accurately estimate BMD will become widespread. We used DXA in live sheep and cadaveric material and the areas of trabecular bone that are most accessible on a simple, repeatable basis in the sheep were the lumbar vertebrae (L4-L6/L5-L7), the CAL and the DR. We performed dual-energy X-ray absorptiometry (DXA) using an Hologic QDR 1000-W bone densitometer to measure bone mineral density (BMD) at various regions of interest in anesthetized sheep and cadaveric specimens of sheep. In vivo measurements of L4-L6/L5-L7, the calcaneus (CAL) and distal radius (DR) in 48 intact 3 to 5-year-old ewes (same breed) were performed. Correlations between the different bones were investigated. In an in vivo precision study, BMD of L3-L6/L7, CAL and DR was determined with one animal repositioned between 10 scans of each bone. In another study, ex-vivo BMD measurements of the proximal and distal femur, proximal tibia, and proximal humerus were performed on isolated bones of 45 ewes of similar age. Excised vertebrae were scanned on the Hologic QDR 1000-W and on a Lunar DPX (at another site) and the data were compared. Correlations of BMD between individual vertebrae in anesthetized sheep were excellent (r = 0.944- 0.843; P < 0.0001). Correlation between BMD of individual vertebrae and CAL was good (r = 0.677-0.630), while correlation between BMD of individual vertebrae and DR was also good (r = 0.551-0.507; P < .0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Specific evaluation of localized bone mass and bone loss in the rat using dual-energy X-ray absorptiometry subregional analysis

Dual-energy X-ray absorptiometry (DXA), together with the use of ultra-high resolution software, recently appeared as an accurate method for determining bone mineral density (BMD) in the rat. In order to assess the ability of this technique to detect changes in bone mass in the rat rapidly and precisely, we measured BMD at various sites of the femur using DXA subregional analysis. In particular, we studied the BMD of the metaphyseal part of the femur (M-BMD) rich in trabecular bone, and compared the values obtained with the cancellous bone volume measured by histomorphometry. In short-term ovariectomized animals (experiment 1), M-BMD was the only parameter to differentiate statistically between 10 ovariectomized (OVX) and 10 SHAM-operated (SHAM) rats (-11.2%, p < 0.01) 9 days after surgery. M-BMD still expressed the greatest variation between OVX and SHAM rats 42 days following ovariectomy (experiment 2) (-16.1%, p < 0.001 v -6.2%, p < 0.01 for the total femur BMD) and confirmed previous data demonstrating a greater loss of cancellous than cortical bone after cessation of ovarian activity. M-BMD was highly correlated with cancellous bone volume (BV) in normal (r = 0.82, p < 0.001, n = 30), OVX (r = 0.77, p < 0.001, n = 22) and SHAM (r = 0.88, p < 0.001, n = 21) rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term performance in vitro and in vivo of dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DXA) is actually considered as one of the most appropriate techniques for measuring bone mineral content (BMC) and bone mineral density (BMD). An anthropomorphic phantom and a 25-year-old girl were repeatedly measured, 160 times and 50 times respectively, over an 18-month period to investigate performance in vitro and in vivo of a commercial DXA equipment (HOLOGIC QDR 1000). DXA is a highly accurate technique, the BMC and BMD determinations only overestimated the exact value of the phantom by 0.20% and 0.51% respectively. In vivo long-term (18 months) reproducibility of BMD of the spine is characterized by an interassay coefficient of variation (CVt) of 0.8% while, for the different regions of interest of the hip, BMD CVt varies from 1.1% (total zone) to 5.3% (Ward's triangle). In the subject tested, BMD sensitivity for changes of 2.2% at the lumbar spine and 3% at the hip were recorded.

Effect of long-term ovariectomy on bone mechanical properties in young female cynomolgus monkeys

Feral adult female cynomolgus monkeys were divided into two groups: normal controls and ovariectomized. Tibiae and trabecular bones from the femoral head, from each group, were tested using a materials testing machine. The bending stiffness of the tibiae was measured by nondestructive three-point bending tests and their maximum torque capacity by destructive torsion tests. The compressive strength of the trabecular bones was measured by compression tests. Ovariectomy caused significant decreases in elastic modulus of the tibiae (p < 0.008), measured by three-point bending tests, and in shear modulus (p < 0.015), failure shear stress (p < 0.01), and failure torque (p < 0.001) of the tibiae, measured by torsion tests. It caused a significant decrease in cortical bone density (p < 0.005), but no significant changes in tibial cross-sectional area and in cortical shaft external and internal diameters. The differences in elastic modulus, maximum compressive strength, and density of femoral trabecular bone samples between the two groups were not significant.

