Estrogen inhibition of periosteal bone formation in rat long bones: down-regulation of gene expression for bone matrix proteins

Estrogen is important for both the sexual dimorphism of the skeleton during growth and the maintenance of bone balance in adults. This report describes the in vivo effects of estrogen on bone formation and gene expression in the tibial diaphysis of ovariectomized rats. Rats were ovariectomized at 8 weeks of age and were given diethylstilbestrol (DES) or placebo 1 week later as sc sustained release pellets. Histomorphometry revealed that that the periosteal bone formation and apposition rates were reduced at the tibial diaphysis 1 week after beginning estrogen treatment and further reduced after 2 weeks. Interestingly, DES treatment had no effect on endosteal bone formation, but suppressed endosteal bone resorption. Northern analysis of freshly isolated periosteal cells from tibiae and femora revealed that DES treatment resulted in dramatic decreases in steady state mRNA levels for the bone matrix proteins osteocalcin, prepro alpha 2(I) chain of type 1 collagen, osteonectin, and osteopontin as well as the osteoblast marker enzyme alkaline phosphatase. The results suggest that the inhibitory effects of estrogen on radial bone growth in rats are mediated, or at least accompanied, by the inhibition of the expression of bone matrix protein genes in periosteal cells.     

Dietary protein restriction lowers plasma insulin-like growth factor I (IGF-I), impairs cortical bone formation, and induces osteoblastic resistance to IGF-I in adult female rats

Dietary protein deficiency, common in elderly, is associated with decreased areal bone mineral density and plasma insulin-like growth factor I (IGF-I). To investigate the early adaptation of bone cells to protein restriction, 6-month-old female rats were pair-fed with isocaloric 15% (control) or 2.5% casein diets for 14 days. Animals were then treated daily with rhIGF-I/IGFBP-3 (1:4, 2.5 mg IGF-I/kg BW) or with vehicle for 10 days. After double-labeling, proximal metaphysis and mid-diaphysis of the tibia were analyzed histomorphometrically. Plasma osteocalcin, IGF-I, and urinary deoxypyridinoline were quantified. After 14 days of protein restriction, significant drops in plasma osteocalcin (13%) and IGF-I (37%), in periosteal formation (83%) and mineral apposition (49%) rates are observed, indicating a decreased osteoblast recruitment and activity. In cancellous bone, a significant decrease in active eroded surfaces (27%) and osteoclast number (24%) indicates a transient depression of resorption. In rats fed the 15% casein diet, rhIGF-I/IGFBP-3 increases cancellous (42%) and periosteal (600%) formation rates, indicating an increased osteoblast recruitment. In protein-restricted rats, rhIGF-I/IGFBP-3 fails to increase cancellous or periosteal bone formation and plasma osteocalcin is significantly lower than in 15% casein+rhIGF-I/ IGFBP-3 rats. Protein restriction induces osteoblast resistance to rhIGF-I/IGFBP-3 in both bone envelopes. Low plasma IGF-I and osteoblast resistance to IGF-I, may contribute to the impaired periosteal formation.     

Sevelamer restores bone volume and improves bone microarchitecture and strength in aged ovariectomized rats

Sevelamer hydrochloride, a noncalcium phosphate binder, has been shown to reduce coronary artery and aortic calcification, and to improve trabecular bone mineral density in hemodialysis patients with chronic kidney disease. Here, we examined whether sevelamer given orally for 12 wk with normal food could restore bone volume (BV) and strength in aged ovariectomized (OVX) rats starting at 4 wk after OVX. Dual-energy x-ray absorptiometry, microcomputerized tomography, and bone histomorphometry analyses showed that OVX animals receiving sevelamer had increased trabecular BV (51%), trabecular number (43%), trabecular thickness (9%), cortical thickness (16%), mineral apposition rate (103%), bone formation rate (25%), and enhanced cortical and trabecular bone mechanical strength as compared with OVX rats. Sevelamer decreased collagen C telopeptide, increased osteocalcin levels, and decreased phosphate and magnesium levels without affecting calcium levels in the blood. Although sevelamer was not absorbed systemically, it stimulated osteoblast differentiation in BM-derived mesenchymal stem cell cultures, as evaluated by alkaline phosphatase positive colony-forming units, and inhibited recombinant human soluble receptor activator of nuclear factor-kappaB ligand-induced osteoclast differentiation, as evaluated by tartrate-resistant acid phosphatase positive cells in bone mineral-hematopoietic stem cell cultures. Surface enhanced laser desorption/ionization time-of-flight mass spectrometry analysis revealed that 69 proteins were differently expressed after OVX, of which 30% (20 of 69) were reversed to sham activity after sevelamer intake. PTH, fibroblast growth factor-23, and cytokine profile in serum were not significantly changed. Together, these results suggest that sevelamer in food increases the BV and improves biomechanical properties of bone in OVX rats.     

