Room temperature housing results in premature cancellous bone loss in growing female mice: implications for the mouse as a preclinical model for age-related bone loss

Room temperature housing (22 °C) results in premature cancellous bone loss in female mice. The bone loss was prevented by housing mice at thermoneutral temperature (32 °C). Thermogenesis differs markedly between mice and humans and mild cold stress induced by standard room temperature housing may introduce an unrecognized confounding variable into preclinical studies.

INTRODUCTION

Female mice are often used as preclinical models for osteoporosis but, in contrast to humans, mice exhibit cancellous bone loss during growth. Mice are routinely housed at room temperature (18-23 °C), a strategy that exaggerates physiological differences in thermoregulation between mice (obligatory daily heterotherms) and humans (homeotherms). The purpose of this investigation was to assess whether housing female mice at thermoneutral (temperature range where the basal rate of energy production is at equilibrium with heat loss) alters bone growth, turnover and microarchitecture.

METHODS

Growing (4-week-old) female C57BL/6J and C3H/HeJ mice were housed at either 22 or 32 °C for up to 18 weeks.

RESULTS

C57BL/6J mice housed at 22 °C experienced a 62 % cancellous bone loss from the distal femur metaphysis during the interval from 8 to 18 weeks of age and lesser bone loss from the distal femur epiphysis, whereas cancellous and cortical bone mass in 32 °C-housed mice were unchanged or increased. The impact of thermoneutral housing on cancellous bone was not limited to C57BL/6J mice as C3H/HeJ mice exhibited a similar skeletal response. The beneficial effects of thermoneutral housing on cancellous bone were associated with decreased Ucp1 gene expression in brown adipose tissue, increased bone marrow adiposity, higher rates of bone formation, higher expression levels of osteogenic genes and locally decreased bone resorption.

CONCLUSIONS

Housing female mice at 22 °C resulted in premature cancellous bone loss. Failure to account for species differences in thermoregulation may seriously confound interpretation of studies utilizing mice as preclinical models for osteoporosis.

Effects of treadmill training on combined goserelin acetate and doxorubicin-induced osteopenia in female rats

OBJECTIVES

This study examined individual and combined effects of the cancer treatments goserelin acetate (GA) and doxorubicin (DOX) on bone and determined if treadmill running (TM) provides osteoprotection.

METHODS

Ten-week-old female Sprague-Dawley rats were randomly assigned to sedentary (SED) or TM groups. SED received GA, DOX, combined GA and DOX (GA+DOX), or placebo and maintained normal cage activity. TM received GA, DOX, GA+DOX, or placebo and participated in a progressive motorized treadmill protocol. After 8 weeks, tibiae were evaluated using micro computed tomography.

RESULTS

Negative drug effects were observed in cancellous bone (bone volume/tissue volume, trabecular number, trabecular thickness, trabecular spacing; P<0.05). An additive bone volume/tissue volume and trabecular spacing effect was observed in SED GA+DOX (vs. SED+GA and SED+DOX, P<0.05) but not in TM GA+DOX (vs. TM+GA and TM+DOX, P>0.05). Negative drug effects were observed in cortical bone (cross-sectional volume, cortical volume, marrow volume; P<0.05), but combined GA+DOX did not exacerbate these effects. Additionally, there were no protective cortical bone effects observed in TM.

CONCLUSIONS

Combined GA+DOX exacerbates cancellous osteopenia in the tibia, and treadmill running provided only minor protection.

Abstract P5-05-01: Endoxifen, a novel breast cancer therapy, elicits unique beneficial effects on bone relative to that of other selective estrogen receptor modulators

Background: Commonly used endocrine therapies for breast cancer, such as aromatase inhibitors in postmenopausal women and tamoxifen in premenopausal women, have deleterious effects on bone mineral density. Therefore, the identification of novel cancer therapies which either maintain or improve bone mass are of clinical need. We and others have previously demonstrated that endoxifen is the most active tamoxifen metabolite responsible for eliciting the anti-cancer effects of this drug and that endoxifen concentrations are an important factor with regard to tamoxifen efficacy. These studies have led to the development of endoxifen as a novel anti-breast cancer drug for which phase I clinical trials are now underway. At present, there are no data regarding endoxifen's effects on bone.

Methods: The effects of endoxifen on osteoblast gene expression profiles were compared to that of estrogen, tamoxifen, raloxifene and lasofoxifene by microarray and RT-PCR analyses in both estrogen receptor alpha (ERα) and ERβ expressing cell lines. The in vivo effects of an anti-cancer dose of endoxifen (50mg/kg/day) on the skeleton were first analyzed in 3-month-old ovariectomized C57BL/6 mice using Dual-energy X-ray absorptiometry, peripheral Quantitative Computed Tomography, micro-Computed Tomography and histomorphometry. In a second set of studies, a pre-clinical rat model was used to determine the effects of endoxifen (10mg/kg/day) on the skeleton in both a pre- and post-menopausal setting.

Results: Endoxifen treatment of ERα and ERβ expressing mouse osteoblast cells led to dramatically different gene expression profiles when compared to that of estrogen and other anti-estrogens. In ovariectomized mice, daily administration of endoxifen led to significant increases in bone mineral density and content throughout the skeleton relative to vehicle control treated animals. The numbers and activity of both osteoblasts and osteoclasts were also found to be significantly higher in endoxifen treated mice. In the pre-clinical model system, endoxifen treatment of 4 month-old ovariectomized Sprague-Dawley rats significantly protected against bone loss following estrogen depletion primarily due to suppression of osteoclast mediated bone resorption. Importantly, in sham operated rats (thus retaining ovarian function), endoxifen treatment enhanced bone volume and trabecular thickness and did not suppress osteoclast activity.

Conclusions: These data are the first to examine the effects of the novel breast cancer therapy, endoxifen, on bone and reveal that the molecular mechanisms of action of this compound are substantially different than that of other SERMs. Endoxifen was shown to protect against bone loss following estrogen depletion in both mice and rats and interestingly, enhanced bone mass in ovary intact rats, an observation that is in stark contrast to the known effects of tamoxifen which induces bone loss in the “pre-menopausal” setting. These studies suggest that endoxifen may have superior bone-beneficial effects compared to tamoxifen, and if efficacy is confirmed in later phase trials, endoxifen may represent a better drug of choice for a sub-set of breast cancer patients.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-05-01.

P3-16-09: Endoxifen, a Newly Developed Breast Cancer Drug, Has Anabolic Actions on the Mouse Skeleton

Background

Commonly used endocrine therapies for breast cancer, such as aromatase inhibitors in postmenopausal women and tamoxifen in premenopausal women, have deleterious effects on bone mineral density. Therefore, the identification of novel cancer therapies which either maintain or improve bone mass are of clinical need. We have recently demonstrated that endoxifen is the most active tamoxifen metabolite with regard to inhibiting the growth of ERα+ breast cancer cells and these studies have led to the development of endoxifen as a novel anti-breast cancer drug for which first-in-human studies are now underway. At present, there are no data regarding endoxifen's effects on bone.

