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Human parathyroid hormone (1-34) and (1-84) increase the mechanical strength and thickness of cortical bone in rats
Abstract
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.
... Some studies have shown rats to have increased cortical bone mass and strength with teriparatide treatment. 12,14 While the positive effects of teriparatide have been well documented in osteoporotic patients, effects on patients' trabecular bone balance are less clear. Ejersted et al. (1993) sought to clarify whether this positive effect is a result of a trade-off in the cortical bone. ...
... 12,14 While the positive effects of teriparatide have been well documented in osteoporotic patients, effects on patients' trabecular bone balance are less clear. Ejersted et al. (1993) sought to clarify whether this positive effect is a result of a trade-off in the cortical bone. To address this, they treated groups of rats either with PTH or teriparatide daily and as hypothesized, no differences between the two treatments was found. ...
... To address this, they treated groups of rats either with PTH or teriparatide daily and as hypothesized, no differences between the two treatments was found. 12 Both groups of rats experienced increased strength and cross sectional area in their femurs. 12 Furthermore, teriparatide treatment has been shown to increase proximal femur strength in ovariectomized nonhuman primates, despite increasing bone porosity. ...
Osteopenia and osteoporosis have become increasingly common in the elderly population, as has the concern from treating spinal surgeons. Many adverse surgical outcomes have been associated with poor bone quality, including decreased fusion rates, hardware complications, and osteoporotic fractures. Teriparatide, a recombinant form of parathyroid hormone, has been used as a major pharmaceutical intervention in osteoporosis treatment. This article provides an overview of the mechanism of teriparatide followed by a detailed review of the literature concerning outcomes of medical management with teriparatide in both animal models and humans with osteoporosis/osteopenia. Improved fusion rates and duration, as well as reduced osteoporosis-related complications are evident upon reviewing clinical and radiographic outcomes of teriparatide therapy in spinal surgery patients.
... PTH stimulated the appearance of an easily-discernible "packet" of endocortical lamellar bone in the central tibia, as previously seen with twice the dose [61,64,66,90,91]. The amount was approximately the same regardless of whether PTH treatment had been preceded by anti-resorptive therapy. ...
... Cortical area and thickness declined by six-nine months after OVX [105]. Both cortical area and thickness were better with antiresorptive monotherapy [106] and, particularly, with treatments that combined PTH [64,[90][91][92] with anti-resorptives, no matter the order of administration. Total area was not affected at any time, perhaps providing further evidence of a stable periosteum. ...
Unlabelled:
Anti-resorptive and anabolic agents are often prescribed for the treatment of osteoporosis continuously or sequentially for many years. However their impact on cortical bone quality and bone strength is not clear.
Methods:
Six-month old female rats were either sham operated or ovariectomized (OVX). OVX rats were left untreated for two months and then were treated with vehicle (Veh), hPTH (1-34) (PTH), alendronate (Aln), or raloxifene (Ral) sequentially for three month intervals, for a total of three periods. Mid-tibial cortical bone architecture, mass, mineralization, and strength were measured on necropsy samples obtained after each period. Bone indentation properties were measured on proximal femur necropsy samples.
Results:
Eight or more months of estrogen deficiency in rats resulted in decreased cortical bone area and thickness. Treatment with PTH for 3months caused the deposition of endocortical lamellar bone that increased cortical bone area, thickness, and strength. These improvements were lost when PTH was withdrawn without followup treatment, but were maintained for the maximum times tested, six months with Ral and three months with Aln. Pre-treatment with anti-resorptives was also somewhat successful in ultimately preserving the additional endocortical lamellar bone formed under PTH treatment. These treatments did not affect bone indentation properties.
Summary:
Sequential therapy that involved both PTH and anti-resorptive agents was required to achieve lasting improvements in cortical area, thickness, and strength in OVX rats. Anti-resorptive therapy, either prior to or following PTH, was required to preserve gains attributable to an anabolic agent.
... The anabolic effects are pronounced in the trabecular bone and on the endosteal surface of cortical bone. In rat, cortical bone mass and strength are increased (Ejersted et al. 1993; Oxlund et al., 1993) [15,16]. In some species such as rat, little remodelling of cortical bone is seen. ...
... The anabolic effects are pronounced in the trabecular bone and on the endosteal surface of cortical bone. In rat, cortical bone mass and strength are increased (Ejersted et al. 1993; Oxlund et al., 1993) [15,16]. In some species such as rat, little remodelling of cortical bone is seen. ...
“Perioceutics” or the use of the pharmacological agents which are specifically developed to manage periodontitis, is an interesting and
an emerging aid in the management of periodontal diseases, along with mechanical debridement. Host modulation therapies are being
proposed and developed to bring down excessive levels of enzymes, cytokines, prostanoids, as well modulate osteoclast functions. Over
the past two decades, many drugs have been investigated for their host modulating properties in both animal and early human clinical
studies. These agents include non-steroidal anti-inflammatory drugs, sub antimicrobial dose doxycycline and systemic bisphosphonates.
Recently, a new drug has been added to the list, namely, teriparatide, which is a bone forming drug. It is a biosynthetic human parathyroid
hormone. Multiple clinical trials have shown that teriparatide is associated with increased bone mineral density. This review has focused on
the mechanism of action of teriparatide and its potential role in the treatment of periodontal disease.
... Cependant, il existe peu de données factuelles concernant l'efficacité du traitement par tériparatide (séquence active de la parathormone humaine endogène) ainsi que sa posologie et sa durée optimale dans la prise en charge de l'ONM. Dans la plupart des études animales sur l'ONM, la dose de tériparatide était basée sur des schémas posologiques (20-200 μg/kg/jour) issus de la littérature orthopédique évaluant les greffes osseuses et les fractures [4][5][6]. En raison des limites de l'étude de l'ONM et de son traitement chez l'homme, et à cause des puissants effets ostéoanaboliques du tériparatide chez le rat, l'utilisation de ce modèle animal pour l'étude de l'ONM a suscité notre intérêt. Notre étude préclinique, randomisée et contrôlée, a donc été conçue pour évaluer les effets de différentes doses et durées de tériparatide sur l'ONM chez les rats males Wistar. ...
... The drug's ability to stimulate bone formation and increase bone mass and mineral density [45,56,113] corroborate the results of the three-way flexion test points, which demonstrated that maximum force (load/N) in the group of ovariectomized rats with bone defects in tibias filled with bioglass associated with 10% teriparatide (BGTO group) exhibited significantly higher values, statistically differing from the other analyzed groups (p < 0.05), which promoted an increase in the biomechanical properties of newly formed bone in rats with endocrine abnormalities when compared to normal animals. Studies with the systemic use of PTH (1-34) for fractures in long bones confirm the increase in mechanical resistance and the amount of newly formed bone [114][115][116][117]. A recent study by Leiblein et al. [118] verified that the maximum force was increased in the biomechanical tests performed in animals treated with PTH (1-34) when compared to animals that received doses of simvastatin, alendronate, and strontium ranelate. ...
With the increase in the population’s life expectancy, there has also been an increase in the rate of osteoporosis, which has expanded the search for strategies to regenerate bone tissue. The ultrasonic sonochemical technique was chosen for the functionalization of the 45S5 bioglass. The samples after the sonochemical process were divided into (a) functionalized bioglass (BG) and (b) functionalized bioglass with 10% teriparatide (BGT). Isolated mesenchymal cells (hMSC) from femurs of ovariectomized rats were differentiated into osteoblasts and submitted to in vitro tests. Bilateral ovariectomy (OVX) and sham ovariectomy (Sham) surgeries were performed in fifty-five female Wistar rats. After a period of 60 days, critical bone defects of 5.0 mm were created in the calvaria of these animals. For biomechanical evaluation, critical bone defects of 3.0 mm were performed in the tibias of some of these rats. The groups were divided into the clot (control) group, the BG group, and the BGT group. After the sonochemical process, the samples showed modified chemical topographic and morphological characteristics, indicating that the surface was chemically altered by the functionalization of the particles. The cell environment was conducive to cell adhesion and differentiation, and the BG and BGT groups did not show cytotoxicity. In addition, the experimental groups exhibited characteristics of new bone formation with the presence of bone tissue in both periods, with the BGT group and the OVX group statistically differing from the other groups (p < 0.05) in both periods. Local treatment with the drug teriparatide in ovariectomized animals promoted positive effects on bone tissue, and longitudinal studies should be carried out to provide additional information on the biological performance of the mutual action between the bioglass and the release of the drug teriparatide.
... Par exemple, chez le Rat, l'accroissement de l'épaisseur corticale ou du périmètre cortical se traduit par un moindre risque de fracture (Ejersted et al. 2009). Dans une étude chez l'Homme, le risque de fractures radiales ou tibiales était associé à une réduction de l'épaisseur ou de la surface corticale, mais pas à la DMO une fois standardisée par le volume osseux (Taes et al. 2010). ...
It is now well established that physical exercise has unquestionable beneficial effects on bone tissue and metabolism. However, no consensus regarding the osteogenic effects of exercise on healthy or healing bone has been reached yet. The objective of this work is (i) to evaluate the effects of two running protocols (continuous vs. intermittent) on the parameters of bone quality and bone metabolism, and (ii) to evaluate the preventive effects of these running protocols on bone repair in Wistar rats.
We demonstrated here that high-intensity interval-running has positive effects on cortical bone quality, while moderate continuous running has beneficial effects on trabecular bone but is detrimental to cortical bone. These effects also depend on the bone (tibia vs. femur). In addition, our data suggest that both running protocols accelerate the repair of a non-critical bone defect in the tibia but not in the femur, possibly by modulating bone resorption.
Associating different types of running is more beneficial to bone health than just one. As part of the refinement of animal models, the use of the tibia would be more suitable to study bone healing than the femur.
... A second line treatment that is a recombinant form of parathyroid hormone (PTH), teriparatide, works to prevent new fractures by increasing and subsequently maintaining anabolic equilibrium between bone formation and resorption (Akhter et al., 2018;Marcus, 2011;Ohtori et al., 2012). Teriparatide has been increasingly used in spine surgery to prevent osteoporotic related surgical complications (Akhter et al., 2018;Lin and Lane, 2004;Marcus, 2011;Ohtori et al., 2012;Ohtori et al., 2013;Rizzoli et al., 2011;Parfitt, 1989;Ejersted et al., 1993;Oxlund et al., 1993). ...
Objective
Teriparatide has been increasingly utilized in the management of osteoporosis. The efficacy of low and high dose teriparatide on lumbar spine bone mineral density, vertebral fracture incidence and pain is unknown. We sought to determine the efficacy of teriparatide on these patient-important outcomes using a systematic review and meta-analysis.
Methods
A systematic search of electronic databases (MEDLINE, EMBASE, CENTRAL, CINAHL) was performed to identify randomized controlled trials (RCTs) that evaluate teriparatide to any comparator for the treatment of osteoporosis in postmenopausal women. The Grades of Recommendation Assessment, Development and Evaluation (GRADE) criteria were used by two independent reviewers to assess the strength and quality of evidence.
