Low-dose Parathyroid Hormone Research Articles

Cortical thickness adaptation to combined mechanical loading and parathyroid hormone treatments is site specific and synergistic in the mouse tibia model

In this study, we aimed to quantify the localised effects of mechanical loading (ML), low (20 μg/kg/day), moderate (40 μg/kg/day) or high (80 μg/kg/day) dosages of parathyroid hormone (PTH), and combined (PTHML) treatments on cortical bone adaptation in healthy 19-week old female C57BL/6 mice. To this end, we utilise a previously reported image analysis algorithm on μCT data of the mouse tibia published by Sugiyama et al. (2008) to measure changes in cortical area, marrow cavity area and local cortical thickness measures (ΔCt.Ar, ΔMa.Ar, ΔCt.Th respectively), evaluated at two cross-sections within the mouse tibia (proximal-middle (37 %) and middle (50 %)), and are compared to a superposed summation (P + M) of individual treatments to determine the effectiveness of combining treatments in vivo. ΔCt.Ar analysis revealed a non-linear, synergistic interactions between PTH and ML in the 37 % cross-section that saturates at higher PTH dosages, whereas the 50 % cross-section experiences an approximately linear, additive adaptation response. This coincided with an increase in ΔMa.Ar (indicating resorption of the endosteal surface), which was only counteracted by combined high dose PTH with ML in the middle cross-section. Regional analysis of ΔCt.Th changes reveal localised cortical thinning in response to low dose PTH treatment in the posteromedial region of the middle cross-section, signifying that PTH does not provide a homogeneous adaptation response around the cortical perimeter. We observe a synergistic response in the proximal-middle cross-section, with regions of compressive strain experiencing the greatest adaptation response to PTHML treatments, (peak ΔCt.Th of 189.32, 213.78 and 239.30 μm for low, moderate and high PTHML groups respectively). In contrast, PTHML treatments in the middle cross-section show a similar response to the superposed P + M group, with the exception of the combined high dose PTHML treatment which shows a synergistic interaction. These analyses suggest that, in mice, adding mechanical loading to PTH treatments leads to region specific bone responses; synergism of PTHML is only achieved in some regions experiencing high loading, while other regions respond additively to this combined treatment.

Dose-dependent effects of pharmaceutical treatments on bone matrix properties in ovariectomized rats

As both anabolic and anti-catabolic osteoporosis drugs affect bone formation and resorption processes, they may contribute to bone's overall mechanical behavior by altering the quality of the bone matrix. We used an ovariectomized rat model and a novel fracture mechanics approach to investigate whether treatment with an anabolic (parathyroid hormone) or anti-catabolic (alendronate) osteoporosis drugs will alter the organic and mineral matrix components and consequently cortical bone fracture toughness. Ovariectomized (at 5 months age) rats were treated with either parathyroid hormone or alendronate at low and high doses for 6 months (age 6–12 months). Specifically, treatment groups included untreated ovariectomized controls (n = 9), high-dose alendronate (n = 10), low-dose alendronate (n = 9), high-dose parathyroid hormone (n = 10), and low-dose parathyroid hormone (n = 9). After euthanasia, cortical microbeams from the lateral quadrant were extracted, notched, and tested in 3-point bending to measure fracture toughness. Portions of the bone were used to measure changes in the 1) organic matrix through quantification of advanced glycation end-products (AGEs) and non-collagenous proteins, and 2) mineral matrix through assessment of mineral crystallinity. Compared to the ovariectomized group, rats treated with high doses of parathyroid hormone and alendronate had significantly increased cortical bone fracture toughness, which corresponded primarily to increased non-collagenous proteins while there was no change in AGEs. Additionally, low-dose PTH treatment increased matrix crystallinity and decreased AGE levels. In summary, ovariectomized rats treated with pharmaceutical drugs had increased non-collagenous matrix proteins and improved fracture toughness compared to controls. Further investigation is required for different doses and longer treatment periods.

Intra-articular low-dose parathyroid hormone (1-34) improves mobility and articular cartilage quality in a preclinical age-related knee osteoarthritis model.

