Parathyroid hormone (1-34) increases vertebral bone mass, compressive strength, and quality in old rats

A Novel Peptide, CK2.3, Improved Bone Formation in Ovariectomized Sprague Dawley Rats

Osteoporosis is a bone disease that has no definite cure. Current treatments for osteoporosis are divided into two categories: anti-resorptive and anabolic. However, these treatments are not perfect and have considerable risks. In addition, bone quality often declines over time with these treatments. We designed a peptide, CK2.3, that has both anabolic and anti-resorptive effects on bone. We reported that CK2.3 induced osteoblastic mineralization, promoted bone formation, and suppressed osteoclastogenesis in vivo. The effect of CK2.3 to rescue an osteoporosis phenotype model has never been shown. In this study, we demonstrated the effect of CK2.3 in ovariectomized rats, a standard model of osteoporosis. We systemically injected CK2.3 at 2.3 µg/kg each day for five consecutive days. Micro-computed tomography indicated that CK2.3 increased bone mineral density, (bone volume/tissue volume) BV/TV and (trabecular number) TbN, and decreased (trabecular space) TbSp in the femoral head. Similarly, single photon absorptiometry showed that treatment with CK2.3 increased bone mineral density in the lumbar spine and the pelvis. Additionally, we observed increased femoral shaft stiffness with ovariectomized rats treated with CK2.3. We also detected no significant changes in the weight of organs such as the heart, lung, liver, kidney, and spleen. An advantage of CK2.3 over current treatments was that it not only promoted bone formation but also improved fracture resistance. In conclusion, we demonstrated CK2.3 as a new anabolic treatment for osteoporosis.

Quantitative study of the influence of swimming therapy on osteoporosis rat models based on synchrotron radiation computed tomogaphy

Osteoporosis is a bone disease with a variety of causes, leading to bone pain and fragility to fracture. Major treatment methods include nutrition therapy, exercise therapy, drug therapy and surgical treatment, among which exercise therapy, such as swimming, is the most effective. To investigate the optimal swimming therapy regime for postmenopausal women, the effects of eight weeks of different intensity swimming exercises were studied in rat models. After the swimming program, lumbar vertebrae were dissected from all the rats and scanned by synchrotron radiation computed tomography (SRCT). Histomorphometry analysis and finite-element analysis were carried out on the trabecular structure of the L4 lumbar based on the acquired SRCT slices. Histomorphometry analysis showed that swimming can alleviate the decrease in bone strength induced by estrogen deficiency, and moderate-intensity swimming was found to have the most significant effect.

Macrophages and skeletal health

Bone is in a constant state of remodeling, a process which was once attributed solely to osteoblasts and osteoclasts. Decades of research has identified many other populations of cells in the bone that participate and mediate skeletal homeostasis. Recently, osteal macrophages emerged as vital participants in skeletal remodeling and osseous repair. The exact mechanistic roles of these tissue-resident macrophages are currently under investigation. Macrophages are highly plastic in response to their micro-environment and are typically classified as being pro- or anti-inflammatory (pro-resolving) in nature. Given that inflammatory states result in decreased bone mass, proinflammatory macrophages may be negative regulators of bone turnover. Pro-resolving macrophages have been shown to release anabolic factors and may present a target for therapeutic intervention in inflammation-induced bone loss and fracture healing. The process of apoptotic cell clearance, termed efferocytosis, is mediated by pro-resolving macrophages and may contribute to steady-state bone turnover as well as fracture healing and anabolic effects of osteoporosis therapies. Parathyroid hormone is an anabolic agent in bone that is more effective in the presence of mature phagocytic macrophages, further supporting the hypothesis that efferocytic macrophages are positive contributors to bone turnover. Therapies which alter macrophage plasticity in tissues other than bone should be explored for their potential to treat bone loss either alone or in conjunction with current bone therapeutics. A better understanding of the exact mechanisms by which macrophages mediate bone homeostasis will lead to an expansion of pharmacologic targets for the treatment of osteoporosis and inflammation-induced bone loss.

One year of abaloparatide, a selective peptide activator of the PTH1 receptor, increased bone mass and strength in ovariectomized rats

Abaloparatide is a novel 34 amino acid peptide selected to be a potent and selective activator of the parathyroid hormone receptor 1 (PTHR1) signaling pathway. The effects of 12months of abaloparatide treatment on bone mass, bone strength and bone quality was assessed in osteopenic ovariectomized (OVX) rats. SD rats were subjected to OVX or sham surgery at 6months of age and left untreated for 3months to allow OVX-induced bone loss. Eighteen OVX rats were sacrificed after this bone depletion period, and the remaining OVX rats received daily s.c. injections of vehicle (n=18) or abaloparatide at 1, 5 or 25μg/kg/d (n=18/dose level) for 12months. Sham controls (n=18) received vehicle daily. Bone changes were assessed by DXA and pQCT after 0, 3, 6 or 12months of treatment, and destructive biomechanical testing was conducted at month 12 to assess bone strength and bone quality. Abaloparatide dose-dependently increased bone mass at the lumbar spine and at the proximal and diaphyseal regions of the tibia and femur. pQCT revealed that increased cortical bone volume at the tibia was a result of periosteal expansion and endocortical bone apposition. Abaloparatide dose-dependently increased structural strength of L4-L5 vertebral bodies, the femur diaphysis, and the femur neck. Increments in peak load for lumbar spine and the femur diaphysis of abaloparatide-treated rats persisted even after adjusting for treatment-related increments in BMC, and estimated material properties were maintained or increased at the femur diaphysis with abaloparatide. The abaloparatide groups also exhibited significant and positive correlations between bone mass and bone strength at these sites. These data indicate that gains in cortical and trabecular bone mass with abaloparatide are accompanied by and correlated with improvements in bone strength, resulting in maintenance or improvement in bone quality. Thus, this study demonstrated that long-term daily administration of abaloparatide to osteopenic OVX rats led to dose-dependent improvements in bone mass, geometry and strength.

Intermittent Administration of Parathyroid Hormone [1-34] Prevents Particle-Induced Periprosthetic Osteolysis in a Rat Model

We examined whether intermittent administration of parathyroid hormone [1-34] (PTH[1-34]; 60 μg/kg/day) can prevent the negative effects of titanium (Ti) particles on implant fixation and periprosthetic osteolysis in a rat model. Eighteen adult male rats (12 weeks old, bones still growing) received intramedullary Ti implants in their bilateral femurs; 6 rats from the blank group received vehicle injections, and 12 rats from the control group and PTH treatment group received Ti particle injections at the time of operation and intra-articular injections 2 and 4 weeks postoperatively. Six of the rats that received Ti particles from the PTH group also received PTH[1-34] treatment. Six weeks postoperatively, all specimens were collected for assessment by X-ray, micro-CT, biomechanical, scanning electron microscopy (SEM), and dynamic histomorphometry. A lower BMD, BV/TV, Tb.N, maximal fixation strength, and mineral apposition rate were observed in the control group compared to the blank group, demonstrating that a periprosthetic osteolysis model had been successfully established. Administration of PTH[1-34] significantly increased the bone mineral density of the distal femur, BV/TV, Tb.N, Tb.Th, Tb.Sp, Con.D, SMI, and maximal fixation strength in the PTH group compared to that in the control group. SEM revealed higher bone-implant contact, thicker lamellar bone, and larger trabecular bone area in the PTH group than in the control group. A higher mineral apposition rate was observed in the PTH group compared to both the blank and control groups. These findings imply that intermittent administration of PTH[1-34] prevents periprosthetic osteolysis by promoting bone formation. The effects of PTH[1-34] were evaluated at a suprapharmacological dosage to the human equivalent in rats; therefore, additional studies are required to demonstrate its therapeutic potential in periprosthetic osteolysis.

Bone's Material Constituents and their Contribution to Bone Strength in Health, Disease, and Treatment

Type 1 collagen matrix volume, its degree of completeness of its mineralization, the extent of collagen crosslinking and water content, and the non-collagenous proteins like osteopontin and osteocalcin comprise the main constituents of bone's material composition. Each influences material strength and change in different ways during advancing age, health, disease, and drug therapy. These traits are not quantifiable using bone densitometry and their plurality is better captured by the term bone 'qualities' than 'quality'. These qualities are the subject of this manuscript.

