Comparative effects of alendronate and alfacalcidol on cancellous and cortical bone mass and bone mechanical properties in ovariectomized rats.

The purpose of the present study was to compare the effects of alendronate and alfacalcidol on cancellous and cortical bone mass and bone mechanical properties in ovariectomized rats. Twenty-six female Sprague-Dawley rats, 7 months of age, were randomized by the stratified weight method into four groups: the sham-operated control (Sham) group and the three ovariectomy (OVX) groups, namely, OVX + vehicle, OVX + alendronate (2.5 mg/kg, p.o., daily), and OVX + alfacalcidol (0.5 mug/kg, p.o., daily). At the end of the 8-week experimental period, bone histomorphometric analyses of cancellous bone at the proximal tibial metaphysis and cortical bone at the tibial diaphysis were performed, and the mechanical properties of the femoral distal metaphysis and femoral diaphysis were evaluated. OVX decreased cancellous bone volume per total tissue volume (BV/TV), and the maximum load of the femoral distal metaphysis, as a result of increases in serum osteocalcin (OC) levels, and also the number of osteoclasts (N.Oc), osteoclast surface (OcS) and bone formation rate (BFR) per bone surface (BS), and BFR/BV, without any effect on cortical area (Ct Ar), or maximum load of the femoral diaphysis. Alendronate prevented this decrease in cancellous BV/TV by suppressing increases in N.Oc/BS, OcS/BS, BFR/BS, and BFR/BV, without any apparent effect on Ct Ar, or maximum load of the femoral distal metaphysis and femoral diaphysis. On the other hand, alfacalcidol increased cancellous BV/TV, Ct Ar, and the maximum load of the femoral distal metaphysis and femoral diaphysis, by mildly decreasing trabecular BFR/BV, maintaining trabecular mineral apposition rate and osteoblast surface per BS, increasing periosteal and endocortical BFR/BS, and preventing an increase in endocortical eroded surface per BS. The present study clearly showed the differential skeletal effects of alendronate and alfacalcidol in ovariectomized rats. Alendronate prevented OVX-induced cancellous bone loss by suppressing bone turnover, while alfacalcidol improved cancellous and cortical bone mass and bone strength by suppressing bone resorption and maintaining or even increasing bone formation.     

Effects of combined administration of alfacalcidol and risedronate on cancellous and cortical bone mass of the tibia in glucocorticoid-treated young rats

The purpose of the present study was to examine the effects of combined administration of alfacalcidol (ALF) and risedronate (RIS) on cancellous and cortical bone mass of the tibia in glucocorticoid (GC)-treated young rats. One hundred and nine female Sprague-Dawley rats, 3 months of age, were randomly divided by the stratified weight method into eleven groups according to the following treatment schedule: baseline control, a 4-week age-matched control, and a 4-week GC administration with a 4-week concomitant administration of vehicle, ALF, RIS, or ALF+RIS, and an 8-week age-matched control and 8-week GC administration with a 4-week administration of vehicle, ALF, RIS, or ALF+RIS that was initiated after a 4-week administration of GC. The GC (methylprednisolone sodium succinate, 5.0 mg/kg) and RIS (10 microg/kg) were administered subcutaneously 3 times a week. ALF (0.08 microg/kg) was administered orally 5 times a week. At the end of the experiment, static and dynamic bone histomorphometric analyses were performed on cancellous bone of the proximal tibial metaphysis and cortical bone of the tibial diaphysis. A 4-week GC administration induced a loss of cancellous bone volume/total tissue volume (BV/TV) compared with the age-matched control as a result of decreased bone formation and increased bone erosion, while an 8-week GC administration induced both losses of cancellous BV/TV and of percent cortical area (Ct Ar) compared with the age-matched control as a result of decreased trabecular bone formation and increased trabecular and endocortical bone erosion. ALF prevented the loss of cancellous BV/TV at the 4th week by mildly suppressing bone erosion without reducing bone formation, and it restored cancellous BV/TV and increased percentage of Ct Ar at the 8th week by preventing a reduction in trabecular bone formation and mildly suppressing trabecular bone erosion and by strongly suppressing endocortical bone erosion, respectively. RIS restored only cancellous BV/TV at 8 weeks by strongly suppressing bone formation and bone erosion. Combined administration of ALF and RIS increased total tissue area of cortical bone at the 4th and 8th weeks by markedly increasing periosteal bone formation. The present study showed the efficacy of combined administration of ALF and RIS for the geometry of cortical bone in GC-treated rats.     