AimsOsteoarthritis (OA) is prevalent among the elderly and incurable. Intra-articular parathyroid hormone (PTH) ameliorated OA in papain-induced and anterior cruciate ligament transection-induced OA models; therefore, we hypothesized that PTH improved OA in a preclinical age-related OA model.MethodsGuinea pigs aged between six and seven months of age were randomized into control or treatment groups. Three- or four-month-old guinea pigs served as the young control group. The knees were administered 40 μl intra-articular injections of 10 nM PTH or vehicle once a week for three months. Their endurance as determined from time on the treadmill was evaluated before kill. Their tibial plateaus were analyzed using microcalculated tomography (μCT) and histological studies.ResultsPTH increased the endurance on the treadmill test, preserved glycosaminoglycans, and reduced Osteoarthritis Research Society International score and chondrocyte apoptosis rate. No difference was observed in the subchondral plate bone density or metaphyseal trabecular bone volume and bone morphogenetic 2 protein staining.ConclusionSubchondral bone is crucial in the initiation and progression of OA. Although previous studies have shown that subcutaneous PTH alleviates knee OA by improving subchondral and metaphyseal bone mass, we demonstrated that intra-articular PTH injections improved spontaneous OA by directly affecting the cartilage rather than the subchondral or metaphyseal bone in a preclinical age-related OA model.Cite this article: Bone Joint Res 2021;10(8):514–525.

The Effects of High-Dose Parathyroid Hormone Treatment on Fusion Outcomes in a Rabbit Model of Posterolateral Lumbar Spinal Fusion Alone and in Combination with Bone Morphogenetic Protein 2 Treatment

Parathyroid hormone (PTH) (1-34) treatment reduces fracture risk in osteoporotic patients. Previously, we demonstrated in a rabbit model that low-dose PTH treatment resulted in increased fusion mass volume. As effects of PTH on bone are dose-dependent, we aimed to evaluate whether increasing dosage of PTH increases both volume and biomechanical stiffness of the resulting fusion masses and/or exhibits synergistic effects with low-dose bone morphogenetic protein 2 (BMP-2). Posterolateral lumbar spinal fusion surgery was performed on 60 New Zealand White rabbits divided into 6 experimental groups: iliac crest autograft alone, autograft plus 20 μg/kg/day PTH, autograft plus 40 μg/kg/day PTH, BMP-2 alone, BMP-2 plus 20 μg/kg/day PTH, and BMP-2 plus 40 μg/kg PTH. Fusion was assessed at postoperative week 6 via manual palpation, volumetric computed tomography analysis, and 4-point bending biomechanical testing. All groups treated with BMP-2 fused. Increasing doses of PTH resulted in increased fusion mass volume compared with autograft alone. Autograft plus 40 μg/kg/day PTH yielded fusion mass volumes comparable to BMP-2. When the autograft groups were considered alone, increased mechanical stiffness was observed only in the 20 μg/kg/day group. No significant stiffness differences were observed between BMP-2 groups. Treatment with the highest dose of PTH resulted in fusion mass volumes similar to those obtained with BMP-2. When the autograft groups were considered alone, significant increases in mechanical stiffness were observed at a dosage of 20 μg/kg/day, suggesting there may be an optimal dose of PTH in the rabbit model. Effects of BMP-2 on fusion were dominant.

Effects of Intermittent Low-Dose Parathyroid Hormone Treatment on Rapid Mandibular Distraction Osteogenesis in Rabbits

To determine whether low-dose recombinant human parathyroid hormone (rhPTH) would have a beneficial effect on regenerate healing and surrounding bone in a rabbit model of rapid mandibular distraction osteogenesis (DO). Twenty-eight rabbits underwent unilateral mandibular lengthening at a rapid rate of 2mm per day for 5days. From the first day of DO, the experimental group received daily subcutaneous injections of rhPTH 10μg/kg for 30days and the control group received the same volume of saline (n=14 in each group). At 6weeks after completion of DO, the distracted callus was examined by micro-computed tomography (micro-CT), histology, and the 3-point bending test. Moreover, bone mineral density of the anterior pin region was evaluated by dual-energy x-ray absorptiometry. Under rapid distraction, poor bone healing was observed in the distracted callus from the control group. In contrast, more mature and abundant bone formation was found in the distracted callus from the experimental group by histologic and micro-CT examinations. Quantitatively, the PTH-treated animals had superior parameters in bone volume fraction, trabecular number, and trabecular thickness and mechanical properties compared with controls (P<.05). Bone mineral density of the anterior pin region was greater in the experimental than in the control group (P<.05). Low-dose intermittent rhPTH administration not only enhances new bone formation but also can prevent fixator-related osteoporosis of surrounding segments after rapid mandibular DO in rabbits.