Methods: The effects of endoxifen on osteoblast (OB) and osteoclast (OC) maturation and gene expression were monitored by cell differentiation assays and real-time PCR. Dual-energy X-ray absorptiometry (DXA), peripheral Quantitative Computed Tomography (pQCT) and micro-Computed Tomography (μCT) were used to determine changes in bone density, mass and architecture following 45 days of oral endoxifen administration (50mg/kg/day) to 3-month-old ovariectomized (OVX) C57BL/6 mice relative to vehicle control treated animals. Alterations in the numbers and activity of OBs and OCs were determined by histomorphometry and serum levels of P1NP and CTX-1 respectively.

Results: Endoxifen treatment of mouse derived bone marrow stromal cells and human OBs led to significant increases in the expression of critical bone marker genes such as Runx2, osterix, osteocalcin, osteoprotegerin and alkaline phosphatase in a dose dependent manner. Daily administration of endoxifen to OVX mice led to significant increases in total body bone mineral density (BMD) (6%) and content (BMC) (9%), which was accompanied by a 50% decrease in fat tissue mass as determined by DXA. pQCT analysis of the tibial metaphysis revealed dramatic increases in BMD (35%) and BMC (20%), as well as trabecular density (52%), cortical content (62%), cortical area (60%) and cortical thickness (78%). μCT analysis of the femoral metaphysis revealed increases in bone volume/total volume (200%), trabecular number (38%) and trabecular thickness (18%), as well as decreased trabecular spacing (29%). Interestingly, there was nearly a 50% increase in the numbers of OCs derived from endoxifen treated mice which was associated with elevated expression of OC marker genes such as NFATcl, RANK, c-fms and cathepsin-K compared to control treated animals. Approximately 4 times as many OBs and OCs were observed on the bone surfaces of endoxifen treated mice which correlated with nearly 2-fold increases in serum levels of the bone formation (P1NP) and resorption (CTX-1) markers.

Conclusions: These data are the first to demonstrate that endoxifen has anabolic effects on the mouse skeleton which are similar to that of estrogen. Additionally, these data reveal that endoxifen's mechanism of action in bone is different than that reported for tamoxifen and other selective estrogen receptor modulators in mice as it increases, rather than decreases, bone formation and remodeling. Therefore, the use of endoxifen for the treatment of endocrine responsive breast cancer may avoid the detrimental skeletal effects of many conventional endocrine therapies.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-09.

The effects of low dose parathyroid hormone on lumbar vertebrae in a rat model for chronic alcohol abuse

This study evaluated the hypothesis that increased bone marrow adipogenesis is coupled to decreased bone formation in rats consuming alcohol. Parathyroid hormone (PTH) increased bone formation but had no effect on marrow adiposity. We conclude that increased adiposity does not prevent the bone anabolic response to PTH.

INTRODUCTION

Alcoholism results in decreased bone formation and increased bone marrow adiposity. The present study tested the hypothesis that these reciprocal changes are coupled by evaluating the effect of intermittent PTH on bone formation and bone marrow adiposity in a rat model for chronic alcohol abuse.

METHODS

Three-month-old male Sprague Dawley rats (n = 10-11/group) were fed the Lieber-DeCarli liquid diet with 35% of the calories derived from ethanol. Control rats were pair-fed an isocaloric alcohol-free diet. The rats were administered low dose PTH (1 µg/kg/day sc, 5 d/week) or vehicle for 6 weeks. Cancellous bone architecture in lumbar vertebrae was evaluated by micro-computed tomography followed by histomorphometric assessment of bone formation and marrow adiposity.

RESULTS

Alcohol increased bone marrow adiposity but reduced bone formation. The latter was due to decreases in mineralizing perimeter/bone perimeter, a surrogate measure of osteoblast number, and mineral apposition rate, a measure of osteoblast activity. PTH increased bone formation by increasing mineralizing perimeter/bone perimeter. In contrast, PTH had no effect on mineral apposition rate or bone marrow adiposity. Interactions between alcohol consumption and PTH treatment were not detected for any endpoints evaluated.

CONCLUSIONS

PTH treatment blunted the decrease in mineralizing perimeter/bone perimeter in alcohol-fed rats but was ineffective in preventing the increase in bone marrow adiposity. These findings suggest that the alcohol-induced increase in adipocytes is not directly responsible for the accompanying reduction in bone formation.

Alcohol alters whole body composition, inhibits bone formation, and increases bone marrow adiposity in rats

Chronic alcohol abuse is a risk factor for osteoporosis and sarcopenia, but the long-term effects of alcohol on the immature musculoskeletal system are less clear. The present investigation in growing rats was designed to determine the effects of alcohol consumption on body composition, muscle mass, and bone mass, architecture, and turnover.

INTRODUCTION

Few studies have focused on the long-term effects of drinking on bone and muscle during skeletal maturation.

METHODS

Alcohol was included in the diet of 4-week-old male Sprague-Dawley rats (35% caloric intake) for 3 months. The controls were fed an isocaloric alcohol-free liquid diet ad libitum. A second study was performed in which the controls were pair-fed to the alcohol-fed animals.

RESULTS

Compared to ad libitum-fed age-matched controls, alcohol-fed rats weighed less and had lower lean mass, fat mass, and percent body fat. In addition, they had lower slow- and fast-twitch muscle mass, lower total body bone mineral content and bone mineral density, and lower cancellous bone volume in the lumbar vertebra and proximal tibia. The effects of alcohol consumption on body composition were reduced when compared to the pair-fed control diet, indicating that caloric restriction was a comorbidity factor. In contrast, the effects of alcohol to decrease bone formation and serum leptin and IGF-I levels and to increase bone marrow adiposity appeared independent of caloric restriction.

CONCLUSIONS

The skeletal abnormalities in growing alcohol-fed rats were due to a combination of effects specific to alcohol consumption and alcohol-induced caloric restriction.

Body mass influences cortical bone mass independent of leptin signaling

Obesity in humans is associated with increased bone mass. Leptin, a hormone produced by fat cells, functions as a sentinel of energy balance, and may mediate the putative positive effects of body mass on bone. We performed studies in male C57Bl/6 wild type (WT) and leptin-deficient ob/ob mice to determine whether body mass gain induced by high fat intake increases bone mass and, if so, whether this requires central leptin signaling. The relationship between body mass and bone mass and architecture was evaluated in 9-week-old and 24-week-old WT mice fed a regular mouse diet. Femora and lumbar vertebrae were analyzed by micro computed tomography. In subsequent studies, slowly and rapidly growing ob/ob mice were injected in the hypothalamus with a recombinant adeno-associated virus containing the leptin gene (rAAV-lep) or a control vector, rAAV-GFP (green fluorescent protein). The mice were maintained on a regular control diet for 5 or 7 weeks and then subdivided into groups and either continued on the control diet or fed a high fat diet (45% of kcal from fat) for 8 weeks. In the WT mice, femoral and vertebral bone mass was positively correlated with body mass (Pearson's r=0.65-0.88 depending on endpoint). rAAV-lep therapy dramatically decreased body mass (-61%) but increased femur length. However, in the distal femur and lumbar vertebra, rAAV-lep therapy reduced cancellous bone volume/tissue volume, trabecular number and trabecular thickness, and increased trabecular spacing. The high fat diet increased body mass, irrespective of vector treatment. Total femur bone volume, length, cross-sectional volume, and cortical volume and thickness were increased in mice with increased body mass, independent of rAAV treatment. In the distal femur, increased body mass had no effect on cancellous architecture and there were no vector x body mass interactions. In WT mice, increased body mass resulted in increased (+33%) vertebral cancellous bone volume/tissue volume. Increased body mass had minimal independent effect on cancellous vertebral bone mass in ob/ob mice. Taken together, these findings suggest that increased body mass has a positive effect on femur cortical bone mass that is independent of leptin signaling.