Restoration of bone mass in the severely osteopenic senescent rat

Studies in humans and rats suggest that age impairs the ability to form bone. This impairment may be due to a depletion or deficit in osteoprogenitor stem cells. Such a deficit would be expected to reduce the ability of the skeleton to respond to therapy designed to restore lost bone. This study evaluated whether severely osteopenic senescent rats are capable of responding to a potent anabolic factor in bone, prostaglandin E2 (PGE). Growing female Sprague Dawley rats were ovariectomized at 3 months and aged until the start of treatment at 23 months. Rats were treated daily with PGE (3 mg/kg sc) or vehicle for 56 days. Tibiae were harvested for bone histomorphometry and femora were obtained for mRNA analysis of bone matrix proteins. The cancellous bone area was fivefold greater in PGE-treated rats than in vehicle-treated controls and not different from age-matched ovary-intact rats. PGE approximately doubled the bone-forming surface and the mineral apposition rate and increased the bone formation rate fourfold. The increased cancellous bone area in PGE-treated rats was primarily due to an increase in osteoblasts over osteoclasts. One hundred percent of the endocortical surface and 72 +/- 9% of the periosteal surface of cortical bone was undergoing mineralization in PGE-treated rats, whereas no mineratization was evident in vehicle-treated rats. An architectural analysis of cancellous bone indicates that trabecular number and thickness were increased and separation decreased in the treated rats. Imaging by microcomputed tomography further revealed that with PGE treatment, trabeculae in the medial plane of the proximal tibial metaphysis were more robust and continuous with the endocortical surface. PGE also significantly induced message levels for the prepro-alpha (I) subunit of type I collagen (collagen), osteonectin, and osteocalcin. In summary, bone mass can be restored to severely osteopenic senescent rats, suggesting that aging does not necessarily diminish the capacity of the skeleton to form bone.     

Dose-dependent effects of tamoxifen on long bones in growing rats: influence of ovarian status

Tamoxifen is a nonsteroidal antiestrogen which has been reported by various investigators to have estrogen agonist and antagonist effects on rat bone. These different interpretations may be due to differences in the ovarian status, estrogen levels, and/or tamoxifen levels of the rats. To address this issue, a dose response was determined for the effects of tamoxifen on bone histomorphometry in intact female and ovariectomized (OVX) rats. The results were compared with those obtained after treatment of OVX rats with estrogen alone or a combination of estrogen and tamoxifen. OVX resulted in increases in growth rate (weight gain) and periosteal bone formation rate and decreases in uterine weight and cancellous bone fractional volume (BV/TV). Treatment of OVX rats with estrogen resulted in dose-dependent decreases in growth rate and periosteal bone formation rate as well as dose-dependent increases in uterine weight and BV/TV. Similarly, tamoxifen treatment resulted in dose-dependent decreases in overall growth rate and periosteal bone formation rate in both OVX and intact rats. Tamoxifen treatment prevented the decrease in BV/TV after OVX, although the highest dose of tamoxifen resulted in a small decrease in BV/TV in intact female rats. In contrast to estrogen, tamoxifen treatment prevented the increase in uterine weight in intact female rats as well as the decrease in uterine weight in OVX rats. Tamoxifen treatment did not alter the effects of 17 beta-estradiol on the periosteal bone formation rate in OVX rats, but reduced the increase in BV/TV to values similar to those in intact rats. These results are consistent with tamoxifen behaving as a partial estrogen agonist on rat bone.     