PTH (1-34), but not strontium ranelate counteract loss of trabecular thickness and bone strength in disuse osteopenic rats

PTH and strontium ranelate (SrR) have both been shown to reduce bone loss induced by immobilization. PTH is a potent bone anabolic agent, whereas SrR has been suggested to be an antiresorptive as well as a bone anabolic agent. The aim of the study was to investigate whether PTH, SrR, and PTH and SrR in combination could counteract immobilization-induced bone loss in a rat model. Immobilization was induced by injecting 4IU Botox (BTX) into the muscles of the right hind limb. Seventy-two female Wistar rats, 3-months-old, were divided into the following groups: Baseline, Controls, BTX, BTX+PTH, BTX+SrR, and BTX+PTH+SrR (n=12 in each group). PTH was given as injections (SC) at a dosage of 60μg/kg/d, and SrR as 900mg/kg/d in the diet. The experiment lasted for 4weeks. BTX resulted in lower trabecular bone formation rate (-68%) and periosteal bone formation rate (-91%), and a higher fraction of osteoclast-covered surfaces (+53%) compared with controls. This was accompanied by significantly lower trabecular bone volume fraction (-24%), trabecular thickness (-16%), and bone strength (-14% to -32% depending on site). PTH alone counteracted immobilization-induced losses in trabecular (4-fold increase vs. BTX) and periosteal (5-fold increase vs. BTX) bone formation rate, trabecular thickness (+25% vs. BTX) and femoral neck strength (+24% vs. BTX). In contrast, SrR did not influence BTX-induced loss of bone formation rate, trabecular bone volume fraction, trabecular thickness, or bone strength. Finally, no additive effect was found when PTH and SrR treatments were combined. In conclusion, PTH counteracted loss in bone architecture and bone strength in immobilized rats, whereas as no effect of SrR was found. Moreover, no additional effect was found by combining PTH with SrR.

Effects of sodium hydroxide, sodium hypochlorite, and gaseous hydrogen peroxide on the natural properties of cancellous bone

Processed xenegeneic cancellous bone represents an alternative to bone autograft. In order to observe the effects of present prion inactivation treatments on the natural properties of xenogeneic cancellous bones, we treated bovine bone granules with sodium hydroxide (NaOH), sodium hypochlorite (NaOCl), and gaseous hydrogen peroxide (gH2 O2 ) respectively in this study. The microstructure, composition, and mineral content of the granules were evaluated by scanning electron micrograph, energy dispersive X-ray spectroscopy, ash analysis, and micro-computed tomography. The biomechanical property was analyzed by a materials testing machine. The cytocompatibility was evaluated by using a mouse fibroblast cell line (3T3). The microstructure, organic content, and mechanical strength were dramatically altered at the surface of bone in both NaOH- and NaOCl-treated groups, but not in the gH2 O2 -treated group. Compared with the gH2 O2 -treated group, attachment and proliferation of 3T3 were reduced in either NaOH- or NaOCl-treated groups. As the consequence, gH2 O2 treatment may be a useful approach of disinfection for the preparation of natural cancellous bone with well-preserved structural, mechanical, and biological properties.

Systemic intermittent parathyroid hormone treatment improves osseointegration of press-fit inserted implants in cancellous bone

BACKGROUND AND PURPOSE

Intermittent administration of parathyroid hormone (PTH) has an anabolic effect on bone, as confirmed in human osteoporosis studies, distraction osteogenesis, and fracture healing. PTH in rat models leads to improved fixation of implants in low-density bone or screw insertion transcortically.

MATERIAL AND METHODS

We examined the effect of human PTH (1-34) on the cancellous osseointegration of unloaded implants inserted press-fit in intact bone of higher animal species. 20 dogs were randomized to treatment with human PTH (1-34), 5 μg/kg/day subcutaneously, or placebo for 4 weeks starting on the day after insertion of a cylindrical porous coated plasma-sprayed titanium alloy implant in the proximal metaphyseal cancellous bone of tibia. Osseointegration was evaluated by histomorphometry and fixation by push-out test to failure.

RESULTS

Surface fraction of woven bone at the implant interface was statistically significantly higher in the PTH group by 1.4 fold with (median (interquartile range) 15% (13-18)) in the PTH group and 11% (7-13) in control. The fraction of lamellar bone was unaltered. No significant difference in bone or fibrous tissue was observed in the circumferential regions of 0-500, 500-1,000, and 1,000-2,000 μm around the implant. Mechanically, the implants treated with PTH showed no significant differences in total energy absorption, maximum shear stiffness, or maximum shear strength.

INTERPRETATION

Intermittent treatment with PTH (1-34) improved histological osseointegration of a prosthesis inserted press-fit at surgery in cancellous bone, with no additional improvement of the initial mechanical fixation at this time point.

Mechanisms for the bone anabolic effect of parathyroid hormone treatment in humans

Intermittent low-dose treatment with parathyroid hormone (PTH) analogues has become widely used in the treatment of severe osteoporosis. During normal physiological conditions, PTH stimulates both bone formation and resorption, and in patients with primary hyperparathyroidism, bone loss is frequent. However, development of the biochemical measurement of PTH in the 1980s led us to understand the regulation of PTH secretion and calcium metabolism which subsequently paved the way for the use of PTH as an anabolic treatment of osteoporosis as, when given intermittently, it has strong anabolic effects in bone. This could not have taken place without the basic understanding achieved by the biochemical measurements of PTH. The stimulatory effects of PTH on bone formation have been explained by the so-called 'anabolic window', which means that during PTH treatment, bone formation is in excess over bone resorption during the first 6-18 months. This is due to the following: (1) PTH up-regulates c-fos expression in bone cells, (2) IGF is essential for PTH's anabolic effect, (3) bone lining cells are driven to differentiate into osteoblasts, (4) mesenchymal stem cells adhesion to bone surface is enhanced, (5) PTH has a direct antiapoptotic effect on osteoblasts and (6) when PTH interferes with remodelling, the osteoblasts over-compensate, and (7) PTH also decreases sclerostin levels, thereby removing inhibition of Wnt signalling which is required for PTH's anabolic actions. Thus, the net formative effect of PTH given in intermittent treatment emerges through a complex network of pathways. In summary, the effects of PTH on bone turnover are dependent on the mode and dose of administration and studies investigating the mechanisms underlying this effect are reviewed in this article.

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.

Can we improve fixation and outcomes in the treatment of femoral neck fractures? The use of pharmaceuticals

Femoral neck fracture rates are on the rise with an estimated 500,000 occurring annually by 2040. Despite the mainstay of open reduction and internal fixation, nonunion rates of up to 33% have been reported for displaced femoral neck fractures. Recently, increasing attention has been focused upon the role of osteobiologics to stimulate fracture repair. This article looks at the role of these anabolic compounds and discusses their potential future roles in augmenting the treatment of this condition.

Parathyroid hormone (1-34) augments spinal fusion, fusion mass volume, and fusion mass quality in a rabbit spinal fusion model

STUDY DESIGN

The posterolateral rabbit spinal fusion model was used to assess the effect of intermittent parathyroid hormone on spinal fusion outcomes.

OBJECTIVE

To test the hypothesis that intermittent parathyroid hormone (PTH) improves spinal fusion outcomes in the rabbit posterolateral spinal fusion model.

SUMMARY OF BACKGROUND DATA

Spinal fusion is the definitive management for spinal deformity or instability, yet despite current technology, 5% to 40% of lumbar fusions result in pseudarthrosis. Animal studies have demonstrated enhanced fracture healing with the use of PTH, but the effect of PTH on spinal fusion is poorly described.

METHODS

Forty-four male New Zealand white rabbits underwent bilateral posterolateral spine fusion (L5-L6 level). Twenty-two rabbits received daily subcutaneous injections of PTH (1-34) (10 microg/kg) and 22 received an injection of saline fluid. All were killed 6 weeks after surgery. L5-L6 vertebral segments were removed and analyzed with manual bending, faxitron radiography, microCT, and histomorphometry.

RESULTS

Manual bending identified fusion in 30% (control) versus 81% (PTH) animals (P < 0.001). A radiographic scoring system ("0" = no bone formation, "5" = full fusion) resulted in an average score of 3.36 (control) versus 4.51 (PTH) (P < 0.001). MicroCT analysis demonstrated a median mass of 3.5 cc (control) (range, 2.25-5.40 cc) versus 6.03 cc (PTH) (range, 4.34-10.58 cc) (P < 0.001). Histology showed a median percentage bone area of 14.3% (control) (n = 12) versus 29.9% (PTH) (n = 15) (P < 0.001). The median percentage cartilage was 2.7% (control) (n = 5) versus 26.6% (PTH) (n = 5) (P < 0.01). Osteoclast quantification revealed median values of 140.5 (control) (n = 6) and 345.0 (PTH) (n = 8) (P < 0.001) respectively, and the percentage of osteoblasts revealed a median value of 31.4% (control) (n = 6) versus 64.4% (PTH) (n = 8) (P < 0.001).

CONCLUSION

Intermittent PTH administration increased posterolateral fusion success in rabbits. Fusion bone mass and histologic determinants were also improved with PTH treatment. PTH has promise for use as an adjunctive agent to improve spinal fusion in clinical medicine.

