Local bone turnover in the metaphysis of the proximal tibia and the lumbar vertebra during the early periods after ovariectomy in rats

Intermittent parathyroid hormone treatment affects the bone structural parameters and mechanical strength of the femoral neck after ovariectomy-induced osteoporosis in rats

Background

Menopause-induced decline in estrogen levels in women is a main factor leading to osteoporosis. The objective of this study was to investigate the effect of intermittent parathyroid hormone (PTH) on bone structural parameters of the femoral neck in ovariectomized rats, in addition to correlations of maximum fracture force.

Methods

Fifteen female Wister rats were divided into three groups: (1) control group; (2) ovariectomized (OVX) group; and (3) OVX  +  PTH group. All rats were then killed and the femurs extracted for microcomputed tomography scanning to measure volumetric bone mineral density (vBMD) and bone structural parameters of the femoral neck. Furthermore, the fracture forces of femoral neck were measured using a material testing system.

Results

Compared with the control and OVX  +  PTH groups, the OVX group had significantly lower aBMD, bone parameter, and mechanical strength values. A comparison between OVX and OVX  +  PTH groups indicated that PTH treatment increased several bone parameters. However, the OVX  +  PTH groups did not significantly differ with the control group with respect to the bone structural parameters, except for trabecular bone thickness of cancellous bone, which was greater. In addition, among the bone structural parameters, the CSA and BSI of cortical bone were significantly correlated with the maximum fracture force of the femoral neck, with correlations of, respectively, 0.682 (p  = 0.005) and 0.700 (p  = 0.004).

Conclusion

Intermittent PTH helped treat ovariectomy-induced osteoporosis of cancellous bone and cortical bone in the femoral necks of rats. The ability of the femoral neck to resist fracture was highly correlated with the two parameters, namely cross-sectional area (CSA) and bone strength index (=  vBMD  ×  CSA), of cortical bone in the femoral neck and was less correlated with aBMD or other bone structural parameters.

Increased Ca2+ signaling through CaV1.2 promotes bone formation and prevents estrogen deficiency-induced bone loss

While the prevalence of osteoporosis is growing rapidly with population aging, therapeutic options remain limited. Here, we identify potentially novel roles for CaV1.2 L-type voltage-gated Ca2+ channels in osteogenesis and exploit a transgenic gain-of-function mutant CaV1.2 to stem bone loss in ovariectomized female mice. We show that endogenous CaV1.2 is expressed in developing bone within proliferating chondrocytes and osteoblasts. Using primary BM stromal cell (BMSC) cultures, we found that Ca2+ influx through CaV1.2 activates osteogenic transcriptional programs and promotes mineralization. We used Prx1-, Col2a1-, or Col1a1-Cre drivers to express an inactivation-deficient CaV1.2 mutant in chondrogenic and/or osteogenic precursors in vivo and found that the resulting increased Ca2+ influx markedly thickened bone not only by promoting osteogenesis, but also by inhibiting osteoclast activity through increased osteoprotegerin secretion from osteoblasts. Activating the CaV1.2 mutant in osteoblasts at the time of ovariectomy stemmed bone loss. Together, these data highlight roles for CaV1.2 in bone and demonstrate the potential dual anabolic and anticatabolic therapeutic actions of tissue-specific CaV1.2 activation in osteoblasts.

Effect of Combined Teriparatide and Monthly Risedronate Therapy on Cancellous Bone Mass in Orchidectomized Rats: A Bone Histomorphometry Study

This study investigated the effects of combined teriparatide (an anabolic agent) and monthly risedronate (an anti-resorptive agent) therapy on cancellous bone mass in orchidectomized (ORX) rats. Fifty 14-week-old male Sprague-Dawley rats were randomized into five groups of ten animals each: sham-operation + vehicle; ORX + vehicle; ORX + risedronate (90 μg/kg subcutaneous, every 4 weeks); ORX + teriparatide (30 μg/kg subcutaneous, three times per week); and ORX + risedronate + teriparatide. After the 12-week experimental period, cancellous bone in the tibial proximal metaphysis was examined by static and dynamic histomorphometric analyses. ORX decreased bone volume per total volume (BV/TV) and trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). Risedronate increased BV/TV and Tb.N above the sham control values, while teriparatide prevented the ORX-induced decrease in BV/TV and increased trabecular width (Tb.Wi) above sham control levels. Risedronate decreased Tb.Sp below control values, while teriparatide prevented the ORX-induced increase in Tb.Sp. The combination of teriparatide and risedronate further increased BV/TV and Tb.N and decreased Tb.Sp as a result of suppression of bone remodeling, compared with teriparatide alone. These results suggest that teriparatide and monthly risedronate exert different effects on cancellous bone structure and thus have additive effects on cancellous bone mass in ORX rats.

Time course of influence by ovariectomy and calcium diet on bone properties in mice

This study was investigated the influence by ovariectomy (OVX) and calcium diet on bone properties in eighty-one female ICR strain mice with age of 5 weeks. The animals were randomly assigned to sham operation (SHAM), OVX, SHAM+low Ca intake (L.Ca) and OVX+L.Ca group. They were euthanized with lethal dose of pentobarbital sodium at day 50, 100 and 140 post-operatively. For determining the bone properties, both femur and tibial bones were excised from the hind limb, and removed off surrounding tissues. Thereafter, bone length, bone dry weight, and also mechanical strength and ash content of the bones were determined. The bone length on both femur and tibia was significantly longer in OVX group than in the other groups after 50 day of experiment, this situation was continued to the end of the experiment. Bone dry weight, mechanical strength, and ash content were significantly decreased by OVX and L.Ca over the time of the experiment, and those of OVX+L.Ca group were the lowest in all groups. OVX and L.Ca have a great potential for weakening the mechanical strength and have an additive effect when combined. OVX and L.Ca block the gain of bone mass.