Therapeutic effect of risedronate on cancellous and cortical bone in ovariectomized osteopenic rats: a comparison with the effects of alfacalcidol.

The purpose of the present study was to compare the therapeutic effects of risedronate (RIS) and alfacalcidol (ALF) on cancellous and cortical bone in ovariectomized osteopenic rats. Forty-two female Sprague-Dawley rats, 7 months of age, were randomized by the stratified weight method into six groups: the sham-operated control (Sham) group, and five ovariectomized groups: treated with vehicle, RIS (0.1, 1.0, or 2.5 mg/kg, p.o., daily), and ALF (0.5 microg/kg, p.o., daily). Treatment was started 6 weeks after surgery and continued for 6 weeks. Evaluation at 12 weeks after surgery revealed that ovariectomy (OVX) decreased the cancellous bone volume/total tissue volume (BV/TV) of the proximal tibial metaphysis as a result of an increase of the bone formation rate/bone surface (BFR/BS), BFR/BV, and eroded surface (ES/BS), while having no effect on the cortical area (Ct Ar) of the tibial diaphysis. OVX also decreased the maximum load of the femoral distal metaphysis, while having no effect on any mechanical property parameters of the femoral diaphysis. RIS (at all the doses) increased the BV/TV relative to the value in the OVX-Vehicle group, but the value was not restored to that observed in the Sham group. The effects of RIS (1.0 mg/kg and 2.5 mg/kg) were similar, and greater than those of RIS (0.1 mg/kg). ALF also increased the BV/TV relative to the OVX-Vehicle group, but the value was not restored to that observed in the Sham group, similar to the results of RIS (1.0 mg/kg and 2.5 mg/kg) treatment. The alterations of the structural parameters induced by RIS (at the doses) were attributable to suppression of the increase of ES/BS, BFR/BS, and BFR/BV. The alterations of the structural parameters induced by ALF were attributable to suppression of the increase of ES/BS and attenuation of the increase of BFR/BV, while the BFR/BS was maintained. ALF also increased the Ct Ar to beyond the value observed in the Sham group. RIS (at all the doses) had no effect on the mechanical properties of the femoral distal metaphysis, whereas ALF prevented the loss of the maximum load of the femoral distal metaphysis. Thus, the results of the present study show differential effects of RIS and ALF on cancellous and cortical bone in ovariectomized osteopenic rats.     

Yeast-Incorporated Gallium Promotes Fracture Healing by Increasing Callus Bony Area and Improving Trabecular Microstructure on Ovariectomized Osteopenic Rats

The purpose of this study was to analyze the impact of yeast-incorporated gallium on fracture healing in ovariectomized osteopenic rats. Forty Wistar female rats used were divided into three groups: sham-operated rats (SHAM), ovariectomized (OVX) rats, and ovx rats treated with yeast-bound gallium (YG). A standardized fracture-healing model with stable plate fixation was established for rat femoral. After 4-week stable fixation, animals were killed to prepare bones for Micro-CT, biomechanical testing, and histomorphometry. In addition, bone samples were obtained to evaluate the content of mineral substances in bones. Quantitative analysis of the bones from animals in the organic gallium group revealed significantly increased mineral contents compared to bones from OVX and SHAM groups. Micro-CT showed that treatment with yeast-incorporated gallium increased BV/TV and trabecular thickness and decreased trabecular separation in ovx animals. Histomorphometric evaluation demonstrated that YG increased callus area and callus bone formation. Yeast-bound gallium also improved the biomechanical properties of bone healing. In conclusion, this study suggests that yeast-incorporated gallium could promote fracture healing in ovariectomized rats.     

Preventive effects of risedronate and calcitriol on cancellous osteopenia in rats treated with high-dose glucocorticoid.

We compared the effects of risedronate (Ris) and calcitriol (Cal) on cancellous osteopenia in rats treated with high-dose glucocorticoid (GC). Forty female Sprague-Dawley rats, 4 months of age, were randomized by the stratified weight method into four groups of 10 rats each according to the following treatment schedule: intact control, and GC administration with vehicle, Ris, or Cal. The GC (methylprednisolone sodium succinate, 5.0 mg/kg, s.c.), Ris (10 microg/kg, s.c.), and Cal (0.1 microg/kg, p.o.) were administered 3 times a week. At the end of the 4-week treatment period, bone histomorphometric analysis was performed for cancellous bone of the proximal tibial metaphysis. The GC administration decreased cancellous bone volume (BV/total tissue volume [TV]), trabecular number (Tb N), and trabecular thickness (Tb Th), as a result of increased bone resorption and decreased bone formation. Ris treatment markedly increased cancellous BV/TV and Tb N above the control level as a result of suppressed bone turnover. On the other hand, Cal treatment attenuated the GC-induced decrease in cancellous BV/TV and Tb Th as a result of suppressed bone resorption and maintained bone formation. This study showed the differential effects of Ris and Cal on cancellous osteopenia in rats treated with high-dose GC.     