Low-dose PTH increases osteoblast activity via decreased Mef2c/Sost in senescent osteopenic mice.

Intermittent administration of parathyroid hormone (PTH) 1-34 at a standard dose has been shown to induce anabolic effects in bone. However, whether low-dose PTH promotes bone formation during senescence is unknown. To address this issue, we determined the effects of low-dose PTH and analysed the underlying mechanisms in prematurely senescent mice that display osteopenia. Treatment of 9-week-old Samp6 mice for 6 weeks with PTH at a standard dose (100 μg/kg per day) increased vertebral and femoral bone mass and improved bone microarchitecture as a result of increased bone-forming surfaces and mineral apposition rate (MAR). At a tenfold lower dose (10 μg/kg per day), PTH increased axial bone volume and trabecular thickness, as detected by bone histomorphometry but not by micro-computed tomography analysis. This anabolic effect resulted from increased osteoblast activity, as reflected by increased serum N-terminal propeptide of type 1 procollagen (P1NP) levels and MAR, with unchanged bone-forming surface or osteoblast surface. Mechanistically, low-dose PTH increased the expression of osteoblast markers in bone marrow stromal cells and mature osteoblasts, which was associated with increased expression of the Wnt effector Wisp1. Moreover, low-dose PTH decreased the expression of the Mef2c transcription factor, resulting in decreased Sost expression in osteoblasts/osteocytes. These results indicate that PTH at a low dose is effective at promoting bone formation and increased bone volume in senescent osteopenic mice through increased osteoblast activity and modulation of specific Wnt effectors, which raises the potential therapeutic use of intermittent PTH at low dose to increase bone forming activity and bone mass in skeletal senescence.

Effects of Different Dosages of Parathyroid Hormone-Related Protein 1–34 on the Bone Metabolism of the Ovariectomized Rat Model of Osteoporosis

Intermittent and low-dose parathyroid hormone (PTH) injection to stimulate bone formation has been used in the treatment of osteoporosis. The N-terminal fragment 1-34 of PTH is quite similar in structure and function to N-terminal PTH-related protein (PTHrP). PTH(1-34) and PTHrP also share a coreceptor, the PTH/PTHrP receptor. Therefore, some studies have suggested that PTHrP could effectively stimulate bone formation, similar to PTH. We used an ovariectomized (OVX) rat model of osteoporosis to study the effects of PTHrP(1-34) on bone metabolism by measuring bone mineral density (BMD), bone histomorphometrics, and biomechanical parameters. We found that subcutaneous injection of PTHrP(1-34) (40 or 80 μg/kg body weight every day) in OVX rats increased lumbar and femoral BMD, improved bone biomechanical properties, enhanced bone strength, and promoted bone formation. We selected 40 μg/kg as the preferred therapeutic dose of PTHrP(1-34) and investigated the effects of frequency of treatment (per 1, 2, 3, or 7 days) on bone metabolism in OVX rats. We found that injection of PTHrP(1-34) once per day or every other day significantly improved the BMD and strength of OVX rats. Serum calcium and phosphate levels in all treated rats did not vary significantly from control rats. Based on our results, intermittent low-dose PTHrP(1-34) injection promoted bone formation in OVX rats, suggesting a high potential for therapeutic use in osteoporosis patients.

