Skeletal efficacy with parathyroid hormone in rats was not entirely beneficial with long-term treatment

Optimal intermittent administration interval of parathyroid hormone 1-34 for bone morphogenetic protein-induced bone formation in a rat spinal fusion model

INTRODUCTION

Both bone morphogenetic protein 2 (BMP-2) and teriparatide (parathyroid hormone [PTH] 1-34) are used to enhance bone healing. There is still no established opinion regarding the optimum dose and administration method. We investigated the optimal administration method for the combination of BMP-2 and PTH 1-34 in a rat spinal fusion model.

METHODS

Group I was implanted with a control carrier. Groups II, III, and IV were implanted with a carrier containing 3 μg of recombinant human BMP-2 (rhBMP-2). In addition, following implantation, PTH 1-34 injections were administered to Group III thrice a week (total, 180 μg/kg/week) and Group IV six times a week (total, 180 μg/kg/week). The rats were euthanized after 8 weeks, and their spines were explanted; assessed by manual palpation, radiographs, and high-resolution micro-computed tomography (micro-CT); and subjected to histological analysis. Serum markers of bone metabolism were also analyzed.

RESULTS

Manual palpation tests showed that the fusion rates in Groups III and IV were considerably higher than those in Group I. They also had higher radiographic scores than Group I and II. Micro-CT analysis revealed Tb.Th in the Group IV had higher values than that in the Group I, II, III with significant differences and Tb.Sp in the Group IV had lower values than that in the Group I, II, III with significant differences. Serum marker analysis revealed that Group IV had higher osteocalcin and lower tartrate-resistant acid phosphatase-5b than Group III. Histological analysis indicated that Group IV had enhanced trabecular bone structure.

CONCLUSIONS

Frequent administration of PTH may be better in making thicker and strengthening the trabecular bone structure in newly formed bone in the rat spinal fusion model using insufficient BMP-2.

PTH coatings on titanium surfaces improved osteogenic integration by increasing expression levels of BMP-2/Runx2/Osterix

The aim of this experiment was to assemble parathyroid hormone (PTH) coatings on titanium surfaces and evaluate the effect on implant osseointegration.

Three-times-weekly administration of teriparatide improves vertebral and peripheral bone density, microarchitecture, and mechanical properties without accelerating bone resorption in ovariectomized rats

Daily and weekly administration of teriparatide (PTH1-34) reduces the risk of osteoporotic bone fractures. However, their effects on markers of bone formation and bone resorption differ. These results indicate that the dosing frequency of teriparatide may affect bone metabolism and bone structure, with different effects on bone strength. In the present study, to evaluate the dose-related effects of a low administration frequency of teriparatide on bone status, we investigated the effects of three-times-weekly administration of teriparatide (1.1, 5.6, or 28.2 µg/kg) for 12 months on bone parameters, including bone metabolism markers, bone mineral density (BMD), micro-computed tomography, and bone strength, using 6-month-old ovariectomized (OVX) rats. Three-times-weekly administration of teriparatide dose-dependently increased the BMD of the lumbar vertebra and femur in OVX rats, and increased serum osteocalcin (a marker of bone formation), but not type I collagen C-telopeptide (a marker of bone resorption). The trabecular number and thickness increased in the vertebrae and femur, as in prior reports of daily teriparatide administration in OVX rats. Cortical thickness increased only toward the endocortical side of the femur, unlike with daily administration. Bone strength of the vertebrae and proximal and shaft of the femur was correlated with the changes in BMD and bone structure. These results demonstrate the effects of low frequency, intermittent administration of teriparatide on the biomechanical, and microstructural properties of bone in OVX rats.

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.

Dose-dependent enhancement of spinal fusion in rats with teriparatide (PTH[1-34])

STUDY DESIGN

Controlled animal experiments.

OBJECTIVE

To test the dose and efficacy of teriparatide in a rat spinal fusion model.

SUMMARY OF BACKGROUND DATA

Teriparatide was shown to enhance spinal fusion in rats and rabbits previously, but the dose-dependent effect of teriparatide in spinal fusion in rats was not well characterized.

