Effects of a weekly injection of human parathyroid hormone (1-34) and withdrawal on bone mass, strength, and turnover in mature ovariectomized rats

Undifferentiated Pleomorphic Sarcoma and Hyperparathyroidism in an Adolescent Male: A Case Report and Review of Hyperparathyroidism-associated Sarcomas

The association between hyperparathyroidism and sarcoma is extremely rare with other reported cases describing the development of osteosarcoma and chondrosarcomas in middle-aged adults. This case describes an adolescent male with hyperparathyroidism and a pathologic fracture of a biopsy-proven brown tumor in the distal right femur. The fracture healed but later developed an undifferentiated pleomorphic sarcoma of the bone at the site of the known brown tumor. Although in vitro and in vivo studies have demonstrated the risks of elevated parathyroid hormone with development of sarcomas, there is limited evidence of a human association. The effects of elevated parathyroid hormone on the skeletally immature bone in the setting of sarcoma formation are currently not well understood without current description of adolescent hyperparathyroidism-associated sarcomas. This case highlights a sarcoma originating at a pathologically proven brown tumor within an adolescent male, discusses the association of sarcoma with hyperparathyroidism, and reviews the other nine reported cases in the literature.

Effects of the combination of vitamin K and teriparatide on the bone metabolism in ovariectomized rats

The purpose of the present study was to evaluate the combined effects of vitamin K (VK) and teriparatide (TPTD) on bone mineral density (BMD), mechanical strength and other parameters for bone metabolism using a rat ovariectomized osteoporosis model. Ovariectomized female Sprague-Dawley rats were administered with VK (an oral dose of 30 mg/kg/day), TPTD (a subcutaneous dose of 30 µg/kg, three times a week) or a combination for 8 weeks. Thereafter, serum levels of γ-carboxylated osteocalcin (Gla-OC) were quantitated by ELISA; BMD and mechanical strength were measured by computed tomography and biomechanical testing, respectively at the femoral metaphysis. Additionally, histomorphometry was performed using the toluidine blue-stained coronal sections of distal femur. The combination of VK and TPTD clearly increased the serum levels of Gla-OC (a specific marker for bone formation) and osteoblast surface (the number of osteoblasts attaching with the surface of cancellous bone), compared to VK or TPTD alone. In addition, the combination of the two agents improved the BMD and bone strength of the femur in the ovariectomized rats, compared to VK or TPTD alone. Taken together, these findings suggest that the treatment with VK and TPTD may have a therapeutic advantage over VK or TPTD monotherapy for postmenopausal osteoporosis, possibly by enhancing the bone formation through the actions on OC and osteoblasts.

Positive alterations of viscoelastic and geometric properties in ovariectomized rat femurs with concurrent administration of ibandronate and PTH

Besides bone mineral density (BMD), structural and nano-level viscoelastic properties of bone are also crucial determinants of bone strength. However, treatment induced viscosity changes in osteoporotic bone have seldom been characterized. In this study, the effects of anabolic, antiresorptive and concurrent treatments on ovariectomized rat bones were thoroughly analyzed using multiple bone strength parameters. A total of 52 female Sprague-Dawley rats of 3 months age were divided into 5 groups and subjected to sham (SHM group) or ovariectomy surgery (OVX, PTH, IBN and COM groups). Weekly low-dose parathyroid hormone (PTH) and/or ibandronate or its vehicle was administered subcutaneously to the respective groups starting from 4th week post-surgery. Four rats per group were euthanized every 4 weeks and their femurs were harvested. The BMD, micro-architectural parameters, cortical bone geometry and viscoelastic parameters were measured at the distal femoral metaphysis. Our results showed that PTH, ibandronate or its concurrent treatment can effectively reverse ovariectomy induced deteriorations in both trabecular and cortical bone. Different drugs had selective effects especially in preserving geometric and viscoelastic properties of the bone. The concurrent administration of PTH and ibandronate was shown to offer an added advantage in preserving mean BMD and had a positive effect on cortical bone geometry, resulting from an increased periosteal formation and a decreased endocortical resorption. Viscosity (η) was prominently restored in combined treatment group. It is in accordance with an observed denser alignment of collagen fibers and hydroxyapatite crystal matrix with fewer pores, which may play an important role in hindering fracture propagation.

A naturally occurring rare analog of quercetin promotes peak bone mass achievement and exerts anabolic effect on osteoporotic bone

The effect of quercetin C-glucoside (QCG) on osteoblast function in vitro and bone formation in vivo was investigated. QCG supplementation promoted peak bone mass achievement in growing rats and new bone formation in osteopenic rats. QCG has substantial oral bioavailability. Findings suggest a significant bone anabolic effect of QCG.

INTRODUCTION

Recently, we showed that extracts of Ulmus wallichiana promoted peak bone mass achievement in growing rats and preserved trabecular bone mass and cortical bone strength in ovariectomized (OVx) rats. 3,3',4',5,7-Pentahydroxyflavone-6-C-β-D-glucopyranoside, a QCG, is the most abundant bioactive compound of U. wallichiana extract. We hypothesize that QCG exerts bone anabolic effects by stimulating osteoblast function.