Effects of Traditional Chinese Medicines on Murine Bone Metabolism in a Microgravity Environment

We investigated the effects of three traditional Chinese medicine prescriptions on changes of bone metabolism in mice, using a gravity device to produce a microgravity environment. We found that Hochu-ekki-to (TJ-41) and Hachimi-jio-gan (TJ-7) suppress the increase in the ratio of serum Ca/P and the increase of calcium in urine. Moreover, TJ-41 and Shin-bu-to (TJ-30) reversed the increase of alkaline phosphatase activity (ALP), and TJ-41 also reversed the decrease of estradiol in the serum. The mechanism may be that the traditional Chinese medicines increased estradiol, causing the decrease of ALP, which induced the changes of Ca and P in serum, leading to a decreased excretion of Ca in urine. In this study, TJ-41 was effective in every parameter while TJ-7 and TJ-30 was effective on some parameters, showing that traditional Chinese medicines have specificities in the space environment. In conclusion, this study suggests that some traditional Chinese medicines may be beneficial for adaptation to a space environment.

Silicon supplementation improves the bone mineral density of calcium-deficient ovariectomized rats by reducing bone resorption

The purpose of this study was to investigate the effect of silicon (Si) supplementation on bone mineral density (BMD) and bone metabolism parameters relative to calcium (Ca) intake levels in ovariectomized rats. A total of 72 female Wistar rats (6 weeks) were ovariectomized (OVX) and divided into six groups, and Si (500 mg of Si per kilogram of feed) was or was not administered with diets containing various levels of Ca (0.1%, 0.5%, and 1.5%) for 10 weeks. The groups were as follows: (1) Ca-deficient group (0.1% Ca), (2) Ca-deficient with Si supplementation group, (3) adequate Ca group (0.5% Ca), (4) adequate Ca with Si supplementation group, (5) high Ca group (1.5% Ca), and (6) high Ca with Si supplementation group. Si supplementation significantly increased the BMD of the femur and tibia in Ca-deficient OVX rats, while no change was observed with Si supplementation in the BMD of the spine, femur, and tibia in the adequate and high Ca groups. Serum alkaline phosphatase and osteocalcin levels were not affected by Si supplementation or Ca intake levels. C-telopeptide type I collagen levels were significantly decreased as a result of Si supplementation in Ca-deficient OVX rats. In summary, Si supplementation produced positive effects on bone mineral density in Ca-deficient OVX rats by reducing bone resorption. Therefore, Si supplementation may also prove to be helpful in preventing osteoporosis in postmenopausal women whose calcium intake is insufficient.

Manganese supplementation improves mineral density of the spine and femur and serum osteocalcin in rats

The effect of manganese (Mn) supplementation on bone mineral density (BMD) and bone metabolism parameters was determined in ovariectomized Sprague-Dawley rats. Rats were divided into four groups (OVX, OVX+Mn, sham, sham+Mn) and fed with different intake levels of manganese (adequate 0.001% Mn, supplementation 0.01% Mn) for 12 weeks. BMD of the lumbar vertebrae, femur, and tibia were significantly lowered in ovariectomized rats compared to the sham group. In addition, BMD of the lumbar vertebrae was significantly increased by Mn supplementation in the sham groups. Serum C-telopeptide cross-links of type I collagen (CTx), bone resorption biomarker, alkaline phosphatase (ALP), and bone formation biomarkers were not significantly different among the four groups. However, serum osteocalcin, a more sensitive bone formation biomarker, was significantly increased by Mn supplementation. To summarize, Mn supplementation resulted in increased BMD and bone formation. Based on our findings, more research is needed to better understand the effects of manganese supplementation on bone formation and resorption.

Beneficial effect of pretreatment and treatment continuation with risedronate and vitamin K2 on cancellous bone loss after ovariectomy in rats: a bone histomorphometry study

The purpose of the present study was to examine the effect of pretreatment with risedronate and/or vitamin K2 and treatment continuation with reduced dosing frequency of the drugs on the early cancellous bone loss induced by ovariectomy (OVX) in rats. Eighty female Sprague-Dawley rats, 4 mo of age, were randomized by the stratified weight method into eight groups (n= 10 in each group); rats subjected to OVX, but not sham-operated rats, were treated with vehicle, risedronate, vitamin K2 (menatetrenone), or risedronate+vitamin K2 for 4 wk before the surgery, and the treatment was either discontinued (pretreatment groups) or continued after the surgery (treatment continuation groups) for 2 wk. Sham-operated rats (controls) were treated with the vehicle throughout the experimental period. During the 4 wk prior to the surgery (pretreatment), risedronate and vitamin K2 were administered five times a week either subcutaneously at a dose of 2.5 microg/kg body weight (risedronate) or orally at the dose of 30 mg/kg body weight (vitamin K2). During the 2 wk after the surgery (treatment continuation), the dosing frequency of the drugs was reduced to twice a week. Risedronate and vitamin K2 had an anti-resorptive effect on the bone. Pretreatment with risedronate alone, but not vitamin K2 alone, prevented the loss of the cancellous bone volume/total volume (BV/TV) of the proximal tibial metaphysis after OVX. Treatment continuation with vitamin K2 alone prevented the loss of the cancellous BV/TV after OVX, while treatment continuation with risedronate alone increased the cancellous BV/TV to beyond the values in controls. Pretreatment with risedronate+vitamin K2 had a more beneficial effect in increasing the cancellous bone mass than pretreatment with risedronate alone. Treatment continuation with risedronate and/or vitamin K_ appeared to have a more beneficial effect in increasing the cancellous bone mass than the respective pretreatment. Neither the total tissue area nor the cortical area of the tibial diaphysis was affected by any treatment. The present study demonstrated that pretreatment with risedronate had a beneficial effect on the early cancellous bone loss after OVX in rats, with a more beneficial effect when combined with vitamin K2. Moreover, even though the dosing frequency of the drugs was reduced after OVX, treatment continuation appeared to be more beneficial than pretreatment for increasing the cancellous bone mass.

Effects of eccentric exercise training on cortical bone and muscle strength in the estrogen-deficient mouse

The purpose of this study was to determine whether eccentrically biased exercise training could attenuate changes in muscle and bone function associated with estrogen deficiency in the mouse model. Four groups of ICR mice were used: control (Con), sham ovariectomized (Sham), ovariectomized (OVX), and ovariectomized + high-force resistance training (OVX+Train). All groups except Con were implanted with a nerve cuff surrounding the peroneal nerve to stimulate the left ankle dorsiflexors. Training consisted of 30 stimulated eccentric contractions of the left ankle dorsiflexors at approximately 150% of peak isometric torque every third day for 8 wk. After the training period, groups were not significantly different with regard to peak torque or muscle size. However, the tibial midshaft of the trained leg in the OVX+Train mice exhibited greater stiffness (+15%) than that in the untrained OVX mice, which could not be explained by changes in cross-sectional geometry of the tibia. Scaling of bone mechanical properties to muscle strength were not altered by ovariectomy or training. These data indicate that eccentric exercise training in adult mice can significantly increase bone stiffness, despite the absence of ovarian hormones.