Effect of IGF-I and PDGF administered in vivo on the expression of osteoblast-related genes in old rats

In order to establish the cellular basis for using growth factors as possible therapeutic agents for the age-dependent deficit in bone formation activity, we examined the individual and combined effects of IGF-I and/or platelet-derived growth factor (PDGF) on the gene expression of osteoblast-related markers in male rats. The expression of osteoblast markers was examined in the femurs of adult and old rats following marrow ablation, which amplifies gene expression activity. The mRNA levels of collagen(alpha1) (I) (COLI), alkaline phosphatase (AP), osteopontin (OP) and osteocalcin (OC) were significantly lower in the old as compared with the adult rats. To determine whether growth factors can abolish the age-related deficits in mRNA expression in old bone, PDGF and/or IGF-I were infused directly into the right femur for 5 days following marrow ablation. The contralateral femur was infused with vehicle only and used as a control. PDGF stimulated the expression of OP mRNA in both adult and old rats, whereas COLI, AP and OC mRNAs were not affected. IGF-I infusion did not have a significant effect on mRNA expression in adult rats. In contrast, treatment with IGF-I significantly enhanced the mRNA levels of COLI, AP and OP in old rats. To examine whether the combination of both factors could affect the expression of osteoblast markers synergistically, PDGF and IGF-I were infused together. In adult bones, the combined treatment with PDGF and IGF-I caused a slight increase in the level of OP gene expression but no change in AP, OC or COLI genes. Although neither IGF-I nor PDGF alone was effective in stimulating the expression of OC, the combined treatment in old bones enhanced OC expression significantly. The expression of COLI, AP and OP was also stimulated, but the stimulation was no different from that of IGF-I alone. In PDGF plus IGF-I treatment with a high dose, no dose-response effects were observed. Within the limits of the present study, it is suggested that IGF-I and, to a much lesser extent, PDGF may partially restore the deficit in the expression of osteoblast markers in old bones, and that the combination of both factors is slightly better than IGF-I alone in stimulating OC expression.     

选择性雌激素受体调节剂雷洛昔芬阻止去卵巢大鼠骨丢失的机制

目的　了解选择性雌激素受体调节剂雷洛昔芬 (RLX)阻止去卵巢大鼠骨丢失的机制。对骨质疏松症模型大鼠进行雌激素及选择性雌激素受体调节剂类药物RLX治疗 ,观察其对去卵巢大鼠骨组织光镜、电镜及骨密度 (BMD)等各种指标的影响。　方法　用 3月龄雌性SD大鼠 32只 ,随机分为卵巢未切除组、卵巢切除组、雌激素治疗组、RLX治疗组 ,5个月后处死 ,检测股骨、腰椎及全身BMD、子宫重量、骨形态。　结果　卵巢切除组经RLX治疗 3个月后腰椎、股骨、全身BMD增加35 %、4 0 %、2 1% ,分别为 (0 2 5 6± 0 0 2 2 ) g/cm2 、(0 2 93± 0 0 15 ) g/cm2 和 (0 36 8± 0 0 2 5 ) g/cm2 ;RLX组大鼠骨小梁表面的破骨细胞数比卵巢切除组减少 ;与卵巢切除组相比 ,雌激素治疗组的子宫重量增加了 5 5 % ,而RLX组则对子宫无明显刺激作用。　结论　RLX及雌激素都具有防治骨质疏松的作用 ,RLX能阻止去卵巢所造成的骨丢失。     

The effects of systemic insulin, insulin-like growth factor-I and growth hormone on bone growth and turnover in spontaneously diabetic BB rats.

