Intermittent Parathyroid Hormone Treatment Research Articles

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 μg/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. © 2003 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 61:471-480, 2003

Anabolic action of parathyroid hormone on cortical and cancellous bone differs between axial and appendicular skeletal sites in mice

The mouse is being increasingly used to study the anabolic action of parathyroid hormone (PTH) on the skeleton. The efficacy of intermittent PTH treatment on bone varies widely among tested strains of mice with differences in peak bone mass and structure. We have therefore examined the responses of skeletal sites with high or low cancellous bone mass to PTH treatment in a single strain with genetically low bone mass. Mature C57BL/6 mice were ovariectomized (ovx) or sham operated and, after 4 weeks, treated with PTH(1–34) (40 μg/kg/day, 5 days/week sc) or vehicle for 3 or 7 weeks. Two doses of fluorescent labels were given to the animals 9 and 3 days before euthanasia. Histomorphometry was performed on sections of the proximal tibia, tibial diaphysis, and vertebral body. The results indicate that 4 to 11 weeks of ovx induced a ∼44% loss of cancellous bone in the proximal tibia and a ∼25% loss of cancellous bone in the vertebra with impaired trabecular architecture and high bone turnover. In the intact animals, PTH increased cancellous bone volume to a greater extent in the vertebral body than in the proximal tibia, a site with lower cancellous bone volume at the outset. In the ovx mice, PTH increased cancellous bone volume to a greater extent in the vertebral body, a site displaying moderate cancellous bone loss, than in the proximal tibia, a site with severe cancellous bone loss. Conversely, the treatment added a little cortical bone to the tibia, a highly loaded site, but did not significantly increase cortical width of the vertebral body, a less loaded site. We conclude that, for intermittent PTH treatment to be maximally effective, there must be an adequate number of trabeculae present at the beginning of treatment, regardless of estrogen status. Our results also support an interaction between PTH anabolic action and mechanical loading.

The cellular and clinical parameters of anabolic therapy for osteoporosis.

A new era in the management of osteoporosis began with the recent approval of parathyroid hormone (PTH) for the treatment of postmenopausal osteoporosis. This peptide holds promise as the first in a series of anabolic growth factors that promote bone formation, enhance mineralization,and stimulate periosteal growth, yet exert relatively limited effects on bone resorption. Daily intermittent PTH treatment for postmenopausal women results in a dramatic increase in bone mineral density (BMD) (i.e., 10-15% improvement in spine BMD) and a significant decline (i.e., a risk reduction of nearly 2/3) in the occurrence of fragility fractures. The mechanism of PTH's anabolic action on the skeleton is complex and involves multiple pathways linked to common signaling peptides that affect gene transcription in osteoblasts. One fascinating aspect of PTH, both at the clinical and molecular level, is the relationship between the frequency of PTH treatment and the bone response. Depending on the type of PTH exposure, there can be an anabolic or catabolic skeletal phenotype that can then be recapitulated by certain in vivo and in vitro model systems. Transcriptional events following ligand binding to the PTH/PTHrP1 receptor have been studied, with particular interest in target genes such as IGF-I that can regulate both bone formation and resorption. Novel in vivo strategies, including temporal and conditional mutagenesis, will almost certainly lead to newer therapeutic paradigms for the treatment of postmenopausal osteoporosis.

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.

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 μg/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 μg/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.

In vivo comparison of activated protein-1 gene activation in response to human parathyroid hormone (hPTH)(1–34) and hPTH(1–84) in the distal femur metaphyses of young mice

Intermittent parathyroid hormone (PTH) treatment increases bone mass in humans and animals. Although intact human PTH has 84 amino acids, the N-terminal 31 to 38 amino acids are sufficient for bone anabolic activity in vivo. Prior studies have evaluated hPTH(1–34) and hPTH(1–84) with respect to bone mass increase and quality, but there have been no in vivo comparisons of dose-dependent molecular responses. After confirming that young male BALB/c mice respond to daily PTH with increased bone mass, we profiled the steady-state mRNA levels of activating protein-1 (AP-1) genes regulated by hPTH(1–34) and hPTH(1–84) at doses ranging from 0 to 19.4 nmol/kg in the distal femur metaphyses. We selected AP-1 genes, which include jun and fos, as they play a fundamental role mediating signals for proliferation, differentiation, and apoptosis in cells of different origins, including bone, and are known to be regulated by PTH. Human PTH(1–34) and hPTH(1–84) increased steady-state mRNA expression of c- jun, junB, c- fos, and fra-2 in an equivalent dose- and time-dependent manner. Expression of fosB or fra-1 was not detected with either peptide. When averaged across dose and time, responses to hPTH(1–34) and hPTH(1–84) were not significantly different from each other. Expression of c- jun, junB, and c- fos peaked 30 minutes after the injection while fra-2 expression peaked 30 minutes later. All AP-1 genes stimulated by PTH returned to the levels of vehicle treated controls by 3 h after injection. The expression level of junD, which was abundant in the distal metaphysis, was not altered by either peptide. No change in magnitude was observed after 1, 3, or 7 days of once-daily subcutaneous treatment of either peptide. When individual comparisons for each dose between peptides were made, the minimum effective dose necessary to stimulate a significant increase in c- fos and junB expression was equivalent for both peptides. The minimum effective dose for hPTH(1–34) was at least tenfold lower than hPTH(1–84) in stimulating c- jun and fra-2 expression. Area under the curve for the highest dose (19.4 nmol/kg) of either peptide showed no significant differences in the expression of any of the genes. In conclusion, in young mice given once-daily subcutaneous injections up to 7 days, hPTH(1–34) and hPTH(1–84) induced equivalent responses by time and dose in the selected AP-1 genes. These data on molecular regulation in mouse bone confirm and extend prior data from rat studies showing equivalence on bone mass at equimolar doses.