Effect of the difference of bone turnover on peri-titanium implant osteogenesis in ovariectomized rats

High and low bone turnover situations, both of which are typically observed as postmenopausal and senile osteoporosis, were created by ovariectomy (OVX), and then an investigation of whether or not the difference of bone turnover affected peri-titanium (Ti) implant osteogenesis in rats was conducted. Female rats were divided into four groups. The experimental and control groups underwent OVX or sham operations at 15 or 27 weeks of age, as high or low bone turnover groups, respectively. Ti implants were inserted into the tibiae at 30 weeks, then fluorochromes were injected 10 or 20 days after the implantation for histometry. The implants were retained for 30 days and then ground sections were prepared. Afterward, the cortical bone growth rate, bone contact ratio (BCR) of the implant in both the cortical bone area and medullary canal area, and the average trabecular bone thickness around the implant were evaluated. Biochemical markers of bone turnover were also measured. Biochemical measurements indicated both increasing osteocalcin production in OVX rats and decreasing tartrate-resistant acid phosphatase activity in the low-turnover group. Histometrical measurements showed decreasing cortical growth and low BCR in the medullary canal of the low-turnover group. The high-turnover group demonstrated BCR as high as that of the control group. There was no significant difference in the average trabecular bone thickness around the implant among the groups. As a result, two types of osteoporotic situations were confirmed and it was shown that the difference of bone turnover was clearly due to the diverse osteogenesis around the Ti implant.

Stage-dependent changes in trabecular bone turnover and osteogenic capacity of marrow cells during development of type II collagen-induced arthritis in mice

Rheumatoid arthritis (RA) is a disease characterized by inflammatory polyarthritis leading to destruction of the joints and reduction in bone mass. However, the relationship between bone mass and turnover is not yet clear in RA patients. To clarify the effect of bone turnover and marrow osteogenic capacity on mass and structure during the development of arthritis, we examined DBA1/J mice for 8 weeks after the first immunization with bovine type II collagen at the age of 9 weeks. Localized arthritis developed at 4 weeks and advanced arthritis at 6 weeks postimmunization. Urinary deoxypyridinoline levels in arthritic mice were significantly higher at 4 weeks, and levels were maintained thereafter. Their serum osteocalcin levels were significantly reduced compared with controls at 2 and 6 weeks, but did not differ significantly from those in the control group at 4 and 8 weeks. Three-dimensional (3D) trabecular bone volume of the proximal tibia measured by 3D microcomputed tomography (micro-CT) in the arthritic mice became significantly lower at 4 weeks and decreased further at 6 weeks compared with controls. Parameters of 3D trabecular bone structure, such as structure model index and trabecular bone pattern factor, were increased at 4 and 6 weeks, respectively. Trabecular osteoclast number increased and bone formation rates decreased at 8 weeks. The number of total bone marrow cells (BMCs), adherent stromal cells, and area of mineralized nodule formation in the tibia of arthritic mice were significantly reduced compared with controls at 6 weeks. Numbers of total fibroblastic colony-forming units (CFU-f) and alkaline phosphatase (ALP)-positive CFU-f colonies also decreased. However, the values of these osteogenic parameters corrected for the total BMCs and/or adherent stromal cells did not differ significantly between the arthritic and control groups. These data indicate that an increase in bone resorption led to the reduction in trabecular bone mass and deterioration of 3D structure during the localized arthritic stage. The reduction in bone marrow osteogenic potential in the advanced arthritic stage was due to the reduction in the number of total bone marrow cells, and differentiation of osteogenic cells was apparently unaffected. The reduction in bone formation may not be substantial in this arthritic model.

Effect of trabecular bone contour on ultimate strength of lumbar vertebra after bilateral ovariectomy in rats

To test the hypothesis that the effect of trabecular microarchitecture on bone strength varies with the duration of estrogen loss, we evaluated the relationship between three-dimensional (3D) parameters for trabecular microarchitecture and bone minerals with the compressive load of the lumbar vertebra in rats. Female Sprague-Dawley rats (n = 190) were divided into 19 groups. Ten rats were killed at day 0. Half of the remaining rats underwent bilateral ovariectomy (ovx), and the others were subjected to sham surgery. Ten rats from each group were killed at 3, 7, 11, 14, 28, 42, 56, 70, and 84 days postsurgery. Urinary deoxypyridinoline and serum osteocalcin increased significantly in the ovx group from days 28 and 11, respectively, compared with the sham group. Bone mineral content (BMC) and bone mineral density (BMD) of the fifth lumbar body diminished from days 42 and 84, respectively, compared with the sham group. In ovx rats, trabecular bone volume (BV/TV), measured using 3D images of microcomputed tomography, diminished from day 28 compared with both baseline control and sham. The trabecular bone pattern factor (TBPf) and structure model index (SMI) increased from day 28 in the ovx group compared with both baseline control and sham. Ultimate compression loads diminished at day 28 compared with baseline control and decreased progressively thereafter. Neither of these parameters changed in the sham group during the same period. Within 4 weeks post-ovx, TBPf, SMI, and BV/TV correlated with load (p < 0.01). BMC and BMD correlated with load from 6 weeks post-ovx (p < 0.01). Stepwise regression analysis showed that TBPf was the most significant determinant of load within 4 weeks post-ovx (coefficient of determination [R(2)] = 0.669; p < 0.01). SMI correlated with TBPf (R(2) = 0.968; p < 0.01). Moreover, R(2) for ultimate load indicated higher values of 0.975 with TBPf and SMI. However, BMC was the most significant determinant of load from 6 weeks post-ovx (R(2) = 0.511; p < 0.01), as it was in the sham group. These data suggest that changes in trabecular bone contour with increased bone turnover are critical for reducing lumbar bone strength during the early post-ovx period in rats.