Spontaneously diabetic BB rats have a markedly depressed longitudinal bone growth and bone formation/turnover. In this study, male diabetic BB rats were infused intraperitoneally or subcutaneously for 2 weeks with hormones that are believed to stimulate skeletal growth and/or trabecular bone formation: insulin (3 or 4 U/day), human GH (hGH; 400 mU/day), recombinant human insulin-like growth factor-I (rhIGF-I; 300 or 600 micrograms/day) and testosterone (80 micrograms/100 g body weight per day). Saline-treated diabetic BB rats had decreased plasma concentrations of IGF-I and osteocalcin (OC) (OC, 3.7 +/- 0.3 vs 13.1 +/- 0.8 (S.E.M.) nmol/l in controls); bone histomorphometry showed decreased epiphyseal width, osteoblast surface (0.04 +/- 0.04 vs 1.5 +/- 0.3%) and osteoid surface, and mineral apposition rate (MAR) (1.8 +/- 0.5 vs 7.9 +/- 0.6 microns/day). Testosterone and hGH infusions had no effect on weight loss or on decreased skeletal growth and bone formation of diabetic rats, nor did they increase plasma IGF-I concentrations. Insulin infusions into diabetic rats resulted in hyperinsulinaemia and accelerated weight gain. The epiphyseal width, osteoblast/osteoid surfaces and OC levels of insulin-treated rats were normalized or stimulated well above control values (osteoblast surface, 4.3 +/- 0.8%; plasma OC, 16.1 +/- 1.4 nmol/l); the MAR (4.0 +/- 0.9 microns/day) was only partly corrected after the 2-week infusion. Infusions of rhIGF-I into diabetic rats doubled but did not restore plasma IGF-I levels to normal; weight gain, however, was similar to that in control rats. IGF-I treatment had no effect on epiphyseal width, osteoblast/osteoid surfaces and OC concentrations, but improved the decreased MAR (4.6 +/- 1.2 microns/day).(ABSTRACT TRUNCATED AT 250 WORDS)     

Bone anabolic effects of basic fibroblast growth factor in ovariectomized rats

The purpose of this study was to characterize the bone anabolic effects of basic fibroblast growth factor (bFGF) in ovariectomized (OVX) rats. Female Sprague Dawley rats were subjected to ovariectomy or sham surgery at 3 months of age and maintained untreated for 2 months post surgery. Groups of OVX rats were then treated iv with bFGF at doses of 100 or 200 microg/kg day for 7 or 14 days. Another group of OVX rats and a group of sham-operated control rats were treated iv with vehicle alone for 14 days. Certain groups of bFGF-treated OVX rats were killed at 7 or 14 days after withdrawal of treatment. The right tibiae were processed undecalcified for quantitative bone histomorphometry. Vehicle-treated OVX rats were characterized by decreased cancellous bone volume associated with increased bone turnover. Treatment of OVX rats with bFGF strongly stimulated bone formation, as indicated by marked increases of at least a factor of 10 in osteoblast surface, osteoid surface, and osteoid volume. Furthermore, new osteoid spicules were observed within the marrow cavity of these animals. Osteoclast surface was markedly decreased in bFGF-treated OVX rats, but this finding may be secondary to the extensive osteoid surface. The strongest bone anabolic effects occurred in OVX rats treated with the higher dose of bFGF for 14 days, but these animals exhibited a bone mineralization defect, as evidenced by abundant osteoid and a lack of double fluorochrome labeling, despite markedly increased osteoblast surface. However, the newly-formed osteoid rapidly calcified after withdrawal of bFGF treatment. The data indicate that bFGF not only stimulates bone formation on pre-existing bone surfaces but also induces de novo formation of bone spicules within the marrow cavity, which results in partial restoration of lost cancellous bone mass in osteopenic OVX rats after only 14 days of treatment with the growth factor. These findings suggest that bFGF merits consideration for development as a potential treatment for patients with severe osteopenia who are unresponsive to conventional osteoporosis therapies.     

Recombinant human insulin-like growth factor-binding protein-5 stimulates bone formation parameters in vitro and in vivo.

