Inhibition of bone resorption by bisphosphonates: Interactions between bisphosphonates,osteoclasts, and bone

Summary Bisphosphonates are nonbiodegradable pyrophosphate analogues that are being used increasingly to inhibit bone resorption in disorders characterized by excessive bone loss. We have previously found that dichloromethylene bisphosphonate (Cl₂MBP) inhibits bone resorption through injury to the cells that resorb Cl₂MBP-contaminated surfaces. 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (AHPrBP) is a more potent inhibitor of bone resorptionin vivo, and we have attempted to identify a step in the resorptive pathway that accounts for this increased potency. We found that when osteoclasts, isolated from neonatal rat long bones, were incubated on bone slices in the presence of bisphosphonates, AHPrBP was less, rather than more potent as a resorption-inhibitor than Cl₂MBP. The greater sensitivity of resorption to AHPrBPin vivo could neither be attributed to an effect of AHPrBP on the ability of osteoblastic cells to stimulate resorption in response to calcium-regulating hormonesin vitro nor to an effect on osteoclast generation: osteoclast formation was unaffected by concentrations of AHPrBP 10-fold higher than those of Cl₂MBP which inhibit bone resorption in the bone slice assay. We also found no evidence for impaired osteoclast generationin vivo in AHPrBP-treated rats. These results suggest that the comparisons of potencyin vitro do not include all the factors responsible for determining bisphosphonate potencyin vivo. Because bisphosphonates owe the specificity of their actions to their ability to bind to bone surfaces, we performed experiments using bone slices that had been immersed in bisphosphonates before use. Bone resorption was virtually abolished on bone slices preincubated in 10⁻³ M AHPrBP. Inhibition was associated with degenerative changes in osteoclasts and a more rapid decrease in the number remaining on the bone surface than occurred with Cl₂MBP. The effect was specific for osteoclasts, could be prevented if bone resorption was suppressed by calcitonin, and was not seen in osteoclasts incubated in AHPrBP on plastic coverslips. These observations suggest that AHPrBP inhibits bone resorption through injury to osteoclasts when they solubilize bisphosphonate-contaminated bone. We found that the concentration of AHPrBP used in the preincubation phase could be reduced by an order of magnitude if the volume of the AHPrBP solution was correspondingly increased. This implies that the concentration of bisphosphonate is less relevant to potency comparisons than the density of bisphosphonate on the bone surface. The latter will be strongly influencedin vivo not only by affinity for bone but by the pharmacokinetic and other properties of the compound.     

Compactin suppresses bone resorption by inhibiting the fusion of prefusion osteoclasts and disrupting the actin ring in osteoclasts.

Compactin (mevastatin), which inhibits 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, and thus biosynthesis of cholesterol and the prenylation of proteins, inhibits osteoclastic bone resorption. Although it has been suggested that compactin inhibits bone resorption by inducing apoptosis of osteoclasts, the pathway by which compactin inhibits resorption has not been established. We investigated the effect of compactin on the differentiation of osteoclasts and the relationship between the morphological changes elicited by compactin and its inhibitory effect on bone resorption. Compactin inhibited the differentiation of osteoclasts, interfering with the fusion process by which prefusion osteoclasts (pOCs) develop into multinucleated osteoclast-like cells (OCLs), and also disrupted the actin ring of OCLs. The potency of compactin to inhibit fusion of pOCs and to disrupt the actin ring of OCLs corresponded to that of compactin to inhibit bone resorption. The effects of compactin were prevented by the addition of MVA lactone or its downstream products farnesylpyrophosphate (FPP) and geranylgeranyl-pyrophosphate (GGPP) but not by squalene. Apoptosis of OCLs was not induced by the concentration of compactin that inhibited fusion of pOCs and disrupted the actin ring. The normal process of pOC fusion and the integrity of the actin ring were restored by the withdrawal of compactin from the cultures after they had been treated with compactin for 24 h, but they were not restored by the addition of zVAD-fmk, a caspase inhibitor. Compactin also reversibly inhibited interleukin-1beta (IL-1beta)-, 1alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3)-, and parathyroid hormone (PTH)-stimulated 45Ca release in bone organ cultures. Our results indicate that the inhibitory effects of compactin on bone resorption result from the inhibition of fusion of pOCs into OCLs and disruption of actin ring in OCLs and that apoptosis of OCLs is not necessary for these inhibitory effects of compactin. These effects of compactin are likely to be a consequence of the inhibition of prenylation of proteins that play an important role in the fusion of pOCs and in maintaining actin ring integrity in OCLs.     