METHODS

Osteoblast cultures were harvested from rat calvaria and bone marrow (BM) to study differentiation and mineralization. In vivo, growing female Sprague Dawley rats and OVx rats with osteopenia were administered QCG (5.0 or 10.0 mg kg(-1) day(-1)) orally for 12 weeks. Efficacy was evaluated by examining changes in bone microarchitecture using histomorphometric and microcomputed tomographic analyses and by determination of new bone formation by fluorescent labeling of bone. Plasma and BM levels of QCG were determined by high-performance liquid chromatography.

RESULTS

QCG was much more potent than quercetin (Q) in stimulating osteoblast differentiation, and the effect of QCG was not mediated by estrogen receptors. In growing rats, QCG increased BM osteoprogenitors, bone mineral density, bone formation rate, and cortical deposition. In osteopenic rats, QCG treatment increased bone formation rate and improved trabecular microarchitecture. Comparison with the sham group (ovary intact) revealed significant restoration of trabecular bone in osteopenic rats treated with QCG. QCG levels in the BM were ~50% of that of the plasma levels.

CONCLUSION

QCG stimulated modeling-directed bone accrual and exerted anabolic effects on osteopenic rats by direct stimulatory effect on osteoprogenitors likely due to substantial QCG delivery at tissue level following oral administration.

Topical and intermittent application of parathyroid hormone recovers alveolar bone loss in rat experimental periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is characterized by periodontal tissue inflammation and alveolar bone loss. The intermittent administration of parathyroid hormone (PTH), a major regulator of bone remodeling, has been demonstrated to stimulate osteoblastic activity. Although the systemic administration of PTH has been reported to protect against periodontitis-associated bone loss, the effect of the topical administration of PTH is unclear. In this study, the effect of intermittent administration of PTH on osteoblastic differentiation was examined in cultured calvaria cells and then the effect of topical and intermittent administration of PTH was determined by measuring the recovery of alveolar bone loss after inducing experimental periodontitis in rats.

MATERIAL AND METHODS

Alkaline phosphatase activity and bone nodule formation were measured in fetal rat calvaria cells. Experimental periodontitis was induced by placing nylon ligature around rat maxillary molars for 20 d. After ligature removal (day 0), PTH was topically injected into buccal gingiva three times a week for 10 wk. Micro-computed tomography analysis and histological examination were performed on days 35 and 70.

RESULTS

Intermittent exposure of PTH in calvaria cells increased alkaline phosphatase activity and bone nodule formation by 1.4- and 2.4-fold, respectively. Ligature procedures induced marked alveolar bone loss around the molars on day 0 and greater bone recovery was observed in the PTH-treated rats on day 70. An increase in osteoid formation on the surface of alveolar bone was detected in the PTH-treated rats.

CONCLUSION

Intermittent treatment with PTH stimulated osteoblastic differentiation in fetal rat calvaria cell cultures, and topical and intermittent administration of PTH recovered alveolar bone loss in rat experimental periodontitis.

Intermittent weekly administration of human parathyroid hormone (1-34) improves bone-hydroxyapatite block bonding in ovariectomized rats

Hydroxyapatite (HA) blocks have been widely used for the reconstruction of bone defects and as a bone substitute. Bone-implant bonding depends on both implant-related factors and patient variables. Intermittent human parathyroid hormone (h-PTH) has a strong anabolic effect on bone formation. The purpose of the present study is to evaluate whether intermittent h-PTH administration enhances bone-HA block bonding in normal versus ovariectomized (OVX) rats. Cancellous bone osteotomy and HA-block implantation were performed on the proximal left tibia in both OVX and sham-operated 7-month-old female Sprague-Dawley rats. Newly formed cancellous bone around the HA block and bone-HA block bonding were evaluated by bone histomorphometry at 8 weeks after the administration of h-PTH (100 μg/kg/week) or its vehicle. The administration of h-PTH significantly increased cancellous bone volume by stimulating bone formation in OVX rats (p < 0.01). Although bone-HA block bonding was significantly decreased in OVX rats compared to that of sham-operated rats (p < 0.01), h-PTH improved the bone-HA block bonding in OVX rats (p < 0.01). These results suggest that intermittent h-PTH treatment may improve bone-HA bonding in osteoporosis by restoring cancellous bone volume and enhancing cancellous bone formation around the HA block.

Effect of intermittent treatment with human Parathyroid Hormone 1-34 in SAMP6 senescence-accelerated mice

We examined trabecular and cortical bone in the senescence-accelerated mouse prone 6 (SAMP6) murine model of senile osteoporosis after treatment with human PTH 1-34. Sixteen-week-old female SAMP6 mice were assigned to control and PTH groups. PTH (20 microg/kg) was administered sc 3 times a week for 12 weeks. The control mouse strain, senescence-accelerated mouse resistant 1 (SAMR1), was used for comparison. The femoral metaphysis and diaphysis were used to measure bone mineral density (BMD), analyze the trabecular and the cortical structure by micro-computed tomography, and for conducting the bone strength test. PTH significantly attenuated the loss of BMD, improved the trabecular bone microstructure, and increased the bone strength in the femoral metaphysis. We did not find any differences in the bone strength of the femoral diaphysis after PTH treatment, although the cortical bone volume and cortical thickness were improved. Although the cortical thickness increased, the cortical bone density decreased, likely because of the increase of cortical porosity in the distal metaphysis after administration of PTH.