Insulin-like growth factor-binding protein-5 (rhIGFBP-5) is stored in bone and stimulates osteoblast cell proliferation in vitro. Bone formation is dependent on the number and activity of osteoblasts. We therefore evaluated the ability of recombinant human (rh) IGFBP-5 to increase osteoblast activity in vitro; both alkaline phosphatase (ALP) activity and osteocalcin levels showed a dose-dependent increase. In in vivo time-course studies, daily s.c. administration of 50 microg rhIGFBP-5/day/mouse significantly increased serum osteocalcin levels by day 7, and these levels were sustained through day 21. We further evaluated whether rhIGFBP-5 was as effective as IGF-I. Daily s.c. administration of rhIGFBP-5 (50 microg/day), IGF-I (13 microg/day), or IGF-I plus rhIGFBP-5 complex for 9 days increased serum osteocalcin levels by 58%, 65%, and 81% (P < 0.001 in all) and femoral bone extract ALP activity by 85% (P < 0.001), 29% (P < 0.05), and 13% (P = NS), respectively, and decreased carboxyl-terminal cross-linked telopeptide of type I collagen by 29% (P < 0.05), 20% (P = NS), and 12.5% (P = NS), respectively. One s.c. injection of rhIGFBP-5 (50 microg/mouse) increased serum osteocalcin and bone ALP activity by 21% (P < 0.05) and 27% (P < 0.02), respectively, after 5 days, but did not significantly increase serum IGF-I (1, 6, or 24 h/postinjection), suggesting that the effects of rhIGFBP-5 on bone are not mediated by increasing circulating IGF-I. Our data demonstrate that systemic administration of rhIGFBP-5, either alone or in combination with IGF-I, increases bone formation parameters in vivo.     

Estrogen treatment prevents osteopenia and depresses bone turnover in ovariectomized rats

Female Sprague-Dawley rats were subjected to bilateral ovariectomy (OVX) or sham surgery (control). Groups of ovariectomized (OVX) and control rats were injected daily with low, medium, or high doses of 17 beta-estradiol (10, 25, or 50 micrograms/kg BW, respectively). An additional group of OVX and control rats was injected daily with vehicle alone. All rats were killed 35 days after OVX, and their proximal tibiae were processed undecalcified for quantitative bone histomorphometry. Trabecular bone volume was markedly reduced in vehicle-treated OVX rats relative to that in control rats (12.1% vs. 26.7%). This bone loss was associated with a 2-fold increase in osteoclast surface and a 4-fold increase in osteoblast surface. The bone formation rate, studied with fluorochrome labeling, was also significantly elevated in vehicle-treated OVX rats (0.111 vs. 0.026 micron3/micron2.day). In contrast, treatment of OVX rats with the three doses of estradiol resulted in normalization of tibial trabecular bone volume and a decline in histomorphometric indices of bone resorption and formation. Our results indicate that estrogen treatment provides complete protection against osteopenia in OVX rats. The protective mechanism involves estrogenic suppression of bone turnover. These findings are consistent with the skeletal effects of estrogen therapy in postmenopausal women.     

Teriparatide [rhPTH (1-34)], but not strontium ranelate, demonstrated bone anabolic efficacy in mature, osteopenic, ovariectomized rats

We compared teriparatide (TPTD) and strontium ranelate (SR) efficacy on bone formation activity in a mature rat model of estrogen-deficiency bone loss. Rats were ovariectomized (OVX) at age 6 months and permitted to lose bone for 2 months to establish osteopenia before initiation of treatment with TPTD (5 or 15 μg/kg · d sc) or SR (150 or 450 mg/kg · d oral gavage). After 3 wk, RT-PCR analyses of bone formation genes in the distal femur metaphysis showed significant elevation of collagen 1α2, osteocalcin, bone sialoprotein, alkaline phosphatase, and Runx2 gene expression at both TPTD doses, relative to OVX controls. SR had no significant effect on expression of these genes. TPTD treatment for 12 wk dose dependently increased lumbar vertebral (LV) and femoral midshaft bone mineral content (BMC) and bone mineral density over pretreatment and age-matched OVX controls. SR 150 increased BMC, and SR 450 increased BMC and bone mineral density of femoral midshaft and LV over OVX controls. There were significant dose-dependent TPTD increases of LV and femoral neck strength, and TPTD 15 also increased midshaft strength compared with pretreatment and age-matched OVX controls. SR did not enhance bone strength relative to pretreatment or age-matched OVX controls. Histomorphometry of the proximal tibial metaphysis showed dose-dependent effects of TPTD on trabecular area, number, width, and osteoblast surface, bone mineralizing surface, and bone formation rate relative to pretreatment and age-matched OVX controls, whereas SR had no effect on these parameters. These findings confirmed the bone anabolic efficacy of teriparatide, but not SR in mature, osteopenic, OVX rats.     