Detrimental effects of reloading recovery on force, shortening velocity, and power of soleus muscles from hindlimb-unloaded rats

To better understand how atrophied muscles recover from prolonged nonweight-bearing, we studied soleus muscles (in vitro at optimal length) from female rats subjected to normal weight bearing (WB), 15 days of hindlimb unloading (HU), or 15 days HU followed by 9 days of weight bearing reloading (HU-R). HU reduced peak tetanic force (P(o)), increased maximal shortening velocity (V(max)), and lowered peak power/muscle volume. Nine days of reloading failed to improve P(o), while depressing V(max) and intrinsic power below WB levels. These functional changes appeared intracellular in origin as HU-induced reductions in soleus mass, fiber cross-sectional area, and physiological cross-sectional area were partially or completely restored by reloading. We calculated that HU-induced reductions in soleus fiber length were of sufficient magnitude to overextend sarcomeres onto the descending limb of their length-tension relationship upon the resumption of WB activity. In conclusion, the force, shortening velocity, and power deficits observed after 9 days of reloading are consistent with contraction-induced damage to the soleus. HU-induced reductions in fiber length indicate that sarcomere hyperextension upon the resumption of weight-bearing activity may be an important mechanism underlying this response.

TIEG-null mice display an osteopenic gender-specific phenotype

TGFbeta inducible early gene-1 (TIEG) was originally cloned from human osteoblasts (OB) and has been shown to play an important role in TGFbeta/Smad signaling, regulation of gene expression and OB growth and differentiation. To better understand the biological role of TIEG in the skeleton, we have generated congenic TIEG-null (TIEG(-/-)) mice in a pure C57BL/6 background. Through the use of DXA and pQCT analysis, we have demonstrated that the femurs and tibias of two-month-old female TIEG(-/-) mice display significant decreases in total bone mineral content, density, and area relative to wild-type (WT) littermates. However, no differences were observed for any of these bone parameters in male mice. Further characterization of the bone phenotype of female TIEG(-/-) mice involved mechanical 3-point bending tests, micro-CT, and histomorphometric analyses of bone. The 3-point bending tests revealed that the femurs of female TIEG(-/-) mice have reduced strength with increased flexibility compared to WT littermates. Micro-CT analysis of femurs of two-month-old female TIEG(-/-) mice revealed significant decreases in cortical bone parameters compared to WT littermates. Histomorphometric evaluation of the distal femur revealed that female TIEG(-/-) mice also display a 31% decrease in cancellous bone area, which is primarily due to a decrease in trabecular number. At the cellular level, female TIEG(-/-) mice exhibit a 42% reduction in bone formation rate which is almost entirely due to a reduction in double labeled perimeter. Differences in mineral apposition rate were not detected between WT and TIEG(-/-) mice. Taken together, these findings suggest that female TIEG(-/-) mice are osteopenic mainly due to a decrease in the total number of functional/mature OBs.

Effects of low-dose parathyroid hormone on bone mass, turnover, and ectopic osteoinduction in a rat model for chronic alcohol abuse

Parathyroid hormone (PTH) is used clinically in osteoporotic patients to increase bone mass by enhancing bone formation. PTH therapy is not uniformly effective at all skeletal sites and "life-style" factors may modulate the skeletal response to PTH. Alcohol may represent one of these factors. Chronic alcohol abuse is associated with osteoporosis and impaired fracture healing. Therefore, the present study investigated the effects of alcohol on the bone anabolic response to a dose of PTH similar to a human therapeutic dose 1) during normal cancellous and cortical bone growth and turnover, and 2) in a model of demineralized allogeneic bone matrix (DABM)-induced osteoinduction. Three-month-old male Sprague Dawley rats were fed a Lieber-DeCarli liquid diet with 35% of the calories derived from ethanol. The controls were pair-fed an alcohol-free isocaloric diet containing maltose-dextran. Following adaptation to the liquid diets, the rats were implanted subcutaneously with DABM cylinders prepared from cortical bone of rats fed normal chow. The rats were subsequently treated daily with PTH (1 microg/kg/d sc, 5 d/week) or vehicle and measurements on bone and DABM implants performed 6 weeks later. Total bone mass was evaluated on the day of necropsy using DXA. Tibiae were processed for histomorphometry. Bone mass and architecture in tibial diaphysis and DABM implants were evaluated by muCT. PTH treatment increased whole body bone mineral content (BMC) and bone mineral density (BMD). The hormone also increased bone formation and bone area/tissue area in the proximal tibial metaphysis. In contrast, PTH treatment had no effect on periosteal bone formation and minimal effects on DABM-induced osteoinduction. Alcohol consumption decreased whole body BMC. Alcohol also decreased cancellous as well as cortical bone formation and bone mass in tibia and impaired DABM-mediated osteoinduction. There was no interaction between PTH treatment and alcohol consumption for any of the endpoints evaluated. Our results indicate that the bone anabolic response to a therapeutic dose of PTH in the rat is largely confined to cancellous bone. In contrast, alcohol consumption inhibits bone formation at all sites. Furthermore, alcohol inhibits osteoinduction and reduces periosteal and cancellous bone formation, irrespective of therapeutic PTH administration. Based on the animal model, our findings suggest that alcohol consumption could impair the beneficial effects of PTH therapy in osteoporosis.

Impaired osteoinduction in a rat model for chronic alcohol abuse

Alcohol abuse is a risk factor for bone fractures. Following a fracture, alcoholics have a higher risk for impaired fracture healing. However, the specific alcohol-induced defect(s) in bone healing are not known. Alcohol is a potent inhibitor of bone formation during bone growth and turnover. Thus, the purpose of this study was to determine the effects of alcohol consumption on induction of new bone formation. Demineralized allogeneic bone matrix (DABM) cylinders were used to model osteoinduction in a rat model for chronic alcohol abuse. DABM cylinders, prepared from femurs and tibiae of rats fed a normal diet, were implanted into sexually mature male rats adapted to alcohol (ethanol contributed 35% of caloric intake) or control liquid diets. Food intake in the control rats was restricted to match food intake of alcohol-fed animals. The implants were recovered 6 weeks later and analyzed by histology, muCT and chemical analysis. Histological evaluation revealed a robust osteoinductive response, resulting in mature bone ossicle formation, in DABM implants in rats fed the control diet. Alcohol consumption affected bone mass and architecture of the DABM implants but not volumetric density or mineral composition. Specifically, alcohol consumption resulted in significant decreases in DABM-induced bone volume, bone volume/mg original cylinder weight, connectivity density, trabecular number and thickness, ash weight and % ash weight. There were no changes in mineral (ash) density nor in the relative amounts of calcium, magnesium, iron, selenium and zinc (microg/mg ash), indicating that alcohol consumption did not impair mineralization. Taken together, these results show that alcohol abuse resulted in decreased bone formation within the DABM implant. We conclude that reduced osteoinduction may contribute to impaired bone healing in alcoholics.