Results
A total of 20 studies (n = 6024) were included in this review, with 2855 patients receiving teriparatide and 3169 patients receiving placebo or control treatment. A teriparatide dose of 20 μg/day increased lumbar spine bone mineral density (BMD) (standardized mean difference (SMD) 0.34 standard deviation (SD) units higher (95% CI 0.19–0.48 SDs higher) in comparison to placebo. Relative to anti-resorptive agents, 20 μg/day of teriparatide had a range from 0.14 SD units to 0.96 SD units higher (95% CI, 0.08 SDs lower to 0.36 SDs higher, CI, 0.33–1.59 SDs higher, respectively). 20 μg/day teriparatide had a significant effect on pain severity to placebo or control (SMD 0.80, 95% CI, 1.16–0.43 SDs lower) and also decreased the incidence of vertebral fractures compared to placebo (relative risk 0.31, 95% CI 0.21 to 0.46). Arthralgia and extremity pain incidence were also calculated; there were 15 and 8 fewer events per 1000 patients with the use of 20 μg/day of teriparatide compared to placebo or control, respectively.
Conclusion
High quality evidence supports the utilization of teriparatide 20 μg/day dose to significantly improve lumbar spine BMD and decrease incidence of vertebral fractures and pain severity relative to all comparators. 40 μg/day dose of teriparatide demonstrated significantly better results with prolonged treatment. This data is valuable for clinicians involved in the care of this growing demographic of patients. Further investigation on the safety and efficacy of teriparatide in higher doses for the long-term treatment of osteoporosis in postmenopausal women should be conducted through high-quality clinical trials.
... A decrease in CRT_THK in the absence of changes in bone size (PERI_C) indicates that all of the changes in CRT_THK are the result of endocortical bone resorption. Examples for treatments which have been shown to increase cortical thickness through endocortical bone apposition as detected by pQCT are PTH [2,25,26], and PGE 2 [27,28]. The magnitude of these changes caused by anabolic agents (decrease in ENDO_C) can be substantial and is thus easily monitored after 4 weeks of treatment or longer. ...
This chapter provides information for the in vivo use of peripheral quantitative computed tomography in rats and mice to determine bone density and cortical geometric data, including suggestions for study design, instrument setting, and data interpretation. This update also provides guidance for the use of pQCT to extract muscle and fat cross-sectional area information from the bone scans.
... The geometry of bone, such as cortical thickness and external diameters (which incorporates cortical area), plays a major role in determining bone strength. [20][21][22] In this study, Oc -/and Opn -/mice adjusted their cortical area and marrow area together such that the absence of either protein resulted in a phenotype that was similar to WT. There were no morphological differences between Oc -/and Opn -/mice and between Oc -/-, Opn -/-, and WT littermates. ...
Osteocalcin (OC) and osteopontin (OPN) are major non-collagenous proteins (NCPs) involved in bone matrix organization and deposition. In spite of this, it is currently unknown whether OC and OPN alter bone morphology and consequently affect bone fracture resistance. The goal of this study is to establish the role of OC and OPN in the determination of cortical bone size, shape, and mechanical properties. Our results show that Oc–/– and Opn–/– mice were no different from each other or wild type (WT) with respect to bone morphology (P > 0.1). Bones from mice lacking both NCPs (Oc–/–Opn–/–) were shorter, with thicker cortices and larger cortical areas, compared with the WT, Oc–/–, and Opn–/– groups (P < 0.05), suggesting a synergistic role for NCPs in the determination of bone morphology. Maximum bending load was significantly different among the groups (P = 0.024), while tissue mineral density and measures of stiffness and strength were not different (P > 0.1). We conclude that the removal of both OC and OPN from bone matrix induces morphological adaptation at the structural level to maintain bone strength.
... 81 However, PTH was also shown as a factor which increases bone mineral density and improves bone mechanical strength, when administered intermittently. 82 In the current study, besides the decreased calcium and elevated PTH level in the carbamazepine-treated group, there was a reduction in both 25(OH)D and 1,12(OH)D serum levels. Thus, it was suggested that there was a low vitamin D levels caused by the effects of the drug on vitamin D metabolism. ...
The severe sole effects of seizures on the cortical part of bone were reported in our previous study. However, the side effects of anti-epileptic drug therapy on bones has not been differentiated from the effects of the convulsive seizures, yet. This study provides the first report on differentiation of the effects of seizures and carbamazepine (a widely used antiepileptic drug) therapy on bones; 50 mg/kg/day drug was given to genetically induced absence epileptic rats for five weeks. Distinct bone regions including cortical, trabecular, and growth plate in each of tibia, femur, and spine tissues were studied using Fourier transform infrared (FT-IR) imaging and Vickers microhardness test. Blood levels of vitamin D and bone turnover biomarkers were also measured. According to the FT-IR imaging results, both seizure and carbamazepine-treated groups, more dominantly the drug-treated group, had lower mineral content with altered collagen crosslinks and higher crystallinity, implying reduced bone strength. Lower microhardness values also supported lower mechanical strength in bones. The most affected bone tissue and region from seizures and treatment was found as the spine and cortical, respectively. While there was a reduction in vitamin D and calcium levels in both seizure and carbamazepin-treated groups, significantly elevated PTH and bone turnover biomarkers were only seen in the drug-treated group.
... 81 However, PTH was also shown as a factor which increases bone mineral density and improves bone mechanical strength, when administered intermittently. 82 In the current study, besides the decreased calcium and elevated PTH level in the carbamazepine-treated group, there was a reduction in both 25(OH)D and 1,12(OH)D serum levels. Thus, it was suggested that there were low vitamin D levels caused by the effects of the drug on vitamin D metabolism. ...
Alterations in microstructure and mineral features can affect the mechanical and chemical properties of bones and their capacity to resist mechanical forces. Controversial results on diabetic bone mineral content have been reported and little is known about the structural alterations in collagen, maturation of apatite crystals, and carbonate content in diabetic bone. This current study is the first to report the mineral and organic properties of cortical, trabecular, and growth plate regions of diabetic rat femurs using Fourier transform infrared (FT-IR) microspectroscopy and the Vickers microhardness test. Femurs of type I diabetic rats were embedded into polymethylmethacrylate blocks, which were used for FT-IR imaging and microhardness studies. A lower mineral content and microhardness, a higher carbonate content especially labile type carbonate content, and an increase in size and maturation of hydroxyapatite crystals were observed in diabetic femurs, which indicate that diabetes has detrimental effects on bone just like osteoporosis. There was a decrease in the level of collagen maturity in diabetic femurs, implying a decrease in bone collagen quality that may contribute to the decrease in tensile strength and bone fragility. Taken together, the findings revealed alterations in structure and composition of mineral and matrix components, and an altered quality and mechanical strength of rat femurs in an early stage of type I diabetes. The results contribute to the knowledge of structure–function relationship of mineral and matrix components in diabetic bone disorder and can further be used for diagnostic or therapeutic purposes.
... Daily intermittent subcutaneous administration of PTH has been reported to enhance bone regeneration (12,13). However, as daily injection of PTH would be stressful to patients, an effective schedule for optimal PTH administration needs to be considered. ...
This study investigated the effects of administration of parathyroid hormone (PTH) at different dosages and schedules on bone regeneration in critical-size bone defects in rat calvariae. After calvarial defects had been prepared in 50 rats, they were divided into five treatment groups: 15 µg/kg PTH daily (PTH-15), 35 µg/kg PTH three times per week (PTH-35), 105 µg/kg once per week (PTH-105-1), 105 µg/kg three times per week (PTH-105-3), and controls given vehicle alone. Bone regeneration was evaluated radiographically using micro-computed tomography (micro-CT) or histologically. The amount of newly generated bone in the calvarial defects was found to be significantly greater in the PTH groups than in the control group, and did not differ significantly among the PTH-15, PTH-35, and PTH-105-1 groups, whereas the PTH-105-3 group showed a significantly greater degree of new bone formation than the other PTH groups. It appeared that a higher dose of PTH stimulated a greater degree of bone regeneration in this experimental setting. The present results also suggest that the total dose of PTH administered is significantly related to the amount of bone regenerated within a defined period, indicating that less frequent administration of PTH might be a feasible protocol for bone regeneration therapy. (J Oral Sci 57, 131-136, 2015).
... The equimolar amount of PTH(1–34) would be 66 µg/kg per day. In vivo studies directly comparing the that the two peptides at equimolar doses increased the bone mass to a similar extent in rats (Mosekilde et al. 1991, Ejersted et al. 1993, Kimmel et al. 1993). Little information is yet available as to the in vivo effect of PTH in mice (Rihani-Bisharat et al. 1998, Zeng et al. 1998). ...
The recent development of different genetically modified mice with potentially interesting bone phenotypes has increased the demand for effective non-invasive methods to evaluate effects on bone of mice during growth and development, and for drug evaluation. In the present study, the skeleton was analyzed by repeated in vivo scans using dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Ovariectomized (ovx) mice treated with parathyroid hormone (PTH) were used as an animal model to evaluate these two techniques at different times after the onset of treatment. Female mice (6 weeks of age) were allocated randomly to four groups: (1) sham-operated+vehicle; (2) ovx+vehicle; (3) sham-operated+PTH(1‐84) 150 µg/ kg per day; (4) ovx+PTH. Six weeks after ovariectomy the drug treatment began and was continued for 8 weeks. The total body bone mineral content (BMC) and total body areal bone mineral density (BMD) were measured by DXA. Ovariectomy reduced total body BMC and total body areal BMD by 6·21·7% and 2·60·9% respectively. No effect of PTH on total body BMC was seen during the treatment period. The trabecular volumetric BMD was measured by pQCT. Ovariectomy reduced the trabecular volumetric BMD by 526·7%. The pQCT technique detected a clear effect on trabecular volumetric BMD after 2 weeks of PTH treatment (ovx 9429% and sham-operated 4610% more than vehicle-treated). The cortical bone was measured in a mid-diaphyseal pQCT scan of the tibia. Ovariectomy reduced the cortical BMC by 92%. PTH treatment for 8 weeks increased cortical BMC in ovx mice. In conclusion, the pQCT technique is more sensitive than the DXA technique in the detection of bone loss after ovariectomy and increased bone mass after PTH treatment in mice. Notably, the pQCT, but not the DXA, technique detected a dramatic effect as early as after 2 weeks of PTH treatment. Dynamic pQCT measurements will be useful for monitoring skeletal changes during growth and development, and for drug evaluation in mice.
... Fig. 5 indicates that the elastic modulus of the rat bone beam in high vacuum is 4.98 ± 0.25 GPa, low vacuum is 5.24 ± 0.11 GPa and wet, in air is 5.22 ± 0.15 GPa and does not vary greatly over the time period examined. Previous mechanical testing on fully hydrated whole rat bone femur using 3-point bending configuration gives an elastic modulus of 5.12 ± 0.77 GPa (Kasra et al., 1997), 8.0 ± 0.4 GPa (Barengolts et al., 1993), 6.88 ± 0.31 GPa (Jorgensen et al., 1991), and 4.9 ± 0.4 GPa (Ejersted et al., 1993) which is similar to the calculated elastic modulus values in our work and indicates that the vacuum of the SEM chamber does not have an effect on elastic modulus of the samples over the time period investigated. Interestingly, the similarity between the elastic modulus of our relatively small bone volumes and whole bone testing suggests an effective transfer of stresses throughout the bone material, indicating that all bone components are not failing or slipping but are tightly bound to one another. ...
