Intermittently administered parathyroid hormone 1-34 reverses bone loss and structural impairment in orchiectomized adult rats

Preventive effects of transcutaneous CO2 application on disuse osteoporosis and muscle atrophy in a rat hindlimb suspension model

We previously demonstrated that transcutaneous CO2 application promotes muscle fiber-type switching, fracture healing, and osteogenesis by increasing blood flow and angiogenesis. Here, we aimed to investigate the preventive effects of transcutaneous CO2 application on disuse osteoporosis and muscle atrophy in a rat hindlimb suspension model. Eleven-week-old male Sprague-Dawley rats were divided into hindlimb suspension (HS), HS with transcutaneous CO2 application (HSCO2), and control groups. HSCO2 rats were administered transcutaneous 100 % CO2 gas in their bilateral hindlimbs, five times a week for 20 min. After 3 weeks, we harvested the gastrocnemius, femur, and tibia for assessment. Histological analysis revealed a significant decrease in the gastrocnemius myofiber cross-sectional area in HS rats compared to the control rats, whereas HSCO2 rats exhibited a significant increase compared to HS rats. Micro-computed tomography showed significant bone atrophy in the trabecular and cortical bones of the femur in HS rats compared to those of the control rats, whereas significant improvement was noted in HSCO2 rats. Histological analysis of the proximal tibia revealed more marrow adipose tissue in the HS rats than in the control rats. However, in the HSCO2 rats, fewer marrow adipose tissue and osteoclasts were observed. Moreover, HSCO2 rats had more osteoblasts and higher expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and vascular endothelial growth factor (VEGF) than the HS rats. The gastrocnemius and distal femur of HSCO2 rats also exhibited elevated PGC-1α and VEGF expression and upregulation of the myogenesis markers and osteogenesis markers compared to those of HS rats. This treatment effectively prevented disuse osteoporosis and muscle atrophy by promoting local angiogenesis and blood flow. PGC-1α is crucial for promoting this angiogenic pathway. Transcutaneous CO2 application may be a novel preventive procedure for disuse osteoporosis and muscle atrophy, complementing medication and rehabilitation.

Influence of bisphosphonate treatment on bone substitute performance in osteoporotic conditions

OBJECTIVE

Considering the elevated number of osteoporotic patients in need of bone graft procedures, we here evaluated the effect of alendronate (ALN) treatment on the regeneration of bone defects in osteoporotic rats. Bone formation was histologically and histomorphometrically assessed in rat femoral condyle bone defects filled with bone graft (Bio-Oss®) or left empty.

METHODS

Male Wistar rats were induced osteoporotic through orchidectomy (ORX) and SHAM-operated. The animals were divided into three groups: osteoporotic (ORX), osteoporotic treated with ALN (ORX + ALN) and healthy (SHAM). Six weeks after ORX or SHAM surgeries, bone defects were created bilaterally in femoral condyles; one defect was filled with Bio-Oss® and the other one left empty. Bone regeneration within the defects was analyzed by histology and histomorphometry after 4 and 12 weeks.

RESULTS

Histological samples showed new bone surrounding Bio-Oss® particles from week 4 onward in all three groups. At week 12, the data further showed that ALN treatment of osteoporotic animals enhanced bone formation to a 10-fold increase compared to non-treated osteoporotic control. Bio-Oss® filling of the defects promoted bone formation at both implantation periods compared to empty controls.

CONCLUSION

Our histological and histomorphometric results demonstrate that the enteral administration of alendronate under osteoporotic bone conditions leverages bone defect regeneration to a level comparable to that in healthy bone. Additionally, Bio-Oss® is an effective bone substitute, increasing bone formation, and acting as an osteoconductive scaffold guiding bone growth in both healthy and osteoporotic bone conditions.

SIGNIFICANCE

Based on the results of this study, enteral use of ALN mitigates adverse effects of an osteoporotic condition on bone defect regeneration.

HU-671, a Novel Oleoyl Serine Derivative, Exhibits Enhanced Efficacy in Reversing Ovariectomy-Induced Osteoporosis and Bone Marrow Adiposity

Oleoyl serine (OS), an endogenous fatty acyl amide (FAA) found in bone, has been shown to have an anti-osteoporotic effect. OS, being an amide, can be hydrolyzed in the body by amidases. Hindering its amide bond by introducing adjacent substituents has been demonstrated as a successful method for prolonging its skeletal activity. Here, we tested the therapeutic efficacy of two methylated OS derivatives, oleoyl α-methyl serine (HU-671) and 2-methyl-oleoyl serine (HU-681), in an ovariectomized mouse model for osteoporosis by utilizing combined micro-computed tomography, histomorphometry, and cell culture analyses. Our findings indicate that daily treatment for 6 weeks with OS or HU-671 completely rescues bone loss, whereas HU-681 has only a partial effect. The increased bone density was primarily due to enhanced trabecular thickness and number. Moreover, the most effective dose of HU-671 was 0.5 mg/kg/day, an order of magnitude lower than with OS. The reversal of bone loss resulted from increased bone formation and decreased bone resorption, as well as reversal of bone marrow adiposity. These results were further confirmed by determining the serum levels of osteocalcin and type 1 collagen C-terminal crosslinks, as well as demonstrating the enhanced antiadipogenic effect of HU-671. Taken together, these data suggest that methylation interferes with OS’s metabolism, thus enhancing its effects by extending its availability to its target cells.