Contribution of the intra-specimen variations in tissue mineralization to PTH- and raloxifene-induced changes in stiffness of rat vertebrae

The intra-specimen spatial variation in mineralization of bone tissue can be changed by drug treatments that alter bone remodeling. However, the contribution of such changes to the overall biomechanical effect of a treatment on bone strength is not known. To provide insight into this issue, we used a rat model to determine the effects of ovariectomy, parathyroid hormone, and raloxifene (vs. sham) on the contribution of spatial variations in mineralization to treatment-induced changes in vertebral stiffness. Mineral density was measured from 6-microm voxel-sized quantitative micro-CT scans. Whole-vertebral and trabecular stiffness values were estimated using finite element analysis of these micro-CT scans, first including all intra-specimen variations in mineral density in the model and then excluding such variations by using a specimen-specific average density throughout each specimen. As expected, we found appreciable effects of treatment on overall bone stiffness, the effect being greater for the trabecular compartment (up to 52% reduction vs. sham, p<0.0001) than the whole vertebra (p=0.055). Intra-specimen mean mineralization was not changed with treatment but the intra-specimen variation in mineralization was, although the effect was small (4%). Intra-specimen spatial variations in mineralization accounted for 10-12% and 5-6% of overall stiffness of the trabecular compartment and whole vertebral body, respectively. However, after accounting for all treatment effects on bone geometry and trabecular microstructure, any treatment effects due to changes in mineralization were negligible (<2%), although statistically detectable (p<0.02). We conclude that, despite a role in the general biomechanical behavior of bone, the spatial variations in tissue mineralization, as measured by quantitative micro-CT, did not appreciably contribute to ovariectomy-, PTH-, or raloxifene-induced changes in stiffness of the whole bone or the trabecular compartment in these rat vertebrae.

Endosseous implant anchorage is critically dependent on mechanostructural determinants of peri-implant bone trabeculae

Low bone mass is highly prevalent among patients receiving endosseous implants. In turn, the implantation prognosis in low-density skeletal sites is poor. However, little is known about the mechanostructural determinants of implant anchorage. Using metabolic manipulations that lead to low bone density and to its rescue, we show here that anchorage is critically dependent on the peri-implant bone (PIB). Titanium implants were inserted horizontally into the proximal tibial metaphysis of adult rats 6 weeks after orchiectomy (ORX) or sham ORX. Systemic intermittent administration of human parathyroid hormone (1-34) [iahPTH(1-34)] or vehicle commenced immediately thereafter for 6 weeks. The bone-implant apparatus was then subjected to image-guided failure assessment, which assesses biomechanical properties and microstructural deformation concomitantly. Anchorage failure occurred mainly in PIB trabeculae, 0.5 to 1.0 mm away from the implant. Mechanically, the anchorage performed poorly in ORX-induced low-density bone, attributable mainly to decreased trabecular number. iahPTH(1-34) rescued the PIB density and implant mechanical function by augmenting trabecular thickness (Tb.Th). However, implant biomechanical properties in low-density bone were relatively insensitive to implant surface treatment that affected only the osseointegration (%bone-implant contact). These results support a model wherein anchorage failure involves buckling of the weakest trabecular struts followed by sequential failure of the stronger trabeculae. Treatment with iahPTH(1-34) induced thicker struts, which were able to delay and even prevent failure of individual elements, thus implicating trabecular thickness as a prime target for enhancing implant anchorage by systemic bone anabolic therapy.

Elcatonin injections suppress systemic bone resorption without affecting cortical bone regeneration after drill-hole injuries in mice

It is assumed that there are systemic changes in mineral metabolism during fracture healing that may cause a predisposition to sequential fractures in osteoporotic patients who suffered from previous fractures. Initial therapies for patients with osteoporotic fractures are important to prevent disabilities in daily life consequent to bone and muscle atrophies, and sequential fractures, although systemic and local bone metabolism during fracture healing have not been well understood. We evaluated the effects of bone injury and elcatonin injection as an initial therapy on systemic and local bone turnover and bone wound healing. Two drill holes were made in the diaphysis of the left femur and tibia of 12-week-old male C57BL/6J mice. They were treated with three doses of elcatonin or a vehicle thrice a week until the end of the 28-day experiment. Urinary crosslinked C-telopeptide of type I collagen (CTX) increased and the bone mineral densities (BMDs) in the lumbar vertebrae decreased in the vehicle-treated mice. Elcatonin injection prevented increases in urinary CTX and reduction of the BMDs. In the noninjured femoral metaphysis, osteoclast surface increased until day 28, whereas elcatonin suppressed it. In the fracture site, elcatonin facilitated osteoblast proliferation and did not delay the healing of the bone defect. Bone injuries accelerated bone turnover systemically and locally, and the elcatonin injections suppressed the systemic acceleration of bone resorption without a delay of filling regenerated cortical bone in the bone defect.