柚皮苷联合运动对去势大鼠骨量和骨强度的影响

目的观察柚皮苷（NG）联合中强度跑台运动对去势大鼠骨质疏松模型的治疗效果。方法2月龄雌性SD大鼠80只,用随机数字法分为假手术组（SHAM）、去势组（OVX）、去势＋不同浓度（40、100、200 mg/kg）柚皮苷组（OVX＋NG）、去势＋跑台＋柚皮苷组（OVX＋EX＋NG）、去势＋跑台组（OVX＋EX）、雌激素组（OVX＋E2）,每组10只。大鼠切除卵巢2个月后开始给药,给药60 d后观察各组大鼠股骨骨密度（BMD）,Micro-CT参数,血清生化指标及及股骨力学性能与组织学改变。结果柚皮苷与跑台运动干预60 d后,OVX＋EX＋NG组大鼠股骨颈力学强度、股骨BMD、BV/TV、Tb.N、Tb.Th等均高于单纯去势组（P〈0.05）,OVX＋EX＋NG组治疗效果与柚皮苷浓度呈正相关,以200 mg/kg柚皮苷效果最佳;200 mg/kg柚皮苷联合中强度跑台运动可进一步提高治疗效果。OVX＋NG组大鼠血清骨钙素升高,Ⅰ型胶原C端肽（CTX-1）降低;OVX＋EX组大鼠骨钙素与CTX-1均降低;OVX＋EX＋NG组大鼠骨钙素水平与柚皮苷组（200 mg/kg）无差异,但高于OVX＋EX。OVX＋EX＋NG组CTX-1水平低于单纯柚皮苷组和单纯跑台组（P〈0.05）。结论柚皮苷联合中强度跑台运动可提高去势大鼠股骨BMD,增加骨小梁数目,改善骨代谢指标,提高股骨力学性能。     

Chronic Alcohol Consumption During Male Rat Adolescence Impairs Skeletal Development Through Effects on Osteoblast Gene Expression, Bone Mineral Density, and Bone Strength