The lamellar unit is a critical component in defining the overall mechanical properties of bone. In this paper, micro-beams of bone with dimensions comparable to the lamellar unit were fabricated using focused ion beam (FIB) microscopy and mechanically tested in bending to failure using atomic force microscopy (AFM). A variation in the mechanical properties, including elastic modulus, strength and work to fracture of the micro-beams was observed and related to the collagen fibril orientation inferred from back-scattered scanning electron microscopy (SEM) imaging. Established mechanical models were further applied to describe the relationship between collagen fibril orientation and mechanical behaviour of the lamellar unit. Our results highlight the ability to measure mechanical properties of discrete bone volumes directly and correlate with structural orientation of collagen fibrils.
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... A previous study found that fractures were more frequent in men with lower cortical thickness but found no association between fracture and cortical BMD [250]. Moreover, changes in cortical bone geometry, such as increases in cortical thickness and perimeter are associated with higher bone strength and lower fracture risk [251][252][253]. Bone strength differences between African and Caucasian postmenopausal women [254,255], and between older men and women [256,257], have also been attributed to differences in femoral shaft CSA. ...
Bone fragility is a major health concern, as the increased risk of bone fractures has devastating outcomes in terms of mortality, decreased autonomy, and healthcare costs. Efforts made to address this problem have considerably increased our knowledge about the mechanisms that regulate bone formation and resorption. In particular, we now have a much better understanding of the cellular events that are triggered when bones are mechanically stimulated and how these events can lead to improvements in bone mass. Despite these findings at the molecular level, most exercise intervention studies reveal either no effects or only minor benefits of exercise programs in improving bone mineral density (BMD) in osteoporotic patients. Nevertheless, and despite that BMD is the gold standard for diagnosing osteoporosis, this measure is only able to provide insights regarding the quantity of bone tissue. In this article, we review the complex structure of bone tissue and highlight the concept that its mechanical strength stems from the interaction of several different features. We revisited the available data showing that bone mineralization degree, hydroxyapatite crystal size and heterogeneity, collagen properties, osteocyte density, trabecular and cortical microarchitecture, as well as whole bone geometry, are determinants of bone strength and that each one of these properties may independently contribute to the increased or decreased risk of fracture, even without meaningful changes in aBMD. Based on these findings, we emphasize that while osteoporosis (almost) always causes bone fragility, bone fragility is not always caused just by osteoporosis, as other important variables also play a major role in this etiology. Furthermore, the results of several studies showing compelling data that physical exercise has the potential to improve bone quality and to decrease fracture risk by influencing each one of these determinants are also reviewed. These findings have meaningful clinical repercussions as they emphasize the fact that, even without leading to improvements in BMD, exercise interventions in patients with osteoporosis may be beneficial by improving other determinants of bone strength.
... Regarding the potency of PTH peptides, teriparatide is thought to be similar to the natural cleavage product; also teriparatide retained the bioactivity of PTH bioassay [10] and has been shown to increase bone mass equivalently in ovariectomized (OVX) and orchidectomized (ORX) young rats [11,12]. Studies have been carried out to compare the effects of these two peptides in bone of OVX rats; experimental works have been done showing no significant biological differences between PTH (1-34) and PTH (1-84) [13][14][15]. However, to our knowledge, no studies have been published on the effect of PTH (1-84) in ORX rats. ...
Aim:
The purpose of this study was to evaluate the effect of parathyroid hormone (PTH) (1-84) in a model of male osteoporosis induced by orchidectomy in rats.
Methods:
Six-month-old Wistar rats were used as follows: SHAM (simulated orchidectomy), orchidectomized (ORX), ORX + PTH1 (ORX and treated with 10 µg/Kg/d of PTH 1-84) and ORX + PTH2 (ORX and treated with 50 µg/Kg/d of PTH 1-84) over 3 months, with treatment beginning three months after orchidectomy.
Results:
Orchidectomy resulted in a decreased of femoral and lumbar bone mineral density (BMD), a worsening of trabecular and cortical microarchitecture and a decrease in biomechanical properties. Both doses of PTH (1-84) partially (low dose) or totally (high dose) restored the ORX-induced changes. Serum C-telopeptide of type I collagen/5b isoenzyme of tartrate-resistant acid phosphatase (CTX/TRAP) resorption index increased after orchidectomy. Osteocalcin (bone Gla protein; BGP) levels were not affected by orchidectomy. PTH (1-84) treatment did not produce any changes in the levels of CTX/TRAP with respect to the ORX group. BGP levels increased with PTH treatment.
Conclusion:
PTH (1-84) is able to restore the adverse effects of orchidectomy on bone as measured by BMD, microstructural and biomechanical properties and bone remodeling markers.
... It stimulates renal tubular re-absorption of calcium and excretion of phosphate, and indirectly increases intestinal absorption of calcium via its effects on 1, 25-dihydroxyvitamin D production. [30][31][32][33][34]Teriparatide is biosynthesized using Escherichia coli as the host. The bioavailability of teriparatide is approximately 95% after subcutaneous administration. ...
Osteoporosis is characterized by reduced bone mass, impaired bone quality, and a propensity to fracture. An "osteoanabolic" should be referred to any therapy that helps increase bone mass. Bone mass represents 80% of bone mechanical strength. A low bone mass therefore provides the strongest association of future risk of fracture. This review aims to discuss all available and future therapies that attempt to increase bone mass be it organic or inorganic.
... A decrease in CRT_THK in the absence of changes in bone size (PERI_C) indicates that all of the changes in CRT_THK are the result of endocortical bone resorption. Treatments which are known to increase cortical thickness through endocortical bone apposition are PTH ( 2, 19, 20 ) and PGE 2 ( 21, 22 ) . The magnitude of these changes (decrease in ENDO_C) is large and can easily be monitored after 4 weeks or longer. ...
This chapter provides information for the use of peripheral quantitative computed tomography in small animals, including suggestions for study design, instrument setting, and data interpretation.
... 5 indicates that the elastic modulus of the rat bone beam in high vacuum is 4.98 ± 0.25 GPa, low vacuum is 5.24 ± 0.11 GPa and wet, in air is 5.22 ± 0.15 GPa and does not vary greatly over the time period examined. Previous mechanical testing on fully hydrated whole rat bone femur using 3-point bending configuration gives an elastic modulus of 5.12 ± 0.77 GPa (Kasra et al., 1997), 8.0 ± 0.4 GPa (Barengolts et al., 1993), 6.88 ± 0.31 GPa (Jorgensen et al., 1991), and 4.9 ± 0.4 GPa (Ejersted et al., 1993) which is similar to the calculated elastic modulus values in our work and indicates that the vacuum of the SEM chamber does not have an effect on elastic modulus of the samples over the time period investigated. Interestingly, the similarity between the elastic modulus of our relatively small bone volumes and whole bone testing suggests an effective transfer of stresses throughout the bone material, indicating that all bone components are not failing or slipping but are tightly bound to one another. ...
The mechanical properties of rat bone at micron length scales have been evaluated as a function of environmental conditions using an in situ atomic force microscope (AFM) setup while observing using scanning electron microscopy (SEM). Focused ion beam fabricated rat bone cantilever samples were tested in both low and high vacuum conditions in the SEM as well as wet in air using the AFM to measure their elastic modulus. The elastic modulus of rat bone at micron length scales is shown to be independent of the environmental testing conditions and indicates water is bound to bone material even under relatively high vacuum conditions. Our work therefore shows how in situ mechanical testing of bone while observing using high resolution SEM can provide results similar to testing wet in air.
Characterizing the release profile for materials-directed local delivery of bioactive molecules and its effect on bone regeneration is an important step to improve our understanding of, and ability to optimize, the bone healing response. This study examined the local delivery of parathyroid hormone (PTH) via a thiol-ene hydrogel embedded in a porous poly(propylene fumarate) (PPF) scaffold for bone regeneration applications. The aim of this study was to characterize the degradation-controlled in vitro release kinetics of PTH from the thiol-ene hydrogels, in vivo hydrogel degradation in a subcutaneous implant model, and bone healing in a rat critical size bone defect. Tethering PTH to the hydrogel matrix eliminated the early timepoint burst release that was observed in previous in vitro work where PTH was free to diffuse out of the matrix. Only 8% of the tethered PTH was released from the hydrogel during the first two weeks, but by day 21, 80% of the PTH was released, and complete release was achieved by day 28. In vivo implantation revealed that complete degradation of the hydrogel alone occurred by day 21; however, when incorporated in a 3D printed osteoconductive PPF scaffold, the hydrogel persisted for more than 56 days. Treatment of bone defects with the composite thiol-ene hydrogel-PPF scaffold, delivering either 3 or 10 µg of tethered PTH 1-84, was found to increase bridging of critical size bone defects, whereas treatment with 30 µg of tethered PTH resulted in less bone ingrowth into the defect area. Continued development of this biomaterial delivery system for PTH could lead to improved therapies for treatment of non-union fractures and critical size bone defects.
Background:
Osteoporosis is a chronic metabolic disease characterized by an imbalance of bone resorption and formation, leading to bone fragility and increased susceptibility to fracture. Parathyroid hormone is approved therapy for the treatment of osteoporosis.
Methods:
The intermittent therapy of parathyroid hormone requires accurate administration. Meta-analysis is conducted to draw a clear picture of the impact of intermittent therapy and dose rates relative to time, on the osteoporotic patients. A novel mathematical model is presented in this article synchronised with the parametric values, depicted from meta-analysis.
Findings:
Results obtained from the mathematical model are in close agreement with the results obtained from the clinical trials. The model can be used to forecast the drug potency and dosage rates, to control the vicious cycle of osteoporosis.
Interpretations:
The intermittent administration of parathyroid hormone, rather than the continuous administration, is more effective, furthermore it is also concluded that a mathematical model, linked with the extensive literature of clinical trials, using meta-analysis can help in drug administration and future clinical studies of drug development.
Changes in the material properties of bone arise from cellular formation and resorption processes, and systemic factors such as serum chemistry. These processes typically act at the nanometer and micron length scales. Treatments of bone disease aim to increase bone strength by altering bone formation or remodeling processes and serum chemistry to increase bone quantity and quality. The purpose of this review is to summarize the changes in the material properties of bone with disease and drug treatment. In this article we review the effects of the most common metabolic bone diseases such as osteoporosis, osteogenesis imperfecta, vitamin D deficiency, and diabetes mellitus, along with their treatments, on tissue material properties in (a) human studies and (b) pre-clinical animal models.
Multiple myeloma (MM) is a plasma cell neoplasm which is defined by strong interactions with the bone marrow microenvironment, a compartment with high cellular heterogeneity and unique structural and extracellular components. This necessitates the use of in vivo models for research to fully recapitulate MM growth conditions. The selection of appropriate model system is crucial, as each has advantages and shortcomings. Here, we describe the murine models available for studying MM, and focus on the methods for inoculating mice with MM cells via intravenous, intratibial or subcutaneous delivery, as well as monitoring of disease and organ processing for further analysis. The interaction and destruction of bone is a hallmark symptom of MM, and therefore many other complementary techniques used in calcified tissue research can be used, such as microCT, histomorphometry, and biomechanical testing.