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

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

Pharmacodynamic Responses to combined treatment regimens with the calcium sensing receptor antagonist JTT-305/MK-5442 and alendronate in osteopenic ovariectomized rats

Parathyroid hormone (PTH) is the anabolic standard of care for patients with severe osteoporosis. The CaSR allosteric antagonist JTT-305/MK-5442, a PTH secretagogue, could offer an oral osteoanabolic treatment alternative for postmenopausal women with osteoporosis.Here we disclose the pharmacokinetic profile of JTT-305/MK-5442 and its activity on bone remodeling in ovariectomized (OVX) osteopenic rats. Daily treatments (0.3 to 2.4mg/kg/d) for 12weeks resulted in plateaued BMD increases (3.8 to 5.3%) at axial and appendicular skeletal sites. However, treatment effects were not statistically significant, in agreement with effects seen in animals treated with low dose PTH (1–84) (5μg/kg/d).In a consecutive study we tested JTT-305/MK-5442 effects on bone formation in OVX-rats challenged with combined alendronate (ALN) treatment paradigms. At 7month, JTT-305/MK-5442 treatment significantly increased BMD in lumbar vertebrae (LV), while no change in BMD was observed in femora or tibiae. ALN add-on co-treatment produced incremental increases in LV, distal femur (DF) and proximal tibia (PT) BMD over the respective ALN control. Histological analyses confirmed modest increases in mineralized surface (MS/BS) and bone formation rate (30.5±1.9%) on trabecular surfaces by JTT-305/MK-5442. As expected, ALN administration profoundly reduced bone formation, however, JTT-305/MK-5442 significantly stimulated MS/BS and BFR in ALN treated groups.In summary, JTT-305/MK-5442 acts as a PTH secretagogue in the osteopenic OVX-rat, eliciting consistent, though modest effects on remediation of BMD due to estrogen depletion. Induction of bone formation by JTT-305/MK-5442 at trabecular bone surfaces appears to be resilient to ALN-mediated suppression of bone formation. This study provides for the first time, a mechanistic evaluation of combination treatment of a PTH secretagogue with ALN.

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

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

Low dose parathyroid hormone maintains normal bone formation in adult male rats during rapid weight loss

A persistent negative energy balance results in bone loss. It is not clear whether the bone loss associated with chronic negative energy balance can be prevented. The objective of this study was to assess the efficacy of intermittent low dose parathyroid hormone (PTH) treatment in maintaining normal bone formation during severe energy restriction. Six-month-old male Fisher 344 rats were divided into 4 treatment groups: (1) baseline, (2) ad libitum (ad lib)-fed control, (3) energy-restricted (to consume 40% ad lib caloric intake), or (4) energy-restricted+low dose (1μg/kg/d) PTH. Severe energy restriction for 14d decreased body weight and serum leptin levels. Compared to ad lib-fed controls, energy-restricted rats had lower cancellous bone formation, higher osteoclast perimeter/bone perimeter and higher bone marrow adiposity in the proximal tibial metaphysis. Also, the energy-restricted rats had a lower periosteal bone formation rate at the tibia–fibula synostosis. Administration of PTH to energy-restricted rats had no effect on weight loss or osteoclast perimeter/bone perimeter. In contrast, energy-restricted rats treated with PTH had higher rates of cancellous and cortical bone formation compared to energy-restricted rats, and did not differ from the ad lib-fed control animals. Furthermore, PTH treatment maintained normal bone marrow adiposity. In conclusion, rapid weight loss in adult male rats was accompanied by decreased bone formation and increased bone marrow adiposity and these changes were prevented by low dose PTH treatment. Taken together, the results suggest that the energy cost of bone formation in adult rats is low and PTH therapy is effective in preventing the reduced bone formation associated with rapid weight loss.

The effects of low dose parathyroid hormone on lumbar vertebrae in a rat model for chronic alcohol abuse