Beta-1 Adrenergic Agonist Treatment Mitigates Negative Changes in Cancellous Bone Microarchitecture and Inhibits Osteocyte Apoptosis during Disuse

The sympathetic nervous system (SNS) plays an important role in mediating bone remodeling. However, the exact role that beta-1 adrenergic receptors (beta1AR) have in this process has not been elucidated. We have previously demonstrated the ability of dobutamine (DOB), primarily a beta1AR agonist, to inhibit reductions in cancellous bone formation and mitigate disuse-induced loss of bone mass. The purpose of this study was to characterize the independent and combined effects of DOB and hindlimb unloading (HU) on cancellous bone microarchitecture, tissue-level bone cell activity, and osteocyte apoptosis. Male Sprague-Dawley rats, aged 6-mos, were assigned to either normal cage activity (CC) or HU (n = 18/group) for 28 days. Animals were administered either daily DOB (4 mg/kg BW/d) or an equal volume of saline (VEH) (n = 9/gp). Unloading resulted in significantly lower distal femur cancellous BV/TV (−33%), Tb.Th (−11%), and Tb.N (−25%) compared to ambulatory controls (CC-VEH). DOB treatment during HU attenuated these changes in cancellous bone microarchitecture, resulting in greater BV/TV (+29%), Tb.Th (+7%), and Tb.N (+21%) vs. HU-VEH. Distal femur cancellous vBMD (+11%) and total BMC (+8%) were significantly greater in DOB- vs. VEH-treated unloaded rats. Administration of DOB during HU resulted in significantly greater osteoid surface (+158%) and osteoblast surface (+110%) vs. HU-VEH group. Furthermore, Oc.S/BS was significantly greater in HU-DOB (+55%) vs. CC-DOB group. DOB treatment during unloading fully restored bone formation, resulting in significantly greater bone formation rate (+200%) than in HU-VEH rats. HU resulted in an increased percentage of apoptotic cancellous osteocytes (+85%), reduced osteocyte number (−16%), lower percentage of occupied osteocytic lacunae (−30%) as compared to CC-VEH, these parameters were all normalized with DOB treatment. Altogether, these data indicate that beta1AR agonist treatment during disuse mitigates negative changes in cancellous bone microarchitecture and inhibits increases in osteocyte apoptosis.     

Response of cortical and cancellous bones to mild calcium deficiency in young growing female rats: a bone histomorphometry study.

The purpose of the present study was to clarify the differences in the alterations of cellular activities of osteoblasts and osteoclasts, mineralization, and bone mass in cortical and cancellous bones of young growing rats with mild calcium deficiency. Twenty female Sprague-Dawley rats, 6 weeks of age, were randomized by the stratified method into two groups with 10 rats in each group: 0.5% (normal) calcium diet group and 0.1% (low) calcium diet group. After 10 weeks of feeding, bone histomorphometric analysis was performed on cancellous bone of the proximal tibia as well as cortical bone of the tibial shaft. Calcium deficiency increased eroded surface (ES/bone surface [BS]) and the number of osteoclast (N.Oc/BS) with an increase in osteoblast surface (ObS/BS), but decreased bone formation rate (BFR/BS) in cancellous bone. However, cancellous bone volume was preserved, while cortical bone area was decreased as a result of decreased periosteal bone gain and enlargement of the marrow cavity. These results suggest that short-term mild calcium deficiency in young growing female rats increased bone resorption by increasing osteoclastic recruitment, and suppressed mineralization followed by increased osteoblastic recruitment in cancellous bone, but cancellous bone loss was counteracted through redistribution of calcium from cortical bone to cancellous bone.     