Delayed healing and/or non‐union occur in approximately 5‐10% of the fractures that occur annually in the United States. Segmental bone loss increases the probability of non‐union. Though grafting can be an effective treatment for segmental bone loss, autografting is limited for large defects since a limited amount of bone is available for harvest. Parathyroid hormone (PTH) is a key regulator of calcium homeostasis in the body and plays an important role in bone metabolism. Presently PTH is FDA approved for use as an anabolic treatment for osteoporosis. The anabolic effect PTH has on bone has led to research on its use for bone regeneration applications. Numerous studies in animal models have indicated enhanced fracture healing as a result of once daily injections of PTH. Similarly, in a human case study, non‐union persisted despite treatment attempts with internal fixation, external fixation, and autograft in combination with BMP‐7, until off label use of PTH1‐84 was utilized. Use of a biomaterial scaffold to locally deliver PTH to a defect site has also been shown to improve bone formation and healing around dental implants in dogs and drill defects in sheep. Thus, PTH may be used to promote bone regeneration and provide an alternative to autograft and BMP for the treatment of large segmental defects and non‐unions. This review briefly summarizes the unmet clinical need for improved bone regeneration techniques and how PTH may help fill that void by both systemically and locally delivered PTH for bone regeneration applications. This article is protected by copyright. All rights reserved
The intermittent administration of parathyroid hormone (PTH) increases the formation of bone by stimulating osteoblastic activity. Our study evaluates the possibility that intermittent treatment with PTH (1-34) may also enhance the implant-bone fixation of stainless-steel screws. Twenty-eight rats received one screw in either one (n = 8) or in both (n = 20) proximal tibiae. We administered either PTH (1-34) in a dosage of 60 μg/kg/day (n = 14) or vehicle (n = 14) over a period of four weeks. At the end of this time, the degree of fixation was assessed by measuring the removal torque on one screw in each rat (n = 28) and the pull-out strength on the contralateral screw (n = 20). PTH increased the mean removal torque from 1.1 to 3.5 Ncm (p = 0.001) and the mean pull-out strength from 66 to 145 N (p = 0.002). No significant differences in body-weight or ash weight of the femora were seen. Histological examination showed that both groups had areas of soft tissue at the implant-bone interface, but these appeared less in the PTH group. These results indicate that intermittent treatment with PTH may enhance the early fixation of orthopaedic implants.
Intermittent treatment with parathyroid hormone (PTH) has an anabolic effect on both intact cancellous and cortical bone. Very little is known about the effect of the administration of PTH on the healing of fractures or the incorporation of orthopaedic implants. We have investigated the spontaneous ingrowth of callus and the formation of bone in a titanium chamber implanted at the medioproximal aspect of the tibial metaphysis of the rat. Four groups of ten male rats weighing approximately 350 g were injected with human PTH (1-34) in a dosage of 0, 15, 60 or 240 μg/kg/day, respectively, for 42 days from the day of implantation of the chamber.
During the observation period the chamber became only partly filled with callus and bone and no difference in ingrowth distance into the chamber was found between the groups. The cancellous density was increased by 90%, 132% and 173% in the groups given PTH in a dosage of 15, 60 or 240 μg/kg/day, respectively. There was a linear correlation between bone density and the log PTH doses (r ² = 0.6).
Our findings suggest that treatment with PTH may have a potential for enhancement of the incorporation of orthopaedic implants as well as a beneficial effect on the healing of fractures when it is given in low dosages.
This review summarises current understanding of how bone is sculpted through adaptive processes, designed to meet the mechanical challenges it faces in everyday life and athletic pursuits, serving as an update for clinicians, researchers and physical therapists. Bone’s ability to resist fracture under the large muscle and locomotory forces it experiences during movement and in falls or collisions is dependent on its established mechanical properties, determined by bone’s complex and multidimensional material and structural organisation. At all levels, bone is highly adaptive to habitual loading, regulating its structure according to components of its loading regime and mechanical environment, inclusive of strain magnitude, rate, frequency, distribution and deformation mode. Indeed, the greatest forces habitually applied to bone arise from muscular contractions, and the past two decades have seen substantial advances in our understanding of how these forces shape bone throughout life. Herein, we also highlight the limitations of in vivo methods to assess and understand bone collagen, and bone mineral at the material or tissue level. The inability to easily measure or closely regulate applied strain in humans is identified, limiting the translation of animal studies to human populations, and our exploration of how components of mechanical loading regimes influence mechanoadaptation.
Nowadays osteoporosis treatment is based primarily on therapy with antiresorptive agents, like the bisphosphonates. Parathyroid hormone (Preotact) and human recombinant parathyroid hormone peptide 1-34 (Teriparatide) are relatively new for the treatment of osteoporosis and belong to the group of anabolic agents. Both agents demonstrated an increase in bone mineral density and a significant reduction in vertebral fractures in postmenopausal women with osteoporosis when given for 18-24 months. Data on nonvertebral fractures are, however, not clear-cut, and so far only bisphosphonates and strontium ranelate have been demonstrated to reduce all types of fractures and therefore remain the front-line option for treatment of osteoporosis. As the safety, tolerability, and cost of the therapy also influence the choice of therapy, Preotact and Teriparatide might be useful additions to the armamentarium for (second-line) treatment of osteoporosis.
Bone strength is the maximal load that can be applied before a fracture occurs. It is influenced by a number of different factors, such as mass, geometry, architecture, and intrinsic bone tissue quality (Figure 3.1). Bone tissue quality is related to microstructure, to the degree of mineralization, and to matrix characteristics, such as the orientation and chemical structure of the collagen fibers. The aim of antiosteoporotic treatments is to improve bone strength, and thus decrease the risk of fracture (Figure 3.2). In humans, the end point used to evaluate bone strength is fracture occurence; large numbers of patients are required to demonstrate significant reductions as a result of therapeutic intervention. Fracture is not only caused by decreased bone mineral mass, or alteration of the microarchitecture, but is also related to falls, which can occur as a result of loss of balance, inappropriate protective responses, or muscle weakness (Figure 3.3). Thus, careful and specific investigation in animal models to examine the effects of antiosteoporotic treatments on bone strength (Figure 3.4) and its determinants is of major importance.
Introduction/Aim of the study: Diabetes mellitus is one of the most common metabolic diseases and leads to an increased fracture risk and impaired fracture healing. The underlying cellular and molecular mechanisms are not fully understood, but a decreased osteoblastic function seems to be operative. Previously, we showed that blocking of inhibitors of the Wnt signaling pathway stimulated osteoblast function and increased bone quality and bone regeneration in diabetic rats. The aim of this study was to mimic diabetic conditions in vitro to understand the molecular mechanisms underlying decreased osteoblast function. Methods: Osteoblast-like UMR-106 cells were cultured in normal (6 mM) and high (30-150 mM) glucose conditions. Cell vitality, proliferation, and mineralization status as well as gene expression of osteoblastic markers and Wnt molecules were assessed. Results: After four days under high glucose conditions, the proliferation rate of the UMR-106 cells decreased significantly (-42%), while cell number remained stable. In addition, the mineralization capacity of UMR-106 cells was reduced (43%). The gene expression of the bone formation marker osteocalcin was significantly diminished (-38%) similar to the expression of osteopontin (-27%). The expression of connexin 43 and the Wnt inhibitor Dickkopf-1 was increased (+15% and +20%). The concentration of cyclic adenosine monophosphate (cAMP), an ubiquitous intracellular second messenger, decreased with increasing glucose amounts (-61%). The concentration of activated downstream target protein kinase A was reduced under high glucose conditions. Conclusion: These data indicate that high concentrations of glucose suppressed osteoblastic function in vitro. Reduction of cAMP and interference with Wnt signaling represent potential mechanisms.
Bone strength is determined by biomechanical parameters such as bone mass, size, shape and tissue quality. Many osteoporosis treatments build bone mass but also change tissue quality. Careful investigation of all determinants of bone strength should be considered in the pathophysiology of osteoporosis and consequently in the selection of proper antiosteoporotic treatment.
Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone released in a pulsatile fashion by the parathyroid gland in vivo, and regulates serum-ionized calcium levels through its actions on kidney and bone. PTH was initially considered to be primarily a bone-resorbing hormone. However, it is now appreciated that PTH exerts its effects on bone primarily through the osteoblast, and its resorptive effects are only part of the PTH stimulation of bone turnover (resorption and formation). Clinical experience of PTH therapy indicates that this is an important anabolic agent with the potential to reverse osteoporosis. Clinical trials have also suggested that PTH offers the promise of rapid increments in skeletal bone mass in osteoporotic subjects, and antifracture efficacy. Although the effect of PTH treatment is most potent in increasing bone formation at trabecular sites, it is not detrimental to cortical bone and there is no evidence of increased risk of fracture in regions where cortical bone predominates. However, combining PTH with other osteoporosis therapies is not generally recommended. After PTH therapy is completed, there is gradual loss of the newly acquired bone mass. The addition of an anticatabolic therapy is therefore usually recommended after completion of a course of PTH. However, the long-term safety profile of PTH peptides remains to be established.
Studies on endocrine safety pharmacology are part of the “supplemental safety pharmacology studies” described in the ICH guideline S7A. These supplemental studies are performed in order to identify the risk of adverse effects on organ system functions which are not addressed by the general methods of the core battery (ICH 2001; Valentin et al. 2005; Porsolt 2006). Supplemental studies are often required as a consequence of endocrine-related findings in repeated-dose toxicity studies. Such findings may be organ weight changes, histopathology, abnormal findings of biochemistry, and changes in biomarkers which were monitored due to the established pharmacological profile. Frequently, there are unexpected findings related to the gonadal system (testis and ovaries in adult rats), the adrenocortical system (stress-related findings, adrenal hyperplasia, increasing blood pressure), the thyroid gland (thyroid hormone abnormalities, histopathology), the endocrine or exocrine pancreas (impaired glucose control, pancreatitis), changes of electrolytes and calcium-regulating hormones (e.g., calcitonin), and biomarkers of bone turnover. Changes may be related to hormone-producing organs and to hormone-responsive tissues. Such changes may appear at the time of performing regulatory toxicology studies or may be anticipated from conspicuous findings of receptor profiling and early toxicology.