METHODS

A 0.5 × 0.5 cm trabecular bone graft was taken and implanted onto the L5 and L6 transverse processes of the same rat. Rats were randomly assigned into 3 groups: saline vehicle control (Vehicle), teriparatide 4 μg/kg per day (PTH4), and teriparatide 23 μg/kg per day (PTH23) subcutaneous injections for 4 weeks (5 d per wk). The L5-L6 spinal segments were harvested at week 4, and assessments included radiography, micro-computed tomography, manual palpation, and histomorphometry. L3 vertebra, femurs, and serum bone markers were examined.

RESULTS

The average radiographical score of L5-L6 fusion in Vehicle, PTH4, and PTH23 groups was 1.53, 2.87, and 4.11, respectively, with the PTH23 being significantly higher (P = 0.001 vs. Vehicle). The average micro-computed tomographic score of L5-L6 fusion in Vehicle, PTH4, and PTH23 groups was 1.53, 2.40, and 3.74, respectively (P = 0.001, PTH23 vs. Vehicle and PTH4). Manual palpation showed that fusion rate was 20%, 50%, and 67.7% in Vehicle, PTH4, and PTH23 groups, respectively. The bone mineralization apposition rate at the fusion site was significantly increased in a dose-dependent manner among the groups. Teriparatide significantly increased vertebral and femoral bone mineral density, bone mineral content, and trabecular area in a dose-dependent manner relative to Vehicle. No difference was found between the circulating Procollagen type I N-terminal propeptide and intact osteocalcin levels in the serum at 4 weeks after treatments.

CONCLUSION

Teriparatide at 23 μg/kg per day for 4 weeks showed anabolic skeletal effects and significantly enhanced spinal fusion rate in rats, whereas teriparatide at 4 μg/kg per day had also anabolic effects but did not significantly enhance spinal fusion rate. Higher doses of teriparatide may be needed to promote spinal fusion in short-term application.

JTT-305, an orally active calcium-sensing receptor antagonist, stimulates transient parathyroid hormone release and bone formation in ovariectomized rats

Intermittent administration of parathyroid hormone (PTH) has a potent anabolic effect on bone in humans and animals. Calcium-sensing receptor (CaSR) antagonists stimulate endogenous PTH secretion through CaSR on the surface of parathyroid cells and thereby may be anabolic agents for osteoporosis. JTT-305 is a potent oral short-acting CaSR antagonist and transiently stimulates endogenous PTH secretion. The objective of the present study was to investigate the effects of JTT-305 on PTH secretion and bone in ovariectomized rats. Female rats, immediately after ovariectomy (OVX), were orally administered vehicle or JTT-305 (0.3, 1, or 3 mg/kg) for 12 weeks. The serum PTH concentrations were transiently elevated with increasing doses of JTT-305. In the proximal tibia, JTT-305 prevented OVX-induced decreases in both the cancellous and total bone mineral density (BMD) except for the 0.3mg/kg dose. At the 3mg/kg dose, JTT-305 increased the mineralizing surface and bone formation rate in histomorphometry. The efficacy of JTT-305 at the 3mg/kg dose on the BMD corresponded to that of exogenous rat PTH1-84 injection at doses between 3 and 10 μg/kg. In conclusion, JTT-305 stimulated endogenous transient PTH secretion and bone formation, and consequently prevented bone loss in OVX rats. These results suggest that JTT-305 is orally active and has the potential to be an anabolic agent for the treatment of osteoporosis.

Ibandronate does not reduce the anabolic effects of PTH in ovariectomized rat tibiae: a microarchitectural and mechanical study