Maintenance of vertebral body bone mass and strength created by human parathyroid hormone treatment in ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone (1-84) (hPTH) followed by maintenance administration of 17beta-estradiol (E2), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on vertebral body bone mineral density (BMD) and bone strength in ovariectomized (ovx) rats. Eight groups of ovx (219 rats) and one group of intact female rats (48 rats) were left untreated for 11 weeks (age 3.5 months at the beginning). For the following 12 weeks, four ovx groups received subcutaneous injections of hPTH (75 microg/kg per day, 3 days/week) and four groups received vehicle. Treatments were then changed to: E2 (10 microg/kg per day, 2 days/week); Ris (3 microg/kg per day, 3 days/week); LowPTH (25 microg/kg per day, 3 days/week); or vehicle for 36 weeks. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). The endpoints were vertebral body BMD, ultimate stress (Ultstr), and moduli of elasticity from compression tests (ModM), and from ultrasound tests (ModUS). Ovariectomy resulted in lower BMD (p < 0.001). The hPTH treatment for 12 weeks restored BMD to the level of intact rats. Ultstr and ModUS followed a similar pattern, but the ovx-induced Ultstr was not significant (p = 0.073, ModUS: p = 0.003), nor was the hPTH-induced increase in ModUS (p = 0.131, Ultstr: p = 0.02). After hPTH withdrawal, BMD, Ultstr, and ModUS levels were not different from levels in ovx animals. In Ris-treated rats pretreated with hPTH, BMD (weeks 24 and 48, p < 0.002) and ModUS (week 24, p = 0.018) values were greater than in ovx animals. In LowPTH-treated rats pretreated with hPTH, BMD (weeks 24 and 48, p < 0.001) and Ultstr (week 48, p = 0.005) were greater than in ovx animals. In E(2)-treated rats pretreated with hPTH, BMD was greater than in ovx rats at week 24 (p = 0.009), but did not differ at weeks 36-48. Neither Ultstr nor ModUS in E(2)-treated rats differed significantly from ovx rats at any timepoint. Of the agents and dosing regimens used, we conclude that the hPTH-related vertebral bone mass gain in ovx rats can be maintained for up to 36 weeks with risedronate and low-dose hPTH treatment. Bone strength is maintained by treatment with low-dose hPTH, but only partially maintained with risedronate.

Acute effects of ovariectomy on wound healing of alveolar bone after maxillary molar extraction in aged rats

Acute effects of ovariectomy on the bone wound healing processes after maxillary molar extraction in aged rats were examined by means of quantitative scanning electron microscopy (SEM), backscattered electron image (BSE) analysis and energy-dispersive X-ray (EDX) microanalysis. Six-month-old female rats underwent either sham operation or bilateral ovariectomy, and 7 days postoperatively, the maxillary first molars were extracted. On post-extraction days 7, 30 and 60, the dissected maxillary bone surfaces were examined by SEM to reveal the bone formative and resorptive areas around the extracted alveolar sockets. In addition, the resin-embedded maxillae were micromilled in the transverse direction through the extracted alveolar sockets, and the newly-formed bone mass on the buccal bone surfaces and within the extracted sockets was examined by BSE analysis. Compared with sham-operated controls, the extent of newly-formed bone mass on the buccal bone surfaces in OVX rats was significantly decreased, due to increased bone resorption. On the other hand, new bone formation within the extracted sockets was similar in the experimental groups. In EDX microanalysis of these newly-formed bone matrices, both Ca and P weight % and Ca/P molar ratio were similar in the experimental groups. Our results suggest that 1) acute estrogen deficiency induced by ovariectomy stimulates sustained bone resorption, but has less effect on bone formation, and 2) bone wound healing after maxillary molar extraction within extracted alveolar sockets is not significantly delayed by ovariectomy, but bony support by newly-formed bone mass on the maxillary bone surfaces at the buccal side of the extracted sockets is significantly decreased, due to increased bone resorption.

Effects on bone loss of manganese alone or with copper supplement in ovariectomized rats. A morphometric and densitomeric study

OBJECTIVE

The aim of this study was to examine the effect of manganese (Mn) alone and with the addition of copper (Cu) in the inhibition of osteopenia induced by ovariectomy (OVX) in rats. STUDY CONDITIONS: Four lots of 100-day-old female Wistar rats were divided into experimental groups of 15 each. One group received a diet supplemented with 40 mg/kg of Mn per kilogram of feed (OVX+Mn). The second group received the same diet as the first, but with an additional 15 mg/kg of copper (OVX+Mn+Cu). The third group of 15 OVX and the fourth group of 15 Sham-OVX received no supplements. At the conclusion of the 30-day experiment, the rats were slaughtered and their femurs and fifth lumbar vertebrae were dissected. Femoral and vertebral length were measured with caliper and bones were weighed on a precision balance. The bone mineral content (BMC) and bone density (BMD) of the femur (F-BMC, mg and F-BMD, mg/cm(2)) and the fifth lumbar vertebra (V-BMC, mg and V-BMD, mg/cm(2)) were measured separately with dual energy X-ray absorptiometry.

RESULTS

The F-BMD, mg/cm(2) was lower in the OVX than in the Sham-OVX group (P<0.0001) and in the other two groups receiving mineral supplements (P<0.005 in both). F-BMC, mg was significantly lower in the OVX group than in the other three (P<0.0001 in all cases). Calculations for V-BMC, mg and V-BMD, mg/cm(2) are similar to findings in the femur.

CONCLUSIONS

These data show that a Mn supplement is an effective inhibitor of loss of bone mass after OVX, both on the axial and the peripheral levels, although this effect is not enhanced with the addition of Cu.

Uncoupling between bone formation and resorption in ovariectomized rats with chronic cadmium exposure