Structural requirements for the action of parathyroid hormone-related protein (PTHrP) on bone resorption by isolated osteoclasts

Parathyroid hormone-related protein (PTHrP) plays a major role in the syndrome of humoral hypercalcemia of malignancy (HHM) by its actions on bone and kidney. In this study an isolated osteoclast bone resorption assay was used to investigate the actions of this peptide and the structure-activity relationships for its resorption effect. As with PTH, neither synthetic nor recombinant PTHrP preparations stimulated resorption within highly purified osteoclast populations. Resorption was stimulated only in the presence of contaminating osteoblasts or in cocultures with the osteoblast-like cell line UMR-106. In the presence of osteoblasts PTHrP-(1-34) and PTHrP-(1-84) stimulated bone resorption in a dose-dependent manner with a potency comparable to that of PTH-(1-34) on a molar basis. The biologic activity of the PTHrP was shown to reside in the first 34 amino acids, and within that region the structural requirements for promotion of osteoclastic resorption resembled closely those for promotion of cyclic AMP formation in osteoblast-like cells. Using emulsion autoradiography with iodinated PTHrP-(1-34) and PTHrP-(1-84) on mixed bone cell preparations from neonatal rats, specific binding was demonstrated only to osteoblasts, not to osteoclasts. These results clearly demonstrate that PTHrP is a potent stimulator of bone resorption and that these effects are, like those of PTH, mediated by initial actions upon cells of the osteoblast lineage.     

Effect of monoterpenes on the formation and activation of osteoclasts in vitro.

Monoterpenes, present in aromatic plants, are known to inhibit bone resorption in vivo. In this in vitro study, they inhibited the activation of osteoclasts only at high concentrations but inhibited the formation at much lower concentrations. Therefore, monoterpenes may act in vivo directly on osteoclastogenesis. INTRODUCTION: Monoterpenes are the major components of essential oils, which are formed in many plants. Typically, they are found in herbs and certain fruits. When fed to rats, they inhibit bone resorption by an unknown mechanism. In this study, their effect on the activity and formation of osteoclasts in vitro was studied. MATERIALS AND METHODS: The effect of monoterpenes on the development of osteoclasts was studied in co-cultures of bone marrow cells and osteoblasts and in cultures of spleen cells grown with colony stimulating factor (CSF)-1 and RANKL. In cultures of primary osteoblasts, alkaline phosphatase activity and levels of mRNA encoding RANKL and osteoprotegerin (OPG) mRNA (RT-PCR), and in osteoblast and spleen cell cultures, lactate dehydrogenase activity, a measure of toxicity, were determined. The activity of isolated rat osteoclasts was determined by counting the osteoclasts with actin rings using histofluorometry. RESULTS: The monoterpenes inhibited the formation of osteoclasts more strongly in co-cultures (> or = 1 microM) than in cultures of spleen cells (> or = 10 microM). They had a minor effect on osteoblasts. Toxic effects were not observed. The inhibition of the formation of osteoclasts was not reversed by the addition of farnesol and geranylgeraniol, excluding an effect of the monoterpenes through the mevalonate pathway. A high concentration of 1 mM was required to inhibit the activation of osteoclasts. This effect, shown for menthol and borneol, was reversible. CONCLUSIONS: The results suggest that the monoterpenes inhibit bone resorption in vivo through a direct effect on the formation of osteoclasts acting mainly on the hemopoietic cells.     