Bisphosphonates can block the deterioration in implant fixation after withdrawal of intermittent doses of parathyroid hormone

We have examined the deterioration of implant fixation after withdrawal of parathyroid hormone (PTH) in rats. First, the pull-out force for stainless-steel screws in the proximal tibia was measured at different times after withdrawal. The stimulatory effect of PTH on fixation was lost after 16 days. We then studied whether bisphosphonates could block this withdrawal effect. Mechanical and histomorphometric measurements were conducted for five weeks after implantation. Subcutaneous injections were given daily. Specimens treated with either PTH or saline during the first two weeks showed no difference in the mechanical or histological results (pull-out force 76 N vs 81 N; bone volume density 19% vs 20%). Treatment with PTH for two weeks followed by pamidronate almost doubled the pull-out force (152 N; p < 0.001) and the bone volume density (37%; ANOVA, p < 0.001). Pamidronate alone did not have this effect (89 N and 25%, respectively). Thus, the deterioration can be blocked by bisphosphonates. The clinical implications are discussed.

Human parathyroid hormone (1-34) accelerates natural fracture healing process in the femoral osteotomy model of cynomolgus monkeys

Several studies in rats have demonstrated that parathyroid hormone accelerates fracture healing by increasing callus formation or stimulating callus remodeling. However the effect of PTH on fracture healing has not been tested using large animals with Haversian remodeling system. Using cynomolgus monkey that has intracortical remodeling similar to humans, we examined whether intermittent treatment with human parathyroid hormone [hPTH(1-34)] accelerates the fracture healing process, especially callus remodeling, and restores geometrical shapes and mechanical properties of osteotomized bone. Seventeen female cynomolgus monkeys aged 18-19 years were allocated into three groups: control (CNT, n=6), low-dose PTH (0.75 microg/kg; PTH-L, n=6), and high-dose PTH (7.5 microg/kg; PTH-H, n=5) groups. In all animals, twice a week subcutaneous injection was given for 3 weeks. Then fracture was produced surgically by transversely cutting the midshaft of the right femur and fixing with stainless plate. After fracture, intermittent PTH treatment was continued until sacrifice at 26 weeks after surgery. The femora were assessed by soft X-ray, three-point bending mechanical test, histomorphometry, and degree of mineralization in bone (DMB) measurement. Soft X-ray showed that complete bone union occurred in all groups, regardless of treatment. Ultimate stress and elastic modulus in fractured femur were significantly higher in PTH-H than in CNT. Total area and percent bone area of the femur were significantly lower in both PTH-L and PTH-H than in CNT. Callus porosity decreased dose-dependently following PTH treatment. Mean DMB of callus was significantly higher in PTH-H than in CNT or PTH-L. These results suggested that PTH decreased callus size and accelerated callus maturation in the fractured femora. PTH accelerates the natural fracture healing process by shrinking callus size and increasing degree of mineralization of the fracture callus, thereby restoring intrinsic material properties of osteotomized femur shaft in cynomolgus monkeys although there were no significant differences among the groups for structural parameters.

Comparative study between coral-mesenchymal stem cells-rhBMP-2 composite and auto-bone-graft in rabbit critical-sized cranial defect model

Tissue engineered bone has become a bone substitute for the treatment of bone defects in animal research. This study investigated the osteogenesis capacity of coral-MSCs-rhBMP-2 composite with the auto-bone-graft as control. Coral-MSCs-rhBMP-2 composite were fabricated by coral (as main scaffold), rhBMP-2 (as growth factor), and MSCs (cultured from iliac marrow as seed cells). Critical-sized defects (d = 15 mm) were made on forty rabbits crania and treated by different composite scaffolds: iliac autograft (n = 8), coral (n = 8), rhBMP-2/coral (n = 8), and MSCs/rhBMP-2/coral (n = 8). The defects were evaluated by gross observation, radiographic examination, histological examination, and histological fluorescence examinations after 8 and 16 weeks. The results showed that repair of bone defect was the least in coral group, and significant ingrowth of new bone formation and incorporation could be seen with 77.45% +/- 0.52% in radiopacity in MSCs/rhBMP-2/coral group, which was similar to that in iliac autograft group (84.61% +/- 0.56% in radiopacity). New bone formation in MSCs/rhBMP-2/coral group was more than that in rhBMP-2/coral group. And osteogenesis rate in MSCs/rhBMP-2/coral group (10.23 +/- 1.45 microm) was much faster than that in rhBMP-2/coral group (5.85 +/- 2.19 microm) according to histological fluorescence examination. Newly formed bone partly came from induced MSCs in composite scaffold according to bromodeoxyuridine immunohistochemical examination. These data implicated that MSCs could produce synergic effect with coral-rhBMP-2, and the tissue engineered bone of coral-MSCs-rhBMP-2 is comparable to auto-bone-graft for the repair of critical-sized bone defect.

Stimulation of implant fixation by parathyroid hormone (1-34)-A histomorphometric comparison of PMMA cement and stainless steel

Whereas continuous exposure to PTH results in bone resorption, PTH administration at intermittent doses results in bone formation by increasing osteoblast number and activity. PTH leads to faster fracture repair and better fixation of orthopaedic implants in animal models. The present study evaluates if PTH is able to increase the contact surface between bone and implant and whether the effect of PTH is dependent on implant material characteristics. The implants were made as rods, either of stainless steel or Palacos R bone-cement. The steel rods had a surface roughness of R(a) 0.1 microm and the cement rods R(a) 2.2 microm. In 40 adult male rats, one cement rod was inserted in the left tibia and one steel rod in the right tibia. After implantation, the rats were divided into groups by random. One group was injected three times a week with human PTH (1-34) at a dose of 60 microg/kg BW/injection. The second group was injected with the vehicle only. Both groups were then divided into groups for 2 and 4 weeks time till tibial harvest. The tibial segments around the hole of the rods were then prepared by standard histological techniques. The linear tissue surfaces, that had been in contact with the surface of the rod, were analyzed in a blind fashion. PTH increased the bone contact fraction compared with the vehicle in the steel group from 7.4 (SD 7.6) to 21.1 (SD 10.7) % after 2 weeks and from 9.8 (SD 8.1) to 47.1 (SD 13.3) % after 4 weeks. In the cement group PTH increased the contact index again compared with the vehicle from 7.8 (SD 10.2) to 53.6 (SD 26.3) % already after 2 weeks and from 14.3 (SD 15) to 65.6 (SD 15.7) % after 4 weeks. The bone trabeculae adjacent to the implant had become fewer and thicker after the treatment with PTH (1-34), with an increase of the bone mass in the area next to the bone-implant-interface. The earlier onset of PTH effects in the rougher cement group suggests that intermittent PTH treatment might lead to an increased micro-interlock between implant and bone, and might therefore be considered as a possible drug to enhance incorporation of orthopedic implants.

Human parathyroid hormone (1-34) accelerates the fracture healing process of woven to lamellar bone replacement and new cortical shell formation in rat femora

This study aimed to test whether intermittent treatment of human parathyroid hormone [hPTH(1-34)] disturbs or accelerates the fracture healing process using rat surgical osteotomy model. One hundred five, 5-week-old SD rats were allocated to vehicle control (CNT) and four PTH groups; 10 and 30 microg/kg of hPTH(1-34) treatment before surgery (P10, P30), and treatment before and after surgery (C10, C30). All animals were given subcutaneous injections three times a week for 3 weeks. Then, fractures were produced by transversely cutting the midshaft of bilateral femora and fixing with intramedullary wire. Human PTH(1-34) treatment was continued in C10 and C30 groups until sacrifice at 3, 6, and 12 weeks after surgery. The femora were assessed by peripheral quantitative computed tomography, three-point bending mechanical test, and histomorphometry. Total cross-sectional area was not significantly different among all groups at any time point. At 3 weeks after surgery, the lamellar bone/callus area was significantly increased in C10 and C30 groups compared to the other groups. At 6 weeks, remodeling of woven bone to lamellar bone in the callus was almost complete in all groups. At 12 weeks, percent new cortical shell area was significantly higher in C10 and C30 groups compared to the other groups, and the ultimate load in mechanical testing was significantly higher in C30 group than in CNT, P10, and P30 groups. Intermittent PTH treatment at 30 microg/kg before and after osteotomy accelerated the healing process as evidenced by earlier replacement of woven bone to lamellar bone, increased new cortical shell formation, and increased the ultimate load up to 12 weeks after osteotomy.

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.