A comparative study of the bone-restorative efficacy of anabolic agents in aged ovariectomized rats

INTRODUCTION

The study was designed to compare the bone anabolic effects of basic fibroblast growth factor (bFGF), a selective agonist for prostaglandin E receptor subtype EP4, and parathyroid hormone (PTH) in aged ovariectomized (OVX) rats with severe cancellous osteopenia.

METHODS

Groups of aged OVX rats were maintained untreated for 1 year postovariectomy (15 months of age) to develop severe tibial cancellous osteopenia. These animals were then treated with bFGF or the EP4 agonist (EP4) for 3 weeks. Other groups of aged OVX rats were treated with EP4 or PTH alone for 11 weeks, or sequentially with bFGF or EP4 for 3 weeks followed by PTH for 8 weeks. Cancellous and cortical bone histomorphometry were performed in the right proximal tibial metaphysis and tibial diaphysis respectively.

RESULTS

Treatment with bFGF for 3 weeks markedly increased serum osteocalcin, osteoid volume, and osteoblast and osteoid surfaces to a greater extent than EP4. Basic FGF, but not EP4 or PTH, induced formation of osteoid islands within bone marrow. EP4 stimulated cancellous bone turnover, but failed to restore lost cancellous bone in the severely osteopenic proximal tibia after 11 weeks of treatment. In contrast, EP4, much like PTH, increased cortical bone mass in the tibial diaphysis by stimulating both periosteal and endocortical bone formation. Treatment of aged OVX rats with PTH alone tended to partially reverse the severe tibial cancellous osteopenia, whereas sequential treatment with bFGF and PTH increased tibial cancellous bone mass to near the level of vehicle-treated control rats. These findings indicate that bFGF had the strongest stimulatory effect on cancellous bone formation, and was the only anabolic agent to induce formation of osteoid islands within the bone marrow of the severely osteopenic proximal tibia. Therefore, bFGF may be more effective for the reversal of severe cancellous osteopenia. PTH and EP4 increased cortical bone mass to nearly the same extent, but cancellous bone mass was greater by two-fold in PTH-treated OVX rats than in EP4-treated OVX rats.

CONCLUSION

These findings in aged OVX rats suggest that PTH is more efficacious than EP4 for augmentation of cancellous bone in the severely osteopenic, estrogen-deplete skeleton.

Effects of disrupted β1-integrin function on the skeletal response to short-term hindlimb unloading in mice

The study was designed to determine whether β1-integrin plays a role in mediating the acute skeletal response to mechanical unloading. Transgenic (TG) mice were generated to express a dominant negative form of β1-integrin under the control of the osteocalcin promoter, which targets expression of the transgene to mature osteoblasts. At 63 days of age, wild-type (WT) and TG mice were subjected to hindlimb unloading by tail suspension for 1 wk. Pair-fed, normally loaded WT and TG mice served as age-matched controls. Bone samples from each mouse were processed for quantitative bone histomorphometry and biomechanical testing. The skeletal phenotype of TG mice was characterized by lower cancellous bone mass in the distal femoral metaphysis (−52%) and lumbar vertebral body (−20%), reduced curvature of the proximal tibia (−20%), and decreased bone strength (−20%) and stiffness (−23%) of the femoral diaphysis with relatively normal indexes of cancellous bone turnover. Hindlimb unloading for only 1 wk induced a 10% decline in tibial curvature and a 30% loss of cancellous bone in the distal femur due to a combination of increased bone resorption and decreased bone formation in both WT and TG mice. However, the strength and stiffness of the femoral diaphysis were unaffected by short-term hindlimb unloading in both genotypes. The observed increase in osteoclast surface was greater in unloaded TG mice (92%) than in unloaded WT mice (52%). Cancellous bone formation rate was decreased in unloaded WT (−29%) and TG (−15%) mice, but, in contrast to osteoclast surface, the genotype by loading interaction was not statistically significant. The results indicate that altered integrin function in mature osteoblasts may enhance the osteoclastic response to mechanical unloading but that it does not have a major effect on the development of cancellous osteopenia in mice during the early stages of hindlimb unloading.

Skeletal phenotype of growing transgenic mice that express a function-perturbing form of beta1 integrin in osteoblasts

Skeletal modeling entails the deposition of large amounts of extracellular matrix (ECM) to form structures tailored to withstand increasing mechanical loads during rapid growth. Specific ECM molecules bind to integrin receptors on the cell surface, thereby triggering a cascade of signaling events that affect critical cell functions. To evaluate the role of integrins during skeletal growth, transgenic mice were engineered to express a function-perturbing fragment of beta1 integrin consisting of the transmembrane domain and cytoplasmic tail under the control of the osteocalcin promoter (TG mice). Thus, transgene expression was targeted to mature cells of the osteoblast lineage, and herein we show that cultured cells resembling osteocytes from 90-day-old TG mice display impaired adhesion to collagen I, a ligand for beta1 integrin. To determine the influence of beta1 integrin on bones that are responsible for providing structural support during periods of rapid growth, we examined the phenotype of the appendicular skeleton in TG mice compared to wild type (WT) mice. According to radiographs, bones from mice of both genotypes between 14 and 90 days of age appeared similar in gross structure and density, although proximal tibiae from 35-90 days old TG mice were less curved than those of WT mice (72-92% TG/WT). Although there were only mild and transient differences in absolute bone mass and strength, once normalized to body mass, the tibial dry mass (79.1% TG/WT females), ash mass (78.5% TG/WT females), and femoral strength in torsion (71.6% TG/WT females) were reduced in TG mice compared to WT mice at 90 days of age. Similar effects of genotype on bone mass and curvature were observed in 1-year-old retired breeders, indicating that these phenotypic differences between TG and WT mice were stable well into adulthood. Effects of genotype on histomorphometric indices of cancellous bone turnover were minimal and evident only transiently during growth, but when present they demonstrated differences in osteoblast rather than osteoclast parameters. Together, these results suggest that integrin signals generated during growth enhance the acquisition of a skeletal mass, structure, and strength to withstand the mechanical loads generated by weight-bearing.

Basic fibroblast growth factor has rapid bone anabolic effects in ovariectomized rats