This study evaluated the hypothesis that increased bone marrow adipogenesis is coupled to decreased bone formation in rats consuming alcohol. Parathyroid hormone (PTH) increased bone formation but had no effect on marrow adiposity. We conclude that increased adiposity does not prevent the bone anabolic response to PTH. Alcoholism results in decreased bone formation and increased bone marrow adiposity. The present study tested the hypothesis that these reciprocal changes are coupled by evaluating the effect of intermittent PTH on bone formation and bone marrow adiposity in a rat model for chronic alcohol abuse. Three-month-old male Sprague Dawley rats (n = 10-11/group) were fed the Lieber-DeCarli liquid diet with 35% of the calories derived from ethanol. Control rats were pair-fed an isocaloric alcohol-free diet. The rats were administered low dose PTH (1 µg/kg/day sc, 5 d/week) or vehicle for 6 weeks. Cancellous bone architecture in lumbar vertebrae was evaluated by micro-computed tomography followed by histomorphometric assessment of bone formation and marrow adiposity. Alcohol increased bone marrow adiposity but reduced bone formation. The latter was due to decreases in mineralizing perimeter/bone perimeter, a surrogate measure of osteoblast number, and mineral apposition rate, a measure of osteoblast activity. PTH increased bone formation by increasing mineralizing perimeter/bone perimeter. In contrast, PTH had no effect on mineral apposition rate or bone marrow adiposity. Interactions between alcohol consumption and PTH treatment were not detected for any endpoints evaluated. PTH treatment blunted the decrease in mineralizing perimeter/bone perimeter in alcohol-fed rats but was ineffective in preventing the increase in bone marrow adiposity. These findings suggest that the alcohol-induced increase in adipocytes is not directly responsible for the accompanying reduction in bone formation.

Effects of low-dose parathyroid hormone on bone mass, turnover, and ectopic osteoinduction in a rat model for chronic alcohol abuse

Parathyroid hormone (PTH) is used clinically in osteoporotic patients to increase bone mass by enhancing bone formation. PTH therapy is not uniformly effective at all skeletal sites and “life-style” factors may modulate the skeletal response to PTH. Alcohol may represent one of these factors. Chronic alcohol abuse is associated with osteoporosis and impaired fracture healing. Therefore, the present study investigated the effects of alcohol on the bone anabolic response to a dose of PTH similar to a human therapeutic dose 1) during normal cancellous and cortical bone growth and turnover, and 2) in a model of demineralized allogeneic bone matrix (DABM)-induced osteoinduction. Three-month-old male Sprague Dawley rats were fed a Lieber–DeCarli liquid diet with 35% of the calories derived from ethanol. The controls were pair-fed an alcohol-free isocaloric diet containing maltose–dextran. Following adaptation to the liquid diets, the rats were implanted subcutaneously with DABM cylinders prepared from cortical bone of rats fed normal chow. The rats were subsequently treated daily with PTH (1 µg/kg/d sc, 5 d/week) or vehicle and measurements on bone and DABM implants performed 6 weeks later. Total bone mass was evaluated on the day of necropsy using DXA. Tibiae were processed for histomorphometry. Bone mass and architecture in tibial diaphysis and DABM implants were evaluated by µCT. PTH treatment increased whole body bone mineral content (BMC) and bone mineral density (BMD). The hormone also increased bone formation and bone area/tissue area in the proximal tibial metaphysis. In contrast, PTH treatment had no effect on periosteal bone formation and minimal effects on DABM-induced osteoinduction. Alcohol consumption decreased whole body BMC. Alcohol also decreased cancellous as well as cortical bone formation and bone mass in tibia and impaired DABM-mediated osteoinduction. There was no interaction between PTH treatment and alcohol consumption for any of the endpoints evaluated. Our results indicate that the bone anabolic response to a therapeutic dose of PTH in the rat is largely confined to cancellous bone. In contrast, alcohol consumption inhibits bone formation at all sites. Furthermore, alcohol inhibits osteoinduction and reduces periosteal and cancellous bone formation, irrespective of therapeutic PTH administration. Based on the animal model, our findings suggest that alcohol consumption could impair the beneficial effects of PTH therapy in osteoporosis.

