Anabolic effects of human biosynthetic parathyroid hormone fragment (1-34), LY333334, on remodeling and mechanical properties of cortical bone in rabbits.

Intermittent administration of parathyroid hormone (PTH) has an anabolic effect in cancellous bone of osteoporotic humans. However, the effect of PTH on cortical bone with Haversian remodeling remains controversial. The aim of this study was to determine the effects of biosynthetic human PTH(1-34) on the histology and mechanical properties of cortical bone in rabbits, which exhibit Haversian remodeling. Mature New Zealand white rabbits were treated with once daily injections of vehicle, or PTH(1-34), LY333334, at 10 micrograms/kg/day or 40 micrograms/kg/day for 140 days. Body weight in rabbits treated with PTH did not change significantly over the experimental period. Serum calcium and phosphate were within the normal range, but a 1 mg/ml increase in serum calcium was observed in rabbits given the higher dose of PTH. Histomorphometry of cortical bone in the midshaft of the tibia showed significant increases in periosteal and endocortical bone formation in these rabbits. Intracortical bone remodeling in the tibia was activated and cortical porosity increased by PTH. Cross-sectional bone area and bone mass of the midshaft of the femur increased significantly after PTH treatment. Ultimate force, stiffness, and work to failure of the midshaft of the femur of rabbits given the 40 micrograms dose of PTH were significantly greater than those in the control group, whereas elastic modulus was significantly lower than that in the rabbits given the 10 micrograms dose of PTH, but not different from controls. In the third lumbar vertebra, PTH increased both formation and resorption without increasing cancellous bone volume. The increases in bone turnover and cortical porosity were accompanied by concurrent increases in bone at the periosteal and endocortical surfaces. The combination of these phenomena resulted in an enhancement of the ultimate stress, stiffness, and work to failure of the femur.     

Continuous parathyroid hormone induces cortical porosity in the rat: effects on bone turnover and mechanical properties.

We examined the time course effects of continuous PTH on cortical bone and mechanical properties. PTH increased cortical bone turnover and induced intracortical porosity with no deleterious effect on bone strength. Withdrawal of PTH increased maximum torque to failure and stiffness with no change in energy absorbed. INTRODUCTION: The skeletal response of cortical bone to parathyroid hormone (PTH) is complex and species dependent. Intermittent administration of PTH to rats increases periosteal and endocortical bone formation but has no known effects on intracortical bone turnover. The effects of continuous PTH on cortical bone are not clearly established. MATERIALS AND METHODS: Eighty-four 6-month-old female Sprague-Dawley rats were divided into three control, six PTH, and two PTH withdrawal (WD) groups. They were subcutaneously implanted with osmotic pumps loaded with vehicle or 40 microg/kg BW/day human PTH(1-34) for 1, 3, 5, 7, 14, and 28 days. After 7 days, PTH was withdrawn from two groups of animals for 7 (7d-PTH/7d-WD) and 21 days (7d-PTH/21d-WD). Histomorphometry was performed on periosteal and endocortical surfaces of the tibial diaphysis in all groups. microCT of tibias and mechanical testing by torsion of femora were performed on 28d-PTH and 7d-PTH/21d-WD animals. RESULTS AND CONCLUSIONS: Continuous PTH increased periosteal and endocortical bone formation, endocortical osteoclast perimeter, and cortical porosity in a time-dependent manner, but did not change the mechanical properties of the femur, possibly because of addition of new bone onto periosteal and endocortical surfaces. Additionally, withdrawal of PTH restored normal cortical porosity and increased maximum torque to failure and stiffness. We conclude that continuous administration of PTH increased cortical porosity in rats without having a detrimental effect on bone mechanical properties.     

Intermittently administered human parathyroid hormone(1-34) treatment increases intracortical bone turnover and porosity without reducing bone strength in the humerus of ovariectomized cynomolgus monkeys.

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 microg/kg (PTH1), 5.0 microg/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.     