In vivo microMRI-based finite element and morphological analyses of tibial trabecular bone in eugonadal and hypogonadal men before and after testosterone treatment

Osteoporosis is a major public health problem in men. Hypogonadal men have decreased BMD and deteriorated trabecular bone architecture compared with eugonadal men. Testosterone treatment improves their BMD and trabecular structure. We tested the hypothesis that testosterone replacement in hypogonadal men would also improve their bone's mechanical properties. Ten untreated severely hypogonadal and 10 eugonadal men were selected. The hypogonadal men were treated with a testosterone gel for 24 mo to maintain their serum testosterone concentrations within the normal range. Each subject was assessed before and after 6, 12, and 24 mo of testosterone treatment by microMRI of the distal tibia. A subvolume of each microMR image was converted to a microfinite element (microFE) model, and six analyses were performed, representing three compression and three shear tests. The anisotropic stiffness tensor was calculated, from which the orthotropic elastic material constants were derived. Changes in microarchitecture were also quantified using newly developed individual trabeculae segmentation (ITS)-based and standard morphological analyses. The accuracy of these techniques was examined with simulated microMR images. Significant differences in four estimated anisotropic elastic material constants and most morphological parameters were detected between the eugonadal and hypogonadal men. No significant change in estimated elastic moduli and morphological parameters was detected in the eugonadal group over 24 mo. After 24 mo of treatment, significant increases in estimated elastic moduli E(22) (9.0%), E(33) (5.1%), G(23) (7.2%), and G(12) (9.4%) of hypogonadal men were detected. These increases were accompanied by significant increases in trabecular plate thickness. These results suggest that 24 mo of testosterone treatment of hypogonadal men improves estimated elastic moduli of tibial trabecular bone by increased trabecular plate thickness.

Intermittent administration of human parathyroid hormone enhances bone formation and union at the site of cancellous bone osteotomy in normal and ovariectomized rats

Intermittent administration of human parathyroid hormone (hPTH) has an anabolic effect on bone in animals and humans and is expected to be a potent agent for the treatment of osteoporosis. However, little is known about the effects of hPTH on cancellous bone healing after cancellous bone fractures or osteotomies. We evaluated whether hPTH enhanced bone union at the site of cancellous bone osteotomy and further elucidated the possible mechanisms of hPTH effects on cancellous bone healing. After a bilateral ovariectomy (OVX) or sham operation in mature female rats, cancellous bone osteotomy was performed on the right proximal tibia. After once-a-week administration of hPTH (1-34) (100 microg/kg) or its vehicle for 4 weeks, bilateral tibiae including osteotomy and non-osteotomy sites were harvested. Along with conventional bone histomorphometry, cancellous bone union at the osteotomy site and the rate of proliferating cells immunostained with proliferating cell nuclear antigen (PCNA) and adipocytes in the surrounding bone marrow were evaluated. hPTH increased cancellous bone volume by stimulating bone formation in both normal and OVX rats and suppressed adipocyte volume (p<0.05). The percentage of PCNA-positive cells at the osteotomy site after PTH treatment was 2- to 3-fold higher than that of vehicle treatment controls both in sham-operated and OVX rats (p<0.05). The magnitude of increase in the percentage of PCNA-positive cells after PTH treatment at the osteotomy site was two times higher than that at the non-osteotomy site. Furthermore, PTH treatment increased cancellous bone union after osteotomy both in sham-operated and OVX rats (p<0.05). These results suggest that hPTH enhances cancellous bone healing at the site of osteotomy with, at least in part, a local regulating action that increases osteoblastogenesis and decreases adipocytogenesis at and around the osteotomy.

Effects of the administration of corticosterone, parathyroid hormone, or both, and of their withdrawal, on rat bone and cartilage histomorphometric parameters, and on osteoprotegerin and RANKL mRNA expression and proteins

We have studied the effects of the treatment with corticosterone (CORT), parathyroid hormone (PTH), or both (CORT + PTH), and of their withdrawal (CORT-rec and CORT + PTH-rec), on the osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL) localization and expression and on histomorphometric parameters in primary and secondary spongiosa of rat femur and tibia metaphyses. In the secondary spongiosa of the CORT group, the bone remodeling and the OPG/RANKL mRNA ratio decreased. In the PTH group, the bone turnover and the structural and connectivity indices increased, and the OPG/RANKL mRNA ratio fell; this ratio rose, however, in the primary spongiosa. In the CORT + PTH group, remodeling values intermediate between those of the CORT and PTH groups, were detected in the secondary spongiosa, where OPG and RANKL mRNA rose. Return towards control values was found in the recovery groups. The Cartilage Growth Plate Width was reduced in the CORT and CORT + PTH groups and returned to normal values in the recovery groups, while it was not affected by PTH. Independently of treatments, both OPG and RANKL mRNA and proteins were co-localized in the same cartilage and bone cells and in several bone marrow cells. In conclusion, the catabolic effects induced by CORT treatment occur together with an OPG fall and a RANKL rise. In the PTH group in which the bone turnover increase, the OPG and RANKL mRNA expressions differ in the primary and secondary spongiosa, confirming that the bone tissue in these sites can have different metabolic trends.

Primary hyperparathyroidism and malignancy: "studies by nature"

The American Food and Drug Administration approval of parathyroid hormone (PTH) administration for osteoporosis as well as the possibility for its future therapeutic applications requires an examination of the suggested association between PTH and cancer, particularly osteosarcomas. The objective was to evaluate such a connection by collecting observational data from two groups of patients, designated as "studies by nature". Cohort 1: Medical records of all patients with primary hyperparathyroidism that were treated in a referral center during a 12-year period were retrospectively reviewed for malignancy before, at the time or after diagnosis. Cohort 2: Records of patients with osteosarcomas that were treated in referral centers during 15 years were retrospectively reviewed for hyperparathyroidism, as indicated by history or laboratory results. There were 582 patients with primary hyperparathyroidism. While 56 (9.6%) had malignancy, 47 (8%) developed cancer after diagnosis with hyperparathyroidism during 6.1 years of documentation. This rate did not exceed the incidence of developing cancer among the general population. Although thyroid cancer was about 4 times the incidence in the general population, this may be attributed to a high level of detection while work-up, treating and following the parathyroid disease. None had osteosarcoma. None of the 126 patients with osteosarcoma had documentation of primary hyperparathyroidism or had biochemical evidence of hyperparathyroidism. No obvious association was found between primary hyperparathyroidism and cancer. Similarly, there was no demonstrable relationship between osteosarcomas and hyperthyroidism biochemical stigmata. Since PTH may contribute to tumor invasiveness, screening for existing neoplasms, especially prostate and breast, before PTH treatment may be of importance.