Osteoporosis remains a challenging problem. Understanding the regulation on osteoclast and osteoblast by drugs has been of great interest. Both anabolic and anti-resorptive drugs yield positive results in the treatment of osteoporosis. However, whether the concurrent administration of parathyroid hormone (1-34) and ibandronate may offer an advantage over monotherapy is still unknown. This study, therefore, attempts to compare the efficacy of two therapeutical approaches and to investigate the beneficial effects in concurrent therapy in a rat model using three-point bending, pQCT and μCT analysis. A total of 60 female Sprague-Dawley rats of age 10 to 12 weeks were divided into 5 groups (SHAM, OVX+VEH, OVX+PTH, OVX+IBAN, OVX+PTH+IBAN) and subjected to ovariectomy or sham surgery accordingly. Low-dose parathyroid hormone (PTH) and/or ibandronate or its vehicle were administered subcutaneously to the respective groups starting from 4th week post-surgery at weekly intervals. Three rats from each group were euthanized every 2 weeks and their tibiae were harvested. The tibiae were subjected to metaphyseal three-point bending, pQCT and μCT analysis. Serum biomarkers for both bone formation (P1NP) and resorption (CTX) were studied. A total of 11 indices showed a significant difference between SHAM and OVX+VEH groups, suggesting the successful establishment of osteoporosis in the rat model. Compared to the previous studies which showed impedance from bisphosphonates in combination therapy with PTH, our study revealed that ibandronate does not block the anabolic effects of PTH in ovariectomized rat tibiae. Maximum load, strength-strain indices and serum bone formation markers of OVX+PTH+IBAN group are significantly higher than both monotherapy groups. With the proper ratio of anabolic and anti-resorptive drugs, the effect could be more pronounced.

Allotransplant of microencapsulated parathyroid tissue in severe postsurgical hypoparathyroidism: a case report

The last therapeutic alternative in severe postsurgical hypoparathyroidism is allotransplantation of microencapsulated parathyroid cells. With this technique, it is possible to implant cells or tissue of parathyroid origin to replace them in such patients, without immusupression. We report an allotransplant of parathyroid tissue in a patient with continous endovenous requirement of calcium to survive. The microencapsulation was carried out with a commercial sodium alginate. We implant 23 microspheres in the nondominant forearm and 40 microspheres in the leg in a second attempt. In this article, we show functionality of the graft for at least 20 months without requirement of endovenous calcium. We report this procedure as a therapeutical alternative in severe hypoparathyroidism.

Effects of PTH treatment on tibial bone of ovariectomized rats assessed by in vivo micro-CT

Using in vivo microcomputed tomography (micro-CT), we found in parathyroid hormone (PTH)-treated osteopenic rats linear increases in cortical and trabecular, due to increased trabecular thickness and number, bone mass. Bone was formed in cavities, leading to restoral of nearly cleaved trabeculae. For the first time, effects in PTH-treated rats were analyzed longitudinally.

INTRODUCTION

Our aims were to over time (1) determine changes in trabecular thickness and number after PTH, (2) compare responses to PTH between the meta- and epiphysis, (3) determine effects of PTH on mineralization and mechanical properties, (4) determine locations of new bone formation due to PTH on a microlevel, and (5) determine the predictive value of bone structural properties for gain in bone mass after PTH.

METHODS

Adult rats were divided into ovariectomy (OVX; n = 8), SHAM-OVX (n = 8), and OVX and PTH treatment (n = 9). Between weeks 8 and 14, PTH rats received daily subcutaneous PTH injections (60 microg/kg/day). At weeks 0, 8, 10, 12, and 14, in vivo micro-CT scans were made of the proximal and diaphyseal tibia. After sacrifice, all tibiae were tested in three-point bending.

RESULTS

PTH increased bone volume fraction linearly over time in meta- and epiphysis, accompanied by increased trabecular thickness in both and increased trabecular number only in the latter one. CT-estimated mineralization increased in trabecular and remained constant in cortical bone. Ultimate load and energy were increased and ultimate displacement and stiffness unaltered compared to SHAM rats. For those trabeculae analyzed, bone was formed initially on places where it was most beneficial for increasing their strength and later on to all surfaces.

Short-term effects of parathyroid hormone on rat lumbar vertebrae

STUDY DESIGN

This study is an experimental study in the rat osteopenia model.

OBJECTIVE

The aim of this study was to evaluate the short-term effects of daily application of parathyroid hormone (PTH) on bone quality and quantity using a new biomechanical compression test for intact rat lumbar vertebrae.