PTH receptor signaling in osteocytes governs periosteal bone formation and intracortical remodeling

The periosteal and endocortical surfaces of cortical bone dictate the geometry and overall mechanical properties of bone. Yet the cellular and molecular mechanisms that regulate activity on these surfaces are far from being understood. Parathyroid hormone (PTH) has profound effects in cortical bone, stimulating periosteal expansion and at the same time accelerating intracortical bone remodeling. We report herein that transgenic mice expressing a constitutive active PTH receptor in osteocytes (DMP1‐caPTHR1 mice) exhibit increased cortical bone area and an elevated rate of periosteal and endocortical bone formation. In addition, DMP1‐caPTHR1 mice display a marked increase in intracortical remodeling and cortical porosity. Crossing DMP1‐caPTHR1 mice with mice lacking the Wnt coreceptor, LDL‐related receptor 5 (LRP5), or with mice overexpressing the Wnt antagonist Sost in osteocytes (DMP1‐Sost mice) reduced or abolished, respectively, the increased cortical bone area, periosteal bone formation rate, and expression of osteoblast markers and Wnt target genes exhibited by the DMP1‐caPTHR1 mice. In addition, DMP1‐caPTHR1 lacking LRP5 or double transgenic DMP1‐caPTHR1;DMP1‐Sost mice exhibit exacerbated intracortical remodeling and increased osteoclast numbers, and markedly decreased expression of the RANK decoy receptor osteoprotegerin. Thus, whereas Sost downregulation and the consequent Wnt activation is required for the stimulatory effect of PTH receptor signaling on periosteal bone formation, the Wnt‐independent increase in osteoclastogenesis induced by PTH receptor activation in osteocytes overrides the effect on Sost. These findings demonstrate that PTH receptor signaling influences cortical bone through actions on osteocytes and defines the role of Wnt signaling in PTH receptor action. © 2011 American Society for Bone and Mineral Research.     

Prediction of cortical bone porosity in vitro by microcomputed tomography

The high importance of intracortical porosity for mechanical strength of cortical bone has been established. The contribution of other parameters of microstructure such as osteon dimensions for strength is in discussion. The aim of this study was to evaluate the predictive value of microcomputed tomography (mCT) for porosity and other microstructural parameters of cortical bone in cortical bone biopsies. Femoral cortical bone specimens from the middiaphysis of 24 patients were harvested during the procedure of total hip replacement at the location where normally one hole (? 4.5 mm) for the relief of the intramedullary pressure is placed. In vitro intracortical porosity and bone mineral density (BMD) measurements by mCT were compared with structural parameters assessed in histological sections of the same specimens. A strong correlation was found between intracortical porosity measured by mCT and histological porosity (r = 0.95, P <0.0001). Porosity measured by mCT was also a strong predictor for other parameters describing dimensions of porous structures. BMD?1 was associated with osteonal area (r = -0.76, P <0.0001). We consider the measurement of porosity by mCT as a very potent procedure for assessing intracortical porosity and parameters related to porous structures of cortical bone nondestructively in vitro.     

Prostaglandin E2 enhances cortical bone mass and activates intracortical bone remodeling in intact and ovariectomized female rats

To assess the efficacy of prostaglandin E2 (PGE2) in augmenting cortical bone mass, graded doses of PGE2 were subcutaneously administered for 30 days to seven-month old sham-ovariectomized (SHAM) and ovariectomized (OVX) rats. Both groups were operated at three months of age. Histomorphometric analyses of double fluorescent labeled tibial shafts were performed on basal control, OVX, and SHAM rats treated with 0, 0.3, 1, 3, and 6 mg PGE2/kg/d for 30 days. Baseline aging data showed increased cortical tissue and cortical bone area and reduced bone formation parameters at the periosteal and endocortical bone envelopes between three and eight months of age. The tibial shafts of OVX rats compared to SHAM controls showed elevated periosteal mineral apposition rate and endocortical bone formation parameters. PGE2 administration to OVX and SHAM rats increased cortical bone by the addition of new circumferential bone on the endocortical and periosteal surfaces, as well as woven cancellous bone in the marrow region. Stimulated osteoblastic recruitment and activity enhanced bone formation at all bone surfaces. The new bone was both lamellar and woven in nature. PGE2 treatment also activated intracortical bone remodeling (not seen in untreated eight-month old rats), creating a porous cortex. Thus, PGE2 administration activated cortical bone modeling in the formation mode (A----F), as well as intracortical bone remodeling (A----R----F). PGE2 administration to OVX rats resulted in more intracortical bone remodeling, periosteal bone formation, and new cancellous bone production than observed in PGE2 treated controls. The findings that PGE2 administration to OVX and intact female rats increases cortical bone mass, coupled with observations that mouse, rat, dog, and man respond similarly to PGE2, suggest that PGE2 administration may be useful in the prevention and treatment of postmenopausal osteoporosis.     