Histamine mediates osteoclastic resorption only during the acute phase of bone loss in ovariectomized rats

Short-term studies have shown that histamine is involved, via its H2 receptors (H2R), in the mediator network regulating trabecular bone loss in long bones of ovariectomized (OVX) rats. It is not known whether this effect of histamine persists over time or involves other skeletal sites. In this study, rats were maintained for 6 months postOVX and treated daily with saline or famotidine (10 mg kg(-1)), an H2R antagonist. At the end of the experimental period, femur trabecular bone mass was markedly decreased in OVX rats, whether or not they were treated with famotidine. In contrast, in the fourth lumbar vertebra, where bone loss starts later than in the femur, famotidine treatment attenuated the decline in trabecular bone volume, protected the trabecular architecture, maintained the thickness of the cortices and reduced the numbers of osteoclasts and tartrate-resistant acid phosphatase-positive preosteoclasts, whereas it had no influence on bone formation parameters. In vertebral bone marrow of OVX rats, the numbers of mast cells (MCs) and non-MC histamine-producing cells increased, while famotidine treatment significantly diminished both cell populations. These data show that H2R antagonism does not protect trabecular bone mass in the long term, and that short-term protection involves all bones. Histamine is involved during the early phase of strong osteoclastic resorption but not during the late phase of slower resorption, suggesting that different mediator networks control the two phases of destruction. Histamine would be part of the network mediating the early phase.

Response of induced bone defects in horses to collagen matrix containing the human parathyroid hormone gene

OBJECTIVE

To determine whether human parathyroid hormone (hPTH) gene in collagen matrix could safely promote bone formation in diaphyseal or subchondral bones of horses.

ANIMALS

8 clinically normal adult horses.

PROCEDURE

Amount, rate, and quality of bone healing for 13 weeks were determined by use of radiography, quantitative computed tomography, and histomorphometric analysis. Diaphyseal cortex and subchondral bone defects of metacarpi were filled with hPTH(1-34) gene-activated matrix (GAM) or remained untreated. Joints were assessed on the basis of circumference, synovial fluid analysis, pain on flexion, lameness, and gross and histologic examination.

RESULTS

Bone volume index was greater for cortical defects treated with hPTH(1-34) GAM, compared with untreated defects. Bone production in cortical defects treated with hPTH(1-34) GAM positively correlated with native bone formation in untreated defects. In contrast, less bone was detected in hPTH(1-34) GAM-treated subchondral bone defects, compared with untreated defects, and histology confirmed poorer healing and residual collagen sponge.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of hPTH(1-34) GAM induced greater total bone, specifically periosteal bone, after 13 weeks of healing in cortical defects of horses. The hPTH(1-34) GAM impeded healing of subchondral bone but was biocompatible with joint tissues. Promotion of periosteal bone formation may be beneficial for healing of cortical fractures in horses, but the delay in onset of bone formation may negate benefits. The hPTH(1-34) GAM used in this study should not be placed in articular subchondral bone defects, but contact with articular surfaces is unlikely to cause short-term adverse effects.

Assessment of bone quality using micro-computed tomography (micro-CT) and synchrotron micro-CT

The latest micro-computed tomography (micro-CT) can provide ultrahigh-resolution images with resolution of less than 10 microm. Geometric three-dimensional (3-D) parameters, including the orientation, shape, and connectivity of trabeculae, are particularly helpful in understanding complex 3-D structure. Micro-CT is helpful for studying bone changes in various pathophysiological states and assessing changes in microarchitecture after treatment with antiosteoporotic agents. Trabecular microarchitecture is strongly related to bone strength, and 3-D micro-CT data can be used to assess bone biomechanical properties with the help of finite-element analysis. High photon flux from synchrotron X-ray sources reveals precise bone surface structure, and the monochromaticity of the beam is suitable for performing accurate density measurements. The preliminary results of an in vivo study of microarchitecture are also shown. Human vertebral microstructure can be revealed using multidetector row CT at a resolution of 200 x 200 x 300 microm. Analysis using high-resolution CT microstructure was found to be more useful in identifying subjects at high risk of fracture than clinical bone density measurements using dual X-ray absorptiometry.

What's new with PTH in osteoporosis: where are we and where are we headed?

A new era in osteoporosis management began with the recent approval of parathyroid hormone (PTH) for postmenopausal and idiopathic osteoporosis treatment. Intermittent PTH dramatically increases spine bone mineral density and significantly reduces fragility fractures. However, the skeletal response to PTH varies greatly and there are few large scale, randomized, placebo-controlled trials in conditions such as glucocorticoid-induced osteoporosis. Moreover, the mechanisms of PTH action are complex, involving multiple pathways linked to common signaling peptides regulating osteoblast gene transcription. In addition, important interactions between osteoclasts and osteoblasts are activated by PTH. This review presents recent findings on PTH signaling in bone and discusses how they could be used to design randomized trials and establish clinical practice guidelines for this novel anabolic peptide.