Osteoclastic bone resorption: in vitro analysis of the rate of resorption and migration of individual osteoclasts

Osteoclasts isolated from the long bones of newborn rabbits were cultured on translucent devitalized bone slices and observed by phase-contrast time-lapse cinemicrography and scanning electron microscopy (SEM). This has allowed us to measure the rate of resorption and the rate of migration of individual osteoclasts. Our films show that osteoclasts do not resorb while migrating. When the osteoclastic resorption areas, which are easily recognizable with phase-contrast microscopy as areas delineated by refractile lines, were observed by SEM, such areas appeared as excavated areas lined with a network of collagen fibrils. The rate of migration was calculated using time lapse recordings, and varied from 30 micron/hr to 248 micron/hr, with a mean +/- SEM of 105 +/- 10 micron/hr. The rate of resorption by individual osteoclasts was calculated using both time lapse and SEM data, and varied from 43 micron 3/hr to 1225 micron 3/hr with a mean +/- SEM of 390 +/- 109 micron 3/hr. Additional observations indicated not only that the same osteoclast can resorb at a different rate at different times without any definable alteration of the culture conditions, but also that the same osteoclast can simultaneously resorb two lacunae at different rates. These observations provide, for the first time, data on the rate of resorption and the rate of migration of individual osteoclasts on a bone substratum.     

Evaluation of bone turnover in type I osteoporosis using biochemical markers specific for both bone formation and bone resorption

The aims of the study were to evaluate the use of bone-specific biochemical markers of turnover in type I osteoporosis, to test for evidence of heterogeneity of bone turnover in this condition, and to attempt to devise an uncoupling index by using the relationship between bone-specific biochemical markers of bone formation and bone resorption. In women with type I osteoporosis (mean age 64 years, SD 5;n=63) the mean level of serum osteocalcin, a specific biochemical marker of bone formation, was 9.9 ng/ml (SD 2.0), which was higher than the level in normal postmenopausal women (mean age 65 years, SD 6;n=8.9 ng/ml (SD 2.0;p<0.01). The variance of serum osteocalcin levels in the two groups was similar. Compared with this 11% increase in the biochemical marker for bone formation, the markers of bone resorption, total urinary deoxypyridinoline (bone-specific), pyridinoline and hydroxyproline were increased by 40% (p<0.0001), 61% (p<0.0001) and 25% (p<0.01), respectively. Furthermore, these biochemical markers of bone resorption had greater variance in women in type I osteoporosis than in the normal postmenopausal women (p<0.001). The urinary excretion of the free crosslinks deoxypyridinoline, pyridinoline and glycosylated pyridinoline were increased by 26% (p<0.001), 17% (p<0.01) and 13% (NS) respectively. An uncoupling index was calculated for the difference between urinary deoxypyridinoline and serum osteocalcin using the results from the normal women and expressed asz-scores. We conclude that the pyridinium crosslinks of collagen enable better discrimination between normal and osteoporotic women than does hydroxyproline. In osteoporosis there appears to be heterogeneity of bone resorption. Finally, an uncoupling index indicated that in osteoporosis bone resorption was increased to a greater extent than bone formation as compared with normal postmenopausal women.     

MicroRNA在强直性脊柱炎成骨、破骨机制中的作用

炎性骨破坏和新骨形成是强直性脊柱炎(ankylosing spondylitis,AS)的典型病理改变,AS早期以炎症为主,晚期出现异位骨化和骨破坏,异位骨化和骨破坏两种矛盾的表现反映了强直性脊柱炎患者成骨与破骨过程之间的动态平衡被打破。其发病机制尚不完全清楚,目前研究认为,AS复杂的新骨形成机制与Wnt/β-catenin信号通路及BMP/Smads通路密切相关,而破骨细胞则在骨破坏过程中起重要作用,RANKL/RANK/OPG系统中的细胞因子是调控破骨细胞分化成熟的关键因子。Micro RNA可调节成骨细胞、软骨细胞和破骨细胞的分化与功能,是骨形成、骨吸收、骨重塑和修复过程中的关键调节因子。研究MicroRNA在强直性脊柱炎成骨、破骨机制中的作用,可为AS的诊断和治疗提供新的依据。     