Effects of daily treatment with parathyroid hormone 1-84 for 16 months on density, architecture and biomechanical properties of cortical bone in adult ovariectomized rhesus monkeys

Treatment with parathyroid hormone 1-84 (PTH) or teriparatide increases osteonal remodeling and decreases bone mineral density (BMD) at cortical (Ct) bone sites but may also increase bone size. Decreases in BMD and increases in size exert opposing effects on bone strength. In adult ovariectomized (OVX) rhesus monkeys, we assessed the effects of daily PTH treatment (5, 10 or 25 microg/kg) for 16 months on BMD at the radial, tibial and femoral diaphyses, and on biomechanical properties (3-point bending) of radial cortical bone and the femoral diaphysis. PTH treatment did not affect areal BMD measured by dual-energy X-ray absorptiometry at the tibial diaphysis but caused a rapid, dose-related decrease at the distal radial diaphysis. Peripheral quantitative computed tomography at the radial and femoral diaphyses confirmed a significant PTH dose-related decrease in volumetric Ct.BMD caused primarily by increased cortical area. Significant increases in cortical thickness were the result of nonsignificant increases in periosteal length and decreases in endocortical length. Histomorphometry revealed increased endocortical bone formation at the tibial diaphysis and rib, higher Haversian remodeling at the rib and increased cortical porosity at the rib and tibia. Biomechanical testing at the femoral diaphysis showed that PTH treatment had no effect on peak load, but significantly decreased stiffness and increased work-to-failure (the energy required to break the bone). Similar changes occurred in radial cortical beams but only stiffness was changed significantly. Thus, PTH treatment of OVX rhesus monkeys decreased BMD and stiffness of cortical bone but did not affect peak load, likely because of increased bone size. However, PTH treatment increased the energy required to break the femur making it more resistant to fracture.     

Thinking inside and outside the envelopes of bone

Introduction  Bone modeling and remodeling is the final common pathway expressing all genetic and environmental factors that influence the attainment and maintenance of bone’s material and structural strength. Modeling and remodeling require a surface, and during growth this cellular machinery fashions bone’s external size, shape, and internal architecture by depositing bone on, and removing bone from, both its periosteal (external) and endosteal (internal) envelopes. Bone is distributed and redistributed to achieve strength commensurate with its loading requirements. Methods  Advancing age is associated with: (1) a reduction in the volume of bone resorbed by each basic multicellular unit (BMU); (2) an even greater reduction in the volume of bone formed by each BMU so that each remodeling event, whether adaptive or reparative, removes bone from the bone; (3) increased remodeling (number of BMUs) on the three (endocortical, intracortical, and trabecular) components of its endosteal envelope in midlife in women and late in life in both sexes; and (4) reduced bone formation on the periosteal envelope. The net effect is cortical thinning, increased intracortical porosity, trabecular thinning, and loss of connectivity. Results  While remodeling intensity on an envelope determines structure (e.g., trabecular perforations), the surface area of the envelope determines remodeling intensity, and, so, structure. High remodeling on trabecular surfaces decreases as trabeculae (with their surface) are lost. Conversely, remodeling on the endocortical and intracortical envelopes increases their surface area, so remodeling intensity increases and bone loss becomes predominantly cortical. Conclusions  Understanding bone structural strength and its decay and the effects of genetic factors, exercise, nutrition, and drug therapy on bone requires thinking outside and inside these envelopes; their absolute and relative movements during growth and aging determine bone structure and its strength.     

Decreased bone remodeling and porosity are associated with improved bone strength in ovariectomized cynomolgus monkeys treated with denosumab, a fully human RANKL antibody