Osteoporosis, osteomalacia, and pathological fractures are characteristic features of Itai-Itai disease. The mechanisms of bone damage caused by cadmium (Cd) exposure have not been fully clarified. We investigated skeletal changes in ovariectomized rats with chronic Cd exposure, using bone histomorphometry and mechanical tests. Female Sprague-Dawley rats at the age of 8 weeks were ovariectomized. Eight weeks after ovariectomy, the rats were divided into two groups: Cd-OVX group (n = 15), ovariectomized rats given cadmium chloride (CdCl(2), 0.18 mg/rat) ip three times a week for 28 weeks; Cont-OVX group (n = 10), ovariectomized rats given distilled water alone for 28 weeks. Cd-OVX rats had a significant increase in serum concentration of intact osteocalcine and showed numerical but not significant increase in urinary excretion of deoxypyridinoline despite a significant decrease in glomerular filtration rate to 40% of the value in Cont-OVX rats. Bone mineral content (BMC) and density were significantly decreased in both the lumbar vertebral body and femur of Cd-OVX rats. Ultimate compressive load in the lumbar body and bending load in the midfemur were significantly lower in Cd-OVX rats than in Cont-OVX rats but the differences were not demonstrated when the values were corrected for BMC. Structural moduli in the lumbar vertebral body and the midfemur were not different between the two groups. Cd-OVX rats showed significant decreases in the trabecular bone volume and trabecular number with increased values in the indices of bone formation and resorption in the lumbar vertebral body cancellous bone in comparison with Cont-OVX rats. In the midfemur, Cd-OVX rats had significantly smaller cortical bone area than Cont-OVX rats but the moment of inertia was identical between the two groups. The indices of bone formation and resorption at endocortical surface of the midfemur were significantly increased in Cd-OVX rats over those in Cont-OVX rats, whereas the indices of bone formation at the periosteal surface were not different between the two groups. These data suggested that chronic Cd exposure exacerbated the uncoupling between bone formation and resorption in ovariectomized rats, which resulted in the osteopenia, structural changes of the bone, and decreased mechanical strength in ovariectomized rats with chronic Cd exposure.

The mechanical properties of cancellous bone in the proximal tibia of ovariectomized rats

The "mature rat model" is an effective and often-used surrogate for studying mechanisms and characteristics of estrogen-deficient osteopenia. The purpose of this study was to extend our understanding of this animal model to include the mechanical properties of cancellous bone in the proximal tibia. Female Sprague-Dawley rats were divided into two groups (n=13 each) at 14 weeks of age: an ovariectomized group (OVX) and a sham-operated control group (sham). The study terminated after a duration of 5 weeks. Specimens 2 mm long were cut from the proximal tibial metaphysis just below the growth plate and tested using two methods: (1) "whole-slice" compression, in which the entire specimen is loaded between two larger flat platens and (2) "reduced-platen" compression (RPC), which uses platens sized and aligned to load only the cancellous bone in the center of the sample. Three-point bending tests also were conducted on the femur. The short duration of estrogen deficiency yielded only minimal differences (< 10%) in femoral cortical bone but dramatic reductions (approximately 60%) in cancellous bone properties as determined by the RPC method. Ultimate stress was 7.23 MPa +/- 1.97 MPa for OVX versus 18.1 MPa +/- 5.21 MPa for sham; and elastic modulus was 252 MPa +/- 104 MPa for OVX versus 603 MPa +/- 180 MPa for sham. These changes in mechanical properties are similar in many respects to the dramatic effects reported in histomorphometric studies. For the whole-slice method, differences in mechanical properties between the two groups were not as large because the test directly loads both cancellous and cortical bone, and the latter is not affected as severely by estrogen deficiency. In this case, ultimate stress and elastic modulus were only 30% (or less) lower for the OVX group.

Reduction in bone formation and elevated bone resorption in ovariectomized rats with special reference to acute inflammation

Changes in bone modeling and remodeling in the tibia of growing rats within 30 days of ovariectomy (ovx) were evaluated by histomorphometric, mechanical; and biochemical means. Three days after ovx, suppressed bone formation was seen. This was shown by reduced osteoid volume, osteoblast surface, and bone formation rate in the secondary spongiosa, and a reduced longitudinal growth rate in the growth plate. In addition, the alkaline phosphatase and tartrate-resistant acid phosphatase activity in bone marrow supernatants was suppressed in conjunction with elevated serum sialic acid levels, indicating inflammation. Although estrogen deprivation itself may provoke the inflammatory process, the serum sialic acid level in the ovx group returned to the baseline level within 5 days after surgery, while that of estradiol in the ovx group remained consistently lower. This suggests that surgical stress, not estrogen deprivation, is the primary cause of the inflammatory response shortly after ovx. A significant difference (p < 0.01) between the ovx and sham rats was seen in the osteoclast surface, which peaked on day 7 in the ovx rats. On day 14 postovariectomy, the bone formation rate peaked and remained constant until day 30. In the ovx rats, there was a sustained reduction in the serum albumin level until day 30. Estrogen deprivation may be the primary cause of these changes, because both surgical ovx and medical oophorectomy with gonadotropin-releasing hormone agonist (G(nRHa) reduce the serum albumin level. In numerous studies dealing with changes after ovx in rats, we have observed: 1) a transient reduction in bone formation in relation to inflammatory changes evoked by ovx surgery, and 2) a sustained reduction in the serum albumin level for at least 30 days after ovx that is possibly due to estrogen deprivation.

Trabecular bone turnover, bone marrow cell development, and gene expression of bone matrix proteins after low calcium feeding in rats

Low-calcium-fed animals have been accepted as one of the experimental models showing a reduction in bone mass. However, the effects of short-term low-calcium feeding on bone turnover, the development of osteoprogenitor cells, and gene expression of bone matrix proteins have not been reported. In this study, we examined the effect of a low-calcium diet on rat tibia and analyzed the changes in the bone by histomorphometry, bone marrow cell culture, and in situ and Northern hybridization of the bone matrix proteins. Rats were fed either a low-calcium diet (0.05% Ca) or a normal calcium diet (0.5% Ca) using the pair feeding technique. They were killed at day 0, 12 h, and days 1, 2, and 3. In the low-calcium group, the serum parathyroid hormone (PTH) level was temporarily increased in 12 h after feeding the low-calcium diet. Bone mineral density in the trabecular bone was significantly decreased from 1 day after the low-calcium feeding, but cortical bone did not show any changes during the experimental period. The bone volume per tissue volume in the proximal tibia also decreased from day 1 in the low-calcium group. The number of osteoclasts and osteoblasts on the trabecular bone surface was increased in the low-calcium group compared with the normal-calcium group. An ex vivo study showed that the number of progenitors of osteoclasts and osteoblasts in bone marrow was also increased in the low-calcium group of rats. The localization of type I collagen mRNA was observed in osteoblasts in the low-calcium group. The Northern hybridization study showed that the gene expression of type I collagen, osteopontin, and osteocalcin was increased at day 3 in the low-calcium group. These results indicated that the trabecular bone surface quickly responded to the low-calcium feeding and that bone remodeling activity was activated probably by PTH. The changes in bone marrow cell populations and the gene expression of bone matrix proteins are closely associated with increased bone turnover induced by the low-calcium diet, resulting in rapid bone loss of the trabecular bone.