电针对去卵巢大鼠骨形成及骨吸收活性的影响

目的研究电针刺对去卵巢骨质疏松模型大鼠的全身骨密度(BMD)、骨矿物含量(BMC)及其血清对体外培养成骨细胞的骨形成因子骨钙素(OPG)和骨吸收因子(RANKL)蛋白表达的影响。方法选取SPF级2月龄SD雌性大鼠40只,随机分为空白组、电针组、药物组和模型组,每组10只。其中空白组不做任何处理,后3组采用手术方法切除双侧卵巢。饲养3个月后,骨密度检测结果显示造模成功。随后药物组大鼠灌胃服用戊酸雌二醇3个疗程,电针组大鼠采用针刺后通电治疗3个疗程并服用药物组相同体积的蒸馏水,模型组服用相应体积的蒸馏水,空白组常规饲养。各组大鼠于SPF级实验室处理3个月后,双能X射线骨密度仪检测全身骨密度和骨矿含量。随后,水合氯醛麻醉各组大鼠,心脏采血,各组血液分别经滤网过滤、56℃水浴处理后加入体外培养的大鼠成骨细胞培养液中,处理3d后多聚甲醛固定成骨细胞,采用免疫细胞化学染色法检测成骨细胞内OPG、RANKL蛋白的表达量。结果与空白组相比,模型组大鼠BMD,BMC显著降低(P0.05),服用药物或针刺处理后,BMD和BMC显著增高(P0.05),与模型组相比差异具有统计学意义。各组大鼠血清处理成骨细胞后,模型组骨形成指标OPG蛋白表达量较低,经药物或针刺后,OPG蛋白表达量显著升高(P0.01)。此外,模型组骨吸收指标RANKL的表达量较高,经药物和针刺处理后,RANKL蛋白表达量显著下降(P0.01)。结论针刺能有效升高大鼠BMD和BMC,同时针刺处理后的大鼠血清具有很好的促进骨形成和抑制骨吸收的能力。     

骨细胞网络结构对骨形成和骨吸收的影响

骨细胞的数量是骨组织中最多的,占骨组织细胞95%以上。骨细胞均匀地分布在矿化的骨基质中,通过细胞膜的多个突触结构互相连接并与骨基质表面的细胞连接形成网状的细胞结构。骨细胞被认为是一种理想的细胞,在骨组织发育和代谢过程中启动细胞的生物化学反应。最新的研究已证实骨细胞通过直接整合骨的矿化基质和其他的多细胞网络结构,感受刺激、调控效应细胞(例如成骨细胞、破骨细胞、骨髓基质干细胞),除此之外骨细胞已被证实作为一种内分泌细胞并且可以调控磷的代谢。随着研究的深入,骨细胞网络结构对骨形成和吸收的影响逐渐明显,在生理条件下骨细胞网络结构通过激活破骨细胞促进骨吸收,通过抑制成骨细胞抑制骨形成。本篇综述将主要讨论骨细胞网络结构对骨生成和骨吸收的影响及其相应的研究和理论依据。     

Initiation and enhancement of bone formation. A review

Knowledge of some of the fundamental biochemical factors that may influence the initiation and continued growth of bone-forming cell lines is presented. The discussion is limited to those factors shown experimentally to be present locally in bone tissue and synthesized in the environment of bone-forming cells. The current state of knowledge of basic research findings on osteogenic factors is given in detail. Cooperative actions of these locally produced and systemic factors are the primary stimuli that result in increased bone growth and volume.     

17β-雌二醇对体外培养破骨细胞凋亡及其骨吸收调节作用

目的 观察17β-雌二醇对体外培养破骨细胞凋亡率的影响及其与骨吸收功能的关系。方法 在培养液中加入17β-雌二醇，透射电镜（transmission electron microscopy，TEM）观察破骨细胞内超微结构的改变，流式细胞仪（flow cytometry，FCM）观察不同浓度的17β-雌二醇在不同时间段对破骨细胞凋亡率的影响，同时用扫描电镜（scanning electron microscopy，SEM）观察破骨细胞在骨片上形成骨吸收陷窝数目及面积的变化。结果 17β-雌二醇可增加破骨细胞的凋亡率，这种作用具有剂量、时间依赖效应，同时，破骨细胞在骨片上形成的骨吸收陷窝的数目和面积减少。结论 17β-雌二醇可促进破骨细胞凋亡，从而抑制破骨细胞的骨吸收功能。     

A clinical study of alveolar bone tissue engineering with cultured autogenous periosteal cells: coordinated activation of bone formation and resorption