PTH and thyroid hormone (T3) stimulate anabolic and catabolic processes in bone predominantly by acting on osteoblasts. Both inadequate and excessive secretion of either hormone can result in clinical bone disorders. In addition, T3 and PTH related peptide (PTHrP) have multiple effects on a wide number of other tissues modulating both cell differentiation and proliferation. To address the question of whether there might be functional mutual regulation of T3 receptors (TR) and PTH/PTHrP receptors (PTHR), we studied their expression and receptor-mediated intracellular effects in rat osteoblastic osteosarcoma (ROS) 17/2.8 cells. PTHR were up-regulated by T3 pretreatment (10⁻¹⁰–10⁻⁶m) in ROS 17/2.8 cells in a dose-dependent manner. T3 pretreatment increased both PTH-induced cyclic AMP response element binding protein (CREB) phosphorylation and PTH-induced intracellular calcium transients, and further decreased PTH-induced down-regulation of alkaline phosphatase activity, suggesting that there are functional consequences of the PTHR up- regulation. Pretreatment with PTH (10⁻¹⁰–10⁻⁶m) or PTHrP (10⁻⁹m) for 3–4 days resulted in a dose-dependent up-regulation of TR in ROS 17/2.8 cells. cAMP analogues or a calcium ionophore were able to mimic the effect of PTH on TR binding, suggesting that either the cAMP-signaling pathway or Ca²⁺ could be involved in PTH-induced up-regulation of the TR. These observations provide a novel example of mutual interactions between nuclear receptors and membrane receptors and may have significant implications for the regulation of bone remodeling in health and disease.
Osteoporosis is a disease known to promote bone fragility but the effect on the mechanical properties of bone material, which is independent of geometric effects, is particularly unclear. To address this problem, micro-beams of osteoporotic bone were prepared using focused ion beam microscopy and mechanically tested in compression using an atomic force microscope while observing them using in situ electron microscopy. This experimental approach was shown to be effective for measuring the subtle changes in the mechanical properties of bone material required to evaluate the effects of osteoporosis. Osteoporotic bone material was found to have lower elastic modulus and increased strain to failure when compared to healthy bone material, while the strength of osteoporotic and healthy bone was similar. Surprisingly, the increased strain to failure for osteoporotic bone material provided enhanced toughness relative to the control samples, suggesting that lowering of bone fragility due to osteoporosis is not defined by material performance. A mechanism is suggested based on these results and previous literature that indicates degradation of the organic material in osteoporosis bone is responsible for resultant mechanical properties.
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 μg/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 μg/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.
This study examined the effects of parathyroid hormone (PTH) on bone augmentation beyond the skeletal envelope within a plastic cap in rat calvaria.
The calvaria of 30 rats were exposed, and 2 plastic caps were placed on each. Each of the 10 rats was treated with 35 or 105 μg/kg (PTH-35, PTH-105) PTH 3 times per week. The control group was injected with sterile saline 3 times per week. Micro-computed tomography (CT) imaging was performed every 2 weeks for 12 weeks. Micro-CT and histological sections were used to determine the amount of bone augmentation within the plastic caps. Bone volume (BV) was calculated using BV-measuring software.
The histomorphometric and histological analyses showed that the amount of bone augmentation was increased significantly in the PTH groups compared with the controls at 12 weeks. The PTH-105 group showed significantly more bone augmentation and osteoblasts compared with the PTH-35 group.
These results indicate that the higher the dose of intermittent PTH administered, the greater the amount of bone formation beyond the skeletal envelop in the rat calvarium.
Distraction osteogenesis is used both for leg lengthening and for bone transportation in the treatment of fractures and nonunions. The main problem with this method is that the time until full recovery may be up to a year, partly because of the time needed for the new formed bone to consolidate and become strong enough for weight bearing. We have studied whether intermittent parathyroid hormone (PTH(1–34)) could accelerate the consolidation of new formed bone after distraction osteogenesis in rats. Forty-seven, 3-months-old male Sprague–Dawley rats underwent lengthening of the right femur using an external fixator. After a middiaphyseal osteotomy and a 7-day latency period, the callus was distracted during 10 days, with a distraction rate of 0.25 mm twice a day. The consolidation time was either 20 days or 40 days after distraction was completed. A dose of 60 μg of human PTH(1–34)/kg body weight/injection or vehicle was given every second day beginning 30 days before the rats were killed. Both femura of each rat were subjected to mechanical testing and dual-energy X-ray absorptiometry. Blinded histological examination was done for the distracted femura.
The transcriptional cofactor CITED1 inhibits osteoblastic differentiation and blunts the stimulation of osteoblastic differentiation by parathyroid hormone (PTH). In the MC3T3-E1 osteoblastic cell line, we found that CITED1 was located predominantly in the cytoplasm and that hPTH(1-34) increased translocation of CITED1 from the cytoplasm to the nucleus. This response to hPTH(1-34) was not observed when all 9 serine residues within the 63-84 domain of CITED1 were mutated to alanines (CITED1 9S>A) or when a single serine to alanine mutation was made at position 79 (CITED1 S(79)>A). CITED1 containing mutations of these 9 serines to glutamic acid (9S>E) retained the same nuclear translocation response to PTH(1-34) as the wild type CITED1. ALP activity and formation of mineralized nodules were inhibited in cells transfected with pcDNA3-CFP-CITED1 or with pcDNA3-CFP-CITED1 9S>E with or without hPTH(1-34) treatment (all P<0.05); these changes were not observed using CITED1 9S>A. Cells exposed to intermittent treatment with hPTH(1-34) expressed more ALP2, Runx2 and osteocalcin than vehicle-treated cells. These effects of hPTH(1-34) were inhibited in cells transfected with pcDNA3-CFP-CITED1 or pcDNA3-CFP-CITED1 9S>E, but were slightly enhanced by the alanine mutants. PKC activator (TPA) increased nuclear translocation of CITED1, whereas a PKC inhibitor (Go6983) blunted the effect of hPTH(1-34) on the nuclear translocation of wildtype CITED1 but not of CITED1 S(79)>E. The data indicated that serine phosphorylation at position 79 in the 63-84 domain is associated with PKC activation, and is required for both CITED1 nuclear translocation induced by PTH and the negative effects of CITED1 on osteoblastic differentiation and mineralization.
This eight-chapter monograph intends to present basic principles and applications of biomechanics in bone tissue engineering in order to assist tissue engineers in design and use of tissue-engineered products for repair and replacement of damaged/deformed bone tissues. Briefly, Chapter 1 gives an overall review of biomechanics in the field of bone tissue engineering. Chapter 2 provides detailed information regarding the composition and architecture of bone. Chapter 3 discusses the current methodologies for mechanical testing of bone properties (i.e., elastic, plastic, damage/fracture, viscoelastic/viscoplastic properties). Chapter 4 presents the current understanding of the mechanical behavior of bone and the associated underlying mechanisms. Chapter 5 discusses the structure and properties of scaffolds currently used for bone tissue engineering applications. Chapter 6 gives a brief discussion of current mechanical and structural tests of repair/tissue engineered bone tissues. Chapter 7 summarizes the properties of repair/tissue engineered bone tissues currently attained. Finally, Chapter 8 discusses the current issues regarding biomechanics in the area of bone tissue engineering.
Table of Contents: Introduction / Bone Composition and Structure / Current Mechanical Test Methodologies / Mechanical Behavior of Bone / Structure and Properties of Scaffolds for Bone Tissue Regeneration / Mechanical and Structural Evaluation of Repair/Tissue Engineered Bone / Mechanical and Structural Properties of Tissues Engineered/Repair Bone / Current Issues of Biomechanics in Bone Tissue Engineering
Intermittent administration of parathyroid hormone (PTH) increases bone formation and has anabolic skeletal effects. Treatment with full-length PTH (1–84) at a dose of 100 µg/day by subcutaneous injection for 18 months, increases lumbar spine and proximal femur bone mineral density and reduces vertebral fracture risk in postmenopausal women with osteoporosis. Concomitant treatment with alendronate does not improve, and may attenuate, its beneficial effects, however, administration of alendronate after withdrawal of PTH (1–84) therapy maintains the beneficial effects on bone mineral density. Hypercalcemia and hypercalciuria may occur with PTH (1–84) treatment and monitoring is required during the first 6 months of treatment. PTH (1–84) provides an additional option for the prevention of fractures in postmenopausal women, particularly those with severe vertebral osteoporosis.
Cortical porosity in patients with hyperparathyroidism has raised the concern that intermittent parathyroid hormone (PTH) given to treat osteoporotic patients may weaken cortical bone by increasing its porosity. We hypothesized that treatment of ovariectomized (OVX) cynomolgus monkeys for up to 18 months with recombinant human PTH(1–34) [hPTH(1–34)] LY333334 would significantly increase porosity in the midshaft of the humerus but would not have a significant effect on the strength or stiffness of the humerus. We also hypothesized that withdrawal of PTH for 6 months after a 12-month treatment period would return porosity to control OVX values. OVX female cynomolgus monkeys were given once daily subcutaneous (sc) injections of recombinant hPTH(1–34) LY333334 at 1.0 μg/kg (PTH1), 5.0 μg/kg (PTH5), or 0.1 ml/kg per day of phosphate-buffered saline (OVX). Sham OVX animals (sham) were also given vehicle. After 12 months, PTH treatment was withdrawn from half of the monkeys in each treatment group (PTH1-W and PTH5-W), and they were treated for the remaining 6 months with vehicle. Double calcein labels were given before death at 18 months. After death, static and dynamic histomorphometric measurements were made intracortically and on periosteal and endocortical surfaces of sections from the middiaphysis of the left humerus. Bone mechanical properties were measured in the right humeral middiaphysis. PTH dose dependently increased intracortical porosity. However, the increased porosity did not have a significant detrimental effect on the mechanical properties of the bone. Most porosity was concentrated near the endocortical surface where its mechanical effect is small. In PTH5 monkeys, cortical area (Ct.Ar) and cortical thickness (Ct.Th) increased because of a significantly increased endocortical mineralizing surface. After withdrawal of treatment, porosity in PTH1-W animals declined to sham values, but porosity in PTH5-W animals remained significantly elevated compared with OVX and sham. We conclude that intermittently administered PTH(1–34) increases intracortical porosity in a dose-dependent manner but does not reduce the strength or stiffness of cortical bone.
The influence of combined parathyroid hormone (PTH) and growth hormone (GH) treatment on bone formation and mechanical strength was investigated in femoral middiaphysial cortical bone from 20-month-old ovariectomized (OVX) rats. The animals were OVX at 10 months of age, and at 18 months they were treated daily for 56 days with PTH(1-34) alone (60 μg/kg), recombinant human GH (rhGH) alone (2.7 mg/kg), or a combination of PTH(1-34) plus rhGH. Vehicle was given to OVX control rats. All animals were labeled at day 28 (calcein) and at day 49 (tetracycline) of the treatment period. PTH(1-34) alone gave rise to formation of a new zone of bone at the endocortical surface. rhGH alone caused substantial bone deposition at the periosteal surface without influencing the endocortical surface. Combined PTH(1-34) plus rhGH administration enhanced bone deposition at the periosteal surface to the same extent as that of rhGH alone. However, the combined treatment resulted in a more pronounced formation of new bone at the endocortical surface than was induced by PTH(1-34) alone. Both PTH(1-34) alone and rhGH alone increased the mechanical strength of the femoral diaphysis, and further increase in mechanical strength resulted from combined PTH(1-34) plus rhGH treatment. OVX by itself induced the characteristic increase in medullary cavity cross-sectional area and a minor decrease in the mechanical quality of the osseous tissue.