Basic fibroblast growth factor (bFGF) has a strong bone anabolic effect in intact and ovariectomized (OVX) rats treated for 7-14 days. Other growth factors such as IGF-I and TGF-beta have been implicated as potential mediators for this effect. The purpose of this study was to examine the early effects of bFGF therapy, in vivo, on bone formation and gene expression in OVX rats in order to determine whether upregulation of gene expression for IGF-I and/or TGF-beta precedes or coincides with the stimulatory effects of bFGF on bone formation. At 3 months of age, Sprague Dawley rats were OVX or sham-operated (SHAM), then maintained untreated for 3 months. One group of baseline OVX rats (BSL OVX) and BSL SHAM rats were then killed. Additional OVX groups were treated IV with bFGF at a daily dose of 200 microg/kg and killed at 1-7 and 10 days. Another group of OVX rats was treated IV with vehicle daily for 10 days, then killed. Lumbar vertebrae were processed for cancellous bone histomorphometry or RNA isolation. Ovariectomy induced increased cancellous bone turnover and a significant decrease in vertebral bone mass. Treatment of OVX rats with bFGF resulted in a significant increase in bone formation. As early as 24 h after bFGF treatment of OVX rats, osteoblast surface, osteoid surface, and osteoid volume were more than double those in BSL OVX rats and continued to increase with time. These variables were also significantly higher in bFGF-treated OVX rats at 10 days compared with vehicle-treated OVX rats. Gene expression for IGF-I was not different between BSL OVX rats and bFGF-treated OVX rats at 1 day, but was significantly higher by approximately 50% in OVX rats treated with bFGF for 2 and 7 days, and was also significantly higher by nearly 75% in OVX rats treated for 10 days compared with OVX rats treated with vehicle. Gene expression for TGF-beta1 was unchanged at early times and only significantly upregulated by a relatively modest 30% in OVX rats treated with bFGF for 10 days. The results indicate that the bone anabolic effects of bFGF in OVX rats begin as early as 24 h following the initial treatment, and increase with time. These early stages of the strong stimulatory effect of bFGF on bone formation were not associated with a large upregulation of gene expression for IGF-I and TGF-beta. The rapid increase in osteoblast surface in bFGF-treated OVX rats suggests that the growth factor induces conversion of bone lining cells to osteoblasts.

Differences in vertebral structure and strength of inbred female mouse strains

This study assessed mouse strain-related differences in vertebral biomechanics and histomorphometry in inbred mice strains shown to differ in bone mineral content (BMC) and areal density (BMD) (as measured by pDEXA). Lumbar vertebrae L3 to L5 were collected from three mice strains (C3H/HeJ[C3], C57BL/6J[B6], and DBA/2J[D2], n=12/strain, 4-month-old female, 22.2 +/- 0.3g). BMC and BMD were measured in L3 and L4 using peripheral dual energy x-ray absorptiometry. The L4 vertebral body was then mechanically tested in compression to determine structural properties (ultimate/yield load, stiffness) from load-displacement curves and derive apparent material properties (ultimate/yield stress, and modulus of elasticity). L5 was processed for histomorphometric evaluation. Vertebral BMC and BMD were greater in C3 than in B6 and D2 mice. Vertebral trabecular/cancellous bone volume was smaller in C3 than in D2 and B6 mice. Trabecular bone formation rates were greater in D2 than in B6 and C3 mice. Osteoid surface was smaller in C3 mice than in B6 and D2 mice. Differences in osteoclast and mineralizing surfaces were not detected among the three mouse strains. In addition, there were no significant differences in biomechanical properties between the three strains. Despite the greatest BMC and areal BMD in C3 mice, the lack of strain-related differences in vertebral body strength data suggests that the biomechanical properties may be affected by the bone distribution and/or complex combination of cortical and cancellous bone at this site.

Bone anabolic effects of subcutaneous treatment with basic fibroblast growth factor alone and in combination with estrogen in osteopenic ovariectomized rats

Although basic fibroblast growth factor (bFGF) is a potent stimulator of bone formation when administered intravenously, less is known regarding the effects of this peptide on bone following subcutaneous (s.c.) administration. In addition, it is unknown whether coadministration of estrogen enhances the bone response to treatment with bFGF. Therefore, the purpose of this study was (1) to characterize the skeletal response to s.c. injection of a high dose of bFGF, and (2) to determine whether concurrent administration of estrogen affects the skeletal response to bFGF treatment. Female Sprague-Dawley rats were ovariectomized (ovx) or sham-operated (sham) at 3 months of age and left untreated for 2 months to establish cancellous osteopenia in the ovx group. The sham rats (n=10) and one group of ovx rats (n=9) were then injected s.c. with vehicle alone for 3 weeks. Two additional groups of ovx rats were injected s.c. with bFGF (n=10) or with bFGF + estrogen (n=10) for 3 weeks. bFGF was administered s.c. at a daily dose of 1 mg/kg/day and estrogen was administered s.c. 4 days per week at a dose of 10 microg/kg for the 3-week duration of treatment. Lumbar vertebrae were collected and processed undecalcified for quantitative bone histomorphometry. Cancellous bone volume was lower and cancellous bone turnover was higher in vehicle-treated ovx rats than in vehicle-treated sham rats. Subcutaneous treatment of ovx rats with bFGF for 3 weeks resulted in a 4-fold increase in osteoblast surface and an 8-fold increase in osteoid surface in comparison to vehicle treatment of ovx rats. Osteoid volume was also markedly increased in the bFGF-treated ovx rats (7 +/- 4%) in comparison to vehicle-treated ovx rats (<0.1%). Osteoblast surface, osteoid surface, and osteoid volume were nearly identical in ovx rats treated with bFGF alone and with bFGF + estrogen. Although the majority of the osteoid in bFGF- and bFGF + estrogen-treated animals was deposited along mineralized bone surfaces, osteoid spicules without any connections to preexisting bone surfaces were also detected, providing definitive proof for bone formation within bone marrow in response to bFGF administration. Osteoclast surface, an index of bone resorption, was not affected by bFGF treatment. However, cotreatment of ovx rats with bFGF + estrogen resulted in lower osteoclast surface in comparison to treatment of ovx rats with either vehicle or bFGF alone. In summary, these findings indicate that administration of a high dose of bFGF via s.c. injection markedly increases bone formation and may be a useful treatment for cancellous osteopenia in the estrogen-deplete skeleton. The anabolic effects of bFGF on bone are not enhanced by concurrent treatment with estrogen at the replacement dose used in this study.

Effects of nicotine on bone mass and strength in aged female rats

This study investigated the effects of nicotine on bone mass and biomechanical properties in aged, estrogen-replete (sham-operated) and estrogen-deplete (ovariectomized) female rats. Eight month old, retired breeder, sham-operated and ovariectomized Sprague-Dawley rats were left untreated for 12 weeks to establish cancellous osteopenia in the ovariectomized group. The animals were then administered saline, low dose nicotine (6.0 mg/kg/day) or high dose nicotine (9.0 mg/kg/day) via osmotic minipumps for 12 weeks. Vertebrae and femora were collected at necropsy for determination of bone mass and strength. As expected, ovariectomy had a negative effect on most endpoints evaluated. Vertebral body bone mineral content (BMC) and density (BMD) and the structural (ultimate load and yield load) and material (ultimate stress, yield stress, and flexural modulus of elasticity) strength properties were lower in the OVX rats than in the sham-operated rats. Femoral diaphysis BMC, BMD, ultimate load, and flexural modulus were also lower in the OVX rats than in the sham-operated rats. The nicotine doses administered resulted in serum nicotine levels that averaged 1.5-4.5-fold greater than those observed in heavy smokers. Despite the high doses used, nicotine had no effect on vertebral BMC, BMD, or any of the structural and material strength properties in either the OVX or the Sham rats. In addition, nicotine had no effect on femoral diaphysis BMC, BMD, ultimate load, stiffness, ultimate stress, or flexural modulus. Femoral yield load and stress were lower in low dose nicotine-treated rats than in vehicle-treated rats. However, differences were not detected between the high dose nicotine- and vehicle-treated rats for either femoral yield load or stress. The results suggest that tobacco agents other than nicotine are responsible for the decreased bone density and increased fracture risk as observed in smokers.