Dependence of mechanical compressive strength on local variations in microarchitecture in cancellous bone of proximal human femur

Human cancellous bone is a heterogeneous material. Despite this, most of the published studies report correlations between mechanical properties and morphometric parameters averaged on the whole specimen. This work investigated whether local variations in morphometric parameters were linked to the localized failure regions of cancellous bone. Additionally, it was examined whether local values of morphometric parameters can predict the ultimate stress better than the average bone volume fraction (BV/TV). Cylindrical cancellous bone specimens extracted along the primary compressive group of human femoral heads were studied. These were microCT-imaged to assess the morphometric parameters, compressed to determine the ultimate stress, and rescanned by microCT to visualize the failure region. Failure involved slightly less than half of the free height of the specimens. Significant differences were found in the morphometric parameters calculated in the failure and in the non-failure regions. The cross-sections containing minimum BV/TV values were those most often located inside the failure region (83%, p<0.001). Regression analysis confirmed that variations in BV/TV best describe variations in ultimate stress (R2=0.84) out of the averaged morphometric parameters. The prediction of ultimate stress increased when minimum or maximum values of the morphometric parameters were taken, with the highest prediction found by considering the minimum BV/TV (R2=0.95). In conclusion, due to the heterogeneity of cancellous bone, there may exist regions characterized by a different microarchitecture, where the bone is weaker and consequently is more likely to fail. These regions mostly contain minimum values in BV/TV, which were found to predict ultimate stress better than average BV/TV.     

Disuse in adult male rats attenuates the bone anabolic response to a therapeutic dose of parathyroid hormone.

Intermittent treatment with parathyroid hormone (PTH) increases bone formation and prevents bone loss in hindlimb-unloaded (HLU) rats. However, the mechanisms of action of PTH are incompletely known. To explore possible interactions between weight bearing and PTH, we treated 6-mo-old weight-bearing and HLU rats with a human therapeutic dose (1 microg.kg(-1).day(-1)) of human PTH(1-34) (hPTH). Cortical and cancellous bone formation was measured in tibia at the diaphysis proximal to the tibia-fibula synostosis and at the proximal metaphysis, respectively. Two weeks of hindlimb unloading resulted in a dramatic decrease in the rate of bone formation at both skeletal sites, which was prevented by PTH treatment at the cancellous site only. In contrast, PTH treatment increased cortical as well as cancellous bone formation in weight-bearing rats. Two-way ANOVA revealed that hPTH and HLU had independent and opposite effects on all histomorphometric indexes of bone formation [mineral apposition rate (MAR), double-labeled perimeter (dLPm), and bone formation rate (BFR)] at both skeletal sites. The bone anabolic effects of weight bearing and hPTH on dLPm and BFR at the cortical site were additive, as were the effects on MAR at the cancellous site. In contrast, weight bearing and hPTH resulted in synergistic increases in cortical bone MAR and cancellous bone dLPm and BFR. We conclude that weight bearing and PTH act cooperatively to increase bone formation by resulting in site-specific additive and synergistic increases in indexes of osteoblast number and activity, suggesting that weight-bearing exercise targeted to osteopenic skeletal sites may improve the efficacy of PTH therapy for osteoporosis.     

Dok-1 and Dok-2 deficiency induces osteopenia via activation of osteoclasts

Osteoporosis causes fractures that lead to reduction in the quality of life and it is one of the most prevalent diseases as it affects approximately 10% of the population. One of the important features of osteoporosis is osteopenia. However, its etiology is not fully elucidated. Dok-1 and Dok-2 are adaptor proteins acting downstream of protein tyrosine kinases that are mainly expressed in the cells of hematopoietic lineage. Although these proteins negatively regulate immune system, their roles in bone metabolism are not understood. Here, we analyzed the effects of Dok-1 and Dok-2 double-deficiency on bone. Dok-1/2 deficiency reduced the levels of trabecular and cortical bone mass compared to wildtype. In addition, Dok-1/2 deficiency increased periosteal perimeters and endosteal perimeters of the mid shaft of long bones. Histomorphometric analysis of the bone parameters indicated that Dok-1/2 deficiency did not significantly alter the levels of bone formation parameters including mineralizing surface/bone surface (MS/BS), mineral apposition rate (MAR) and bone formation rate (BFR). In contrast, Dok-1/2 deficiency enhanced the levels of bone resorption parameters including osteoclast number (N.Oc/BS) and osteoclast surface (Oc.S/BS). Analyses of individual osteoclastic activity indicated that Dok-1/2 deficiency enhanced pit formation. Systemically, Dok-1/2 deficiency increased the levels of urinary deoxypyridinoline (Dpyr). Search for the target point of the Dok-1/2 deficiency effects on osteoclasts identified that the mutation enhanced sensitivity of osteoclast precursors to macrophage colony-stimulating factor. These data revealed that Dok-1 and Dok-2 deficiency induces osteopenia by activation of osteoclasts.     