Prostaglandin E2 receptor (EP4) selective agonist (ONO-4819.CD) accelerates bone repair of femoral cortex after drill-hole injury associated with local upregulation of bone turnover in mature rats

Prostaglandin E(2) (PGE(2)) is essential for fracture healing. Systemic administration of EP4 ligands such as PGE(2) and other synthetic EP4 agonists appears to transduce anabolic signals by binding to receptor EP4. Therefore, the present study was designed to test whether administration of EP4 agonist accelerates the healing of drill-hole injury in the femoral diaphysis. After surgery, a total of 128 Wistar rats, at the age of 12 weeks, were assigned to basal control (n = 8), and three groups with respective doses of 0 (vehicle control), 10 (low-dose), and 30 (high-dose) microg/kg body weight of the agent were subcutaneously injected twice a day. Femoral specimens were obtained at 0, 5, 7, 14, 21, and 28 days. In EP4 agonist-treated groups, the total bone volume of the regenerating bone in the defect did not significantly differ, but the regenerated cortical bone volume measured by histomorphometry and cortical bone mineral content (Ct. BMC) by pQCT dose-dependently increased at 14 and 21 days compared to the control. In the high-dose group, the value of osteoclast surface significantly increased compared with that in the control at 14 days. Expression levels of osteocalcin and TRAP mRNAs in the injured tissue increased at 14 days. Expression levels of EP4, BMP-2, and RANKL mRNAs increased at 7 days in the high-dose group. The bone mineral values of the lumbar bone at 28 days, measured by DXA, did not differ in the three groups. These data indicated that systemic administration of EP4 agonist ONO-4819.CD accelerated cortical bone healing after drill-hole injury by upregulating the local turnover of the regenerating bone.

Effects of h-PTH on cancellous bone mass, connectivity, and bone strength in ovariectomized rats with and without sciatic-neurectomy

The purpose of this study was to determine whether h-PTH (1-34) treatment would recover cancellous bone connectivity and bone strength in ovariectomized (OVX) or ovariectomized and sciatic-neurectomized (OVX+NX) rats. Seven-month-old female Wistar rats were treated with h-PTH or vehicle (6.0 microg/kg, six times a week, subcutaneously) for four weeks beginning 4, 8, or 12 weeks after OVX or OVX+NX. These were compared to age-matched baseline and sham-operated groups. Right tibiae were used for bone histomorphometry and node-strut analysis, and left tibiae were used for mechanical testing. The bone formation rates in the OVX and OVX+NX rats treated with h-PTH were significantly higher than those in their baseline controls. h-PTH treatment increased the node numbers and failure energies in the OVX rats, compared to their baseline controls, at all time points. However, in the OVX+NX rats, the effects of h-PTH treatment on the node number and failure energy were observed only at four weeks after surgery, but not at eight weeks or 12 weeks after surgery. These results suggest that the lowest limit, at which trabecular connectivity and bone strength are able to be restored by h-PTH, occurred between four and eight weeks in OVX+NX rats, but not in OVX rats. h-PTH cannot recover trabecular connectivity and bone strength in advanced osteopenia.

Tower climbing exercise started 3 months after ovariectomy recovers bone strength of the femur and lumbar vertebrae in aged osteopenic rats

To determine both the preventive and recovery effects of tower climbing exercise on mass, strength, and local turnover of bone in ovariectomized (OVX) rats, we carried out two experiments. In experiment I, 60 Sprague-Dawley rats, 12 months of age, were assigned to four groups: a Baseline Control, Sham-Operated Sedentary, OVX-Sedentary and OVX-Exercise rats. Rats voluntarily climbed a 200-cm tower to drink water from a bottle set at the top. At 3 months, OVX elevated both the femoral cortex and lumbar trabecular turnover, leading to a reduction in bone mass and strength. However, in OVX-Exercise rats, those values were maintained at the same level as in the Sham-Sedentary rats. Thus, the climbing exercise, started after 3 days of OVX, prevented OVX-induced cortical and trabecular bone loss by depressing turnover elevation. After confirming the preventive effect, we evaluated the recovery effect of exercise. In experiment II, 90 Sprague-Dawley rats, 12 months of age, were assigned to six groups: a Baseline control, two groups of Sham-Operated Sedentary and OVX-Sedentary, and OVX-Exercise rats. The exercise started 3 months after the OVX operation. At 3 months, OVX increased the trabecular bone formation rate and osteoclast surface, leading to a decrease in compressive strength. In the midfemur, the cross-sectional area, moment of inertia, and bending load values decreased. At 6 months, in the OVX-Exercise rats, the parameters of breaking load in both the lumbar and midfemur, lumbar bone mass, and the total cross-sectional area recovered to the same levels as those in the Sham-Sedentary rats. However, the cortical bone area did not recover. Periosteal bone formation increased, while endosteal bone formation decreased. These results showed that the climbing exercise had both a preventive and recovery effect on bone strength in OVX rats. In the mid-femur, effects on bone formation were site-specific, and the cross-sectional morphology was improved without an increase in cortical bone area, supporting cortical drift by mechanical stimulation.