Differential transcriptional effects of PTH and estrogen during anabolic bone formation

The aim of this study was to compare transcriptional regulation in vivo during anabolic bone formation induced by either estradiol (E2) treatment or intermittent parathyroid hormone[1-34] (PTH) therapy. We utilized an ovariectomized (OVX) mouse model of osteoporosis and transcriptional profiling to identify genes upregulated by either high-dose E2 or PTH. Five weeks post-OVX, the mice were administered either E2 and/or PTH, or vehicle for 4 weeks. Femoral bones were analyzed by microCT and histomorphometry to confirm the anabolic effect of each treatment. OVX vehicle-treated control mice lost metaphyseal trabecular bone, with significant decrease in trabecular number, thickness, and connectivity. Both E2 and PTH treatments increased trabecular and cortical bone indices above the level of the sham operated controls, fully restoring both bone volume and bone mineral density (BMD). Moreover, PTH/E2 combination treatment led to significantly greater increase in cancellous bone and BMD than would be expected from the additive effects of the separate treatments. To determine whether PTH and E2 treatments were stimulating similar bone anabolic mechanisms, or were activating distinct signaling pathways, we compared patterns of gene expression using transcriptional profiling after either E2 or PTH treatment. After 4, 11, and 24 days of treatment, total RNA was collected from both the distal femoral metaphysis and diaphysis. Transcriptional profiling was performed using Affymetrix GeneChip probe arrays, comprised of approximately 36,000 full-length mouse genes and EST clusters from the UniGene database. Several markers of osteoblast activity, including c-fos, RANKL, PHEX, and PTHR1, were consistently upregulated by PTH in both skeletal sites. PTH treatment also increased expression of Cathespin K, consistent with the predicted increase in osteoclast activity. E2 treatment upregulated a largely distinct set of genes, including TGFbeta3, and BMP1, as well as several genes critical for cell cycle control, including Cyclin D1 and CDK inhibitor 1A. Overall, comparison of transcriptional profiles suggest that anabolic responses in bone to PTH and high-dose E2 treatment after OVX-induced osteoporosis involve largely distinct patterns of gene regulation, each resulting in restoration of bone mass.

Teriparatide (Biosynthetic Human Parathyroid Hormone 1-34): A New Paradigm in the Treatment of Osteoporosis

The ideal treatment of osteoporosis should preferably prevent fractures through normalization of bone mass and bone micro-architecture. Biosynthetic human parathyroid hormone 1-34 (teriparatide) was recently approved in the EU and the USA as the first anabolic treatment of osteoporosis. The effects of teriparatide are mediated by the G-protein-dependent, parathyroid hormone receptor-1 in the cell membrane. The binding of the ligand to the receptor activates adenylate cyclase and a number of phospholipases (A, C, and D) and increases intracellular levels of cAMP and calcium. Intermittent teriparatide increases the number of osteoblasts and bone formation by activation of pre-existing osteoblasts, increased differentiation of lining cells, and reduced osteoblast apoptosis. Anabolic effects of teriparatide on bone have been demonstrated in several species. It increases bone mass, structural integrity, bone diameter, and bone strength. Clinical efficacy was demonstrated in a randomized study comprising 1637 post-menopausal women with osteoporosis showing a 65% and 35% reduction of the relative risk of vertebral and appendicular fractures, respectively, during 18 months of treatment. Moreover, bone mineral density in the lumbar spine and hip increased by 9.7% and 2.6%, respectively. Similar effects on bone mineral density have been reported in men with osteoporosis and in glucocorticoid-induced osteoporosis, however, fracture data are limited in these groups. Direct comparison with alendronate revealed that teriparatide has a more pronounced effect on bone mineral density. Teriparatide should be used in combination with calcium plus vitamin D, and may be combined with hormonal replacement therapy. In contrast, alendronate attenuates the effect of teriparatide. The efficacy of other combinations remains uncertain. After termination of teriparatide, bone mineral density of the lumbar spine is reduced by approximately 2-3% after 2 1/2 years. This decrease is prevented by treatment with bisphosphonates. The most frequent adverse effects with teriparatide are nausea, headache, dizziness, and leg cramps, however, only the latter two differed significantly between the groups receiving teriparatide 20 microg/day and placebo. In the pivotal clinical study, reduced dosage or termination of therapy due to hypercalcaemia was necessary in 3% and 0.2%, respectively. In a rat toxicology study, in which teriparatide was administered in high dosages for an extended period of time, osteosarcoma was seen in a significant number of animals. However, none of the approximately 2800 patients in clinical trials has developed osteosarcoma. Teriparatide constitutes a break-through in the treatment of severe osteoporosis, although a number of issues about the optimal use of teriparatide remains unsettled. The published data provide proof of concept on anabolic therapy which changes several paradigms of bone physiology. Other parathyroid hormone analogues are being investigated in clinical trials and the development of non-peptide, small molecules targeted at the parathyroid hormone receptor may be envisaged.

Effect of intermittent parathyroid hormone (1-34) treatment on the bone response after placement of titanium implants into the tibia of ovariectomized rats

PURPOSE

This study investigated the effect of parathyroid hormone (1-34) [PTH(1-34)] on bone reactions after tibial placement of titanium screw implants into ovariectomized rats.

MATERIALS AND METHODS

Twelve-week-old female Wistar rats were divided into 3 groups of 24. The first group (Sham group) was sham-operated; the second group (OVX group) was ovariectomized only; and the third group (PTH group) was subcutaneously administered 30 microg/kg PTH in the dorsal region 3 days per week starting the fourth week after ovariectomy until the end of the experiment. Titanium screw implants were placed in the proximal metaphysis of the tibia of all 3 groups at 168 days after surgery. The animals were killed 7, 14, 28, and 56 days after implantation. Undecalcified sections were prepared and evaluated by light microscopy. Histomorphometric measurements were obtained using a computer-based image analyzer to quantify the unit bone mass around the implant and the rate of implant-bone contact.

RESULTS

When PTH administration was started 21 days after ovariectomy, the volume density of bone around implants in the PTH group was almost the same as that of the Sham group throughout the entire observation period. This finding suggests that not only can intermittent human PTH(1-34) administration prevent resorption of newly generated trabeculae around an implant but also it can aid in the recovery of bone volume lost due to ovariectomy.

CONCLUSION

When dental implants are applied to jaw bone showing trabecular bone loss, it may be possible to increase bone density around an implant by intermittent human PTH(1-34) administration and thereby improve clinical results.

Bone alterations in children with idiopathic hypercalciuria at the time of diagnosis

Some children with idiopathic hypercalciuria (IH) develop bone alterations at some stage of the disease. The aims of this study were to evaluate bone mass in 88 children with IH (G1) at the time of diagnosis and to compare the findings with data for a control group of 29 normal children (G2). Kidney and bone metabolism markers were measured in both groups, and bone densitometry was performed. Serum alkaline phosphatase, intact parathyroid hormone, urinary calcium and uric acid were significantly higher in G1, whereas urinary volume and urinary citrate excretion were lower. The following densitometric parameters were significantly lower in G1: (1) lumbar spine (L(2)-L(4)) bone mineral density (BMD), bone mineral content (BMC), BMC corrected for height and for width of the vertebra, volumetric BMD (BMDvol), and Z score; (2) whole-body BMD; (3) femoral neck BMD. Lumbar spine BMDvol was reduced (osteopenia) in 35% of the patients compared with G2. N telopeptide, a urinary marker of bone resorption, was significantly higher in G1 than in G2, and was negatively correlated with lumbar spine BMD and BMDvol. Children with urinary lithiasis or idiopathic hyperuricosuria associated with IH showed no significant differences in bone metabolism compared with children without these associations. We conclude that (1) there is an altered bone metabolism in IH, with osteopenia already present at diagnosis in 35% of the patients; (2) N telopeptide is one of the most useful markers of bone alterations in IH, especially at an early stage of the disease; (3) investigation of bone metabolism is necessary in IH to prevent future serious consequences such as osteoporosis and bone fractures.

Mechanical and chemical characteristics of mineral produced by basic fibroblast growth factor-treated bone marrow stromal cells in vitro

It has been shown that various organ and cell cultures exhibit increased mineral formation with the addition of basic fibroblast growth factor (bFGF) and phosphate ions in the medium. However, to date there has been no attempt to relate the chemical composition of mineral formed in vitro to a measure of its mechanical properties. This information is important for understanding the in vivo mineralization process, the development of in vitro models, and the design of tissue-engineered bone substitutes. In this study we examined the reduced modulus; hardness; and mineral-to-matrix, crystallinity, carbonate-to-mineral, and calcium-to-phosphorus ratios of mineral formed by bFGF-treated rat-derived bone marrow stromal cells in vitro. The cells were treated with 1 or 3 mM beta-glycerophosphate for 3 and 4 weeks. Both mechanical parameters, reduced modulus and hardness, increased with increasing beta-glycerophosphate concentration. The only chemical measure of the mineral composition that exhibited the same dependency was the mineral-to-matrix ratio. The values of crystallinity and carbonate fraction were similar to those for intact cortical bone, but the calcium-to-phosphorus ratio was substantially lower than that of normal bone. These data indicate that the mineral formed by bFGF-treated bone cells is mechanically and chemically different from naturally formed lamellar bone tissue after 4 weeks in culture. These results can be used to improve in vitro models of mineral formation as well as enhance the design of tissue-engineered bone substitutes.