This study examined the effects of denosumab, an anti-RANKL antibody that inhibits bone resorption, on bone histomorphometry in adult ovariectomized cynomolgus monkeys (OVX cynos). A month after surgery, OVX cynos were treated with subcutaneous vehicle (OVX-Veh) or denosumab (25 or 50mg/kg/month) for 16months (n=14-20/group). Sham controls were treated with vehicle (Sham-Veh; n=17). Areal and volumetric BMD, urine NTx, and serum osteocalcin were measured at baseline and months 3, 6, 12, and 16. Double fluorochrome labels were injected prior to iliac and rib biopsies at month 6 and month 12, and prior to sacrifice at month 16. Histomorphometry was performed on these biopsies, the tibial diaphysis, the L2 vertebra, and the proximal femur. Strength of humeral cortical beams, femur diaphysis, femur neck, and trabecular cores of L5-L6 vertebrae was determined by destructive biomechanical testing. There was no evidence of woven bone, osteomalacia, or other bone histopathologic changes with OVX or with denosumab. OVX-Veh animals exhibited significantly greater bone remodeling at all skeletal sites relative to Sham-Veh controls. Both doses of denosumab markedly inhibited bone remodeling at all sites, including significant reductions in trabecular eroded surfaces (48-86% lower than OVX-Veh controls), cortical porosity (28-72% lower), and dynamic parameters of bone formation (81-100% lower). Decreased fluorochrome labeling with denosumab was related to reductions in cortical porosity and trabecular eroded surfaces, and regression analyses suggested that these reductions contributed to denosumab-related increments in BMD and bone strength. Denosumab-treated animals with the lowest levels of fluorescent labeling exhibited the greatest structural bone strength values at each site. Intracortical remodeling had no relationship with material properties including ultimate strength, elastic modulus or toughness (r(2)=0.00-0.01). These data suggest that remodeling inhibition with denosumab improved structural strength without altering material properties under these experimental conditions. Greater structural strength in the denosumab-treated animals can be primarily explained by the combined effects of increased trabecular and cortical bone mass, and reductions in trabecular eroded surfaces and cortical porosity.     

Changes in Geometry and Cortical Porosity in Adult, Ovary-Intact Rabbits after 5 Months Treatment with LY333334 (hPTH 1-34)

The purpose of this study was to determine if the increased cortical bone porosity induced by intermittently administered parathyroid hormone (PTH) reduces bone strength significantly. Mature ovary-intact New Zealand white rabbits were treated with once daily injections of vehicle, or PTH(1-34), LY333334, at 10 or 40 μg/kg/day for 140 days. Geometry of the femoral midshaft was measured to evaluate changes in the cross-sectional moment of inertia (CSMI). Cortical porosity was measured in the midshaft of the tibia by dividing cortical area into three zones based on equal divisions of cortical diameter: near endocortical (Zone I), near intermediate (Zone II), and near periosteal (Zone III) regions. Total cortical porosity significantly increased after PTH treatment from 1.4% in the controls to 6.3% in the higher dose group, but the location of the new porosities was not randomly distributed. In the controls, porosity of Zones I and II (both 1.7%) was almost twice as much as that of Zone III (0.9%). In the lower dose group, cortical porosity of Zone I (5.5%) and II (1.8%) was greater than in Zone III (0.9%), but these differences were not statistically significant. In the higher dose group, cortical porosity of Zone I (11.5%) and II (6.1%) significantly increased compared with Zone III (1.4%) (P < 0.0005). Histomorphometric measurements showed that bone formation rate on both periosteal and endocortical surfaces increased, resulting in increased bone area and cortical area in the higher dose group. A model was developed to evaluate the effect of the changes in geometry and porosity on CSMI in the different zones. This simulation model indicated that CSMI in the higher dose group was significantly greater than in the other two groups, despite the increased porosity. We speculate the reason to be that porosity increased near the endocortical surface, where its mechanical effect is small. This increase was more than offset by apposition of new bone on the periosteal surface. These data suggest that (1) PTH increases cortical porosity in a dose-dependent manner, primarily near endocortical surfaces; (2) because of this nonhomogeneous distribution, the mechanical effect of increased porosity is small; (3) the increased cortical porosity associated with PTH treatment is more than offset by periosteal apposition of new bone, causing an overall increase in the bending rigidity of cortical bone; and (4) these changes cannot be accurately evaluated using noninvasive methods of bone densitometry, which cannot account for the location of bone gain and bone loss. Received: 20 May 1999 / Accepted: 10 January 2000     

Decreased bone turnover with balanced resorption and formation prevent cortical bone loss during disuse (hibernation) in grizzly bears (Ursus arctos horribilis)