Inhibitory effect of vitamin K2 (menatetrenone) on bone resorption in ovariectomized rats: a histomorphometric and dual energy X-ray absorptiometric study

To clarify how vitamin K2 prevents bone loss in vivo, it was given to ovariectomized 20-week-old rats for 2 weeks. Bone mineral density (BMD) in the whole femur and in 7 specific portions (F1 to F7 from the proximal to the distal end) was determined by dual-energy X-ray absorptiometry, and histomorphometry was also performed in proximal tibial metaphysis. Ovariectomy (OVX) resulted in significant decreases in the BMD in the whole femur and the F1, F2, F6 and F7 portions. Histomorphometrical analysis of the tibia showed that the bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th) and trabecular number (Tb.N) were decreased, while trabecular separation (Tb.Sp) and osteoclast number/bone surface (Oc.N/BS) were increased by OVX. The parameters for bone formation were not changed by OVX. These data indicate that the bone loss within 2 weeks is due to the enhancement of bone resorption. Vitamin K2 at 50 mg/kg inhibited the decrease in the BMD of the whole femur together with the F6 and F7 portions. Vitamin K2 also inhibited the decrease in Tb.N and the increases in Tb.Sp, Oc.N/BS and osteoclast surface/bone surface (Oc.S/BS) caused by OVX. These results suggest that vitamin K2 prevents bone loss through the inhibition of bone resorption and osteoclast formation in vivo.

Histomorphometric assessment of bone changes in rats with type II collagen-induced arthritis

Numerous studies have demonstrated bone loss in rats following immobilization by tenotomy or nerve sectioning and following ovariectomy. However, few experiments have focused on bone change in rats with arthritis. We investigated bone loss in the proximal tibia and lumbar vertebra in rats with type II collagen-induced arthritis, an experimental model of rheumatoid arthritis, using histomorphometry. Bone loss in the early phase after immunization reflected a significant increase in numbers of osteoclasts and temporarily decreased bone formation. In the proximal tibia, near an arthritic joint, osteoclast numbers associated with bone trabeculae were increased four times over control numbers 4 weeks after immunization. In the lumbar vertebra, where arthritis was not shown, recruitment of osteoclasts occurred later than in the proximal tibia. With time, in both the proximal tibia and lumbar vertebra bone resorption normalized, but bone formation rate and double-label surface by tetracycline, a parameter reflecting bone formation, were increased above control values. We conclude that differences between the proximal tibia and lumbar vertebra probably reflected resumption of function as well as distance from areas of inflammation. These findings indicate that collagen-induced arthritis in rats is a useful model not only of autoimmunity, but also of juxta-articular and generalized osteoporosis in rheumatoid arthritis.

Morphometric evidence that YM175, a bisphosphonate, reduces trabecular bone resorption in ovariectomized dogs with dietary calcium restriction

We examined mechanisms by which incadronate disodium (YM175) prevented bone resorption in ovariectomized dogs with dietary calcium restriction using the morphometrical method. YM175 (0.01-1.0 mg/kg) was given to ovariectomized dogs for 18 months. Because lumbar bone mineral density remained constant at month 17, we assumed that the trabecular bone resorption rate was equal to the bone formation rate and that wall thickness equaled resorption cavity depth. YM175 decreased both the bone resorption rate per number of osteoclasts and resorption cavity depth of cancellous pockets which were increased in ovariectomized dogs. These results suggest that YM175 reduces bone loss by decreasing the resorbing activity of osteoclasts.

Bone marrow cell development and trabecular bone dynamics after ovariectomy in ddy mice

To clarify the relationship between the sequential changes of trabecular bone turnover and bone marrow cell development in ovariectomized (ovx) mice, bilateral tibiae of 8-week-old ddy mice were obtained. Histomorphometric analyses of the trabecular bone of the proximal tibia of ovx mice revealed increases in the bone formation rate and the osteoclast surface for the first 28 days postovariectomy. The trabecular bone volume showed a rapid decrease for the first 28 days and a steady state for the subsequent 14 days. In bone marrow cell culture experiments, the numbers of total and nonadherent bone marrow cells per tibia obtained from the ovx mice increased. The formation of osteogenic nodules and osteoclast-like multinucleated cells in the marrow cultures obtained from ovx limbs showed a significant increase on days 14 and 28 and returned to the sham-operated level by day 42. The numbers of colony forming units (fibroblastic) and colony forming units (granulocytes and macrophages) that developed from the marrow cells did not differ between the ovx and sham limbs at any time during the study period. Fluorescence-activated cell-sorter analysis revealed no population changes in the cell development of macrophages. These results demonstrate that there are two stages in the development of osteopenia after ovx. During the first 28 days after ovx, the ovariectomy enhances the developmental process from bone marrow stromal cells to osteoblasts and the terminal differentiation from osteoclast precursors to mature osteoclasts. The trabecular bone turnover also increases. In the subsequent 14 days, the changes in the osteogenic and osteoclastogenic potentials of the bone marrow cells are alleviated and the trabecular bone dynamics are in a steady state. The changes in bone marrow cell development are closely associated with those at the trabecular bone surface.

Effect of exercise on tibial and lumbar vertebral bone mass in mature osteopenic rats: bone histomorphometry study

The effect of moderate running exercise on tibial and lumbar vertebral bone mass was examined in mature osteopenic rats by bone histomorphometry. Ten 37-week-old female Wistar rats, with bone loss resulting from being fed a relatively low-calcium diet for 14 weeks after ovariectomy at the age of 23 weeks, were randomly divided into two groups of five animals each; control and exercise groups. The exercise consisted of treadmill running at 12 m/min for 1 h per day on 5 days per week for 12 weeks. During the exercise period, all animals were fed a standard calcium diet. After 12 weeks of exercise, bone histomorphometry was evaluated for cancellous bone (secondary spongiosa) of the proximal tibia and the fourth lumbar vertebra and for cortical bone of the tibial shaft. The findings suggested that in the mature osteopenic rat, there was a beneficial effect of moderate running exercise with adequate calcium intake on bone mass only in a weight-bearing long bone, the tibia. The mechanism for increased bone mass appeared to be both decreased bone resorption and increased bone formation in cancellous bone and increased bone formation in cortical bone.