SUMMARY OF BACKGROUND DATA

Because of their high clinical relevance, trabecular content and thick cortical shell vertebrae are of high interest for osteoporosis research. Biomechanical stability depends on both trabecular and cortical bone. Anabolic effects on bone after long-term application of PTH have already been proven.

METHODS

After an intraindividual comparison (n = 20), the capability of a new test to identify biomechanical properties of the mature rat model was assessed. In the following, 33 three-month-old rats were ovariectomized. After 10 weeks, the animals were divided into 3 groups. The control group (C) received no additional food supplementation. The other groups received hormone treatment with either estradiol (E) or PTH for another 5 weeks. The effects on bone biomechanical properties and bone microstructure were analyzed.

RESULTS

After establishing the new biomechanical test for intact rat lumbar vertebrae, PTH-treated (yield stress: 2.95 N/mm, elastic limit: 2.39 N/mm) and then E-treated (yield stress: 2.13 N/mm, elastic limit: 1.68 N/mm) animals showed superior biomechanical results. Compression strength was significantly improved in these rats in comparison to the control group rats (yield stress: 1.86 N/mm, elastic limit: 1.38 N/mm). In the microradiographic evaluation, PTH significantly improved the morphologic results to produce thicker trabeculae. E led to a more densely branched trabecular network, which was not as important as trabecular thickness for bone stability.

CONCLUSION

After a short-term application, PTH is superior to E in recreating bone biomechanical propertiesand lumbar vertebral microstructure in advanced osteoporosis. The cortical shell and trabecular thickness are primarily responsible for the biomechanical strength of vertebrae.

Bone parameters are improved with intermittent dosing of vitamin D3 and calcitonin

Intermittent combination of an anabolic agent to promote bone formation and an antiresorptive agent that would prevent further bone loss is a theoretically attractive approach for restoring bone mass. We tested the potential of intermittently dosed calcitriol and calcitonin (CT) to restore bone properties in ovariectomized (Ovx) rats. Rats had Ovx or sham surgery at 8 weeks old and 4 weeks later were assigned to experimental groups: (1) sham vehicle, (2) Ovx vehicle, (3) Ovx + parathyroid hormone (PTH, 40 microg/kg), and (4) Ovx + calcitriol (2 microg/kg) + CT (2 microg/kg). Group 3 received PTH every week throughout the study, and group 4 received calcitriol at weeks 1, 3, 5, and 7 and CT at weeks 2, 4, 6, and 8. Dosing was carried out for 8 weeks with serum, and micro-computed tomographic analysis was done at 0, 4, and 8 weeks. Femurs and tibias were used for radiological analyses and for mechanical testing. Dosing with PTH improved bone mass and structure of cancellous bone at metaphyses of tibias and femurs as well as properties of cortical bone including geometry and strength. Intermittent dosing with calcitriol and CT was less potent in correcting loss of cancellous bone relative to treatment with PTH and had no effect on cortical bone parameters. However, intermittent dosing with calcitriol and CT was robust enough to improve cancellous bone mass and structure through bone formation without causing deleterious side effects. Our data provide additional evidence that therapies can be devised to ameliorate the skeletal defects associated with established osteoporosis.

Effects of once versus twice-daily parathyroid hormone 1-34 therapy in children with hypoparathyroidism

CONTEXT

Hypoparathyroidism is among the few hormonal insufficiency states not treated with replacement of the missing hormone. Long-term conventional therapy with vitamin D and analogs may lead to nephrocalcinosis and renal insufficiency.

OBJECTIVE

Our objective was to compare the response of once-daily vs. twice-daily PTH 1-34 treatment in children with hypoparathyroidism.

SETTING

The study was conducted at a clinical research center.

SUBJECTS

Fourteen children ages 4-17 yr with chronic hypoparathyroidism were studied.

STUDY DESIGN

This was a randomized cross-over trial, lasting 28 wk, which compared two dose regimens, once-daily vs. twice-daily PTH1-34. Each 14-wk study arm was divided into a 2-wk inpatient dose-adjustment phase and a 12-wk outpatient phase.