Effects of increased hypothalamic leptin gene expression on ovariectomy-induced bone loss in rats

Estrogen deficiency results in accelerated bone turnover with a net increase in bone resorption. Subcutaneous administration of leptin attenuates bone loss in ovariectomized (ovx) rats by reducing bone resorption. However, in addition to its direct beneficial effects, leptin has been reported to have indirect (central nervous system-mediated) antiosteogenic effects on bone, which may limit the efficacy of elevated serum leptin to prevent estrogen deficiency-associated bone loss. The present study evaluated the long-term effects of increased hypothalamic leptin transgene expression, using recombinant adeno-associated virus-leptin (rAAV-Lep) gene therapy, on bone mass, architecture, and cellular endpoints in sexually mature ovx Sprague-Dawley rats. Ovx rats were implanted with cannulae in the 3rd ventricle of the hypothalamus and injected with either rAAV-Lep or rAAV-GFP (control vector encoding green fluorescent protein) and maintained for 10 weeks. Additional controls consisted of ovary-intact rats and ovx rats pair-fed to rAAV-Lep rats. Lumbar vertebrae were analyzed by micro-computed tomography and tibiae by histomorphometry. Cancellous bone volume was lower and osteoclast perimeter, osteoblast perimeter, and bone marrow adipocyte density were greater in ovx rats compared to ovary-intact controls. In contrast, differences among ovx groups were not detected for any endpoint evaluated. In conclusion, whereas estrogen deficiency resulted in marked cancellous osteopenia, increased bone turnover and marrow adiposity, increasing hypothalamic leptin transgene expression in ovx rats had neither detrimental nor beneficial effects on bone mass, architecture, or cellular endpoints. These findings demonstrate that the antiresorptive effects of subcutaneous leptin administration in ovx rats are mediated through leptin targets in the periphery.     

生物衍生松质骨支架材料的Micro—CT量化分析

目的：在骨组织工程中,如何制备出理想的支架材料一直是研究重点;目前主要的有天然生物支架材料、人工合成有机材料和无机材料等;生物衍生骨即天然生物支架材料的一种,由于其与天然骨在形态结构上较为相似,是近年来研究较多的支架材料之一;既往形态学研究局限于在二维层面,对于其三维结构参数分析较少。故本实验主要运用Micro-CT对生物衍生松质骨的三维结构参数进行分析,量化评价其作为骨组织工程支架材料的结构参数。方法：截取新鲜猪松质骨,经脱脂脱蛋白部分脱钙及去抗原处理后,制作成生物衍生骨支架;应用Micro．CT扫描,重建三维图并量化分析其结构参数,统计软件SPSS分析各参数间的相关性。结果：经Micro．CT扫描,得到二维CT图和三维重建图。各三维结构参数的值分别为：BV／TV（20．48±5．14）％;BS／BV（41．66±5．39）1／ram;Porosity（79．52±5．14）％;Tb．Th（0．10±0．01）mm;Tb．N（1．99±0．47）l／mm;Tb．Sp（0．32±0．05）mm;Tb．Pf（2．03±4．70）1／mm;SMI（1．28±0．35）;DA（1．60±0．23）;Corm．Dn（158．53±106．09）I／mm3。各参数间相关系数具有统计学意义的为：（1）Porosity与BS／BV、Tb．Th;（2）BV／TV与BS／BV、Tb．Th;（3）BS／BV与Coma．Dn、Porosity、BV/TV、;（4）Tb．Th与Porosity、BV厂IV、Conn．Dn;（5）DA与Corm．Dn;（6）Conn．Dn与Bs／BV、Tb．Th、DA。结论：Micro-CT扫描、量化分析是评价支架材料结构参数的理想方法;也证明生物衍生骨支架符合骨组织工程对支架材料的三维结构要求,尤其在孔径大小、孔隙率、表面积体积比等三维结构参数,此外,也可为其他支架材料的制备在三维结构上的要求提供参考依据。     

Tensile properties of rat femoral bone as functions of bone volume fraction, apparent density and volumetric bone mineral density