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).

Intermittent parathyroid hormone treatment can promote linear growth in the ovariectomized growing rat.

To compare the effect of intermittent parathyroid hormone (PTH) treatment with that of estrogen treatment on epiphyseal growth in ovariectomized rats, 46 Sprague-Dawley female rats aged 9-10 weeks (about 200-220 g) were either ovariectomized or sham operated. From 6 weeks after ovariectomy (ovx), rats were daily injected with subcutaneous human recombinant PTH (1-84)-dosed 30 micrograms/kg (the low dose PTH-treated group) or 300 micrograms/kg (the high dose PTH-treated group), 17 beta-estradiol (the 17 beta-estradiol-treated group, 30 micrograms/kg) or vehicle (the ovx-alone group), 5 times a week for 4 weeks. The decalcified sections of the distal femoral epiphyseal plate were analyzed on light microscopy after H&E stain, and the lengths of the zones of proliferation, maturing and hypertrophic chondrocytes were measured. The length of the growth plate, the zone of proliferation and the zone of hypertrophic chondrocyte in the ovx-alone group were significantly shorter than those of the sham-operated group. The treatment of 17 beta-estradiol speeded up the differentiation of cells from proliferating chondrocytes to maturing and hypertrophic chondrocytes even though the length of the growth plate was comparable to that of the sham-operated group. Both low and high dose PTH treatments increased the length of the growth plate, and those lengths were comparable to that of the sham-operated group. The fractions of proliferating, maturing and hypertrophic zone in the low dose PTH-treated group were also comparable to those of the sham-operated group. However, high dose PTH treatment slowed down the differentiation of cells from proliferating chondrocytes to maturing and hypertrophic chondrocytes to a greater extent, and therefore the fraction of proliferating chondrocytes of the high dose PTH-treated group was larger than that of the low dose PTH-treated group (73.8 +/- 1.8 Vs 63.3 +/- 1.3%, p < 0.005). From these results, we showed that intermittent PTH treatment could promote linear growth in the ovariectomized growing rat. We propose that PTH may be an alternative drug candidate for promoting linear growth of long bones without the risk for early closure of the growth plate.

Intermittent parathyroid hormone administration stimulates bone formation in the mandibles of aged ovariectomized rats.

Intermittent administration of parathyroid hormone (PTH) is known to stimulate bone formation in many skeletal sites and is being investigated as a possible therapeutic agent for the treatment of osteopenic conditions, including post-menopausal osteoporosis. The purpose of this study was to determine the ability of PTH to stimulate bone formation in the mandibles of aged ovariectomized (Ovx) rats, and the results are compared with a site in the appendicular skeleton (humerus). The Ovx rat is a useful model of estrogen deficiency, replicating many aspects of post-menopausal osteoporosis. Female rats were ovariectomized or sham-operated, and one year later a group of the ovariectomized rats was treated with the 1-34 fragment of human PTH daily, five days a week for 10 weeks. During the experiment, the animals were given fluorochrome bone markers for histomorphometry. More than one year after ovariectomy or sham surgery, there were few differences in the histomorphometric indices of bone formation in the humerus or mandible. PTH treatment had no effect on dentin formation, measured in the mandibular incisor; however, most indices of bone formation-including the double-labeled surface, mineralizing surface, mineral appositional rate, new bone area, and surface-referent bone formation rates-were substantially greater in the PTH-treated group compared with both the Ovx and the Sham controls measured at the periosteal and endocortical surfaces of the humerus and the periosteal and cancellous bone surfaces of the mandible. In addition, bone formation at the alveolar crest, particularly on the buccal side, was greater in the PTH-treated group. The results from this study demonstrate that systemic intermittent PTH treatment stimulates bone formation in the mandibles in aged, estrogen-deficient animals.