RESULTS

Mean predose serum calcium was maintained at levels just below the normal range. Repeated serum measures over a 24-h period showed that twice-daily PTH 1-34 increased serum calcium and magnesium levels more effectively than a once-daily dose. This was especially evident during the second half of the day (12-24 h). PTH 1-34 normalized mean 24-h urine calcium excretion on both treatment schedules. This was achieved with half the PTH 1-34 dose during the twice-daily regimen compared with the once-daily regimen (twice-daily, 25 +/-15 microg/d vs. once-daily, 58 +/- 28 microg/d; P < 0.001).

CONCLUSIONS

We conclude that a twice-daily PTH 1-34 regimen provides a more effective treatment of hypoparathyroidism compared with once-daily treatment because it reduces the variation in serum calcium levels and accomplishes this at a lower total daily PTH 1-34 dose. The results showed, as in the previous study of adult patients with hypoparathyroidism, that a twice-daily regimen produced significantly improved metabolic control compared with once-daily PTH 1-34.

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.

Daily treatment of aged ovariectomized rats with human parathyroid hormone (1-84) for 12 months reverses bone loss and enhances trabecular and cortical bone strength

Most studies that have investigated the anabolic effects of parathyroid hormone (1-84) (PTH) or PTH fragments on the skeleton of ovariectomized (OVX) rats have evaluated the short-term effects of high-dose PTH(1-34) in young animals. This study used densitometry, histomorphometry, and biomechanical testing to evaluate the effects of 12-month daily treatment with low-dose PTH (15 or 30 microg/kg) in rats that were 10 months old at baseline, 4 months after OVX. Bone mineral density (BMD) and bone strength were reduced substantially in control OVX rats. The 15 microg/kg dose of PTH restored BMD to levels similar to those in sham animals within 6 months at the lumbar spine, distal and central femur, and whole body and maintained the BMD gain from 6 to 12 months. The 30 microg/kg dose produced greater effects. Both PTH doses normalized the trabecular bone volume-to-total volume ratio (BV/TV) at lumbar vertebra 3 but not at the proximal tibia (where baseline BV/TV was very low), solely by increasing trabecular thickness. PTH dose-dependently increased bone formation by increasing the mineralizing surface, but only the 30 microg/kg dose increased resorption. PTH increased cortical BMD, area, and thickness, primarily by increasing endocortical bone formation, and restored all measures of bone strength to levels similar to those in sham animals at all skeletal sites. PTH increased bone mass safely; there was no osteoid accumulation, mineralization defect, or marrow fibrosis and there were no abnormal cells. Thus, long-term PTH therapy normalized bone strength in the aged OVX rat, a model of postmenopausal osteoporosis, through increased bone turnover and enhanced formation of both trabecular and cortical bone.

Effect of daily parathyroid hormone (1-34) on lumbar fusion in a rat model

BACKGROUND CONTEXT

Despite numerous studies evaluating the anabolic effects of intermittent administration of parathyroid hormone (PTH) on bone, there are no published studies examining its effect on spinal fusion outcomes.

PURPOSE

To determine the effect of daily injection of human recombinant PTH(1-34) on posterolateral lumbar fusions in a rat model.

STUDY DESIGN

Prospective, case-controlled, preclinical animal study.

OUTCOME MEASURES

Manual palpation and serum osteocalcin.

METHODS

Single-level, intertransverse process spinal fusions were performed with iliac crest autograft in 56 Sprague-Dawley rats. Animals received daily injections of placebo or PTH(1-34). At 6 weeks, fusion masses were assessed by manual palpation. Serum osteocalcin levels were assessed in a subset of the animals.

RESULTS

Manual palpation revealed the control group to have a fusion rate of 37% (10/27) and the PTH(1-34)-treated group to have a fusion rate of 52% (15/29). Mean serum osteocalcin levels were 59.8 and 88.6 ng/L for the control and PTH(1-34) groups, respectively.

CONCLUSIONS

There was a trend towards greater fusion rate in the PTH(1-34) group as compared with the placebo group. Further, PTH(1-34) administration was associated with a significant increase in osteocalcin levels. Certainly, further investigations are warranted, as an injectable agent capable of increasing fusion rates would be of great clinical value.