Bone mineral density of total body, spine, and femoral neck in children and young adults: a cross-sectional and longitudinal study

Bone mineral density (BMD) of total body (TBMD), lumbar spine (L2-4), and femoral neck was measured in 266 normal subjects (136 males) aged 4-27 years (mean 13 years) using dual-energy x-ray absorptiometry (DXA). BMD of all sites increased significantly with age until 17.5 years in males and 15.8 years in females, except for femoral neck BMD in females, which peaked at age 14.1 years. Males had higher peak TBMD, which was attributed to greater weight and lean tissue mass. In contrast, despite a later timing, peak L2-4 BMD in males was not different from that in females. Before peak BMD, weight was the best predictor of TBMD and L2-4 BMD in both sexes (r2 ranged from 0.77 to 0.88), whereas femoral neck BMD was predicted equally by height and weight. Longitudinal information collected from 53 (25 boys) of these children, aged 4-16.9 years, showed that the average annualized gain in TBMD was 0.047 g/cm2 for boys and 0.039 g/cm2 for girls. No significant difference in the association between age and BMD (slopes) was found between cross-sectional and longitudinal data for either sex. We conclude that the timing for peak BMD was consistent for total body, lumbar spine, and femoral neck for each sex. The earlier peak BMD in females is most likely related to earlier puberty. The cross-sectional normative data of this study are useful in serving as a standard for serial assessment in health and disease states.

Osteoarthritis in cynomolgus macaques: a primate model of naturally occurring disease

The objective of the present study was to determine if naturally occurring osteoarthritis of the knee joints that is similar to the condition in humans develops in cynomolgus macaques. Knee joints from 58 young adult (mean age, 7.4 years) female cynomolgus macaques were studied with x-ray densitometry, high-detail radiography, and histology. The animals studied were subjects in a triad designed to examine the effects of the administration of sex steroids on atherosclerosis; except for a control group, the monkeys had been either ovariectomized or treated with sex steroids for 2 years. Therefore, the data were analyzed to determine if these treatments, both of which can influence bone density, affected the severity of osteoarthritis. There was a high prevalence of osteoarthritic lesions, morphologically similar to those seen in humans. Bone changes were more common and severe than cartilage changes and morphologically appeared to precede the cartilage changes. Treatment with testosterone resulted in increased body weight, body mass index, and bone mineral content in the femur and tibia but did not affect the severity of osteoarthritis. These data indicate that naturally occurring osteoarthritis developed in the knee joints of cynomolgus macaques; these animals may be a useful model for the study of osteoarthritis in humans.

Bone functional changes in intact, ovariectomized, and ovariectomized, hormone-supplemented adult cynomolgus monkeys (Macaca fascicularis) evaluated by serum markers and dynamic histomorphometry

Several parameters of bone mass and function were investigated in three experiments involving intact, ovariectomized, or hormone-supplemented ovariectomized female cynomolgus monkeys. Ovariectomized animals had increased serum levels of alkaline phosphatase and acid phosphatase compared with intact and hormone-supplemented animals. Vertebral bone mass measured ex vivo by dual-photon absorptiometry was reduced by 11-19% in ovariectomized animals compared with intact and hormone-supplemented animals. The most dramatic effects observed with ovariectomy were markedly increased (30-60%) bone formation rates in vertebral cancellous bone, primarily caused by higher activation frequency of basic multicellular units of bone. In addition, combined resorption and reversal periods were decreased and formation period increased in untreated ovariectomized animals. Changes in static histomorphometry parameters were less dramatic, cancellous bone volume being 1-14% lower in ovariectomized animals compared with intact or ovariectomized hormone-supplemented animals. The data indicate that changes in bone resorption are primarily responsible for the lower bone mass of estrogen deficiency and increased bone mass in hormone-supplemented animals. Bone changes in ovariectomized cynomolgus monkeys resemble those in women after menopause and similarly respond positively to hormone supplementation. As such, cynomolgus monkeys are an excellent model for studying the basic mechanisms of osteoporosis and for the development of suitable therapeutic regimens.

Bone mass in female cynomolgus macaques: a cross-sectional and longitudinal study by age

A cross-sectional study by age was designed to evaluate and describe the bone mineral content (BMC, g) and density (BMD, g/cm2) in a population of female cynomolgus macaques (Macaca fascicularis). Dual-energy X-ray absorptiometry was used to measure, in segments L2-L4 of the lumbar spine, the BMC (BMCs), BMD (BMDs), length, and total-body BMC(BMCTB) in 171 female monkeys ranging in age between 3.7 and 22.0 years. The animals were divided into three age groups: (1) young (< 6.5 years, n = 51); (2) adult (> 6.5 years and < 10.5 years, n = 63); and (3) mature (> 10.5 years, n = 57). Young animals had a significantly lower (P < 0.05) body weight and shorter trunk length than adult or mature animals. Young animals also had significantly less (P < 0.05) BMCS, BMDS, and BMCTB than adult or mature animals, and had significantly shorter (P < 0.01) lumbar spine vertebral segments than the other two groups. Longitudinally, 63 animals had repeated lumbar spine scans to examine changes over time. Young animals showed a positive and significant change (P < 0.05) in BMCs and BMDs through time, whereas these parameters did not change in adult animals, and mature animals had a trend towards bone loss through time. Densitometric results suggested that peak bone mass in the lumbar spine was achieved by 9 years of age. Radiographic and dental criteria were developed to identify animals that had reached peak bone mass, and the combined radiographic and dental scoring system reliably identified animals 9 years and older. Female cynomolgus macaques 9 years old or older are recommended for investigations of bone remodeling and associated conditions, such as osteoporosis.