Proliferating cells in the primary spongiosa express osteoblastic phenotype in vitro

We have shown that intermittent parathyroid hormone (PTH) treatment targets proliferating cells in the primary spogiosa of trabecular bone of young rats, resulting in an increased number of osteoblasts. To further characterize these proliferating osteoprogenitor cells, bromodeoxyuridine (BrdUrd) incorporated in vivo, was used as a marker to identify and isolate cells for in vitro studies. Proliferating cells were labeled in vivo in young rats with BrdUrd and 24 h later were isolated by trypsinization of sections of the primary spongiosa of the distal femur metaphysis. Within 12 h of isolation, BrdUrd+ cells formed distinct foci containing 20–500 cells with fibroblast morphology. Stimulation of proliferation as determined by [ 3H]-thymidine incorporation was observed for these cells in response to fetal bovine serum, platelet derived growth factor, and transforming growth factor β-1. Neither insulin-like growth factor-1 (IGF-1) nor insulin stimulated proliferation PTH (1–34) and dexamethasone inhibited proliferation. The effects of PTH and dexamethasone were additive. Cells expressed the osteoblast phenotype as evidenced by synthesis of type I collagen, expression of high alkaline phosphatase activity, and production of increased intracellular cAMP in response to PTH (1–34). Confluent cell aggregates spontaneously formed mineralized nodules within 4–7 days, in the absence of inducers. These observations suggest that the primary spongiosa cells recapitulates the differentiation process in vitro in an accelerated fashion and may serve as a useful model to study osteoblast differentiation.

Intermittent parathyroid hormone treatment increases osteoblast number, steady state messenger ribonucleic acid levels for osteocalcin, and bone formation in tibial metaphysis of hypophysectomized female rats

Intermittent parathyroid hormone treatment increases osteoblast number, steady state messenger ribonucleic acid levels for osteocalcin, and bone formation in tibial metaphysis of hypophysectomized female rats

Intermittent parathyroid hormone treatment increases osteoblast number, steady state messenger ribonucleic acid levels for osteocalcin, and bone formation in tibial metaphysis of hypophysectomized female rats.

The effects of GH and PTH on cancellous histomorphometry were determined in the proximal tibial metaphysis of hypophysectomized (HYPOX) sexually mature female rats. HYPOX resulted in uterine atrophy and a loss in body weight. Longitudinal bone growth ceased and bone formation was greatly reduced. There were decreases in cancellous bone area, trabecular number, and trabecular thickness. Intermittent treatment with GH did not influence uterine weight in HYPOX rats. However, GH resulted in resumption of whole body weight gain, as well as maintenance of normal longitudinal bone growth. Additionally, GH partially maintained bone formation in HY POX rats and did not have a significant effect on steady state messenger RNA levels for osteocalcin. Intermittent treatment with PTH had no effect on whole body weight gain, uterine weight, or longitudinal bone growth. In contrast, PTH increased bone formation compared with the baseline, HYPOX, and GH-treated HYPOX rats, and dramatically increased osteocalcin messenger RNA levels compared with the latter two groups. The increased bone formation was primarily due to an increase in osteoblast number; the mineral apposition rate, an index of osteoblast activity, was increased compared with control and GH-treated rats but not compared with baseline values. Interestingly, neither treatment influenced indices of bone resorption.

Human parathyroid hormone (1–34) and (1–84) increase the mechanical strength and thickness of cortical bone in rats

An anabolic effect on bone of intermittent parathyroid hormone (PTH) treatment has been found in patients with osteoporosis and also in experimental animals. Controversies exist, however, about whether the positive effect on the trabecular bone balance occurs at the expense of the cortical bone. We examined the biomechanical quality of cortical bone after intermittent treatment with different doses of PTH and, furthermore, compared the effects of PTH-(1-34) and PTH-(1-84). Groups of rats were treated with biosynthetic human PTH-(1-34) or PTH-(1-84), 1.1, 3.3, 10, or 30 nmol/kg/day for 30 days. No changes in the body weights and no changes in the lengths of the femora were observed after the PTH treatments. The biomechanical properties were analyzed by means of a materials-testing machine. A dose-related increase in the bending strength and stiffness of the femora was found, and this increase in mechanical strength corresponds with a 9-12% increase in the cross-sectional area of the femoral diaphyses. The deflection capability and energy absorption were not influenced by any of the PTH treatments. No differences were found between the effects of PTH-(1-34) or PTH-(1-84) on the biomechanical properties of the femora. Consequently, intermittent treatment with biosynthetic PTH-(1-34) or PTH-(1-84) increased the formation of cortical bone, and the biomechanical competence of the femora was found to be preserved.