Contribution of trabecular and cortical components to the mechanical properties of bone and their regulating parameters

To evaluate the mechanical contributions of the spongiosa and cortex to the whole rat vertebra, we developed a finite element analysis (FEA) system linked to three-dimensional data from microcomputed tomography (micro-CT). Twenty-eight fifth lumbar vertebrae (L-5) were obtained from 10-month-old female rats, comprised of ovariectomized (ovx, n = 6), sham operated (n = 7), and alfacalcidol-treated after ovx (0.1 microg/kg [n = 8] and 0.2 microg/kg [n = 7]) groups. The trabecular microstructure of L-5 was measured by micro-CT. Yield strength at the tissue level (YS), defined as the value at which 0.034% of all elements reached yield stress, was calculated by the FEA. Then, the ultimate compressive load of each specimen was measured by mechanical testing. The YS of the whole bone (YSw) showed a significant correlation with ultimate load (r = 0.91, p < 0.0001). The YS values of the isolated spongiosa (YSs) and cortex (YSc) were calculated in models with varying amounts of trabecular or cortical bone mass. The mechanical contribution of the spongiosa showed a nonlinear relationship with bone mass, and ovx reduced the mean mechanical contribution of the spongiosa to the whole bone by 13% in comparison to the sham group. YSs had a strong relationship with trabecular microstructure, especially with trabecular bone pattern factor (TBPf) and structure model index (SMI), and YSc had a strong relationship with cortical bone volume. The structural parameters most strongly related to YSw were BV/TV and TBPf. Our micro-FEA system was validated to assess the mechanical properties of bone, including the individual properties of the spongiosa and cortex, in the osteoporotic rat model. We found that the mechanical property of each component had a significant relationship with the respective bone mass, volume, or structure. Although trabecular microstructure has a significant relationship with bone strength, in ovx bone with deteriorated trabecular microstructure, the strength depended mainly on the cortical component.

Mechanical consequence of trabecular bone loss and its treatment: a three-dimensional model simulation

Age-related changes in the microstructure of trabecular bone, such as decreases in trabecular number and trabecular thickness, lead to reductions in mechanical properties, such as Young's modulus and strength. Current drug therapy, such as bisphosphonate or parathyroid hormone, improves the mechanical properties of bone mainly by increasing the trabecular thickness, but not increasing the trabecular number. However, the mechanical efficacy of these treatments has not been fully quantified using trabecular bone models. In this study, we used an idealized three-dimensional (3D) microstructural model of trabecular bone to create bone loss either through trabeculae thinning or random removal of trabeculae, and simulated treatment by increasing the trabeculae thickness of the remaining trabeculae. The reduction in either the Young's modulus or the strength due to trabeculae loss was proportional to a much higher power of reduction in bone volume fraction than due to trabeculae thinning. This indicates that bone loss due to trabeculae loss is much more detrimental to Young's modulus and strength of trabecular bone than due to trabeculae thinning, indicating the importance of trabecular number and connectivity in the mechanical integrity of trabecular bone. In general, treatments by increasing the trabecular thickness of remaining trabeculae after trabeculae loss cannot fully recover the initial mechanical properties of intact bone, even if bone loss is fully recovered, whereas trabecular thickening can fully restore the mechanical properties after bone loss by trabeculae thinning. The results also show that the residual loss in mechanical properties is dependent on the extent of trabeculae loss.

Human parathyroid hormone 1-34 reverses bone loss in ovariectomized mice

The experimental work characterizing the anabolic effect of parathyroid hormone (PTH) in bone has been performed in nonmurine ovariectomized (OVX) animals, mainly rats. A major drawback of these animal models is their inaccessibility to genetic manipulations such as gene knockout and overexpression. Therefore, this study on PTH anabolic activity was carried out in OVX mice that can be manipulated genetically in future studies. Adult Swiss-Webster mice were OVX, and after the fifth postoperative week were treated intermittently with human PTH(1-34) [hPTH(1-34)] or vehicle for 4 weeks. Femoral bones were evaluated by microcomputed tomography (microCT) followed by histomorphometry. A tight correlation was observed between trabecular density (BV/TV) determinations made by both methods. The BV/TV showed >60% loss in the distal metaphysis in 5-week and 9-week post-OVX, non-PTH-treated animals. PTH induced a approximately 35% recovery of this loss and a approximately 40% reversal of the associated decreases in trabecular number (Tb.N) and connectivity. PTH also caused a shift from single to double calcein-labeled trabecular surfaces, a significant enhancement in the mineralizing perimeter and a respective 2- and 3-fold stimulation of the mineral appositional rate (MAR) and bone formation rate (BFR). Diaphyseal endosteal cortical MAR and thickness also were increased with a high correlation between these parameters. These data show that OVX osteoporotic mice respond to PTH by increased osteoblast activity and the consequent restoration of trabecular network. The Swiss-Webster mouse model will be useful in future studies investigating molecular mechanisms involved in the pathogenesis and treatment of osteoporosis, including the mechanisms of action of known and future bone antiresorptive and anabolic agents.