Effects of nicotine on bone and calciotropic hormones in aged ovariectomized rats

The objective of this investigation was to assess the effects of chronic nicotine administration on bone status and serum calcium and calciotropic hormone levels in aged, estrogen-replete (intact, sham-operated) and estrogen-deplete (ovariectomized) female rats. Eight-month-old sham-operated (sham) and ovariectomized (ovx) retired breeder rats were maintained untreated for 3 months to allow for the development of osteopenia in the ovx group. The animals were then administered either saline, low dose nicotine (6.0 mg/kg/day), or high dose nicotine (9.0 mg/kg/day) via osmotic minipumps for 3 months. Blood was drawn at necropsy for determination of serum nicotine, cotinine, Ca, PTH, 25(OH)D, and 1,25(OH)(2)D. Right tibiae were collected and processed undecalcified for cancellous and cortical bone histomorphometry. Histomorphometric endpoints evaluated at the proximal tibial metaphysis included cancellous bone volume (BV/TV), osteoclast surface (Oc.S), osteoid surface (OS), mineralizing surface (MS), mineral apposition rate (MAR), and bone formation rate (BFR). Histomorphometric endpoints evaluated at the tibial diaphysis included cortical area (Ct.Ar), marrow area (Ma.Ar), and periosteal and endocortical MS, MAR, and BFR. Ovariectomy resulted in lower cancellous BV/TV and Ct.Ar and higher cancellous, endocortical, and periosteal MS and BFR. The presence of nicotine in serum confirmed successful delivery of the drug via osmotic minipumps. Administration of nicotine at the high dose resulted in lower serum 25(OH)D levels but differences in serum Ca or PTH were not detected with either nicotine treatment. Differences with nicotine treatment were also not detected for Oc.S at the proximal tibia. While treatment with nicotine at the high dose resulted in higher MS and BFR, in both sham and ovx rats, there were no differences due to nicotine treatment in cancellous BV/TV. Marrow area was greater in rats treated with nicotine than in rats treated with vehicle. However, differences with nicotine treatment were not detected in Ct.Ar in either intact or ovx rats. Overall, these findings indicate that steady state nicotine exposure does not alter bone mass in intact or ovx rats but may have detrimental effects on body storage of vitamin D.

Changes in gene expression associated with the bone anabolic effects of basic fibroblast growth factor in aged ovariectomized rats

Basic fibroblast growth factor (bFGF) stimulates bone formation in vitro and in vivo. The purpose of this study was to determine changes in gene expression for bone matrix proteins, growth factors, and cytokines associated with the stimulatory effects of bFGF on bone formation in aged ovariectomized (ovx) rats. At 3 months of age, female Sprague-Dawley rats were sham-operated (sham) or ovariectomized (ovx), then maintained untreated for 1 year. At 15 months of age, baseline (BSL) sham and ovx rats were killed. All other rats received daily intravenous injections of bFGF (200 microg/kg) or vehicle (veh) for 14 days. Lumbar vertebrae were processed for quantitative bone histomorphometry or molecular analyses. Ovariectomy decreased vertebral cancellous bone volume by approximately 33% and increased most indices of bone turnover. Treatment of aged ovx rats with bFGF for only 14 days significantly increased cancellous bone volume compared with vehicle treatment of ovx rats, but this variable remained lower than in sham + veh rats. Osteoid volume, osteoblast surface, and osteoid surface were markedly increased, and osteoclast surface was significantly decreased in ovx + bFGF rats compared with sham + veh and ovx + veh rats. Northern analyses revealed that mRNA levels for osteocalcin and type I collagen, relative to 18S RNA, were significantly higher in ovx + bFGF rats than in ovx + veh rats by a factor of >10. RNase protection assays revealed that insulin-like growth factor (IGF-I) mRNA levels, relative to L32 housekeeping gene, were also significantly higher, by nearly a factor of 3, in ovx + bFGF rats than in ovx + veh rats. Treatment of ovx rats with bFGF did not appear to affect message levels for transforming growth factor-beta (TGF-beta), interleukin-6 (IL-6), and interferon-gamma (IFN-gamma). These in vivo results suggest that bFGF treatment upregulates gene expression for IGF-I, which may mediate, at least in part, the increased gene expression for bone matrix proteins and the bone anabolic effects of bFGF in aged ovx rats.

Sequential treatment with basic fibroblast growth factor and PTH is more efficacious than treatment with PTH alone for increasing vertebral bone mass and strength in osteopenic ovariectomized rats

The study was designed 1) to determine whether treatment with basic fibroblast growth factor (bFGF) and PTH is more efficacious than treatment with PTH alone for increasing bone mass and strength and improving trabecular microarchitecture in osteopenic ovariectomized rats, and 2) to assess whether prior and concurrent administration of the antiresorptive agents estrogen and risedronate suppresses the bone anabolic response to treatment with bFGF alone and sequential treatment with bFGF and PTH. Three-month-old female Sprague Dawley rats were ovariectomized (OVX) or sham-operated (sham) and maintained untreated for 1 yr. Baseline sham and OVX rats were killed at this time (15 months of age). Groups of rats were injected sc with estrogen (10 microg/kg, 4 d/wk), risedronate (5 microg/kg, 2 d/wk), or vehicle. At the end of the second week of antiresorptive treatment, catheters were inserted into the jugular veins of all rats, and vehicle or bFGF at a dose of 250 microg/kg was injected daily for 14 d. Three groups of rats were killed at the end of bFGF treatment. The remaining rats were continued on their respective antiresorptive therapy and injected sc with vehicle or synthetic human PTH-(1-34) at a dose of 80 microg/kg, 5 d/wk, for 8 wk. Lumbar vertebrae were processed for cancellous bone histomorphometry and biomechanical testing. Ovariectomy resulted in a decrease in vertebral bone mass and strength. Treatment of OVX rats for 14 d with bFGF markedly increased osteoblast surface, osteoid surface, and osteoid volume compared with vehicle treatment of sham and OVX rats. Furthermore, osteoid bridges were observed extending between preexisting trabeculae in bFGF-treated OVX rats. Prior and concurrent administration of estrogen and risedronate did not suppress these bone anabolic effects of bFGF. Treatment of OVX rats with PTH alone increased vertebral cancellous bone mass and strength to the level of vehicle-treated sham rats. Sequential treatment of OVX rats with bFGF and PTH further augmented vertebral bone mass and strength to a level above that observed in OVX rats treated with PTH alone. The improvements in bone mass and strength were associated with an increase in trabecular thickness in OVX rats treated with PTH alone and with an increase in trabecular thickness and node to terminus ratio, an index of trabecular connectivity, in OVX rats treated sequentially with bFGF and PTH. Cotreatment with estrogen and risedronate did not suppress the anabolic response of bone to bFGF and PTH. In fact, a trend for an even greater increase in cancellous bone mass and node to terminus ratio was observed in OVX rats treated with risedronate, bFGF, and PTH. These findings indicate that sequential treatment with bFGF and PTH is more efficacious than treatment with PTH alone for increasing bone mass and strength and improving trabecular microarchitecture in osteopenic OVX rats.