Intermittent parathyroid hormone therapy to increase bone formation

Clinical data suggested that parathyroid hormone (PTH) might be effective in improving bone mass in patients with osteoporosis, providing its resorptive effects, which are particularly marked at cortical sites, were kept under control. We reviewed the evidence that intermittent PTH therapy is a valid treatment option whose predominant effect is bone anabolism. In cell culture studies, PTH affected both bone formation and bone resorption, suggesting that the net result of PTH therapy may be either bone gain or bone loss depending on the dosage, mode of administration, bone site, and animal species. Histological studies established that intermittent PTH therapy was associated with an increase in trabecular bone and, importantly, with improvements in trabecular and cortical microarchitectural parameters that have not been reported with antiresorptive drugs. This anabolic effect of intermittent PTH therapy translates into increased biomechanical strength, despite the increase in endocortical porosity seen in humans and nonhuman primates. The biochemical response profile to intermittent PTH therapy in clinical trials indicated a phase of isolated anabolism followed by an overall increase in bone remodeling that predominantly affected bone formation, the result being a large increase in spinal bone mineral density as early as the first treatment year. Thus, intermittent PTH therapy exerts predominantly anabolic effects on bone.

Intermittently administered parathyroid hormone 1-34 reverses bone loss and structural impairment in orchiectomized adult rats

Male osteoporosis is emerging as a central theme in bone research. As in females, hypogonadism appears as a principal risk factor in men that leads to bone loss and increased fracture incidence. Intermittently administered parathyroid hormone (PTH) reverses bone loss in sex hormone-deprived women and female animals and increases bone mass in elderly men and normal male animals. This study was carried out to assess whether the PTH anabolic activity is also effective in adult castrated males and to gain insight into the underlying tissue processes. Bilateral orchiectomy (ORX) or sham-ORX was performed in 13-week old rats. Five weeks later, the ORX rats were treated intermittently with human PTH(1-34), 80 microg/kg/day or vehicle for 6 weeks. Femora were evaluated by quantitative micro-computed tomography followed by dynamic histomorphometry. The trabecular bone volume density showed 40% and 56% ORX-induced loss in the distal metaphysis at 6 weeks and 12 weeks post-ORX, respectively. PTH(1-34) induced supraphysiologic recovery of this bone loss (155% recovery) consequent to a vast increase in trabecular thickness (174% over sham-ORX controls) and a partial reversal (62%) of the decrease in trabecular number. As compared with the results in 12-week, orchiectomized vehicle-administered rats, the PTH(1-34) treatment induced a significant decrease in osteoclast number (20%) and twofold increase in bone formation rate. While ORX did not affect the femoral diaphysis, PTH(1-34) induced marked cortical thickening via the stimulation of endosteal mineral appositional rate (154% over ORX rats). These data portray PTH(1-34) as a highly potent bone anabolic agent in adult ORX rats, mainly by increasing both the trabecular and cortical thicknesses through its effect on osteoblasts and osteoclasts. The adult ORX rat is useful for investigating the processes involved in bone anabolic activity in castrated osteoporotic males and for the development of bone anabolic agents for treating this condition.

High-throughput in vivo screening for bone anabolic compounds with zebrafish

Osteoporosis and diseases of bone loss are a major public health problem for the present and the future since longevity and prevalence of the disease are increasing in all parts of the world. The bisphosphonates, widely used in the treatment of osteoporosis, act by inhibiting bone resorption. However, there are few agents that promote or increase bone formation in patients who have suffered substantial bone loss. To facilitate the identification of novel anabolic therapies, the authors have developed a rapid, high-throughput in vivo screen using larval zebrafish (Danio rerio) in which they are able to identify agents with anabolic effects in the skeleton within a 6-day time period. Vitamin D3 analogs and intermittent parathyroid hormone (PTH) result in dose-dependent increases in the formation of mineralized bone, whereas continuous exposure to PTH results in net bone loss. Because this model is fast, economical, and genetically tractable, it provides a powerful adjunct to mammalian models for the identification of new anabolic bone agents and offers the potential for genetic elucidation of pathways important in osteoblastic activity.

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.