Primary joint replacements generally function well with excellent clinical results. However, failure rates for young patients are still high and increasing in number. The longterm survival of an uncemented prosthesis is influenced by multiple factors depending on host physiology as well as properties of implanted material, initial mechanical stability, early osseointegration, and the surrounding bone. Parathyroid hormone is the principal regulator of calcium homeostasis and involved in the control of bone remodelling. Parathyroid hormone administered intermittently increases bone formation and mass by osteoblast stimulation. Early osseointegration and implant fixation could potentially be enhanced with adjuvant parathyroid hormone treatment. The aim of the studies in this PhD thesis was to determine if implant fixation of experimental implants can be improved with adjuvant intermittent administration of parathyroid hormone.
All studies used an experimental canine model of early implant fixation inserting porous coated titanium alloy implants with no weight bearing in a bed of cancellous bone. The study design was un-paired. Test animals were randomised to PTH (1-34) 5 μm/kg daily for 4 weeks. Implant fixation was defined by mechanical stability and osseointegration. Study I investigated the effect of parathyroid hormone on implant fixation of implants inserted press fit with surrounding bone in the proximal tibia of 20 canines. Histomorphometric analysis showed increased amount of new bone in contact with the implant. No improvement was observed in the surrounding bone. PTH did not increase mechanical fixation in pushout test. Study II investigated the effect of parathyroid hormone on implant fixation of implants surrounded by a critical 1 mm gap. Implants where inserted in the tibia of 20 canines. Bone density was increased in the inner gap and outer gap with PTH treatment. Bone at implant interface improved with PTH but did not achieve significance. Push-out testing showed that PTH Increased mechanical implant fixation in shear stiffness and total energy absorption. Shear strength was not significantly increased. Study III investigated the effect on implant fixation of implants surrounded by a 2.5 mm gap in which morsellised allograft was impacted. Implants were inserted in 20 Canines in the humerus. Histomorphometric analysis showed that PTH increased the amount of new bone within the gap, but not in contact the implant. There were no differences in amount of allograft. The push-out testing showed no differences in mechanical parameters.
The studies in this PhD thesis demonstrated that parathyroid hormone increases bone healing around implants in situations of insertion in press-fit or in more challenging environments of empty and grafted gaps. Early fixation was increased in implants with gaps, in which pure gap bone stimulation improved fixation. This warrants further preclinical studies.
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.
This study was designed to determine the fate of new parathyroid hormone (PTH)-induced cortical bone after withdrawal of PTH treatment, and to evaluate whether subsequent treatment with a bisphosphonate would influence this. Six groups of 21-month-old rats were used: a baseline group killed at the beginning of the experiment, three groups injected with human PTH (1-34) (62 mug/kg) daily for 8 weeks (day 1-56), then one group was killed and the other two groups were injected for another 8 weeks (day 57-112) with either saline or bisphosphonate (risedronate 5 mug/kg twice a week). Two control groups were injected with vehicle for the first 8 weeks, then one group was killed and the other group injected with saline the next 8 weeks. All animals were labeled with tetracycline and calcein on day 35 and day 49 of the experiment, respectively. PTH increased periosteal (35%) and in particular endosteal mineralizing surfaces (188%), mineral appositional rates, and bone formation rates at the femur diaphysis, leading to an increase in cortical cross-sectional area of 31%. Withdrawal of PTH induced a fast and pronounced endosteal bone resorption whereas risedronate prevented this resorption. No differences were seen in apparent density of dry defatted bone and ash among the groups. PTH increased the mechanical strength of the femur diaphysis; ultimate load increased by 64% and ultimate stress by 25%. A pronounced decrease in mechanical strength and competence was found after withdrawal of PTH: ultimate load decreased by 31% and ultimate stress by 21%. Risedronate, however, prevented this decrease in mechanical strength and competence in these 2-year-old rats.
Intermittent parathyroid hormone (PTH) administration shows an anabolic effect on bone. However, the mechanisms are not fully studied. Recent studies suggest that Wnt signaling is involved in PTH-induced bone formation. The current study was to examine if Wnt/β-catenin pathway is required during PTH-induced osteoblast differentiation. Osteoblastic MC3T3-E1 cells were treated with human PTH (1-34) (hPTH [1-34]) and expression levels of osteoblast differentiation markers were detected by real-time PCR. RNA levels of β-catenin, Runx2, Osteocalcin, Alkaline phosphatase, and Bone sialoprotein were significantly up-regulated after treatment with 10(-8) M of hPTH (1-34) for 6 h. Alkaline phosphatase activity and protein expression of β-catenin were also increased after 6 days of intermittent treatment with hPTH (1-34) in MC3T3-E1 cells. hPTH (1-34) significantly enhanced Topflash Luciferase activity after 6 h of treatment. More important, PTH-induced Alkaline phosphatase activity was significantly inhibited by knocking down β-catenin expression in cells using siRNA. Real-time RT-PCR results further showed down regulation of Runx2, Osteocalcin, Alkaline phosphatase, Bone sialoprotein gene expression in β-catenin siRNA transfected cells with/without PTH treatment. These results clearly indicate that PTH stimulates Wnt/β-catenin pathway in MC3T3-E1 cells and osteoblast differentiation markers expression was up-regulated by activation of Wnt/β-catenin signaling. Our study demonstrated that PTH-induced osteoblast differentiation mainly through activation of Wnt/β-catenin pathway in osteoblastic MC3T3-E1 cells.
To evaluate the need for a randomised study of treatment of spinal osteoporosis with human parathyroid peptide in the secondary prevention of crush fractures; to study the effect of human parathyroid hormone peptide 1-34 plus sex hormones on vertebral body cancellous bone; and, separately, to determine the effect of relatively low doses of sodium fluoride plus calcium on spinal bone mineral density.
Open study of patients with primary or postmenopausal osteoporosis. All patients had serial bone densitometry of the spine by quantitative computed tomography and dual photon absorptiometry as well as serial densitometry of the radial midshaft (cortical) and radial distal (trabecular) bone by quantitative computed tomography. Changes in the spinal bone not forming the spongiosa of the vertebral bodies ("cortical" bone) were determined from the difference between the two axial measurements, after correction to the same units of measurement.
Northwick Park Hospital and Medical Research Council Clinical Research Centre.
24 Patients who fulfilled the conventional criteria for type 1 (vertebral) osteoporosis not secondary to recognised causes other than sex hormone deficiency and with at least one crush or wedge vertebral fracture and a spinal bone density (quantitative computed tomography) less than 80 mg/cm3 or two or more fractures. Twelve patients received human parathyroid peptide and 12 sodium fluoride; they were not randomised.
Trends in axial and peripheral bone mass values determined by linear, time dependent regression analyses.
The patients receiving the peptide showed a substantial increase in vertebral spongiosa (mean 25.6 mg/cm2 two years after the start of treatment). No significant changes were seen in spinal cortical or radial bone density. The patients receiving sodium fluoride showed roughly equal increases in cancellous and cortical bone over the same period (mean increase in vertebral spongiosa 16.1 mg/cm3). No significant changes were seen in radial bone.
Treatment of postmenopausal women with human parathyroid peptide selectively increases spinal cancellous bone density by amounts that may prove useful in secondary prevention. Peptide treatment should now be tested in a randomised study in which the important end point is prevention of fractures as the usefulness of sodium fluoride in this context is doubtful.
Although fluoride increases bone mass, the newly formed bone may have reduced strength. To assess the effect of fluoride treatment on the fracture rate in osteoporosis, we conducted a four-year prospective clinical trial in 202 postmenopausal women with osteoporosis and vertebral fractures who were randomly assigned to receive sodium fluoride (75 mg per day) or placebo. All received a calcium supplement (1500 mg per day). Sixty-six women in the fluoride group and 69 women in the placebo group completed the trial. As compared with the placebo group, the treatment group had increases in median bone mineral density of 35 percent (P less than 0.0001) in the lumbar spine (predominantly cancellous bone), 12 percent (P less than 0.0001) in the femoral neck, and 10 percent (P less than 0.0001) in the femoral trochanter (sites of mixed cortical and cancellous bone), but the bone mineral density decreased by 4 percent (P less than 0.02) in the shaft of the radius (predominantly cortical bone). The number of new vertebral fractures was similar in the treatment and placebo groups (163 and 136, respectively; P not significant), but the number of nonvertebral fractures was higher in the treatment group (72 vs. 24; P less than 0.01). Fifty-four women in the fluoride group and 24 in the placebo group had side effects sufficiently severe to warrant dose reduction; the major side effects were gastrointestinal symptoms and lower-extremity pain. We conclude that fluoride therapy increases cancellous but decreases cortical bone mineral density and increases skeletal fragility. Thus, under the conditions of this study, the fluoride-calcium regimen was not effective treatment for postmenopausal osteoporosis.
After baseline studies, 21 patients with osteoporosis were treated with human parathyroid hormone fragment (PTH 1-34) given as once-daily subcutaneous injections for 6-24 months. The dose used did not cause hypercalcaemia even in the first few hours after injection. Calcium and phosphate balances improved in some patients, but there was no significant improvement in the group values. There were, however, substantial increases in iliac trabecular bone volume: the mean increase, confirmed by repeat blind measurements, was 70% above mean baseline volume. The new bone was histologically normal. Those patients who had the largest increases in 47Ca-kinetic and histomorphometric indices of new bone formation showed the greatest increases in trabecular bone volume, suggesting that treatment with human parathyroid hormone fragment caused a dissociation between formation and resorption rates that was confined to trabecular bone. Since vertebrae are four-fifths composed of trabecular bone, this hormone fragment may prove useful in treating patients with the crush fracture syndrome.
This is a book review by A. W. F. Edwards (published in Biometrics, 31(2) 229-230) of my books Biometry (by Sokal and Rohlf) and Statistical Tables (by Rohlf and Sokal) both published in 1981.
Specific insulin-like growth factor-binding proteins (IGFBPs) that may enhance or inhibit insulin-like growth factor (IGF) action are produced in various tissues. In the present study we demonstrated that IGFBPs are synthesized and secreted by rat osteoblast-like cells (UMR 106-01). PTH and PTH-related peptide (PTHrP) were potent stimuli for IGFBP production by UMR cells, whereas GH, IGF-I, insulin, epidermal growth factor, and T3 had little or no effect. A maximal 8- to 30-fold increase in IGFBP production was attained at 10(-7)-10(-6) M PTH and PTHrP, with a half-maximal effect at approximately 10(-9) M. By Western blot analysis, PTH and PTHrP markedly and selectively increased the production of 29,000 mol wt (Mr) and, to a lesser extent, 24,000 Mr IGFBPs. Agents that elevate intracellular cAMP by different mechanisms [(Bu)2cAMP, forskolin, and isobutylmethylxanthine] mimicked the effect of PTH and PTHrP on IGFBP synthesis. In comparison, PTH did not stimulate IGFBP production in fibroblasts and ROS 17/2.8 cells, which secrete IGFBPs of 42,000, 38,000, 34,000, 28,000, and 24,000 Mr, but not of 29,000 Mr. The PTH-responsive IGFBPs from UMR cells were nonglycosylated proteins with preferential affinity for IGF-I over IGF-II. These IGFBPs were not immunoprecipitated with antisera against rat IGFBP-2 or human IGFBP-1. Thus, PTH and PTHrP increase the production in UMR 106-01 cells of discrete IGFBP forms with Mr of 29,000 and 24,000 through a cAMP-mediated mechanism, independent of IGF-I synthesis. Taken with the known effects of PTH on IGF production in bone cells, the data suggest that PTH and PTHrP may modulate local IGF action in bone through the regulation of specific IGFBP availability.