Disuse uncouples bone formation from resorption, leading to increased porosity, decreased bone geometrical properties, and decreased bone mineral content which compromises bone mechanical properties and increases fracture risk. However, black bear bone properties are not adversely affected by aging despite annual periods of disuse (i.e., hibernation), which suggests that bears either prevent bone loss during disuse or lose bone and subsequently recover it at a faster rate than other animals. Here we show decreased cortical bone turnover during hibernation with balanced formation and resorption in grizzly bear femurs. Hibernating grizzly bear femurs were less porous and more mineralized, and did not demonstrate any changes in cortical bone geometry or whole bone mechanical properties compared to active grizzly bear femurs. The activation frequency of intracortical remodeling was 75% lower during hibernation than during periods of physical activity, but the normalized mineral apposition rate was unchanged. These data indicate that bone turnover decreases during hibernation, but osteons continue to refill at normal rates. There were no changes in regional variation of porosity, geometry, or remodeling indices in femurs from hibernating bears, indicating that hibernation did not preferentially affect one region of the cortex. Thus, grizzly bears prevent bone loss during disuse by decreasing bone turnover and maintaining balanced formation and resorption, which preserves bone structure and strength. These results support the idea that bears possess a biological mechanism to prevent disuse osteoporosis.     

Intracortical remodeling during human bone development--a histomorphometric study

Although intracortical bone remodeling is a key aspect of bone physiology, very little is known about this process during human bone development. In this study, we examined transiliac bone samples from 56 individuals between 1.5 and 22.9 years of age (31 female; tetracycline labeling present in 42 subjects) who did not have evidence of metabolic bone disease. Parameters of osteonal structure (osteon diameter, wall thickness, diameter of osteonal canals) and dynamic measures of intracortical remodeling were determined separately for the external and internal cortex. We found that measures of osteonal structure were independent of age. However, the percentage of osteons showing metabolic activity was lower in the older study subjects, corresponding to a slowdown in the turnover of cortical bone. Most dynamic parameters of bone metabolism were higher in the internal cortex than in the external cortex. Cortical porosity was negatively associated with age on the external, but not on the internal cortex. The bone forming activity that refills the remodeling cavities seemed to favor the side of the osteonal canal that faced towards the periosteum. In summary, intracortical remodeling activity varies markedly during bone development, and is slightly asymmetric between the two cortices of an iliac bone specimen. Remodeling during development is thus an age-dependent process that varies with location even within the same bone.     

Transient effects of subcutaneously administered prostaglandin E2 on cancellous and cortical bone in young adult dogs

The transient effects of prostaglandin E2 (PGE2) on cancellous and cortical bone in iliac crests and mid-tibial shafts of nine intact young adult dogs were evaluated following 31 days of treatment. Histomorphometric bone changes were characterized from in vivo fluorescent double-labeled undecalcified bone specimens. PGE2 caused an increase in cancellous bone remodeling evidence by increased in activation frequency; increased percent eroded and formation surfaces; increased mineral apposition and bone formation rates; and shortened resorption, formation, and total bone remodeling periods. Activated cancellous bone remodeling did not lead to decreased cancellous bone mass, indicating an imbalance between bone resorption and formation in favor of formation (activation----resorption----stimulated formation; A----R----F increases) at remodeling sites. The PGE2 treatment activated bone modeling in the formation mode (activation----formation; A----F) at the periosteal and endocortical surfaces and increased activation frequency of intracortical bone remodeling in the tibial shaft. Increased modeling activation converted quiescent bone surfaces to formation surfaces with stimulated osteoblastic activity (i.e., increased percent labeled periosteal and endocortical surfaces, mineral apposition rates, and woven and lamellar trabecular bone formation) leading to 9- to 26-fold increases in newly formed bone mass in subperiosteal, subendosteal, and marrow regions, compared to controls. However, increased intracortical bone remodelling elevated remodeling space (i.e., increased cortical porosity), producing a bone loss that partially offsets the bone gain. The combined events lead to a positive bone balance in PGE2-treated cortical bone, compared to a negative bone balance in control bones. Collectively our data suggest that in vivo PGE2 is a powerful activator of cancellous and cortical bone formation, which may be able to build a peak bone mass to prevent and/or correct the skeletal defects to cure osteoporosis.     