Mechanisms for the enhancement of fracture healing in rats treated with intermittent low-dose human parathyroid hormone (1-34)

Recent reports have demonstrated that intermittent treatment with parathyroid hormone (1-34) [PTH(1-34)] increases callus formation and mechanical strength in experimental fracture healing. However, little is known about the optimal dose required for enhancement of fracture repair or the molecular mechanisms by which PTH regulates the healing process. In this study, we analyzed the underlying molecular mechanisms by which PTH affects fracture healing and tested the hypothesis that intermittent low-dose treatment with human PTH(1-34) can increase callus formation and mechanical strength. Unilateral femoral fractures were produced and a daily subcutaneous injection of 10 microg/kg of PTH(1-34) was administered during the entire healing period. Control animals were injected with vehicle solution alone. The results showed that on day 28 and day 42 after fracture, bone mineral content (BMC), bone mineral density (BMD), and ultimate load to failure of the calluses were significantly increased in the PTH-treated group compared with controls (day 28, 61, 46, and 32%; day 42, 119, 74, and 55%, respectively). The number of proliferating cell nuclear antigen (PCNA)-positive subperiosteal osteoprogenitor cells was significantly increased in the calluses of the PTH-treated group on day 2, and TRAP+ multinucleated cells were significantly increased in areas of callus cancellous bone on day 7. The levels of expression of type I collagen (COLlA1), osteonectin (ON), ALP, and osteocalcin (OC) mRNA were increased markedly in the PTH-treated group and accompanied by enhanced expression of insulin-like growth factor (IGF)-I mRNA during the early stages of healing (days 4-7). The increased expression of COL1A1, ON, ALP, and OC mRNA continued during the later stages of healing (days 14-21) despite a lack of up-regulation of IGF-I mRNA. These results suggest that treatment of fractures with intermittent low dose PTH(1-34) enhances callus formation by the early stimulation of proliferation and differentiation of osteoprogenitor cells, increases production of bone matrix proteins, and enhances osteoclastogenesis during the phase of callus remodeling. The resultant effect to increase callus mechanical strength supports the concept that clinical investigations on the ability of injectable low-dose PTH(1-34) to enhance fracture healing are indicated.

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

We report the consequences of prolonged treatment with recombinant human parathyroid hormone (1-34) (PTH) in male and ovariectomized female rats with mature skeletons. Intact male and osteopenic, ovariectomized, female F-344 rats were evaluated after 1 year of treatment with 0, 8, or 40 microg/kg/day s.c. PTH. Males and females were about 6 months of age at study initiation; females were ovariectomized (Ovx) for 5 weeks before initiation of PTH treatment. PTH did not affect the survival of either intact males or ovariectomized females. Qualitative histopathology showed expected changes associated with aging in kidneys and proximal tibiae, with no treatment-related anomalies after 1 year of PTH administration. PTH slightly increased the femoral length of ovariectomized females but not that of males. No significant differences in femoral length were observed between sham and Ovx controls. Proximal femora of the males and ovariectomized females given the high dose of 40 microg/kg showed 211 and 186% greater trabecular bone area, 118 and 94% greater cortical thickness, 170 and 189% greater trabecular number, and 321 and 404% greater connectivity (node-to-node struts) compared with respective vehicle controls. Increased trabecular and endocortical surface apposition coincided with a 78 and 70% loss of marrow space for males and females treated with PTH, respectively. Biomechanical strength (ultimate load) of the femoral neck increased by 73 and 76%, respectively, in males and ovariectomized females. Cortical bone analyses of the femoral midshaft showed 105 and 72% increases in bone mineral content, 67 and 55% increases in bone mineral density, and 22 and 10% increases in cross-sectional area for males and ovariectomized females, respectively, with altered shape of femora. Biomechanical analyses of the midshaft showed substantial increases in strength and stiffness but a reduction in ultimate strain, which was likely due to the altered geometry of the midshaft for PTH groups. Aging effects on strength of vertebra and femoral midshaft were reversed by PTH treatment. In summary, the 1-year treatment duration, which represents about 50% of lifetime, did not affect survival and was not associated with any treatment-related anomalies in the kidney or skeleton. PTH reversed the aging process in bones but not kidneys and substantially increased bone mass and strength to well beyond normally attained levels. However, compared with short-term studies reported previously, there seemed to be no advantages to extending PTH treatment to 12 months in rat bones.

Parathyroid hormone (1-34) increases attachment of PMMA cement to bone

The attachment of an implant material to bone is related to the surface of the implanted material and the ability of the bone to form around the implant. Intermittent parathyroid (PTH) administration increases bone formation by stimulating osteoblastic activity. Little is known about the effect of PTH administration on orthopedic implant incorporation. The present study determined how PTH (1-34) administration influenced bone bonding, i.e., the bone-cement interfacial tensile strength, of vacuum-mixed polymethylmethacrylate (PMMA) bone cement (surface roughness; Ra, 4.8 microm). Bone bonding was evaluated by a detachment test. We used unloaded cement surfaces, which could be detached from the bone. Titanium plates were developed such that a cement fill was contained within a plate that was contained within a titanium holder. Thus, a flat cement surface came into contact with traumatized bone only, and the rest of the plate had no contact with tissue. After implantation of the plate in the left tibia, 20 adult male rats were injected daily with human PTH (1-34) at 60 microg/kg per injection (n = 10) or vehicle (n = 10); the animals were killed after 4 weeks. The plates were detached from the bone by a perpendicular force. PTH treatment increased the median pull-away strength (0.21 MPa), compared with that in the vehicle-treated rats, (0.04 MPa) (P = 0.02). The results suggest that PTH treatment may have the potential to enhance the incorporation of cemented orthopedic implants.

Early effect of parathyroid hormone (1-34) on implant fixation

Intermittent systemic administration of parathyroid hormone increases bone formation by stimulating osteoblastic activity. The current study determined how parathyroid hormone (1-34) administration influences the bony fixation of stainless steel screws with time. A screw was implanted in the left tibia and a metal rod was implanted in the right tibia in 30 adult male rats that then were injected three times a week with human parathyroid hormone (1-34) at 60 microg/kg/injection (n = 15) or saline (n = 15). The animals were euthanized after 1, 2, or 4 weeks of treatment. Eight additional rats received only the screw and were euthanized immediately after implantation. No significant effects of parathyroid hormone on body weight change or ash weight of the femurs were seen. The degree of fixation was assessed by measuring pullout strength of the screws. The mean pullout strength immediately after implantation was 12 N. The pullout strength of the group injected with saline was 33 N after 1 week, 23 N after 2 weeks, and 41 N after 4 weeks. The pullout strength of the group injected with parathyroid hormone increased to 43 N after 1 week, 58 N after 2 weeks, and 100 N after 4 weeks. The increase at 2 and 4 weeks was statistically significant. Strength reflects the mechanical properties of the bone within the screw threads. The contralateral tibia with its metal rod was used for blinded histologic assessment. Parathyroid hormone increased the fraction of the metal surface having contract with bone without an intervening soft tissue layer from 45% to 69% after 1 week. The current results suggest that intermittent parathyroid hormone treatment can enhance early implant fixation by enhancing the density of the surrounding bone and by increasing the implant bone contact.

Reconstructing the skeleton with intermittent parathyroid hormone

The aim of treating osteoporosis is to restore bone strength by increasing its mass and reconstructing its architecture. Antiresorptive drugs reduce bone remodeling, allowing more complete secondary mineralization of the existing bone; the mass, macro- and microarchitecture of the bone remains unchanged. Anabolic agents have the potential to achieve this goal. Parathyroid hormone (PTH) is famous for its catabolic actions. Its anabolic effects, known by a select few over 70 years ago, are finally being appreciated. There is widely reproduced and compelling evidence in a range of species made osteoporotic by gonadectomy that intermittent PTH administration restores bone strength by stimulating new bone formation on the periosteal (outer) and endosteal (inner) bone surfaces, enlarging bone diameter, thickening the cortices and existing trabeculae, and perhaps increasing trabecular numbers and their connectivity.