Activin increases bone mass and mechanical strength of lumbar vertebrae in aged ovariectomized rats

Activin is a member of the transforming growth factor-beta superfamily and is thought to be involved in the regulation of bone formation due to its presence in bone tissue and its osteogenic activity both in vitro and in vivo. We recently found that systemic administration of activin increased both tibial bone mass and mechanical strength in young growing rats. The present study investigated the effects of activin in aged ovariectomized (ovx) rats. Twelve-month-old Fischer rats were ovariectomized and maintained for 10 months. Recombinant human activin A (activin) or human parathyroid hormone 1-34 (PTH) was administered intramuscularly three times a week for 12 weeks. Activin (1 and 5 microg/kg) markedly increased lumbar vertebral bone mineral content and bone mineral density. Activin also increased the mechanical strength of the vertebral body, which was highly correlated to the bone mineral density of the vertebral body. The maximal response in bone mass and strength was observed at 1 microg/kg of activin, which was approximately equal to that induced by PTH at 40 microg/kg. Peripheral quantitative computed tomography revealed that activin enlarged the cross-sectional size of the vertebrae without changing the foramen area, indicating its effects on cortical shells. Histomorphometric analysis of cancellous bone of vertebral body in similar experiment showed that activin (3 microg/kg) increased bone volume and the mineralizing surface, although its effects were less than PTH. The present results indicate that low doses of activin are effective against vertebral bone loss in aged ovx rats.

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.

Skeletal changes in rats bearing mammosomatotrophic pituitary tumors: a model of acromegaly with gonadal dysfunction

Growth hormone (GH) exerts potent effects on bone metabolism, resulting in an increased bone formation in animals and humans. Acromegaly has been associated with increased bone turnover, whereas the net effect of the increased bone metabolism has been obscured because patients with acromegaly are often associated with hypogonadism. We investigated changes in cortical and cancellous bone in adult rats implanted mammosomatotrophic pituitary tumor cells (GH3) as a model of acromegaly with gonadal dysfunction. Acromegaly model rats were prepared by implanting GH3 cells into female Wistar-Furth rats at 17 weeks of age. At 28 weeks of age, GH3-bearing rats (GH rats) showed very high serum GH levels and a moderate increase in serum prolactin levels, resulting in low circulating estradiol levels. The GH rats showed significant increases in body weight and in length and volume of both the femur and vertebral body. Bone mineral content values of either the midfemur or the whole lumbar body were significantly greater in the GH rats compared with littermate controls, while the areal bone mineral density values of the respective bones were not different between the two groups. The parameters of mechanical strength of the femur were significantly larger in the GH rats than in controls, whereas those of the lumbar vertebral body cylinder specimen were not different between the two groups. Respective normalized mechanical parameters of the femur and the vertebral body were the same in the GH rats as in controls. In the midfemur, the GH rats showed a significant increase in the total cross-sectional area without influencing the bone marrow area, resulting in an increase in the cortical bone area and the moment of inertia compared with controls. The indices of periosteal bone formation in the midfemur were greater in the GH rats compared with controls, but the endocortical bone formation and resorption were not different between the two groups. In the vertebral body cancellous bone, the GH rats had an increase in bone turnover rate, whereas the structural parameters were not different between the two groups. These results from GH3-bearing rats demonstrate that an excess of GH increases cortical bone mass in rats accompanied with estrogen deficiency, while no large effect on vertebral body cancellous bone mass is seen.

Intermittent administration of human parathyroid Hormone(1-34) prevents immobilization-related bone loss by regulating bone marrow capacity for bone cells in ddY mice

ddY mice, 6 weeks of age, were neurectomized (Nx) in the right hindlimbs and sham-operated (Sham) in the left limbs for evaluation of the effects of intermittent injections of human parathyroid hormone (hPTH) on trabecular bone turnover and bone marrow cell development in unloaded and loaded limbs. Mice were given subcutaneous injections of hPTH(1-34) five times a week at a dose of 0 (vehicle), 4 (low dose), or 40 (high dose) microg/kg of body weight for 2, 4, or 6 weeks. Histomorphometric analyses of the trabecular bone of the proximal tibiae revealed that high-dose hPTH injections preserved the trabecular bone volume of the Nx limbs, which was reduced after neurectomy, at the same level as that of the contralateral Sham limbs. The mineral apposition rate in the Nx limbs was elevated to values above even that of the Sham limbs by high-dose hPTH injections. The bone formation rate reduced by neurectomy was maintained at the Sham level by low- and high-dose hPTH injections. The neurectomy-induced increase in osteoclast number was suppressed by high-dose hPTH injections. In the bone marrow cells, the numbers of nonadherent and adherent cells per tibia obtained from the Nx and Sham limbs did not change. The hPTH injections decreased the numbers of nonadherent cells and increased those of adherent cells in both the Nx and the Sham limbs, but the effects were less marked in the Nx than in the Sham limbs even at high-dose injections. The formation of osteogenic nodules in the marrow cultures obtained from the Nx limbs was decreased after surgery and was maintained at the level of the Sham limbs by high-dose hPTH injections. The number of osteoclast-like multinucleated cells was reduced in the Sham limbs by high-dose hPTH injections. The value was increased at 2 weeks after neurectomy, but it was maintained at the Sham level by high-dose hPTH injections through the experimental period. The numbers of colony forming units-fibroblastic, which were reduced by neurectomy, and those of colony forming units for granulocytes and macrophages were not altered by hPTH injections. These results demonstrate that intermittent high-dose hPTH administration in the Nx limbs as well as in the contralateral Sham limbs has similar anabolic effects, stimulating osteoblast cell lineage and suppressing osteoclast cell lineage. The anabolic effects at 4 microg were reduced, but the effects at 40 microg seemed to be less affected by unloading due to sciatic neurectomy.