Yellow-bellied marmots (Marmota flaviventris) preserve bone strength and microstructure during hibernation

Reduced skeletal loading typically results in decreased bone strength and increased fracture risk for humans and many other animals. Previous studies have shown bears are able to prevent bone loss during the disuse that occurs during hibernation. Studies with smaller hibernators, which arouse intermittently during hibernation, show that they may lose bone at the microstructural level. These small hibernators, like bats and squirrels, do not utilize intracortical remodeling. However, slightly larger mammals like marmots do. In this study we examined the effects of hibernation on bone structural, mineral, and mechanical properties in yellow-bellied marmots (Marmota flaviventris). This was done by comparing cortical bone properties in femurs and trabecular bone properties in tibias from marmots killed before hibernation (fall) and after hibernation (spring). Age data were not available for this study; however, based on femur length the post-hibernation marmots were larger than the pre-hibernation marmots. Thus, cross-sectional properties were normalized by allometric functions of bone length for comparisons between pre- and post-hibernation. Cortical thickness and normalized cortical area were higher in post-hibernation samples; no other normalized cross-sectional properties were different. No cortical bone microstructural loss was evident in osteocyte lacunar measurements, intracortical porosity, or intracortical remodeling cavity density. Osteocyte lacunar area, porosity, and density were surprisingly lower in post-hibernation samples. Trabecular bone volume fraction was not different between pre- and post-hibernation. Measures of both trabecular and cortical bone mineral content were higher in post-hibernation samples. Three-point bending failure load, failure energy, elastic energy, ultimate stress, and yield stress were all higher in post-hibernation samples. These results support the idea that, like bears, marmots are able to prevent disuse osteoporosis during hibernation, thus preventing increased fracture risk and promoting survival of the extreme environmental conditions that occur in hibernation.     

Indomethacin and bone trauma. Effects on remodeling of rabbit bone

The influence of indomethacin on remodeling activity in normal trabecular and cortical bone and its influence on cortical bone close to a midtibial drill hole, 2 mm in diameter were histomorphometrically evaluated. Eight rabbits were treated with indomethacin (12.5 mg/kg/day), and another 8 rabbits served as controls. After 3 days, the mean plasma indomethacin level was 542 ng/mL, resulting in an almost complete inhibition of prostaglandin synthesis as reflected by the serum levels. In the control rabbits the remodeling activity after 6 weeks was increased 1 mm away from the drill hole but not at 3 and 8 mm. In conclusion, indomethacin had no effect on the activated remodeling process in cortical bone neighboring a small drill hole or on remodeling in nontraumatized cortical and cancellous bone. This suggests that the inhibitory effect of indomethacin on the remodeling process following local trauma to bone depends on the extent of the trauma.     

Indomethacin and bone trauma: Effects on remodeling of rabbit bone

The influence of indomethacin on remodeling activity in normal trabecular and cortical bone and its influence on cortical bone close to a mid-tibial drill hole, 2 mm in diameter were histomorphometrically evaluated. Eight rabbits were treated with indomethacin (12.5 mg/kg/day), and another 8 rabbits served as controls. After 3 days, the mean plasma indomethacin level was 542 ng/mL, resulting in an almost complete inhibition of prostaglandin synthesis as reflected by the serum levels. In the control rabbits the remodeling activity after 6 weeks was increased 1 mm away from the drill hole but not at 3 and 8 mm.

In conclusion, indomethacin had no effect on the activated remodeling process in cortical bone neighboring a small drill hole or on remodeling in nontraumatized cortical and cancellous bone. This suggests that the inhibitory effect of indomethacin on the remodeling process following local trauma to bone depends on the extent of the trauma.     

Enhancement of experimental fracture-healing by systemic administration of recombinant human parathyroid hormone (PTH 1-34)

BACKGROUND: Recombinant human parathyroid hormone (PTH [1-34]; teriparatide) is a new treatment for postmenopausal osteoporosis that can be systemically administered for the primary purpose of increasing bone formation. Because several studies have described the enhancement of fracture-healing and osteointegration in animals after use of PTH, we sought to critically analyze this skeletal effect. METHODS: Two hundred and seventy male Sprague-Dawley rats underwent standard, closed femoral fractures and were divided into three groups that were administered daily subcutaneous injections of 5 or 30 mug/kg of PTH (1-34) or vehicle (control). The dosing was administered for up to thirty-five days. Groups were further divided into three subgroups and were killed on day 21, 35, or 84 after the fracture. The bones were subjected to mechanical torsion testing, histomorphometric analysis, or microquantitative computed tomography. RESULTS: By day 21, calluses from the group treated with 30 mug of PTH showed significant increases over the controls with respect to torsional strength, stiffness, bone mineral content, bone mineral density, and cartilage volume. By day 35, both groups treated with PTH showed significant increases in bone mineral content and density and total osseous tissue volume, and they demonstrated significant decreases in void space and cartilage volume (p < 0.05). Torsional strength was significantly increased at this time-point in the group treated with 30 mug of PTH (p < 0.05). While dosing was discontinued on day 35, analyses performed after eighty-four days in the group treated with 30 mug of PTH showed sustained increases over the controls with respect to torsional strength and bone mineral density. No change was noted in osteoclast density at the time-points measured, suggesting that treatment with PTH enhanced bone formation but did not induce bone resorption. CONCLUSIONS: These data show that daily systemic administration of PTH (1-34) enhances fracture-healing by increasing bone mineral content and density and strength, and it produces a sustained anabolic effect throughout the remodeling phase of fracture-healing.     