Effects of human parathyroid hormone (1-34), LY333334, on bone mass, remodeling, and mechanical properties of cortical bone during the first remodeling cycle in rabbits

We have previously shown that parathyroid hormone (PTH) increases cortical bone mass and mechanical strength of female rabbits after 140 days of treatment. However, cortical porosity was also shown to increase. If cortical porosity increases prior to the change in geometry, there may be a transient decrease in cortical bone strength that could make the bone more susceptible to fracture in the early phase of treatment. The purpose of this study is to examine the effects of PTH on the remodeling dynamics and mechanical properties of cortical bone in rabbits, which exhibit haversian remodeling, during the first remodeling cycle after the initiation of treatment. Fifty 9-month-old intact female New Zealand white rabbits were randomized into five groups. A baseline control group was killed at the start of the experiment. The two PTH-treated groups were given human PTH(1-34) at 10 microg/kg daily subcutaneously for 35 (P35) or 70 (P70) days. Two respective age-matched control groups (V35, V70) were injected with vehicle. Histomorphometry of the cortical bone in the tibial midshaft showed that, although intracortical activation frequency was significantly increased by PTH at 35 days, there was no significant increase of cortical porosity in the first remodeling cycle (70 days). Moreover, stimulation of cortical surface bone formation in the treated animals led to significantly greater cortical area and greater bone strength in both P35 and P70. We conclude that, although intracortical remodeling increases within the first remodeling period (70 days) in animals treated with 10 microg/kg PTH, the greater cortical area due to acceleration of bone formation on cortical surfaces increases cortical bone strength. There is no mechanical risk during the first remodeling cycle associated with intermittent PTH treatment in animals with normal bone mass.

Maintenance of vertebral body bone mass and strength created by human parathyroid hormone treatment in ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone (1-84) (hPTH) followed by maintenance administration of 17beta-estradiol (E2), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on vertebral body bone mineral density (BMD) and bone strength in ovariectomized (ovx) rats. Eight groups of ovx (219 rats) and one group of intact female rats (48 rats) were left untreated for 11 weeks (age 3.5 months at the beginning). For the following 12 weeks, four ovx groups received subcutaneous injections of hPTH (75 microg/kg per day, 3 days/week) and four groups received vehicle. Treatments were then changed to: E2 (10 microg/kg per day, 2 days/week); Ris (3 microg/kg per day, 3 days/week); LowPTH (25 microg/kg per day, 3 days/week); or vehicle for 36 weeks. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). The endpoints were vertebral body BMD, ultimate stress (Ultstr), and moduli of elasticity from compression tests (ModM), and from ultrasound tests (ModUS). Ovariectomy resulted in lower BMD (p < 0.001). The hPTH treatment for 12 weeks restored BMD to the level of intact rats. Ultstr and ModUS followed a similar pattern, but the ovx-induced Ultstr was not significant (p = 0.073, ModUS: p = 0.003), nor was the hPTH-induced increase in ModUS (p = 0.131, Ultstr: p = 0.02). After hPTH withdrawal, BMD, Ultstr, and ModUS levels were not different from levels in ovx animals. In Ris-treated rats pretreated with hPTH, BMD (weeks 24 and 48, p < 0.002) and ModUS (week 24, p = 0.018) values were greater than in ovx animals. In LowPTH-treated rats pretreated with hPTH, BMD (weeks 24 and 48, p < 0.001) and Ultstr (week 48, p = 0.005) were greater than in ovx animals. In E(2)-treated rats pretreated with hPTH, BMD was greater than in ovx rats at week 24 (p = 0.009), but did not differ at weeks 36-48. Neither Ultstr nor ModUS in E(2)-treated rats differed significantly from ovx rats at any timepoint. Of the agents and dosing regimens used, we conclude that the hPTH-related vertebral bone mass gain in ovx rats can be maintained for up to 36 weeks with risedronate and low-dose hPTH treatment. Bone strength is maintained by treatment with low-dose hPTH, but only partially maintained with risedronate.

Bone tissue and its mineralization in aged estrogen-depleted rats after long-term intermittent treatment with parathyroid hormone (PTH) analog SDZ PTS 893 or human PTH(1-34)

Intermittently administered parathyroid hormone (PTH) is a potent bone anabolic agent. We aimed to determine the impact of long-term treatment with PTH on bone structure, dynamics, and mineralization. We ovariectomized (ovx) 1-year-old rats with the exception of a baseline and a sham-operated group. Twelve weeks later, a 36 week treatment with PTH analog SDZ PTS 893 (12.5, 25, 50, 100 microg/kg), human PTH(1-34) (25, 50, 100 microg/kg), or vehicle (ovx, sham) was initiated. Bone dynamics, structure, and mineralization were evaluated in the lumbar spine and in the femoral diaphysis. Cancellous bone turnover was elevated 12 weeks postovariectomy in estrogen-deficient, vehicle-treated animals, but returned to the level of the sham group by 48 weeks. The animals experienced substantial cancellous bone loss associated with a reduction of trabecular number and presented with a partly rod-like trabecular network. After 36 weeks of treatment with SDZ PTS 893 or human PTH(1-34), cancellous bone formation rates and turnover were raised in all treated groups compared with age-matched controls. The mineral apposition rate was increasing with dose. This amplified matrix synthesis led to trabecular thickening, but not to an increase in trabecular number, resulting in a crude, plate-like cancellous network with a high bone volume fraction. Fluorochrome label-based cortical bone dynamics demonstrated that a thick ring of new bone was formed at the endocortex by activation of modeling drifts during treatment. Treatment-induced cortical bone formation was increased with dose at the subperiosteal and endocortical envelopes, but substantially higher at the latter. Intracortical bone turnover was elevated near the endocortex. Bone mineralization was undisturbed in all compartments. The average degree of mineralization was lowered slightly, reflecting the increased portion of new bone formed during treatment. In summary, the main anabolic effect was mediated for both peptides by an increase in bone apposition with dose, persisting throughout treatment that lasted more than one third of the lifespan of the rats, and direct activation of bone-forming surfaces. As a result, a substantial amount of new bone, maintained at elevated turnover and adequate mineralization levels, formed predominantly at compartments exposed to bone marrow.

Antagonizing the parathyroid calcium receptor stimulates parathyroid hormone secretion and bone formation in osteopenic rats

Parathyroid hormone (PTH) is an effective bone anabolic agent, but it must be administered parenterally. An orally active anabolic agent would provide a valuable alternative for treating osteoporosis. NPS 2143 is a novel, selective antagonist (a "calcilytic") of the parathyroid cell Ca(2+) receptor. Daily oral administration of NPS 2143 to osteopenic ovariectomized (OVX) rats caused a sustained increase in plasma PTH levels, provoking a dramatic increase in bone turnover but no net change in bone mineral density. Concurrent oral administration of NPS 2143 and subcutaneous infusion of 17beta-estradiol also resulted in increased bone turnover. However, the antiresorptive action of estrogen decreased the extent of bone resorption stimulated by the elevated PTH levels, leading to an increase in bone mass compared with OVX controls or to either treatment alone. Despite the sustained stimulation to the parathyroid gland, parathyroid cells did not undergo hyperplasia. These data demonstrate that an increase in endogenous PTH secretion, induced by antagonism of the parathyroid cell Ca(2+) receptor with a small molecule, leads to a dramatic increase in bone turnover, and they suggest a novel approach to the treatment of osteoporosis.

Mandibular bone formation rates in aged ovariectomized rats treated with anti-resorptive agents alone and in combination with intermittent parathyroid hormone

Anti-resorptive agents--including estrogen (E), calcitonin (CT), and bisphosphonates--are established in the treatment of osteoporosis. Intermittent administration of parathyroid hormone (PTH) stimulates bone formation and is a possible therapeutic agent for the restoration of bone mass. The purpose was to determine the effects of the anti-resorptive agents alone and in combination with intermittent PTH on bone formation in the mandible and a long bone in the aged ovariectomized (Ovx) rat. Female rats were ovariectomized or sham-operated. One year later, groups of Ovx rats were treated with E, CT, or the bisphosphonate, Risedronate (NE). Additional groups of Ovx rats were treated with each of these agents in combination with human PTH for 10 weeks. Estrogen treatment suppressed most indices of bone formation in the humerus and mandible, while NE decreased some indices of formation at the endocortical and endosteal surfaces of the mandible and humerus. Increased double-labeled surface and mineral apposition rates were observed only on the mandibular endosteal surfaces following CT treatment. When the anti-resorptive agents were combined with intermittent PTH, most indices of bone formation at all skeletal sites were substantially greater than those of the untreated Ovx controls as well as the E-, CT-, and NE-treated groups, respectively. These results provide additional evidence that established and emerging therapies for osteoporosis affect osseous tissues in the oral cavity, and this may influence the progression of diseases and/or aging changes at this site.