BACKGROUND: The effect of chronic alcohol ingestion on bone formation is mediated through its direct actions on osteoblasts. The affected population of mature osteoblasts declines in both number and function resulting in decreased cancellous bone volume and cortical bone strength. Although the mechanism of action on osteoblasts is unknown, alcohol alters osteoblast gene expression and matrix synthesis. METHODS: Male rats consuming alcohol (EtOH) daily for 60 days from 35 days of age until 95 days of age (unrecovered group) were compared to rats switched to a regular diet of rat chow without EtOH for an additional 90 days (recovered group). The effects of chronic dietary EtOH on skeletal development during adolescence were examined in the unrecovered and recovered rats by hormonal analysis, bone mineral density determination, bone histomorphometry, metaphyseal gene expression for osteoblast-specific proteins, and biomechanical analysis. RESULTS: The unrecovered EtOH imbibing rats weighed less than their paired isocaloric-fed and ad libitum mates. Statistically significant reductions occurred in femur lengths in the unrecovered EtOH-fed group compared to controls. Serum testosterone levels were significantly decreased by EtOH consumption but returned to higher normal levels during the recovery period. Serum insulin-like growth factor-1 (IGF-1) levels were unaffected by EtOH. Serum osteocalcin levels in the unrecovered EtOH-fed group were higher than those in the recovered group but EtOH intake did not elevate the unrecovered levels compared to isocaloric or ad libitum control rats. Quantitative computed tomography (QCT) determination of bone mineral density (BMD) revealed a statistically significant reduction only in the distal femur metaphysis in the unrecovered EtOH-fed rats. BMD increased during recovery in the distal femur metaphysis and femur mid-cortex. Image analysis of midsagittal sections of the proximal tibial metaphysis of unrecovered rats revealed reductions in cancellous area, trabecular cellularity and thickness, and increased trabecular separation. Cortical widths were significantly reduced by chronic EtOH consumption. These changes remained statistically significant at the end of the recovery period. Four-point biomechanical testing of femurs from EtOH-fed and control unrecovered groups revealed significant reductions in cortical strength, energy-to-failure, and stiffness. These cortical characteristics returned to normal values with abstinence. Tibial metaphyseal alpha-1 type I collagen and osteocalcin mRNA expression levels were significantly elevated above the paired isocaloric control levels after 60 days of EtOH consumption. Metaphyseal alkaline phosphatase mRNA levels remained unaltered by EtOH consumption in the unrecovered group. After 90 days of abstinence alpha-1 type I collagen and alkaline phosphatase gene expression levels remained significantly elevated over the isocaloric and ad libitum control levels (collagen) and the isocaloric control value (alkaline phosphatase). However, metaphyseal osteocalcin mRNA levels declined to normal levels during abstinence. CONCLUSIONS: Chronic consumption of EtOH during the peripubertal period of skeletal growth leads directly to decreased metaphyseal and cortical bone mediated through effects on osteoblasts. Removal of EtOH from the diet is accompanied by incomplete restoration of normal bone metabolism during skeletal growth.     

Increased bone formation and bone mass induced by sclerostin antibody is not affected by pretreatment or cotreatment with alendronate in osteopenic, ovariectomized rats

Clinical studies have revealed a blunting of the bone anabolic effects of parathyroid hormone treatment in osteoporotic patients in the setting of pre- or cotreatment with the antiresorptive agent alendronate (ALN). Sclerostin monoclonal antibody (Scl-Ab) is currently under clinical investigation as a new potential anabolic therapy for postmenopausal osteoporosis. The purpose of these experiments was to examine the influence of pretreatment or cotreatment with ALN on the bone anabolic actions of Scl-Ab in ovariectomized (OVX) rats. Ten-month-old osteopenic OVX rats were treated with ALN or vehicle for 6 wk, before the start of Scl-Ab treatment. ALN-pretreated OVX rats were switched to Scl-Ab alone or to a combination of ALN and Scl-Ab for another 6 wk. Vehicle-pretreated OVX rats were switched to Scl-Ab or continued on vehicle to serve as controls. Scl-Ab treatment increased areal bone mineral density, volumetric bone mineral density, trabecular and cortical bone mass, and bone strength similarly in OVX rats pretreated with ALN or vehicle. Serum osteocalcin and bone formation rate on trabecular, endocortical, and periosteal surfaces responded similarly to Scl-Ab in ALN or vehicle-pretreated OVX rats. Furthermore, cotreatment with ALN did not have significant effects on the increased bone formation, bone mass, and bone strength induced by Scl-Ab in the OVX rats that were pretreated with ALN. These results indicate that the increases in bone formation, bone mass, and bone strength with Scl-Ab treatment were not affected by pre- or cotreatment with ALN in OVX rats with established osteopenia.     