In ongoing clinical research into the use of cultured autogenous periosteal cells (CAPCs) in alveolar bone regeneration, CAPCs were grafted into 33 sites (15 for alveolar ridge augmentation and 18 for maxillary sinus lift) in 25 cases. CAPCs were cultured for 6weeks, mixed with particulate autogenous bone and platelet-rich plasma, and then grafted into the sites. Clinical outcomes were determined from high-resolution three-dimensional computed tomography (3D-CT) images and histological findings. No serious adverse events were attributable to the use of grafted CAPCs. Bone regeneration was satisfactory even in cases of advanced atrophy of the alveolar process. Bone biopsy after bone grafting with CAPCs revealed prominent recruitment of osteoblasts and osteoclasts accompanied by angiogenesis around the regenerated bone. 3D-CT imaging suggested that remodeling of the grafted autogenous cortical bone particles was faster in bone grafting with CAPCs than in conventional bone grafting. The use of CAPCs offers cell-based bone regeneration therapy, affording complex bone regeneration across a wide area, and thus expanding the indications for dental implants. Also, it enables the content of particulate autogenous bone in the graft material to be reduced to as low as 40%, making the procedure less invasive, or enabling larger amounts of graft materials to be prepared. It may also be possible to dispense with the use of autogenous bone altogether in the future. The results suggest that CAPC grafting induces bone remodeling, thereby enhancing osseointegration and consequently reducing postoperative waiting time after dental implant placement.     

Ankylosing spondylitis and its variants. A review of recent developments for orthopedic surgeons

Recent developments in genetic tissue typing have altered concepts of ankylosing spondylitis (AS) or variants of this spondylitic arthritis. It is now apparent that AS is separate and distinct from rheumatoid arthritis; and the term "rheumatoid" should be avoided except as it applies to the latter, usually characterized by rheumatoid factor or nodules and symmetrical arthritis of peripheral joints. Classical definitions of AS require X-ray evidence of sacroiliitis and/or restriction of chest expansion. Recent studies suggest that many patients, especially women, may have symptoms of AS without typical roentgenographic or clinical findings. Use of the HL-A B27 genetic test is useful for identifying AS patients. Radioisotope bone or joint scanning techniques further augment present diagnostic capabilities. Atypical AS may be a very common form of morbidity among patients with back pain in the United States. Since patients have a tendency to form osseous reankylosis after total hip replacement, it is especially important for orthopedic surgeons to identify incipient AS and related disorders. Inappropriate treatment or procedures may be avoided by use of these newer clinical tools in the evaluation of patients with chronic back or skeletal pain.     

Inhibition of bone resorption by inorganic phosphate is mediated by both reduced osteoclast formation and decreased activity of mature osteoclasts

High concentrations of inorganic phosphate (Pi) are known to inhibit bone resorption, although the mechanism(s) underlying this effect is unclear. To investigate whether Pi can inhibit the formation of osteoclasts we studied the effects of changes in Pi concentration between 1 and 4 mM on osteoclast-like cell formation in 1 week cultures of mouse bone marrow. Osteoclast-like cells were identified by multinuclearity, positive staining for tartrate-resistant acid phosphatase (TRAP), and contraction in response to calcitonin. Increasing concentrations of Pi inhibited formation of these cells in a dose-dependent manner. To study effects of Pi on the bone-resorbing activity of mature osteoclasts we isolated osteoclasts from calcium-deficient egg-laying hens or rat pups and incubated them on sperm whale dentine slices. High Pi concentrations markedly reduced both the number of resorption pits formed per dentine slice and the mean area of each pit in both avian and mammalian systems. These data indicate that high concentrations of Pi act on bone directly, both to inhibit generation of new osteoclasts from their precursor cells and to inhibit bone resorption by mature osteoclasts. These effects of extracellular Pi concentration may play an important modulatory role on bone turnover in vivo and have potential importance in several disease states in which Pi metabolism is perturbed.     

Effects of parathyroid hormone on the osteoclastic pool,bone resorption and formation in rat alveolar bone

Summary The osteoclast number and its relation to parathyroid hormone have been studied in rat alveolar bone by quantitative histology and fluorescent labeling. The osteoclast number decreases 60 h after parathyroidectomy and remains constant for the next 132 h. Parathyroid hormone administration to parathyroidectomized animals 96 h after the operation induces an increase in osteoclast number within 12 h to some-what above those of control animals. The elevated osteoclast counts remain constant for 60 h then rapidly fall over the next 24 h to the level seen in untreated parathyroidectomized animals. As determined by fluorescent labeling, normal alveolar bone resorption and formation were disturbed by parathyroidectomy, such that significant bone formation occurred for only 6 days after surgery, after which a quiescent state followed.