Primary hyperparathyroidism: bone structure, balance, and remodeling before and 3 years after surgical treatment

In 19 patients with primary hyperparathyroidism (PHPT) (14 women and 5 men; age 53 +/- 11 years, range 29-69 years), bone densitometry, biochemical markers of bone turnover, and iliac crest bone biopsies were obtained before and 3 years after successful surgical treatment. A significant increase in bone mineral content (BMC) was observed in both the lumbar spine (p < 0.001) and the proximal part of the distal forearm (p < 0.001), whereas the increase in BMC in the femoral neck was insignificant. Biochemical markers of bone formation (serum alkaline phosphatase, serum bone alkaline phosphatase and serum osteocalcin) and resorption (serum pyridinoline cross-linked telopeptide of type I collagen and urine N-telopeptide of type I collagen) all decreased following treatment. In cortical bone, relative cortical width increased following surgery (p < 0.05) and cortical porosity decreased (p < 0.01). No changes were observed in core width or cortical width. In cancellous bone, no significant changes were observed in any of the measured structural parameters. However, significant reductions in the extent of osteoid- (p < 0.01) and tetracycline-labeled surfaces (p < 0.001), and in bone formation rate (p < 0.001) and activation frequency (p < 0.001), were found. The numerical decrease in the extent of eroded surfaces did not reach significance (p = 0.057). No changes were observed in mineral appositional rate and adjusted appositional rate. The amount of bone resorbed (expressed as the resorption depth) and the amount of bone reformed (expressed as wall thickness) per remodeling cycle seemed unaffected by the treatment. Consequently, no effect on bone balance per remodeling cycle could be detected. The present study of PHPT patients showed that, within 3 years after surgery, BMC of both cancellous and cortical bone areas had increased. At the same time, bone turnover decreased markedly, as judged from biochemical as well as histomorphometric data, but no changes were seen in trabecular bone structure. In cortical bone, the relative cortical width increased and the cortical porosity decreased.

Parathyroid hormone enhances fracture healing. A preliminary report

This investigation tested the hypothesis that daily parenterally administered parathyroid hormone (1-34) improves fracture healing. Twenty, 3-month-old, male Sprague Dawley rats weighing approximately 400 g each, underwent the production of closed, unilateral mid-diaphyseal femoral fractures. Animals were divided into two groups of 10; the animals received either a daily subcutaneous injection of delivery vehicle (0.9% saline) or 80 micrograms/kg parathyroid hormone. On Day 21 after fracture the animals were euthanized, the femurs were removed and subjected to biomechanical testing, bone densitometry (dual energy x-ray absorptiometry, peripheral quantitative computed tomography), and histologic examination. Treatment with parathyroid hormone resulted in statistically significant increases in callus area and strength. Histologic examination of the calluses showed an increase in the amount of new bone formed. No differences were observed in the weights of the animals or the sizes of the bones. Values obtained using dual energy x-ray absorptiometry and peripheral quantitative computed tomography indicate an increase in density in the parathyroid hormone treated fractures consistent with the histologic appearance and the findings of increased strength, although these bone density changes did not achieve statistical significance. These results suggest that parenterally administered parathyroid hormone (1-34) may enhance or accelerate normal fracture healing and support the concept that this hormone be tested clinically as a systemic treatment for fractures that are slow to heal.

Intermittent parathyroid hormone (1-34) treatment increases callus formation and mechanical strength of healing rat fractures

The influence of intermittent parathyroid hormone (PTH(1-34)) administration on callus formation and mechanical strength of tibial fractures in rats was investigated after 20 and 40 days of healing. A dose of 60 microg of PTH(1-34)/kg/day and 200 microg of PTH(1-34)/kg/day, respectively, was administered during the entire periods of healing, and control animals with fractures were given vehicle. The dose of 200 microg of PTH(1-34)/kg/day increased the ultimate load and the external callus volume of the fractures by 75% and 99%, respectively, after 20 days of healing and by 175% and 72%, respectively, after 40 days of healing. The dose of 60 microg of PTH(1-34)/kg/day did not influence either ultimate load or external callus volume of the fractures after 20 days of healing, but the ultimate load was increased by 132% and the external callus volume was increased by 42% after 40 days of healing. During the healing period, the callus bone mineral content (BMC) increased in all groups. After 40 days of healing, the callus BMC was increased by 108% in the 200 microg of PTH(1-34)/kg/day group and by 76% in the 60 microg of PTH(1-34)/kg/day group. Both doses of PTH(1-34) steadily augmented the contralateral intact tibia BMC (20 days and 40 days: 60 microg of PTH (1-34)/kg/day 9% and 19%, respectively; 200 microg of PTH (1-34)/kg/day 12% and 27%, respectively) and bone mineral density (20 days and 40 days: 60 microg of PTH(1-34)/kg/day 11% and 12%, respectively; 200 microg of PTH(1-34)/kg/day 11% and 15%, respectively).

Parathyroid hormone is not a key hormone in the rapid minute-to-minute regulation of plasma Ca2+ homeostasis in rats

BACKGROUND

The role of parathyroid hormone (PTH) in the rapid minute-to-minute regulation of plasma Ca2+ (p-Ca2+) was studied in vivo in rats.

MATERIALS AND METHODS

The rapid calcaemic response to exogenous rat PTH1-34 (16 microg) was examined in normal rats, and the long-term calcaemic response was examined in parathyroidectomized (PTX) rats receiving PTH1-34 for 24 h at 0.2, 0. 4 and 0.8 microg h-1. Acute hypocalcaemia was induced by EGTA for 30 min, and then the rapid recovery of p-Ca2+ was studied for 130 min in normal rats, 24 h after PTX and in PTX rats infused with exogenous rat PTH1-34. The dynamics of the rapid recovery of p-Ca2+ was studied at two additional doses of EGTA.

RESULTS

No rapid calcaemic response was observed in the first 60 min after administration of PTH and no hypocalcaemia was seen for 2 h after acute PTX. This slow effect of PTH suggests that PTH might not be responsible for maintaining the stable p-Ca2+ on a rapid minute-to-minute basis. EGTA induced acute hypocalcaemia in both normal and PTX rats (P < 0.01). In both groups a rapid and similar increase in p-Ca2+ took place 10 min after discontinuing EGTA (P < 0. 05). Within 60 min, p-Ca2+ increased further, independently of the presence of PTH. Infusion of PTH to PTX rats did not affect the rapid recovery of p-Ca2+ (P < 0.05) from EGTA induced hypocalcaemia.

CONCLUSION

PTH is not a key hormone in the rapid recovery of p-Ca2+ after induction of hypocalcaemia, but might, however, set the long-term levels of p-Ca2+ maintained by mammalian organisms. The involvement of an as yet unknown factor in the rapid regulation of p-Ca2+ is suggested.

Withdrawal of parathyroid hormone treatment causes rapid resorption of newly formed vertebral cancellous and endocortical bone in old rats

When administered intermittently, parathyroid hormone (PTH) is a strong anabolic agent, increasing both bone mass and bone mechanical strength and competence. This study evaluates the fate of PTH-induced bone in vertebral bodies after withdrawal of PTH treatment in normal old rats. Sixty-seven 21-month-old male rats were treated with 62 microg/kg/day PTH(1-34) for 8 weeks, followed by saline or bisphosphonate (risedronate, 5 microg/kg twice a week) for another 8 weeks. The rats were scanned by dual-energy X-ray absorptiometry at intervals. The bone mineral content (BMC) of L2-5 increased by 33% during the PTH treatment. The BMC started decreasing shortly after withdrawal of PTH and continued to decline during the 8 weeks after withdrawal of PTH. Risedronate, however, prevented this decrease in BMC. All rats were labeled with tetracycline and calcein 3 weeks and 1 week before the cessation of PTH therapy. In the cancellous bone, PTH increased the mineralized surface: 32.9% +/- 2.8% (mean +/- standard error of the mean) vs. controls 12.0% +/- 1.5%, the mineral appositional rate (0.65 +/- 0.02 to 0.88 +/- 0.06 microm/day), and the cancellous bone volume (BV/TV: 14.5% +/- 0.7% to 27.5% +/- 1.7%). Withdrawal of PTH induced a fast and pronounced bone resorption, decreasing both the extent of the fluorochrome labels and the cancellous bone volume to control values. Risedronate prevented this resorption. In the cortical bone of the vertebral shell, PTH induced large increases in the endocortical mineralized surface, mineral appositional rate, and cortical area. The endocortical fluorochrome labels were, however, resorbed after withdrawal of PTH. Risedronate maintained both the fluorochrome labels and the cortical area. At the periosteum, the response to PTH was less evident, however, and hardly any labeling was seen at the periosteum facing the vertebral canal either in the controls or in the PTH-treated rats. The compressive strength of the vertebral body specimens increased with PTH treatment whether measured in newtons (317 +/- 23 to 623 +/- 54 N), normalized to cross-sectional area (23.0 +/- 1.4 to 44.7 +/- 2.5 N/mm2), or to ash content per millimeter height (58 +/- 2 to 76 +/- 2 N x mm/mg). Withdrawal of PTH decreased the compressive strength and competence to control values. Risedronate, however, maintained the PTH-induced mechanical strength and competence. The study discloses that even in very old rats withdrawal of PTH treatment causes a rapid and pronounced decline in the bone mass deposited during PTH treatment; treatment with risedronate can, however, maintain the PTH-induced bone properties in the axial skeleton of old rats.