The influence of biosynthetic human growth hormone (b-hGH) on female rat cortical femur and tibia was studied after administration of hormone doses of 0.16, 1.10, or 8.33 mg/kg body weight/day for 90 days. The mechanical properties, dimensions, real density, ash weight, and the mineral and collagen concentrations of the bones were measured. In both femur and tibia a positive linear relation was found between the dose of hormone and ultimate load, ultimate stiffness, energy absorption at ultimate load, load at failure, energy absorption at failure, and deflection at failure. In the femur a positive correlation between dose and deflection at ultimate load was also found. After normalizing the mechanical data for the dimensions of the bones, no differences were found in the hormone treated groups compared to placebo, except for the elastic modulus (Young's modulus), which was decreased in the femur in the group given 8.33 mg b-hGH. The mineral and collagen concentration were unaffected in both femur and tibia, whereas the real density was decreased in the femur. The growth-hormone-induced changes in the mechanical properties seem to be caused mainly by increased dimensions of the bones.
The effect of onset and duration of growth hormone administration on the biomechanical properties of healing rat tibial fractures was investigated after 40 days of healing. Biosynthetic human growth hormone, 2.7 mg/kg body weight/day, was given in two daily injections to three groups of rats: (1) for the entire healing period; (2) for the first 20 days; and (3) for the last 20 days of healing. Three corresponding groups of control rats were injected with saline. In Group 1, maximum load and stiffness of the healing fractures increased to 165% and 175%, respectively, compared to the control group. In Group 2, maximum load, stiffness, maximum stress, and energy absorption at maximum load increased to 222%, 175%, 171%, and 247%, respectively, compared to the control group. In Group 3, no statistically detectable effects were found. The results show that growth hormone stimulates fracture healing both when given during the first part of the healing period and when given during the entire healing period.
PTH has a proven anabolic effect on bone mass, as has been shown in several animal models and treatment regimens. The aim of this study was to ascertain whether the positive effect on bone mass is also reflected in the quality of bone formed. The study was performed in a rat model using human PTH (hPTH). One hundred and twenty male Wistar rats, divided into 10 groups, were given either hPTH-(1-34) or hPTH-(1-84) in daily sc doses. Dose levels ranged from 0.11-3.00 nmol/100 g BW.day for a period of 30 days. At death all six lumbar vertebrae were obtained from each rat. A combination of methods was applied to these vertebral bodies in order to ascertain the effect of hPTH on vertebral bone volume, density, trabecular structure, and biomechanical competence. The results revealed a dose-dependent increase in total volume, dry weight, ash weight, and trabecular bone volume. Also, a dose-dependent increase in load values could be demonstrated. The increase in bone strength remained significant after normalization for both cross-sectional area and bone mass. This indicates that the increase in bone size and bone mass was not achieved at the expense of the quality of the bone present. When the two treatments were administered at the same molar dose level, no difference between hPTH-(1-34) and hPTH-(1-84) was revealed. On the basis of this study, it is concluded that PTH could prove to be a promising treatment in the management of osteopenic states.
A group of 3-month-old Sprague-Dawley rats were sham operated or ovariectomized and given daily injections of human PTH-(1-34) (8 or 16 micrograms per 100 g body weight) for 5 weeks. At the termination of the study histomorphometric techniques were used to examine changes in cortical and cancellous bone in the diaphysis and proximal metaphysis of the tibia. Ovariectomy resulted in a 50% decrease in cancellous bone that was accompanied by a 41 and 120% increase in osteoclasts and osteoblasts, respectively. In contrast, in the ovariectomized animals treated with PTH, the metaphyseal cancellous bone increased by over 300% to a level in excess of that present in the sham-operated control animals. The increase in cancellous bone induced by PTH was associated with an over 70% increase in osteoblasts and tetracycline-labeled area and an unexpected decrease in trabecular osteoclasts. In the tibial diaphysis PTH also decreased endosteal osteoclasts and at the same time increased osteoblast size and number as well as endosteal and periosteal bone formation; ovariectomy increased only periosteal bone formation. Our findings demonstrate that intermittent administration of PTH prevents ovariectomy-induced bone loss and augments cancellous and cortical bone formation in sexually mature ovariectomized rats. Although the basis of the bone anabolic action of PTH remains elusive, our data indicate that it may involve the uncoupling of bone formation and resorption such that the latter is inhibited as bone formation is enhanced. Our findings are also compatible with the view that intermittent administration of PTH increases bone mass, in part by stimulating the proliferation and differentiation of osteoblast progenitors while inhibiting osteoclast proliferation.
Many recent in vitro studies have shown effects of insulin-like growth factor I (IGF I), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF beta) on the proliferation and differential functions of bone-forming osteoblasts; however, the question whether these factors might ultimately lead to a net increase or decrease in bone formation has been difficult to assess. In this study, we have used an autoradiographic method based on the incorporation of [3H]proline into freshly synthesized bone matrix to determine the overall effects of these factors on bone matrix apposition in 21-day-old fetal rat calvariae. IGF I, PDGF, and TGF beta increased bone matrix apposition in a dose-dependent manner up to 2-fold within 48 h. In addition, they partially or completely reversed the inhibition of bone matrix apposition observed with PTH. Exogenously added TGF beta was significantly more potent than equimolar concentrations of PDGF or IGF I in stimulating bone formation. Matrix apposition was greatest when IGF I, PDGF, and TGF beta were added simultaneously to the culture medium, indicating that these factors can enhance each other in stimulating bone formation. In conclusion, our results provide direct evidence that IGF I, PDGF, and TGF beta are capable of stimulating bone formation in vitro.
We tested whether GH is required for the anabolic effect of PTH on bone, using sham-operated (sham) and hypophysectomized (HX) young male rats. HX rats were supplemented daily with 3% sucrose water, T4, and corticosterone. Rats received vehicle or human PTH-(1-34) at 8 micrograms/100 g, sc, once daily, alone or in combination with rat or ovine GH at 0.2 mg/100 g, sc, twice daily or 12 micrograms ovine GH/100 g.day by continuous sc infusion. After 12 days, rats were sedated, and blood, femurs, and tibias were removed. Femur trabecular and cortical bone calcium (Ca), dry weight (DW), and hydroxyproline were measured. PTH increased bone Ca, DW, and hydroxyproline in shams by approximately 30%, but consistently failed to induce an anabolic response in HX rats. GH alone stimulated systemic growth in HX rats and increased their bone Ca and DW by 2-fold. The anabolic effect of PTH was restored in HX rats given both PTH and GH. Total bone mass in these rats was approximately 20% more (P less than 0.05) than the bone mass of rats given GH alone. When food was restricted in shams to limit systemic growth, PTH still induced an increase in bone mass. We conclude that GH or GH-dependent factors, such as insulin-like growth factor-I, which increases in PTH-treated bones in vitro, are required for the anabolic response of bone to PTH in vivo.
Combination therapy with the biologically active (1-38) human parathyroid hormone peptide and calcitonin using pulsatile and sequential activation of the skeleton for 14 months in patients with low-turnover osteoporosis resulted in an increase in trabecular bone mass. These favorable responses were observed without any significant changes in cortical (forearm) bone mass content.
Chronic low doses of hPTH‐(1–34) stimulate bone growth in rats in vivo. The objective of these studies was to determine if the anabolic effect of hPTH‐(1–34) on rat bone in vivo is dependent on an initial stimulation of resorption by blocking resorption with either salmon calcitonin (CT) or dichloromethylene diphosphonate (Cl 2 MDP).
Male Sprague‐Dawley rats, 70–100 g, were treated with daily subcutaneous (SC) injections of vehicle (V) or hPTH‐(1–34), 8 μg per 100 g (PTH), for 12 days. In experiment 1, rats were given CT for 3 (CT3) or 12 (CT12) days, either alone or in combination with hPTH‐(1–34) (CT3‐PTH and CT12‐PTH) or vehicle for 12 days. In experiment 2, rats were pretreated for 4 days with Cl 2 MDP or its vehicle before starting the daily PTH or vehicle injections. Rats were then killed. Sera, femora, tibiae, and kidneys were removed for chemical and histomorphometric analyses.
PTH, PTH‐CT3, and PTH‐CT12 rats showed significant increases in total bone calcium (18–23%), dry weight (DW, 13–25%), and bone‐forming surfaces compared with their respective controls. Eroded (resorption) surfaces were comparable between the groups. Although weight gain and serum calcium were normal in rats treated for 3 days with CT, rats treated for 12 days with CT gained 14% less weight than controls and were hypophosphatemic, with reduced serum calcium and urea nitrogen. Total bone mass increased both in Cl 2 MDP rats (Ca 21%, DW 2%), where resorption was presumably blocked, and in PTH rats (Ca 31%, DW 19%). The increase in bone mass was greater in PTH‐Cl 2 MDP rats (Ca 48%, DW 29%) than in rats treated with Cl 2 MDP alone, suggesting that although Cl 2 MDP blocked resorption, the anabolic response to PTH was not altered. As neither short‐term treatment with CT nor Cl 2 MDP blocked the anabolic response of bone to hPTH‐(1–34), this response does not appear to depend on the early stimulation of resorption.
We have previously reported that low doses of hPTH 1-34 given daily to rats exert an anabolic effect on bone. The objective of this study was to determine if the anabolic effect of PTH was dependent upon continued daily administration of the hormone. Young, male rats were given daily subcutaneous injections of either vehicle or 8 micrograms/100g bw hPTH 1-34 for 12, 16, 20, or 24 days. Additional groups were treated with 8 micrograms/100g bw hPTH for 12 days followed by vehicle for the next 4, 8, or 12 days; or 8 micrograms/100g bw hPTH 1-34 for 16 days followed by 4 days of vehicle. We measured calcium (Ca), dry weight (DW), and hydroxyproline (Hyp) of the distal femur; percent of osteoblast (Ob.S/BS) and osteoclast (Oc.S/BS) surface, mineral apposition rate (MAR), double label surface (DLS/BS), and bone formation rate (BFR) in the metaphysis of the proximal tibia, and serum calcium and phosphate. Trabecular and cortical bone Ca and DW and the histologic measures of bone formation increased in all PTH-treated rats. Serum calcium and phosphate were comparable in all rats. The PTH-stimulated bone mass was lost 12 days after discontinuation of PTH. Discontinuation of PTH administration for 4, 8, or 12 days, respectively, resulted in a 72%, 68%, or 50% decrease in Ob.S/BS from the 2- to 3-fold increase associated with PTH treatment (p less than .05). Oc.S/BS increased compared to controls after 4 days of PTH withdrawal (NS), but was comparable to controls 8 days after withdrawal of PTH.(ABSTRACT TRUNCATED AT 250 WORDS)
PTH stimulates bone resorption and formation, but the mechanism of its anabolic effect is unknown. The effects of PTH on bone formation could be mediated by local regulators, either by altering their binding to receptors or by modulating their synthesis. Cell extracts from PTH-treated osteoblast-enriched cultures isolated from fetal rat parietal bones were examined by Northern blot analysis for changes in mRNAs encoding insulin-like growth factor I (IGF-I), transforming growth factor-beta, and beta 2-microglobulin. PTH did not influence transforming growth factor-beta or beta 2-microglobulin transcript levels. In contrast, PTH-(1-34) had a biphasic stimulatory effect on IGF-I transcript levels; 0.1-10 nM PTH increased IGF-I transcripts by 100-200% after a 6-h treatment, while 100 nM PTH induced a 100% increase. In addition, PTH at 0.01-10 nM increased immunoreactive IGF-I (iIGF-I) in culture medium by 40-200% at 24 h. Maximal increases in IGF-I transcripts occurred at 6 h, while iIGF-I accumulated throughout 24 h of culture. These results are compared to the effects of 0.5-50 nM GH, which increased IGF-I transcripts by 30% and iIGF-I by 50-100%. Therefore, PTH enhanced local IGF-I synthesis by increasing IGF-I transcripts, and this effect may in part mediate the anabolic actions of PTH on bone.