Effects of exercise on bone mineral density in mature osteopenic rats

Dual-energy X-ray absorptiometry (DXA) was used to examine the effects of quantitative application of treadmill running exercise on bone mineral density (BMD) of the tibia and the fourth and fifth lumbar (L4 + L5) vertebrae in mature osteopenic rats. Twenty 37-week-old rats with bone loss, resulting from feeding a relatively low calcium diet for 14 weeks after ovariectomy at the age of 23 weeks, were divided into four groups of five rats each according to the intensity and duration of the exercise: 12 m/minute, 1 h/day in group EX1; 18 m/minute, 1 h/day in group EX2; 12 m/minute, 2 h/day in group EX3; and sedentary control in group CON. With a standard calcium diet, the exercise was performed 5 days a week for 12 weeks, and the BMD of both the right tibia and the L4 + L5 vertebrae was measured using DXA at weeks 0, 4, 8, and 12. At the end of 12 weeks of exercise, the right femur and the L5 vertebra were dissected and the mechanical strength was measured using a three-point bending test and a compression test, respectively. After 12 weeks of exercise, a significant increase in the tibial BMD was observed in only group EX1 compared with that in group CON (p = 0.0039, by two-way analysis of variance). However, any significant increase in the L4 + L5 vertebral BMD was not observed in any exercise groups compared with that in the control group. While a maximum breaking force of the femoral shaft in group EX1 was significantly greater than that in group CON (p < 0.05, by Mann-Whitney's U-test), that in groups EX2 and EX3 did not significantly differ from that in group CON. However, there was no significant difference in a maximum breaking force of the L5 vertebral body among all the exercise and control groups. These results indicated that the beneficial effects of treadmill running exercise under a standard calcium diet were recognized only in the weight-bearing bones of the mature osteopenic rats resulting from estrogen deficiency and inadequate calcium intake only when an optimal level of exercise was applied.

Ovariectomy causes cell proliferation and matrix synthesis in the growth plate cartilage of the adult rat

The in vivo effects of ovariectomy in rats have been studied on cell proliferation and matrix synthesis in the growth plate cartilage by assessing immunohistochemically the levels of proliferating cell nuclear antigen and chondroitin sulphate proteoglycan(s). The serum levels of insulin-like growth factor-I and growth hormone were also measured by radioimmunoassay procedures. At 5 weeks after ovariectomy, the serum levels of the growth factor were significantly higher than those in sham-operated rats. In contrast, the level of growth hormone was lower. The nuclear staining of proliferating cell nuclear antigen was generally seen in the zone of proliferative chondrocytes from both groups of rats. Whereas almost all chondrocytes in the proliferative zone of ovariectomized rats expressed proliferating cell nuclear antigen immunoreactivity, fewer did so in that of the sham rats. Quantitative image analysis by ACAS 570 laser cytometry demonstrated that the nuclear antigen-positive sites in ovariectomized rats had significantly higher integrated values (staining intensity), areas and perimeters than those in sham rats. In addition, the number of chondroitin sulphate proteoglycan-immunoreactive cells in the proliferative chondrocytes was also higher in ovariectomized rats than in sham ones. These results suggest that ovariectomy significantly stimulates the cell proliferation and matrix synthesis in the growth plate cartilage, probably through the higher serum level of insulin-like growth factor-I.

Responses of trabecular and cortical bone turnover and bone mass and strength to bisphosphonate YH529 in ovariohysterectomized beagles with calcium restriction

Thirty-six beagles, 18 months of age, underwent ovariohysterectomy (OHX) or a sham operation. Sham-operated animals were given a diet with standard calcium (1.4%) (group 1, n = 6) or a restricted calcium diet (0.14%) (group 2, n = 6). The OHX animals were given the restricted calcium diet and YH529 orally with respective daily doses of 0, 0.02, 0.1, and 0.5 mg/kg of body weight (groups 3-6, n = 6 each) for 12 months. At the end of this period, the lumbar bone mineral densities (BMDs) in groups 2 and 3 and the load values for group 3 were significantly smaller than those for group 1. The midfemur BMD did not differ among the groups. The urinary deoxypyridinoline (U-Dpy) and bone formation rates (BFR/BS, BFR/BV) in groups 2 and 3 and the osteonal BFR/BS and trabecular osteoclast number (Oc.N/BS) in group 3 were significantly larger than the respective values for group 1. However, these parameters did not significantly differ between groups 2 and 3. The serum osteocalcin (OC) level, wall thickness (W.Th), and mineral apposition rate values for group 3 were significantly larger than those for group 2. In group 2, the trabecular activation frequency (Ac.F) increased by 3.11 times, and the percent values of the number of labeled osteons (L-Ot.N/T-Ot.N, %) in the tibia by 3.28 times over those for group 1. In group 3, the Ac.F increased by 3.20 times and the number of labeled osteons by 3.77 times over those for group 1. In groups 4-6, the U-Dpy and Oc.N/BS values were smaller, but their OC levels did not significantly differ from the level for group 3. The lumbar BMD, the load, and W.Th were dose-dependently significantly larger than those for group 3. The Ac.F values were significantly smaller, and the respective value in groups 4-6 was 67.9, 25.5, and 10.2% of that in group 3. The BMDs of the midfemur in groups 4-6 were significantly larger than those in group 3, but the ultimate load values did not significantly differ. The L-Ot.N/T-Ot.N values were also significantly smaller, and the respective value in groups 4-6 was 82.0, 48.5, and 55.2% of that in group 3. The tibial endocortical and periosteal BFR/BSs did not differ significantly. These data demonstrate that the effects of OHX on bone mass and turnover were small in the beagles fed a restricted calcium diet. YH529 maintained the mass and strength of the lumbar bone by reducing the bone resorption. The cortical bone appeared to be less sensitive to the agent than the trabecular bone in this animal model.