Maintenance of cancellous bone in ovariectomized, human parathyroid hormone [hPTH(1-84)]-treated rats by estrogen, risedronate, or reduced hPTH

This study compares effects of maintenance doses of human parathyroid hormone [hPTH(1-84)], 17beta-estradiol (E2), and risedronate on distal femur bone mineral density and proximal tibia cancellous bone histomorphometry in ovariectomized (ovx), osteopenic rats previously administered a higher dose of hPTH. Nine groups (n = 8) of 3.5-month-old ovx or intact Sprague-Dawley rats were left untreated for 11 weeks to allow for the development of cancellous osteopenia in the ovx groups. Next, the ovx rats received subcutaneous injections of hPTH (75 microg/kg per day, three times per week) or vehicle for 12 weeks. Treatments were then changed to E2 (10 microg/kg per day, two times per week), risedronate (Ris; 3 microg/kg per day, three times per week), low-dose hPTH(1-84) (LowPTH; 25 microg/kg per day, three times per week), or vehicle, and administered for 36 weeks. The intact control group remained untreated for the duration of study. Femora and tibiae were collected at weeks -11 (baseline); 0 (ovx effect); 12 (hPTH effect), and 24, 36, and 48 (maintenance effects). Endpoints evaluated included distal femur bone mineral density (BMD) and proximal tibia cancellous bone volume (BV/TV), osteoclast surface (Oc.S), mineralizing surface (MS), mineral apposition rate (MAR), and bone formation rate (BFR). Ovariectomy had a negative effect on distal femur BMD and proximal tibia BV/TV. Treatment of ovx rats with hPTH for 12 weeks resulted in higher BMD in comparison to intact controls, and higher cancellous BV/TV in comparison to ovx controls. Discontinuation of hPTH resulted in loss of gained BMD within 24 weeks and loss of gained BV/TV within 12 weeks. Treatment of ovx rats with hPTH for 12 weeks followed by E2 treatment left BMD and BV/TV similar to vehicle-treated ovx rats by week 48 (36 weeks after commencement of the E2 maintenance treatment). Maintenance treatment with risedronate resulted in BMD and BV/TV similar to that of intact controls. Maintenance treatment with low-dose hPTH resulted in greater BMD and similar BV/TV in comparison to intact controls. MS and BFR were highest after low-dose hPTH administration. MS and BFR were lowest after E2 or risedronate, whereas Oc.S was lowest after risedronate administration. Thus, in osteopenic rats, the increment in distal femur BMD and proximal tibia BV/TV gained by 12 weeks of hPTH treatment was lost within 24 and 12 weeks of treatment termination, respectively. Low-dose hPTH maintained BMD and BV/TV after hPTH treatment by stimulating bone formation, whereas risedronate maintained BMD and BV/TV by reducing bone resorption. E2 in a maintenance dose failed to maintain BMD and BV/TV after withdrawal of hPTH treatment.

Effects of nicotine on bone mass, turnover, and strength in adult female rats

This study investigated the effects of nicotine, the chemical responsible for tobacco addiction, on bone and on serum mineral and calcitropic hormone levels in adult, female rats to help resolve a current controversy regarding the impact of nicotine on bone health. Seven-month-old rats received either saline (n = 12), low-dose nicotine (4.5 mg/kg/day, n = 2), or high-dose nicotine (6.0 mg/kg/day, n = 12) administered subcutaneously via osmotic minipumps for 3 months. Blood, femora, tibiae, and lumbar vertebrae (3-5) were collected at necropsy for determination of serum mineral and hormonal concentrations, bone density (femora and vertebrae), bone turnover (tibiae), and bone strength (femora). The presence of nicotine in serum (111 +/- 7 and 137 +/- 10 ng/ml for the low- and high-dose nicotine groups, respectively) confirmed successful delivery of the drug via osmotic minipumps. Nicotine-induced treatment differences were not detected in serum calcium, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D. However, serum phosphorus and parathyroid hormone (PTH) were higher in rats treated with high-dose nicotine, and serum calcitonin was lower in rats treated with both high- and low-dose nicotine than in control rats. Nicotine treatment had no effect on tibial cancellous or cortical bone turnover or femoral bone mineral content (BMC) and density (BMD). Femoral ultimate load and vertebral BMC were lower in rats treated with high-dose nicotine than in control rats. We conclude that nicotine at serum concentrations 2.5-fold greater than the average in smokers has limited detrimental effects on bone in normal, healthy female rats.

Maintenance of cortical bone in human parathyroid hormone(1-84)-treated ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone(1-84) (hPTH) followed by maintenance treatment with 17beta-estradiol (E(2)), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on cortical bone in the ovariectomized (ovx) rat. Eight groups of ovx and one group of intact female rats (3.5 months) were left untreated for 11 weeks. For the following 12 weeks, four groups received subcutaneous injections of hPTH (75 microg/kg per day on 3 days/week) and four groups received vehicle. Treatments were then changed to E(2) (10 microg/kg per day on 2 days/week), Ris (3 microg/kg per day on 3 days/week), LowPTH (25 microg/kg per day on 3 days/week), or vehicle. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). Bone mineral density (BMD) and bone mineral content (BMC) of the diaphyseal femur and total cross-sectional area (Tt.Ar), marrow area (Ma.Ar), cortical area (Ct.Ar), and periosteal and endocortical bone formation of the tibia were measured. Ovariectomy resulted in lower BMD (weeks 0-48), unaffected BMC, and greater Tt.Ar (weeks 12 and 36), Ma.Ar (week 48), and Ct.Ar (weeks 0 and 12) compared with intact rats. Endocortical and periosteal bone formation were greater in the ovx than in the intact rats up to 23 weeks postovariectomy. Treatment of ovx rats with hPTH for 12 weeks resulted in greater cortical BMD, BMC, and endocortical bone formation than in intact or ovx controls. In ovx rats pretreated with hPTH and then treated with Ris for 36 weeks, BMD and BMC were greater and Ma.Ar was smaller than in ovx controls. In ovx rats pretreated with hPTH and then treated with LowPTH, BMD, BMC, Ct.Ar, and endocortical bone formation were greater and Ma.Ar was smaller than in ovx controls. Treatment of hPTH-pretreated rats with E(2) for 36 weeks did not affect cortical BMD, BMC, and Ct.Ar, although periosteal bone formation was lower in the E(2) group compared with the ovx group. Thus, in ovariectomized rats, cortical bone gained by 12 weeks of hPTH treatment was maintained for up to 36 weeks by treatment with risedronate or low-dose hPTH, but not with 17beta-estradiol.