PTH was studied for its effects on bone formation in cultured rat calvariae. 0.01-10 nM PTH stimulated [3H]thymidine incorporation into DNA by up to 4.8-fold. Although continuous treatment with PTH for 24-72 h inhibited [3H]proline incorporation into collagen, transient (24 h) treatment enhanced [3H]proline incorporation into collagen 24-48 h after the hormone was removed. The collagen stimulated by PTH was type I and the effect was observed in the periosteum-free bone and was not blocked by hydroxyurea. Furthermore, treatment with 1-100 nM PTH for 24 h increased insulin-like growth factor (IGF) I concentrations by two to fourfold, and an IGF I antibody prevented the PTH stimulation of collagen synthesis, but not its mitogenic effect. In conclusion, continuous treatment with PTH inhibits calvarial collagen, whereas transient treatment stimulates collagen synthesis, and the stimulatory effect is mediated by local production of IGF I.
It has been suggested that intracellular Ca2+, in addition to cAMP, plays an important role in PTH-stimulated bone resorption. There is now strong evidence indicating that the osteoblast is the main target cell for PTH action, regulating indirectly, via cell-cell communication, osteoclastic bone resorption. In order to investigate the possible role of free cytosolic calcium in stimulated bone resorption, we studied the effects of the intact hormone (bPTH 1-84) and some of its fragments (bPTH (1-34), bPTH(3-34,) (Nle-8, Nle-18,Tyr-34) bPTH (3-34) amide) on their capacity to modify the cytosolic Ca2+ concentration in rat osteoblast-like cells. The experiments were performed using Quin-2, a fluorescent indicator of free calcium. We found an excellent correlation between the ability of PTH and PTH fragments to transiently increase cytosolic Ca2+ concentration in rat osteoblast-like cells and their ability to stimulate bone resorption in embryonic rat calvaria in vitro. On the other hand, no direct correlation was found for the cAMP and bone-resorbing responses. On the ground of these data we propose a two-receptor model for PTH action in osteoblasts, in which one receptor is coupled to the production of cAMP, whereas the other is involved in the increase of cytosolic Ca2+. Activation of both receptors by PTH (1-84) or PTH (1-34) leads to the full physiological response in osteoblasts, most probably the release of one or more factors which stimulate the activity of existing osteoclasts and others which stimulate the recruitment of additional osteoclasts.
The aim of the present study was to examine the effect of therapeutic doses of glucocorticoids on the mechanical strength of rat femora. Groups of rats were treated with a glucocorticoid--methylprednisolone (Solu-Medrol)--1 mg/kg/day for 5, 10, 30, and 90 days. One group served as intact control, two control groups were injected with saline for 30 and 90 days and another group of rats had restricted access to food so that their weight gain was reduced to the same extent as the group treated with glucocorticoid for 90 days. The strength of the femora was analyzed by means of a materials testing machine. No differences were found in the short-term treated groups compared to the control groups, but in the group treated with glucocorticoid for 90 days, a reduction in the bending strength of the rat cortical bone was found. Furthermore, this reduction in strength was found after correction for the reduced thickness of cortical bone in the glucocorticoid-treated rats. The results could not be explained solely by the fact that glucocorticoid-treated rats had smaller bones. No alterations were found in bone density or bone ash weight relative to dry weight. The data indicate that the reduction in bone strength induced by glucocorticoids is not only caused by a reduction in bone quantity, but also by a decrease in bone quality.
In intact growing rats, intermittent administration of low doses of PTH increases bone mass. As gonadal hormones are considered to be essential for normal bone growth, the anabolic effect of PTH may be mediated or modified by these hormones. The objective of this research was to determine if the anabolic effect of PTH would be altered in female ovariectomized (OVX) and male orchidectomized (ORCHX) rats. Two weeks after ovariectomy, orchidectomy, or sham operations, 5-week-old rats (eight per group) were given daily sc injections of human PTH (1-34) (8 micrograms/100 g) or vehicle. After 12 days of treatment, all rats were killed; castration was confirmed, and sera, femurs, tibias, and kidneys were collected. Calcium (Ca) and dry weight (DW) of trabecular and cortical bone of distal half-femurs were measured. Female OVX rats were osteopenic compared to their sham-operated controls, as the bone mass of distal femurs decreased while body weight increased. In PTH-treated females, total bone Ca and DW per 100 g BW increased significantly by 16% and 21%, respectively, in sham-operated rats and by 21% and 25%, respectively, in OVX rats compared to the appropriate control values. ORCHX rats were also osteopenic, as the bone mass of distal femurs was significantly decreased compared to that in sham-operated males. However, as body weight also decreased, the bone mass per unit BW was not altered. In PTH-treated males, total bone Ca and DW per 100 g BW increased significantly by 34% and 25%, respectively, in sham-operated rats by 32% and 29%, respectively, in ORCHX rats compared to their appropriate control values. Serum Ca, creatinine, and alkaline phosphatase levels were normal and comparable in all rats. We conclude that PTH increased bone mass in control, OVX, and ORCHX rats, and the anabolic response to PTH is not dependent on gonadal hormones.
Daily subcutaneous injection of a synthetic human parathyroid hormone fragment, combined with daily ingestion of 1,25(OH)2 vitamin D, significantly increased trabecular bone density in the spine (p less than .01), and improved intestinal calcium and phosphorus absorption and total body retention of dietary calcium and phosphorus in middle-aged men with idiopathic osteoporosis. The increases in spinal bone mineral were marked and progressive during a year of treatment. These results indicate that increasing intestinal absorption of dietary calcium while simultaneously stimulating new bone formation with small doses of parathyroid hormone can restore spinal bone in osteoporotic men.
Tests were done in growing rats to see whether the osteosclerotic changes provoked by parathyroid extract could be due to a compensatory secretion of calcitonin. Parathyroid extract increased metaphyseal bone in both intact and thyroparathyroidectomised animals. Likewise, peptide-pure parathyroid hormone induced similar changes in thyroparathyroidectomised rats. Incorporation of 3H-proline into bone hydroxyproline in these animals was strikingly augmented. It is concluded that (1) parathyroid-extract-induced osteosclerosis is not due to compensatory changes in calcitonin secretion; (2) parathyroid hormone itself, and not a contaminating peptide, is the cause; and (3) parathyroid hormone induces osteosclerosis by increasing bone formation, unlike calcitonin which does so by inhibiting bone resorption.
The deposition of mineralized bone matrix by differentiated osteoblasts was studied in rats in vivo by labeling the bone with three doses of tetracycline given at 48-h intervals. Only bone formation loci bearing all three tetracycline doses were measured, thus eliminating sites where bone formation was not continuous during the labeling period. Using this technique, the effects of intact bovine parathyroid hormone [bPTH-(1-84)] and of a synthetic amino-terminal fragment of human PTH [hPTH-(1-34)] were measured in thyroparathyroidectomized animals. bPTH-(1-84), administered sc, and hPTH-(1-34), administered iv, caused a dose-dependent increase in the bone apposition. Subcutaneous administration of hPTH-(1-34) in doses varying from 2.7-173.0 pmol/rat.day had no effect, probably due to the degradation of the hormone when administered this way. We also compared the effects of bPTH-(1-84) when administered by either daily sc injections or continuous infusion. Continuous infusion of bPTH-(1-84) resulted in an increased apposition rate. Using a morphometric technique, we also found an increase in both formation and resorption surfaces and a net decrease in the trabecular bone volume in this group. Daily injection of the hormone caused an increase in the bone apposition rate, accompanied by an increase in the formation surface without an increase in the resorption surface. This resulted in a net increase in trabecular bone volume. The results thus suggest that the resorptive effects of bPTH-(1-84) can be separated from the effects of the hormone on the apposition rate.
Tdrring 0, Nilsson MHL 1991 The anabolic effects of human parathy-roid hormone (hPTH) on rat vertebral body mass are also re-flected in the quality of bone, assessed by biomechanical test-ing: A comparison study between hPTH-(l-34) and hPTH-(1-84)
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Mosekilde L. Sdgaard CH, Danielscn CC, Tdrring 0, Nilsson MHL 1991 The anabolic effects of human parathy-roid hormone (hPTH) on rat vertebral body mass are also re-flected in the quality of bone, assessed by biomechanical test-ing: A comparison study between hPTH-(l-34) and hPTH-(1-84). Endocrinology 129421-428.
Jdrgensen PH, Andreassen IT 1991 The stimulating effect of growth hormone on fracture healing is dependent on onset and duration of administration Andreassen TT 1991 Mechanical properties of rat cortical femur and tibia after long term treatment with biosynthetic human growth hormone
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Brtoft G. Oxlund H 1988 Reduced strength of rat cortical bone after glucocorticoid treatment. Calcif Tissue Int 43: 376-382. Bak B, Jdrgensen PH, Andreassen IT 1991 The stimulating effect of growth hormone on fracture healing is dependent on onset and duration of administration. Clin Orthop 264: Jdrgensen PH, Bak B, Andreassen TT 1991 Mechanical properties of rat cortical femur and tibia after long term treatment with biosynthetic human growth hormone. Bone Kenedi RM 1980 A Textbook of Biomedical Engineering. Blackie & Sons, Glasgow, pp. 39-73.
Parathy-roid hormone and experimental osteosclerosis Lancet 1: Hock JM. Gera 1, Fonseca J, Raisz LG 1988 Human para-thyroid hormone-(l-34) increases bone mass i n ovariecto-mized and orchidectomized rats
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11050&512. Kalu DN. Doyle FH, Pennock J, Foster GV 1970 Parathy-roid hormone and experimental osteosclerosis. Lancet 1: Hock JM. Gera 1, Fonseca J, Raisz LG 1988 Human para-thyroid hormone-(l-34) increases bone mass i n ovariecto-mized and orchidectomized rats. Endocrinology 122:2899-2904.