Bone responses at various skeletal sites to human parathyroid hormone in ovariectomized rats: effects of long-term administration, withdrawal, and readministration

This study was undertaken to examine bone responses to human parathyroid hormone (hPTH) at various skeletal sites. Forty 6-month-old female Wistar rats were divided into four groups, and bilateral ovariectomy (ovx) was performed in three of the four groups (n=30). The other group (n=10) received sham surgery (sham). Four weeks after the ovx, hPTH(1-34) administration was started. The ovx rats received 5 microg/kg per day of PTH (PTH-5; n=10), 10 microg/kg per day of PTH (PTH-10; n=10), or vehicle (PTH-v; n=10), three times a week for 24 weeks. Thereafter, PTH was withdrawn for 16 weeks followed by readministration at the same dosage for 8 weeks. The bone mineral content (BMC) at the whole skeleton and the bone mineral density (BMD) at the lumbar vertebrae, caudal vertebrae, distal femur, diaphysis of the femur, proximal tibia, and skull were longitudinally measured by dual-energy x-ray absorptiometry (DXA) at 4-week intervals during the experimental period. Thirteen rats that died during the experimental period were excluded from the analysis. As a result, the whole skeleton showed an increase in BMC during the PTH administration, whereas no withdrawal or readministration effects were observed. The metaphysis showed a highly sensitive bone response, while the lumbar vertebrae and diaphysis showed a moderate magnitude of changes in bone mass during the PTH administration. The skull and the caudal vertebrae did not show sensitive responses to PTH. After withdrawal, the BMD was markedly decreased at the sites that showed marked increases in BMD after PTH administration. The PTH readministration increased the BMD again at the sites that showed sensitive responses after the initial administration. Strength tests were also performed when the readministration was completed. The ultimate loads for the femur and vertebral body in the PTH-treated groups were significantly higher than those in the vehicle-treated group. In conclusion, the response to PTH in ovx rats varied among skeletal sites; withdrawal-related decreases were marked at the sites showing marked increases in bone mass related to PTH administration, and PTH readministration may be sufficiently effective.

Growth hormone and mild exercise in combination markedly enhance cortical bone formation and strength in old rats

The effects of a combination of mild exercise and GH injections on bone were studied in old female rats. Biosynthetic human GH, 2.7 mg/kg/day, was injected s.c. for 73 days. Exercised rats ran 8 m/min on a treadmill for 1 h/day. All rats (age 21 months old) were labeled with a tetracycline injection 56 days and a calcein injection 11 days before killing. The GH injections resulted in an 11-fold increase in femoral middiaphyseal bone formation rate and a 12% increase in cross-sectional area compared with the saline-injected group. The mild exercise doubled the mineralizing surface but did not influence the bone formation rate significantly. The combination of GH injections plus exercise, however, resulted in a further increase of 39% in bone formation rate, primarily at the anterolateral aspects, and an increase of 5% in cross-sectional area compared with the group injected with GH only. The femur ultimate breaking load was increased by 37% and the stiffness by 42% in the group injected with GH compared with the saline-injected group. Exercise alone did not influence the femur mechanical properties. The combination of GH injections plus exercise induced a 4% further increase in ultimate breaking load and 7% further increase in stiffness compared with the group injected with GH alone. The GH injections induced a 117% increase in serum insulin-like growth factor I. The GH-insulin-like growth factor I axis stimulates recruitment of osteoblast precursor cells, resulting in increased bone formation at the periosteal surface. GH injections and mild excercise in combination modulate and increase further the formation and strength of cortical bone in old female rats.

Early effects of short-term parathyroid hormone administration on bone mass, mineral content, and strength in female rats

The present study was designed to examine the metabolic changes and early effects of short-term parathyroid hormone (PTH) treatment on bone mass, mineral content, and strength. Forty-eight 10-week-old intact female rats were randomized into six groups. The three PTH-treated groups were subcutaneously given PTH 50 microg/kg body weight daily for 5 (PTH5), 10 (PTH10), or 15 (PTH15) days. The three respective time control groups (C5, C10, and C15) were injected with saline solution. In serum, total calcium, alkaline phosphatase, and insulin-like growth factor-I (IGF-I) were analyzed. Bone mass was estimated with wet and dry weights of the femora and hydroxyproline content of the tibiae. Ash weight and calcium, magnesium, and phosphorus contents (determined by AAS) were used to measure femoral mineral content. Bone mineral density (BMD) of the femora was measured using dual-energy X-ray absorptiometry (DXA) and the biomechanical properties of the femoral neck were tested. After 5 days of PTH treatment, some trends of the anabolic actions of PTH could be observed, but there was no significant effect on relevant parameters of bone formation. After 10 days, bone mass, mineral content (assessed by ash weight), and BMD of the PTH-treated rats were significantly increased compared with those of controls. The relative femoral magnesium content of the PTH-treated animals was significantly higher than that of controls. After 15 days, the length of the femora, bone mass, mineral content, BMD, and the width of the femoral neck were increased, and its biomechanical properties were significantly improved in PTH-treated rats compared with the respective time control group. PTH treatment significantly increased circulating alkaline phosphatase and decreased systemic IGF-I concentrations throughout the study. In conclusion, intermittent PTH administration to still growing female rats is anabolic in bone with significant effects already taking place after 10 days of treatment. The effects of PTH consisted of: (1) an increase in bone mass and mineral content with a transient augmentation of relative magnesium content; and (2) improved width and mechanical properties of the femoral neck after 15 days of treatment. These effects are accompanied by an increase in longitudinal bone growth. They are unlikely related to any changes in systemic IGF-I concentrations.

Growth hormone and bone

It is well known that GH is important in the regulation of longitudinal bone growth. Its role in the regulation of bone metabolism in man has not been understood until recently. Several in vivo and in vitro studies have demonstrated that GH is important in the regulation of both bone formation and bone resorption. In Figure 9 a simplified model for the cellular effects of GH in the regulation of bone remodeling is presented (Fig. 9). GH increases bone formation in two ways: via a direct interaction with GHRs on osteoblasts and via an induction of endocrine and autocrine/paracrine IGF-I. It is difficult to say how much of the GH effect is mediated by IGFs and how much is IGF-independent. GH treatment also results in increased bone resorption. It is still unknown whether osteoclasts express functional GHRs, but recent in vitro studies indicate that GH regulates osteoclast formation in bone marrow cultures. Possible modulations of the GH/IGF axis by glucocorticoids and estrogens are also included in Fig. 9. GH deficiency results in a decreased bone mass in both man and experimental animals. Long-term treatment (> 18 months) of GHD patients with GH results in an increased bone mass. GH treatment also increases bone mass and the total mechanical strength of bones in rats with a normal GH secretion. Recent clinical studies demonstrate that GH treatment of patients with normal GH secretion increases biochemical markers for both bone formation and bone resorption. Because of the short duration of GH treatment in man with normal GH secretion, the effect on bone mass is still inconclusive. Interestingly, GH treatment to GHD adults initially results in increased bone resorption with an increased number of bone-remodeling units and more newly produced unmineralized bone, resulting in an apparent low or unchanged bone mass. However, GH treatment for more than 18 months gives increased bone formation and bone mineralization of newly produced bone and a concomitant increase in bone mass as determined with DEXA. Thus, the action of GH on bone metabolism in GHD adults is 2-fold: it stimulates both bone resorption and bone formation. We therefore propose "the biphasic model" of GH action in bone remodeling (Fig. 10). According to this model, GH initially increases bone resorption with a concomitant bone loss that is followed by a phase of increased bone formation. After the moment when bone formation is stimulated more than bone resorption (transition point), bone mass is increased. However, a net gain of bone mass caused by GH may take some time as the initial decrease in bone mass must first be replaced (Fig. 10). When all clinical studies of GH treatment of GHD adults are taken into account, it appears that the "transition point" occurs after approximately 6 months and that a net increase of bone mass will be seen after 12-18 months of GH treatment. It should be emphasized that the biphasic model of GH action in bone remodeling is based on findings in GHD adults. It remains to be clarified whether or not it is valid for subjects with normal GH secretion. A treatment intended to increase the effects of GH/IGF-I axis on bone metabolism might include: 1) GH, 2) IGF, 3) other hormones/factors increasing the local IGF-I production in bone, and 4) GH-releasing factors. Other hormones/growth factors increasing local IGF may be important but are not discussed in this article. IGF-I has been shown to increase bone mass in animal models and biochemical markers in humans. However, no effect on bone mass has yet been presented in humans. Because the financial cost for GH treatment is high it has been suggested that GH-releasing factors might be used to stimulate the GH/IGF-I axis. The advantage of GH-releasing factors over GH is that some of them can be administered orally and that they may induce a more physiological GH secretion. (ABSTRACT TRUNCATED)