雌激素对大鼠去卵巢后白细胞介素-6介导的骨吸收的影响

目的观察雌激素对去卵巢大鼠骨髓细胞白细胞介素6(IL6)、IL6受体、gp130基因表达以及骨髓源性破骨细胞形成的影响。方法健康3月龄雌性SD大鼠72只,随机平均分为假手术对照组、去卵巢组和雌激素组(苯甲酸雌二醇02mg/kg,皮下注射,每周1次)。分别于术后2、4、6、12周每组各取6只大鼠骨髓细胞作细胞培养和提取RNA。培养第6天计数破骨细胞数,第12周取左侧胫骨作骨形态计量学检测。结果骨形态学显示去卵巢后出现骨吸收亢进,雌激素对其有抑制作用。去卵巢后2周,去卵巢组破骨细胞形成数即多于对照组(1450±169对901±141,P<005),骨髓细胞IL6和IL6受体mRNA表达均显著升高(P<005,P<001),第4～6周,上述改变达高峰,至第12周仍呈有意义增高;从2～12周,上述各指标雌激素组均明显低于去卵巢组(P<005,P<001)。各组未见gp130基因表达水平有明显变化。结论雌激素可以抑制大鼠去卵巢后骨髓源性破骨细胞的生成,这一效应可能与其抑制骨髓细胞在去卵巢后过度表达IL6、IL6受体基因有关。     

Bone mineral homeostasis in spontaneously diabetic BB rats. II. Impaired bone turnover and decreased osteocalcin synthesis

Bone morphology and function were studied in male spontaneously diabetic BB rats after 3-4 weeks of diabetes. The tibia and lumbar vertebrae weights were decreased, but the bone calcium percentage remained normal. Bone volumes in the tibial metaphysis and the first lumbar vertebra were normal on quantitative histomorphometry. Osteoclast, osteoblast, and osteoid surface percentages, however, and the calculated daily mineral apposition rate in the tibia (1.0 +/- 0.4 vs. 5.6 +/- 0.6 microns/day) and vertebra (0.2 +/- 0.1 vs. 2.3 +/- 0.2 microns/day) were all severely decreased in diabetic rats. Plasma osteocalcin concentrations were also markedly decreased in diabetic rats (24 +/- 2 vs. 108 +/- 10 ng/ml); the half-times of [125I]osteocalcin were similar in diabetic and nondiabetic rats, indicating that decreased plasma osteocalcin was due to decreased synthesis. Plasma osteocalcin levels were more decreased than expected from their suppressed 1,25-dihydroxyvitamin D3 levels, and 1,25-dihydroxyvitamin D3 injections did not increase plasma osteocalcin in diabetic rats as they did in nondiabetic rats. Bone osteocalcin content was normal in diabetic rats. Photon absorptiometry of tibiae showed a similar bone mineral content in diabetic and nondiabetic rats. Biomechanical properties of diabetic rat femora were all in the normal range. Nondiabetic semistarved rats with the same body weight as diabetic rats exhibited a similar delay in bone growth as diabetic rats, but the osteoblast and osteoid surfaces were normal, and the mineral apposition rate was normal (tibia) or slightly decreased (vertebra). Plasma osteocalcin concentrations were also normal in semistarved rats. Thus, the number and/or function of osteoblasts are severely suppressed in diabetes, and this results in decreased osteoid surface, mineral apposition rate, and plasma osteocalcin levels; moreover, these changes cannot be explained by simple weight loss.     

The Effect of Low-Dose Methotrexate on Bone Metabolism and Histomorphometry in Rats

Objective. To ascertain the effects of low-dose methotrexate (MTX) on bone metabolism and histomorphometry in rats. Methods. Female Sprague-Dawley rats (6 months old, n = 42) were divided into the following 4 groups: intraperitoneal (IP) injections of MTX, with and without ovariectomy, and IP saline (controls), with and without ovariectomy. Injections were given for 16 weeks. The MTX dose was equivalent to a standard dose for rheumatoid arthritis in humans that would yield similar serum MTX levels (0.6 ± 0.1 μmoles). Results. Bone formation (assessed by serum alkaline phosphatase and osteocalcin levels and histomorphometry) was significantly lower in the MTX groups, and bone resorption (assessed by urinary hydroxyproline levels and histomorphometry) was increased in the MTX groups. Bone mass was significantly diminished in the MTX groups. Conclusion. Prolonged administration of lowdose MTX in rats causes significant osteopenia via suppression of osteoblast activity and stimulation of osteoclast recruitment, which results in increased bone resorption.