Mechanical testing has been regarded as the gold standard to investigate the effects of pathologies on the structure-function properties of the skeleton. Tensile properties of cancellous and cortical bone have been reported previously; however, no relationships describing these properties for rat bone as a function of volumetric bone mineral density (ρ(MIN)), apparent density or bone volume fraction (BV/TV) have been reported in the literature. We have shown that at macro level, compression and torsion properties of rat cortical and cancellous bone can be well described as a function of BV/TV, apparent density or ρ(MIN) using non-destructive micro-computed tomographic imaging and mechanical testing to failure. Therefore, the aim of this study is to derive a relationship expressing the tensile properties of rat cortical bone as a function of BV/TV, apparent density or ρ(MIN) over a range of normal and pathologic bones. We used bones from normal, ovariectomized and osteomalacic animals. All specimens underwent micro-computed tomographic imaging to assess bone morphometric and densitometric indices and uniaxial tension to failure. We obtained univariate relationships describing 74-77% of the tensile properties of rat cortical bone as a function of BV/TV, apparent density or ρ(MIN) over a range of density and common skeletal pathologies. The relationships reported in this study can be used in the structural rigidity to provide a non-invasive method to assess the tensile behavior of bones affected by pathology and/or treatment options.     

Alfacalcidol prevents age-related bone loss and causes an atypical pattern of bone formation in aged male rats

The current study was designed to investigate the skeletal effects of alfacalcidol in aged rats. Eighteen-month-old male rats were treated with 0, 0.1, or 0.2 microg/kg/d of alfacalcidol by daily oral gavage, 5 days/week for 12 weeks. At the beginning of the treatments, one group of rats was euthanized to serve as a baseline control. At the end of the study, the second lumbar vertebrae and the right tibial diaphysess were processed for bone histomorphometric analysis. The fourth lumbar vertebrae were subjected to strength testing. The control group of rats at 21 months of age had decreased serum testosterone levels and decreased cancellous bone mass associated with increased bone turnover on the trabecular surface. The older rats had increased bone turnover on the endocortical surface and decreased bone formation on the periosteal surface compared with the 18-month group. In contrast, alfacalcidol treatment increased cancellous and cortical bone mass in aged male rats. Trabecular bone resorption was decreased whereas bone formation was maintained or increased in the rats treated with alfacalcidol. In addition, endocortical bone formation was decreased whereas periosteal bone formation was increased in the rats treated with alfacalcidol compared with vehicle-treated rats. Marrow trabecular bone area was increased by alfacalcidol treatment in tibial diaphyses. Furthermore, bone strength of the lumbar vertebral body was increased after alfacalcidol treatment. An atypical pattern of bone formation on endosteal bone surfaces was seen in the rats treated with alfacalcidol. The atypical bone formation is characterized by small, focal packets of newly formed bone on trabecular and endocortical bone surfaces. This gave the appearance of the formation of "bone buds" emanating from trabecular surfaces. These bony outgrowths were mineralized and demonstrated significant fluorochrome label indicating recent mineralization. Also, lamellae of the bony buds did not run parallel to those of the trabecular plate to which they are attached. Arrest lines presented in most of the "bone buds". In summary, alfacalcidol treatment increased cancellous and cortical bone mass and improved bone strength, resulting in the prevention of age-related bone loss in aged male rats. An atypical pattern of bone formation observed in this study may be a result of minimodeling based bone formation stimulated by alfacalcidol treatment.     

人体颈椎松质骨显微结构和力学性能的区域性差异研究

目的:探讨人体脊柱松质骨骨骼显微结构和力学性能的区域性差异,为松质骨三维结构采样部位的选取提供参考。方法:显微CT扫描6块颈6椎体标本获得三维图像,依据椎体内解剖位置的不同,将松质骨划分为6个位置组:外侧、内侧、腹侧、背侧、头侧和尾侧。利用显微结构参数骨体积分数(Bone volume to tissue volume,BV/TV)、骨表面积和骨体积的比值(Bone surface to bone volume,BS/BV)、骨小梁数量(Trabecular number,Tb.N)、骨小梁厚度(Trabecular thickness,Tb.Th)、骨小梁分离度(Trabecular separation,Tb.Sp)和个体化骨小梁分割方法(Individual trabeculae segmentation,ITS)分析6个位置组内松质骨显微结构,并利用有限元分析,获得6个位置组内松质骨的力学性能参数表观弹性模量和表观剪切模量。分别两两对比外侧和内侧,腹侧和背侧,头侧和尾侧松质骨的显微结构参数(BV/TV、BS/BV、Tb.N、Tb.Th、Tb.Sp和个体化骨小梁分割得到的参数)和力学性能参数(表观弹性模量和表观剪切模量)。结果:头侧和尾侧的主要显微结构参数BV/TV、Tb.Th、Tb.N等和表观弹性模量均存在显著差异(P0.05)。腹侧和背侧、内侧和外侧的主要显微结构参数BV/TV、Tb.Th、Tb.N等无显著差异。外侧和内侧的表观弹性模量在非主方向即内外方向和腹背放上上存在显著差异(P0.05),在主方向即头尾上无显著差异。结论:在实验中采集椎体松质骨样本以及临床上利用高分辨率CT分析椎体松质骨结构时,感兴趣区域要同时涵盖头侧和尾侧。     