Acute changes in trabecular bone connectivity and osteoclast activity in the ovariectomized rat in vivo

Estrogen deficiency results in a loss of trabecular bone mass and structure that leads to an increased incidence of osteoporotic fractures. The purpose of this study was to determine the time course for trabecular structure deterioration and changes in bone turnover just after ovariectomy in the rat. Six-month-old female virgin Sprague-Dawley rats had their right proximal tibia scanned by X-ray tomographic microscopy (XTM) at baseline (day 0). Animals were then randomized into two groups, and in each group 9 were sham-operated and 11 were ovariectomized and had repeat XTM scans on days 5, 13, 29, and 42 postovariectomy in group 1 and on days 8, 13, 33, and 50 postovariectomy in group 2. Urine was collected for deoxypyridinoline (DPD) cross-link measurements 24 h before each XTM scan and analyzed by ELISA. Trabecular bone structural variables and bone turnover endpoints were calculated from XTM data and standard histomorphometry. Trabecular connectivity decreased 27% by days 5 and 8 postovariectomy (p < 0.01) and continued to decrease up to day 50 postovariectomy (p < 0.01). The trabecular bone volume decreased 25% by 8 days postovariectomy (p < 0.01), and it continued to decrease through day 50. DPD cross-link excretion had increased 37% on day 13 (p < 0.01) and by over 100% of baseline by day 50 postovariectomy. Trabecular bone connectivity and volume deteriorate rapidly while DPD cross-link excretion increased more slowly in acute estrogen deficiency. These data suggest that if an agent is to preserve fully trabecular bone structure, it must be instituted very early in the estrogen-deficient state. They also suggest that a lag time exists before DPD excretion properly mirrors newly induced conditions of high bone turnover in this rat model.

Long-term treatment of indomethacin reduces vertebral bone mass and strength in ovariectomized rats

We investigated the effect of the long-term treatment of indomethacin, on lumbar spinal bone mineral density (LSBMD), cancellous bone mass, structure, and strength of vertebral body in old ovariectomized (OVX) rats. Ten-month-old female Wistar rats were divided into five groups: the sham operated + vehicle (sham + VEH) group, the OVX + vehicle (OVX + VEH) group, the OVX + indomethacin (IN) 1.5 mg/kg/week (OVX + IN1.5) group, the OVX + IN 6.0 mg/kg/week (OVX + IN6.0) group, and the OVX + IN 15.0 mg/kg/week (OVX + IN15.0) group. IN or vehicle were given by subcutaneous injection (s.c.) three times per week. The treatments were started at 1 week after operation and continued for 24 weeks. LSBMD (L2-L5) was measured at 0, 12, and 24 weeks after the beginning of treatment. At the end of the experimental period, the animals were sacrificed, and bone histomorphometrical and biomechanical analysis of lumbar vertebral body were done. LSBMD, trabecular bone volume (BV/TV), and trabecular thickness (Tb.Th) decreased significantly in a dose-related manner with IN. In the OVX + IN15.0 group, LSBMD decreased by 12.7%, BV/TV decreased by 65.5%, and Tb.Th decreased by 32.8%, compared with the OVX + VEH group. In addition, the maximum stress in a compressive mechanical test of L4 vertebral body in OVX groups was also decreased in a dose-related manner with IN, and this value in the OVX + IN15.0 group was 31.3% lower than in the OVX + VEH group. We conclude that long-term treatment with IN accentuated the OVX-related decrease in trabecular bone mass and the compressive strength of lumbar vertebrae.

Bisphosphonate tiludronate increases bone strength by improving mass and structure in established osteopenia after ovariectomy in rats

We examined the mechanical properties of bone in ovariectomized rats treated with tiludronate. 186 Sprague-Dawley (SD) rats, 6 months of age, were assigned to 13 groups and were maintained for 3-9 months after surgery. Ovariectomy (ovx) groups were given tiludronate orally at the respective doses of 0 (vehicle), 12.5 (low), 25 (medium), and 50 (high) mg/kg body weight daily for 3 months beginning 3 months after surgery. Rats were killed at 0 (start), 3, 6, and 9 months. Whereas bone mineral density (BMD) values of the midfemur did not increase after ovx, the values in the sham-operated groups increased age-dependently. Bending moment to failure of the femur in the sham group was larger than that of the ovx control group at 9 months. In the ovx control groups, the ultimate compressive load values of the third lumbar body were reduced compared with those in the sham groups at 3 months and thereafter. Although serum osteocalcin levels were decreased in the medium- and high-dose tiludronate groups, both serum PTH and 1,25(OH)2D levels were increased only in the high-dose group. Femoral BMD, mechanical properties, and the cortical bone area were increased by the high dose at 9 months. Lumbar ultimate compressive load and the circumscribing cortical shell area in the high-dose group were increased at 6 months and thereafter. The trabecular number values were maintained at 6 and 9 months by the high dose. These data demonstrate that tiludronate administration increased the mechanical properties of bone by preserving the age-dependent increases in the cortical bone mass and three-dimensional structure of trabecular bone. These effects seemed to be due to reduced bone turnover by the agent.

Effects of long-term diabetes and/or high-dose 17 beta-estradiol on bone formation, bone mineral density, and strength in ovariectomized rats

Long-term diabetes in female rats preserves the bone mineral density (BMD) but impairs the strength of the femur. In this study, we have compared the effects of diabetes and high-dose 17 beta-estradiol (E2), two conditions of low bone formation, in ovariectomized (ovx) rats. Spontaneously diabetic BB rats were ovx 0-3 days after onset, and nondiabetic ovx littermates were used as controls; the rats were either untreated or treated with E2 (30 micrograms/day, subcutaneously), for 6 or 12 weeks (n = 9 in each of the eight groups). Analysis included: plasma 1,25-dihydroxyvitamin D3, insulin-like growth factor-I (IGF-I), and osteocalcin concentrations; histomorphometry of the proximal tibial metaphysis (PTM); and DXA and biomechanical testing of the femur. Both E2 treatment and diabetes markedly lowered plasma IGF-I and osteocalcin concentrations, as well as dynamic morphometric parameters of bone formation in the PTM. Plasma IGF-I and osteocalcin were correlated (R2 = 0.55; p < 0.0001). E2 treatment in both control and diabetic ovx rats increased the trabecular bone volume in the PTM and the BMD in the metaphysis of the distal femur; there was no difference between control and diabetic rats, however. The diaphyseal area and BMC were decreased in E2-treated or/and diabetic ovx rats, but the diaphyseal BMD remained unchanged compared with untreated ovx rats. The biomechanical properties of the whole femur (strength, angular deformation, and stiffness) were decreased in E2-treated and diabetic E2-treated ovx rats after 12 weeks. The data indicate that in situations of chronic low bone formation, whole bone strength does not reflect total BMD but correlates better with bone size and bone mineral content measurements.