Genetic variations in bone density, histomorphometry, and strength in mice

The purpose of this study was to assess breed-related differences in bone histomorphometry, bone biomechanics, and serum biochemistry in three mouse breeds shown to differ in bone mineral density (BMD) (as measured by DXA) and bone mineral content (BMC). Femurs, tibiae, and sera were collected from 16-week-old C3H/HeJ C3H, C57BL/6J BL6, and DBA/2J DBAmice (n = 12/breed). Data collected included BMC and BMD (femora), histomorphometry of cancellous (distal femur) and cortical bone (diaphyseal tibiae and femora), bone strength (femora), and serum alkaline phosphatase (ALP). Consistent with previous reports, BMC and BMD were higher in C3H than in BL6 or DBA mice. The higher BMD in the C3H breed was associated with greater cancellous bone volume, cortical bone area, periosteal bone formation rate, biomechanical strength, and serum ALP. However, mid-diaphyseal total femoral and tibial cross-sectional area and moment of inertia were greatest in BL6, intermediate in C3H, and lowest in DBA mice. The specific distribution of cortical bone in C3H, BL6, DBA mice represents a difference in adaptive response to similar mechanical loads in these breeds. This difference in adaptive response may be intrinsic to the adaptive mechanism, or may be intrinsic to the bone tissue material properties. In either case, the bone-adaptive response to ordinary mechanical loads in the BL6 mice yields bones of lower mechanical efficiency (less stiffness per unit mass of bone tissue) and does not adapt as well as that of the C3H mice where the final product is a bone with greater resistance to bending under load. We suggest that the size, shape, and BMD of the bone are a result of breed-specific genetically regulated cellular mechanisms. Compared with the C3H mice, the lower BMD in BL6 mice is associated with long bones that are weaker because the larger cross-sectional area fails to compensate completely for their lower BMD and BMC.

Effects of nicotine on bone and calciotropic hormones in growing female rats

Limited research in young adults and immature animals suggests a detrimental effect of tobacco on bone during growth. This study investigated the effects of nicotine, the major alkaloid component of tobacco, on calciotropic hormone concentrations and bone status in growing female rats. One-month-old animals received either saline (n = 10), nicotine at 3.0 mg/kg/day (n = 10), or nicotine at 4.5 mg/kg/day (n = 10) administered subcutaneously via osmotic minipumps for either 2 or 3 months. Sera, femora, tibiae, and lumbar vertebrae (3-5) were collected at necropsy. The concentrations of serum calcium, phosphorus, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, parathyroid hormone, calcitonin, and insulin-like growth factor-I were determined. Bone variables evaluated included mineral content and density (vertebrae and femora), cancellous and cortical histomorphometry (tibiae), and bone strength (vertebrae and femora). Statistically significant differences in serum mineral and hormone concentrations were not associated with nicotine dose or exposure time. No significant nicotine treatment effects were detected for bone mineral content and density, bone histomorphometry, or bone strength. We conclude that nicotine treatment for 2 or 3 months at serum concentrations in the upper range of those found in smokers has no detrimental effect on bone mass, volume, or strength in the growing rat.

Methods for improving the efficiency of estimating total osteon density in the human anterior mid-diaphyseal femur

In order to preserve whole bone integrity and minimize destruction, paleohistologists often rely on histomorphometric data obtained from small areas (1.5-50 mm2) sampled within the anterior mid-diaphyseal femur. Because bone exhibits significant histological variation, the validity of results based on such sampling is questionable. The accuracy of various subareas (columns, rows, squares approximating dimensions and locations assessed by paleohistologists) in predicting total osteon density in the anterior mid-diaphyseal femur is assessed in the present study. Thirty-five specimens (12.7 mm wide, 100 microm thick, average area 56.7 mm2) were chosen at random from a skeletal population of 94 Inuits and Pueblo agriculturists. The specimens were photographed and enlarged; an acetate grid (12 columns, 10 rows, 120 squares, square = 1 mm2 of bone surface) was superimposed over the photograph; and secondary osteons and fragments were identified. Alternate columns (50% total area, T.Ar) predicted over 98% of entire section total osteon density. Two column combinations (15% T.Ar), separated by at least one column, predicted 91 to 95% of total osteon density. Individual column (8% T.Ar) predictability ranged from 48 to 86%. Two row combination (32 to 40% T.Ar) predictability values ranged from 86 to 95%. Individual rows (<1 to 20% T.Ar) predicted from 45 to 92% of total variation. Combinations of squares approximating areas and locations assessed by other paleohistologists ranged in predictability values from 80 to 94%. The results demonstrate that subareas of as little as 15% predict 95% of variation in total osteon density in the entire anterior mid-diaphyseal femoral section. A minimization of histological area evaluated without the loss of accuracy allows for a minimization of time invested in data collection and the utilization of partially damaged specimens.

Distribution of mineralization indices of modeling and remodeling over eight months in middiaphyseal cross sections of femurs from adult swine

BACKGROUND

This study assessed the distribution of active mineral formation sites within the middiaphyseal femoral cross section of swine and determined the extent to which various subsections represented bone formation activity in the entire cross section.

METHODS

Twenty adult female swine (sows) were injected with two double (10-day intervals) labels 8 months apart. Labels involved fluorochrome markers of active mineral formation sites. Intact femoral middiaphyseal cross sections were embedded in polymethylmethacrylate, cut, and ground to 80 microm for analysis. Each specimen was subdivided into 16 anatomical and eight geometric subsections. Labeled mineralizing surface and mineral apposition rate were determined in the periosteal and endocortical envelopes. The number of labeled osteons per unit area of bone and osteonal mineral apposition rate were determined in the intracortical envelope.

RESULTS

Periosteal mineralizing surface followed a bimodal distribution with highest surface activation on the anterior and posterior segments. Periosteal mineral apposition rate followed a modal distribution with highest apposition rates in the posterior portion of the cross section. The distribution of forming osteons was modal with highest frequencies of labeled osteons in the posterior segment. No significant regional differences were detected for osteonal mineral apposition rate, endocortical mineralizing surface, or endocortical mineral apposition rate. The location of either a single or a combination of two to four subsections that best predicted mineralizing surface and mineral apposition rate in the entire cross section differed with each trait and envelope. Fifty percent of the entire area as alternate anatomical subsections was required to predict > 90% of variation in all traits evaluated. Overall, the predictability of mineralizing surface and mineral apposition rate was similar for geometrically defined subsections.

CONCLUSION

At least 50% of the cross-sectional area from alternate anatomical subsections must be measured to predict > 90% of variation in periosteal, intracortical, and endocortical mineralizing surface and mineral apposition rate in the sow middiaphyseal femur.

Stable isotope ratios indicate diet and habitat use in New World monkeys

This paper demonstrates the use of stable isotope ratios of carbon and nitrogen in animal tissue for indicating aspects of species behavioral strategy. We analyzed hair from individuals representing four species of New World monkeys (Alouatta palliata, the mantled howler; Ateles geoffroyi, the spider monkey; Cebus capucinus, the capuchin; and Brachyteles arachnoides, the woolly-spider monkey or muriqui) for delta 13C and delta 15N using previously developed methods. There are no significant differences in either carbon or nitrogen ratios between sexes, sampling year, or year of analysis. Seasonal differences in delta 13C reached a low level of significance but do not affect general patterns. Variation within species was similar to that recorded previously within single individuals. The omega 13C data show a bimodal distribution with significant difference between the means. The two monkey populations living in an evergreen forest were similar to each other and different from the other two monkey populations that inhabited dry, deciduous forests. This bimodal distribution is independent of any particular species' diet and reflects the level of leaf cover in the two types of forest. The delta 15N data display three significantly different modes. The omnivorous capuchins were most positive reflecting a trophic level offset. The spider monkeys and the muriquis were similar to one another and significantly more positive than the howlers. This distribution among totally herbivorous species correlates with the ingestion of legumes by the howler monkey population. In combination, these data indicate that museum-curated primate material can be analyzed to yield information on forest cover and diet in populations and species lacking behavioral data.