Effect of treatment for 6 months with human parathyroid hormone (1-34) peptide in ovariectomized cynomolgus monkeys (Macaca fascicularis).

A potential negative side effect of intermittent parathyroid hormone (PTH) therapy to treat osteoporosis is the loss of cortical bone concomitant with increased cancellous bone mass. We addressed this issue by studying the effects of PTH on whole-body, axial, and appendicular bone mass in an animal model with haversian cortical bone remodeling. Ovariectomized, young adult female cynomolgus monkeys were assigned to placebo (n = 9) or PTH groups (n = 10). The PTH group received 10 microg/kg synthetic human PTH(1-34) peptide by subcutaneous injection, 3 days/week for 6 months, and the placebo group received vehicle. Multiple endpoints of bone mass, strength, and turnover in the axial and appendicular skeleton were assessed, including dual-energy X-ray absorptiometry (DEXA), quantitative computed tomography (qCT), analysis of serum (calcium, phosphorus, alkaline phosphatase, osteocalcin, and tartrate-resistant acid phosphatase) and urinary (calcium and creatinine) biomarkers, histomorphometry, and biomechanical testing. Compared with placebo-treated animals, PTH-treated monkeys had no change in whole-body bone mass, but a 6.7% increase in spinal areal bone mineral density (aBMD) was observed. Cortical bone mass measured by qCT at appendicular sites was not affected by PTH treatment, but there were significant increases in cancellous bone mass in the proximal tibia, and a similar trend in the distal radius. Small, transient increases in serum and urinary calcium were observed, but there were no treatment-related effects on other biochemical endpoints. Increased bone formation rate (BFR/BV) in the midradius and midfemur was accompanied by a nonsignificant increase in midfemur porosity. Increased vertebral cancellous bone volume (BV/TV) was associated with greater trabecular and interstitial thickness with no effect on wall thickness. Increases in bone strength were observed in both axial (vertebral maximum stress and load at fracture) and appendicular (femoral neck fracture load) skeleton. Together, these results indicate that PTH therapy in the cynomolgus monkey results in a net gain of spinal and appendicular cancellous bone mass with no adverse effect on cortical bone.     

硬化蛋白抗体和跑台运动对老龄去势大鼠骨重建的影响

目的探讨硬化蛋白抗体和跑台运动对老龄去势大鼠骨重建的影响。方法 8月龄雌性Wistar大鼠,按体质量随机分层分为5组:Sham组(假手术组)、OVX组(去卵巢组)、OVX+E组(去卵巢+运动组)、OVX+S组(去卵巢+硬化蛋白抗体组)、OVX+E+S组(去卵巢+运动+硬化蛋白抗体组)。在14w后取材进行相关指标测试。结果 1单纯性的运动锻炼能降低脂肪量,增加骨小梁数目,减少骨吸收标记物NTx水平,防止老龄去势大鼠全身、股骨骨密度发生下降。2单纯性的硬化蛋白抗体治疗能增加骨形成标志物OC,提高去势大鼠的皮质孔隙率、皮质骨体积和皮质骨厚度,提高骨密度。3运动与硬化蛋白抗体交互作用时,可以降低脂肪量,提高骨密度和皮质骨参数,增加骨量和骨强度,提高OC水平、降低NTx水平。结论适度的跑台运动可以防止老龄去势大鼠骨量丢失,改善去势大鼠骨健康。硬化蛋白抗体疗法可以增加皮质骨骨量和骨强度,预防去势大鼠绝经后对骨代谢的不良影响。硬化蛋白和运动表现出良好的协同作用,对老龄去势大鼠骨重建具有积极的作用。     

The influence of combined parathyroid hormone and growth hormone treatment on cortical bone in aged ovariectomized rats.

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 microg/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.