Sequential Treatment with Intermittent Low-Dose Human Parathyroid Hormone (1-34) and Bisphosphonate Enhances Large-Size Skeletal Reconstruction by Vascularized Bone Transplantation

Vascularized bone transplantation enables reconstruction of large skeletal defects, but this process needs a long time. Since short-term intermittent parathyroid hormone (PTH) enhances rat fracture healing, we investigated the effects of 4-week intermittent low-dose (10 microg/kg/day) or high-dose (100 microg/kg/day) PTH followed by 4-week vehicle, low-dose or high-dose intermittent PTH, or zoledronic acid (ZOL, 2 micro/kg/week), a potent bisphosphonate, on large skeletal reconstruction by vascularized tibial grafting in rats. Compared to 8-week vehicle, 8-week low-dose PTH did not significantly increase the serum osteocalcin level as well as the urinary deoxypyridinoline level, while 4-week low-dose or high-dose PTH followed by 4-week ZOL decreased both of these levels. Eight-week PTH increased the bone mass of the graft and strength of the reconstructed skeleton in a dose-dependent manner; notably, the reconstructed skeleton showed an obviously higher response to PTH compared to the contralateral nonoperated femur. In contrast, 4-week PTH followed by 4-week vehicle reduced these effects and caused local bone loss at the host-graft junctions. Four-week PTH followed by 4-week ZOL did not induce such bone loss; however, 4-week high-dose PTH followed by 4-week ZOL caused a large callus in the distal cortical junction. Four-week PTH followed by 4-week ZOL increased the bone mass and strength similarly to 8-week PTH. These preliminary findings suggest, for the first time, that sequential treatment with short-term intermittent low-dose PTH and bisphosphonate as well as long-term intermittent low-dose PTH treatment enhance large skeletal reconstruction by vascularized bone transplantation, though early timing of sequential antiresorptive treatment could result in delay of bone repair.

Resolution of Bisphosphonate-Associated Osteonecrosis of the Mandible: Possible Application for Intermittent Low-Dose Parathyroid Hormone [rhPTH(1-34)

Activation of bone cell populations including osteoclasts, osteoblasts, and osteocytes occurs to varying degrees with normal bone remodeling and at different phases of wound healing in an extraction socket or as a result of an inflammatory process secondary to periodontal disease or apical bone necrosis secondary to pulpal necrosis. Therapeutics that use bisphosphonates for the management of bone diseases such as osteoporosis, metastatic cancer, multiple myeloma, and Paget’s disease affect the balance of osteoclast, osteoblast, and osteocyte populations. Consequently, the normal physiologic response of the mandibular or maxillary bone to insult or injury may be compromised in these patients. ErratumJournal of Oral and Maxillofacial SurgeryVol. 65Issue 5PreviewIn the March 2007 issue of the Journal of Oral and Maxillofacial Surgery (Volume 65, Number 3), in the article entitled, “Resolution of Bisphosphonate-Associated Osteonecrosis of the Mandible: Possible Application for Intermittent Low-Dose Parathyroid Hormone [rhPTH(1-34)]” (J Oral Maxillofac Surg 65:573-580, 2007) by Harper and Fung, there is a dosing error reported by the authors as follows: The dose of Fosamax and the duration of the dose schedule originally reported by the patient as “70 mg daily for 1 year” were inaccurate. Full-Text PDF

Identification and Validation of the Relationship of the Anabolic Effect of Parathyroid Hormone with the Wnt/β-catenin Canonical Pathway

2,3 ABSTRACT Background: It has been well established that daily injections of low dose parathyroid hormone (PTH) increase bone mass in animals and humans. However, the precise mechanisms by which PTH exerts its anabolic action on bone are incompletely understood. The canonical Wnt-β-catenin signaling pathway has recently been demonstrated to have an important role in bone cell function. In the present study, we have examined the interaction between the PTH and Wnt signaling pathways in mouse osteoblastic MC3T3-E1 cells. Methods & Results: MC3T3-E1 cells were treated with 0.01-0.84 μM recombinant PTH. β-catenin expression was significantly increased after 30 minutes of exposure to PTH and reached a maximum 2.7 fold increase at 1 hr and expression then faded at 6 hrs. In addition, treatment with PTH increased nuclear accumulation of activated β-catenin; the ratio between the nuclear to cytoplasmic protein was more than three fold at 30 minutes and beyond. Moreover, PTH stimulated T-cell factor/lymphoid enhancer factor (TCF/LEF) reporter gene activity in MC3T3-E1 cells. Confocal microscopy revealed nuclear translocation of β-catenin by PTH as compared with a glycogen synthase kinase-3β (GSK-3β) inhibitor. Conclusion: These results suggest that the anabolic mechanism of PTH might be partially associated with the Wnt-canonical pathway. The appropriate target of another anabolic agent should be determined through further studies of this pathway. (J Kor Endocr Soc 22:411~418, 2007) ꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏ

Low-dose parathyroid hormone and estrogen reverse alkaline phosphatase activity suppressed by dexamethasone in mouse osteoblastic cells

Glucocorticoid (GC)-induced osteoporosis (GIO) is frequently seen in patients with excessive GC. Numerous questions remain to be clarified about the pathogenesis and treatment of GIO, and the mechanism of GC-inhibited bone formation is not well known. Several studies suggest that parathyroid hormone (PTH) and hormone replacement therapy are effective for GIO. We therefore investigated whether PTH and estrogen would affect cell proliferation and alkaline phosphatase (ALP) activity inhibited by dexamethasone (Dex) in mouse osteoblastic cell-line MC3T3-E1 cells. Low-dose (10(-11) M) PTH as well as 10(-8) M 17-beta-estradiol (17beta-E2) significantly attenuated Dex-inhibited ALP activity, although 10(-8) M PTH did not affect it. ICI 182780 (10(-8) M) antagonized the effects of 17beta-E(2) on Dex-suppressed ALP activity. Neutralizing anti-IGF-I antibody (3 microg/ml) blocked the reverse effects of 17beta-E2 on ALP activity suppressed by Dex. PTH (10(-11) M), but not 17beta-E2, significantly attenuated [3H]thymidine incorporation inhibited by Dex. On the other hand, PTH and estrogen did not affect the level of 11-beta-hydrosteroid dehydrogenase type I mRNA increased by Dex. In conclusion, the present study demonstrated that low-dose PTH and estrogen reversed Dex-inhibited ALP activity in the mouse osteoblastic cell-line.

Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia.

The purpose of this study was to evaluate whether the natriuresis and polyuria seen in parathyroid hormone (PTH)-induced hypercalcemia are associated with dysregulation of renal Na transporters. Rats were infused with three different doses of human PTH [PTH (1-34); 7.5, 10, and 15 microg.kg(-1).day(-1) s.c.] or vehicle for 48 h using osmotic minipumps. The rats treated with PTH developed significant hypercalcemia (plasma total calcium levels: 2.71 +/- 0.03, 2.77 +/- 0.02, and 3.42 +/- 0.06 mmol/l, respectively, P < 0.05 compared with corresponding controls). The rats with severe hypercalcemia induced by high-dose PTH developed a decreased glomerular filtration rate (GFR), increased urine output, reduced urinary osmolality, increased urinary Na excretion, and fractional excretion of Na. This was associated with downregulation (calculated as a fraction of control levels) of whole kidney expression of type 2 Na-P(i) cotransporter (NaPi-2; 16 +/- 6%), type 3 Na/H exchanger (NHE3; 42 +/- 7%), Na-K-ATPase (55 +/- 2%), and bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1; 25 +/- 4%). In contrast, an upregulation of the Ca(2+)-sensing receptor (CaR) was observed. Rats treated with moderate-dose PTH exhibited unchanged GFR but decreased urinary concentration. The whole kidney expression of NHE3 (52 +/- 8%) and NaPi-2 (26 +/- 5%) was persistently decreased, whereas BSC-1 and Na-K-ATPase protein levels were not altered. CaR expression was also increased. Moreover, rats treated with low-dose PTH showed very mild hypercalcemia but unchanged GFR, normal urinary concentration, and unchanged expression of Na transporters and CaR. In conclusion, the reduced expression of major renal Na transporters is likely to play a role in the increased urinary Na excretion and decreased urinary concentration in rats with PTH-induced hypercalcemia. Moreover, the increase in the CaR in the thick ascending limb (TAL) may indicate a potential role of the CaR in inhibiting Na transport in the TAL.

A role for interleukin-6 in parathyroid hormone-induced bone resorption in vivo.