Continuous infusion of PGE2 is catabolic with a negative bone balance on both cancellous and cortical bone in rats

It is well documented that intermittent PGE(2) treatment increases both trabecular and cortical bone mass. However, the effects of continuous PGE(2) administration remain undocumented. The aim of the study was to investigate the effects of continuous prostaglandin E(2) (PGE(2)) on different bone sites in skeletally mature rats. Six-month-old Sprague Dawley rats were treated with PGE(2) at 1 or 3 mg/kg/d continuously via infusion pump for 21 days. Two other groups of rats received PGE(2) at the same doses by intermittent (daily) subcutaneous injections and served as positive controls. Histomorphometry was performed on cancellous bone of the proximal tibial metaphysis and cortical bone of the tibial shaft. As expected, intermittent PGE(2) treatment increased both cancellous and cortical bone mass by stimulating bone formation at the cancellous, periosteal and endocortical bone surfaces. In contrast, continuous PGE(2) treatment decreased cancellous bone mass with bone resorption exceeding bone formation. In addition, continuous PGE(2) treatment increased endocortical and intracortical bone remodeling, inducing bone loss which was partially offset by stimulating periosteal expansion. We conclude that continuous PGE(2) treatment induces overall catabolic effects on both cancellous and cortical bone envelopes, which differs from intermittent PGE(2) treatment that is anabolic. Lastly, we speculate that superior bone mass may be achieved by co-treatment of continuous PGE(2) in combination with an anti-catabolic agent.     

Simulated resistance training, but not alendronate, increases cortical bone formation and suppresses sclerostin during disuse

Mechanical loading modulates the osteocyte-derived protein sclerostin, a potent inhibitor of bone formation. We hypothesized that simulated resistance training (SRT), combined with alendronate (ALEN) treatment, during hindlimb unloading (HU) would most effectively mitigate disuse-induced decrements in cortical bone geometry and formation rate (BFR). Sixty male, Sprague-Dawley rats (6-mo-old) were randomly assigned to either cage control (CC), HU, HU plus either ALEN (HU+ALEN), or SRT (HU+SRT), or combined ALEN and SRT (HU+SRT/ALEN) for 28 days. Computed tomography scans on days -1 and 28 were taken at the middiaphyseal tibia. HU+SRT and HU+SRT/ALEN rats were subjected to muscle contractions once every 3 days during HU (4 sets of 5 repetitions; 1,000 ms isometric + 1,000 ms eccentric). The HU+ALEN and HU+SRT/ALEN rats received 10 μg/kg ALEN 3 times/wk. Compared with the CC animals, HU suppressed the normal slow growth-induced increases of cortical bone mineral content, cortical bone area, and polar cross-sectional moment of inertia; however, SRT during HU restored cortical bone growth. HU suppressed middiaphyseal tibia periosteal BFR by 56% vs. CC (P < 0.05). However, SRT during HU restored BFR at both periosteal (to 2.6-fold higher than CC) and endocortical (14-fold higher than CC) surfaces (P < 0.01). ALEN attenuated the SRT-induced BFR gains during HU. The proportion of sclerostin-positive osteocytes in cortical bone was significantly higher (+121% vs. CC) in the HU group; SRT during HU effectively suppressed the higher proportion of sclerostin-positive osteocytes. In conclusion, a minimum number of high-intensity muscle contractions, performed during disuse, restores cortical BFR and suppress unloading-induced increases in sclerostin-positive osteocytes.     

Increased osteoblastogenesis and decreased bone resorption protect against ovariectomy-induced bone loss in thrombospondin-2-null mice.