Parathyroid hormone (PTH) exerts its regulatory effects on calcium homeostasis in part by stimulating the release of calcium from the skeleton. PTH stimulates bone resorption indirectly, by inducing the production by stromal/osteoblastic cells of paracrine agents which recruit and activate the bone-resorbing cell, the osteoclast. The identity of the stromal cell/osteoblast-derived paracrine factor(s) responsible for mediating the effects of PTH on osteoclasts is uncertain. Recently, it has been demonstrated that the cytokine interleukin-6 (IL-6), which potently induces osteoclastogenesis, is produced by osteoblastic cells in response to PTH. Further, we have reported that circulating levels of IL-6 are elevated in patients with primary hyperparathyroidism, and correlate with biochemical markers of bone resorption. Thus, IL-6 may play a permissive role in PTH-induced bone resorption. In the current studies, we demonstrate that low-dose PTH infusion in rodents increased serum levels of IL-6, coincident with a rise in biochemical markers of bone resorption. In mice, both acute neutralization and chronic deficiency of IL-6 were associated with markedly lower levels of biochemical markers of bone resorption in response to PTH infusion than were observed in animals with normal IL-6 production. Acute neutralization of IL-6 did not affect PTH-induced changes in markers of bone formation. These findings demonstrate that PTH regulates systemic levels of IL-6 in experimental animals, that IL-6 is an important mediator of the bone-resorbing actions of PTH in vivo and suggest that IL-6 plays a role in coupling PTH-induced bone resorption and formation.

In vitro evidence that local and systemic skeletal effectors can regulate 3[H]-thymidine incorporation in chick calvarial cell cultures and modulate the stimulatory actions(s) of embryonic chick bone extract.

These investigations were intended to determine whether local and systemic skeletal effectors--3'5'-cyclic adenosine monophosphate (cAMP), prostaglandin E2 (PGE2), parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25(OH)2D), calcitonin, and NaF--could regulate 3[H]-thymidine incorporation (i.e., into DNA) in serum-free, monolayer cultures of embryonic chick calvarial cells, and/or modulate the activity of embryonic chick bone extracts to increase 3[H]-thymidine incorporation. In the absence of added bone extract, we found that calcitonin (0.1 U/ml), NaF (100 microM) and low-dose PTH (0.1 nM) stimulated 3[H]-thymidine incorporation, P less than .05 for each; isobutylmethylxanthine (IBMX--1 mM), 1,25OHD (10 nM), and high-dose PTH (10 nM) decreased 3[H]-thymidine incorporation; and PGE2 (1 microM) had no effect. The stimulatory actions of calcitonin, fluoride, and low-dose PTH were inductive, and the inhibitory actions of IBMX and 1,25(OH)2D were acute. PTH had complex time-dependent actions on 3[H]-thymidine incorporation, being inhibitory after 4-8 hours of exposure and stimulatory after 20-24 hours (P less than .001 for each). The effects of calcitonin, fluoride, and low-dose PTH to increase 3[H]-thymidine incorporation were greater in calvarial cell cultures enriched for undifferentiated osteoprogenitor cells than in cultures enriched for differentiated osteoblastlike cells. PTH inhibited 3[H]-thymidine incorporation in the latter (i.e., osteoblastlike) cultures (P less than .005). The inhibitory actions of IBMX and 1,25(OH)2D were independent of cell differentiation. Additional studies further revealed that these local and systemic skeletal effectors could also modulate the activity of embryonic chick bone extracts to increase 3[H]-thymidine incorporation in calvarial cell cultures. We found that calcitonin, fluoride, and low-dose PTH enhanced the effect of the extracts to increase 3[H]-thymidine incorporation (P less than .001 for each). These activations were noncompetitive, indicating (1) mechanistic differences between the stimulatory actions of the effectors and the chick bone extract (i.e., different rate-limiting steps for the effects of each on 3[H]-thymidine incorporation); and (2) that neither calcitonin, fluoride, nor 0.1 nM PTH altered the apparent affinity of the cells for stimulatory activity(s) in the extract. High-dose PTH was a noncompetitive inhibitor with respect to bone extract activity, indicating that the effect of 10 nM PTH to decrease 3[H]-thymidine incorporation was mechanistically distinct from the effect of the bone extract to increase 3[H]-thymidine incorporation.(ABSTRACT TRUNCATED AT 400 WORDS)