Although bone is composed primarily of extracellular matrix (ECM), the dynamic role that the ECM plays in regulating bone remodeling secondary to estrogen loss is relatively unexplored. Previous studies have shown that mice deficient in the matricellular protein thrombospondin-2 (TSP2-null) form excess endocortical bone; thus, we postulated that enhanced bone formation in TSP2-null mice could protect against ovariectomy (OVX)-induced bone loss. Wild-type (WT) OVX mice showed a significant loss of both midfemoral endocortical and proximal tibial trabecular bone, but OVX did not significantly alter TSP2-null bone. TSP2-null mice showed an increase in bone formation, as indicated by a 70% increase in serum osteocalcin two weeks post OVX and a two-fold increase in bone formation rate (BFR) five weeks post OVX as measured by dynamic histomorphometry. WT animals showed only a 20% increase in serum osteocalcin at two weeks and no change in BFR at five weeks. This increase in bone formation in TSP2-null OVX mice was accompanied by a three-fold increase in osteoprogenitor number. Although these results provide a partial explanation for the maintenance of bone geometry post-OVX, TSP2-null mice five weeks post-OVX also showed a significantly lower level of bone resorption than OVX WT mice, as determined by serum levels of the amino-terminal telopeptide of type I collagen (NTx). We conclude that the absence of TSP2 protects against OVX-induced bone loss by two complementary processes: increased formation and decreased resorption.     

Effects of vitamin K2 administration on calcium balance and bone mass in young rats fed normal or low calcium diet

OBJECTIVE: The purpose of this study was to examine the effects of vitamin K2 administration on calcium balance and bone mass in young rats fed a normal or low calcium diet. METHODS: Forty female Sprague-Dawley rats, 6 weeks of age, were randomized by stratified weight method into four groups with 10 rats in each group: 0.5% (normal) calcium diet, 0.1% (low) calcium diet, 0.5% calcium diet + vitamin K2 (menatetrenone, 30 mg/100 g chow diet), and 0.1% calcium diet + vitamin K2. After 10 weeks of feeding, serum calcium and calciotropic hormone levels were measured, and intestinal calcium absorption and renal calcium reabsorption were evaluated. Bone histomorphometric analyses were performed on cortical bone of the tibial shaft and cancellous bone of the proximal tibia. RESULTS: Feeding a low calcium diet induced hypocalcemia, increased serum parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25(OH)2D] levels with decreased serum 25-hydrovyvitamin D [25(OH)D] level, stimulated intestinal calcium absorption and renal calcium reabsorption, and reduced cortical bone mass as a result of decreased periosteal bone gain and enlarged marrow cavity, but did not significantly influence cancellous bone mass. Vitamin K2 administration in rats fed a low calcium diet stimulated renal calcium reabsorption, retarded the abnormal elevation of serum PTH level, increased cancellous bone mass, and retarded cortical bone loss, while vitamin K2 administration in rats fed a normal calcium diet stimulated intestinal calcium absorption by increasing serum 1,25(OH)2D level, and increased cortical bone mass. CONCLUSION: This study clearly shows the differential response of calcium balance and bone mass to vitamin K2 administration in rats fed a normal or low calcium diet.     

Organic Gallium Treatment Improves Osteoporotic Fracture Healing Through Affecting the OPG/RANKL Ratio and Expression of Serum Inflammatory Cytokines in Ovariectomized Rats

This study aimed to investigate the impact of organic gallium (OG) on osteoporotic fracture healing in ovariectomized female Sprague-Dawley rats, as well as study the mechanisms of OG on osteoporotic fracture healing. Forty-five female Sprague-Dawley rats were divided into three groups: sham operation group (Sxas control group), ovariectomized group (Ovx), and Ovx treated with OG group (Ovx + OG). Rat femoral fractures were studied using a standardized fracture-healing model utilizing bone fixation with an intramedullary pin. Six weeks later, analyses of micro-CT, histomorphometric, RNA extraction, RT-qPCR, and serum were performed following sacrifice of all mice. In comparison with Ovx group, OG can significantly increase bone volume (BV), tissue volume (TV), BV/TV radio, bone strength, callus bony area, and as similar to BMP-2 expression. OG treatment elevated OPG messenger RNA (mRNA) and inhibited RANKL mRNA, and showed an effect on OPG/RANKL ratio. OG treatment can inhibit the expression of TNF-α and IL-6. In conclusion, current study results indicate that organic OG can positively affect the OPG/RANKL ratio and inhibit the expression of serum inflammatory cytokines; thus, it can improve osteoporotic fracture healing.