Abaloparatide improves cortical geometry and trabecular microarchitecture and increases vertebral and femoral neck strength in a rat model of male osteoporosis

Androgen deficiency is a leading cause of male osteoporosis, with bone loss driven by an inadequate level of bone formation relative to the extent of bone resorption. Abaloparatide, an osteoanabolic PTH receptor agonist used to treat women with postmenopausal osteoporosis at high risk for fracture, increases bone formation and bone strength in estrogen-deficient animals without increasing bone resorption. This study examined the effects of abaloparatide on bone formation, bone mass, and bone strength in androgen-deficient orchiectomized (ORX) rats, a male osteoporosis model. Four-month-old Sprague-Dawley rats underwent ORX or sham surgery. Eight weeks later, sham-operated rats received vehicle (saline; n = 10) while ORX rats (n = 10/group) received vehicle (Veh) or abaloparatide at 5 or 25 μg/kg (ABL5 or ABL25) by daily s.c. injection for 8 weeks, followed by sacrifice. Dynamic bone histomorphometry indicated that the tibial diaphysis of one or both abaloparatide groups had higher periosteal mineralizing surface, intracortical bone formation rate (BFR), endocortical BFR, and cortical thickness vs Veh controls. Vertebral trabecular BFR was also higher in both abaloparatide groups vs Veh, and the ABL25 group had higher trabecular osteoblast surface without increased osteoclast surface. By micro-CT, the vertebra and distal femur of both abaloparatide-groups had improved trabecular bone volume and micro-architecture, and the femur diaphysis of the ABL25 group had greater cortical thickness with no increase in porosity vs Veh. Biomechanical testing indicated that both abaloparatide-groups had stronger vertebrae and femoral necks vs Veh controls. These findings provide preclinical support for evaluating abaloparatide as an investigational treatment for male osteoporosis.

Phospholipase C signaling activated by parathyroid hormone mediates the rapid osteoclastogenesis in the fracture healing of orchiectomized mice

Background

The age-related osteoporosis is an increasing risk severely threatening the live quality of aged people. Human parathyroid hormone (hPTH) is applied to the therapy of osteoporosis successfully, however, the mechanism, especially the signaling pathway activated in the healing fracture by PTH is still unknown.

Methods

The once daily injections of hPTH(1–34) and GR (1–34) (the PLC deficient analog) into the orchiectomized male mice with bone fracture, were started at the second day after fracture and lasted for 4 weeks. To explore the role of phospholipase C signaling in the androgen-deficient fracture healing, the fracture healing were evaluated via radiography, micro-CT, biomechanics testing, serum biochemistry, bone marrow cell culture and gene expression quantification.

Results

After two weeks of fracture, both peptides significantly increased bone mineral density (BMD), bone mass content (BMC) and bone volume (BV/TV) in the healing area. However, compared to hPTH(1–34), GR(1–34) induced more woven bones, the higher BMC and BMD, as well as the less serum TRAP and osteoclasts. After four weeks of treatment, the effects of hPTH(1–34) on fracture healing showed no difference to those of GR(1–34). Consistently, GR(1–34) induced the similar osteogenesis but less osteoclastogenesis under the ex vivo condition immediately after administration compared to hPTH(1–34), which was verified by the weaker activation of RANKL, NFATC1, TRAP and Cathepsin K in GR(1–34) treatment.

Conclusion

These results indicated that the PLC signaling activated by the intermittent injection of hPTH(1–34) leads to the bone resorption by rapidly activating the osteoclastogenesis in the fracture healing zone.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2231-3) contains supplementary material, which is available to authorized users.

Effects of standardized quassinoid-rich Eurycoma longifolia extract in a rat model of osteoporosis due to testosterone deficiency: A densitometric, morphometric and biomechanical study

BACKGROUND

Eurycoma longifolia (EL) is a well-known aphrodisiac herb for men. Recently, the crude extract of EL was reported to possess anti-osteoporotic activities.

OBJECTIVE

This study aims to determine the bone protective effects of the standardized quassinoid-rich EL extract in testosterone-deficient rat model.

METHODS

Ninety-six intact male Sprague-Dawley rats were randomized into baseline, sham, orchidectomized, and chemically castrated groups. Chemical castration was performed via subcutaneous injection of degarelix at 2 mg/kg. The orchidectomized and degarelix-induced rats were administered with vehicle, intramuscularly injected with testosterone once a week, or orally supplemented with EL extract at doses of 25 mg/kg, 50 mg/kg or 100 mg/kg daily for 10 weeks. Bone mass, microarchitecture and strength were analyzed by dual-energy x-ray absorptiometry (DEXA), micro-CT and three-point bending test.

RESULTS

Whole body bone mineral density and femoral bone mineral content significantly increased in testosterone groups (p <  0.05). Micro-CT analysis revealed that trabecular bone volume, number, separation and connectivity density were significantly improved by testosterone administration. However, the structural model index was only improved in degarelix group supplemented with 100 mg/kg EL extract (P <  0.05). The improvement of cortical thickness by EL extract was similar to that of testosterone groups (p <  0.05). Biomechanically, EL extract supplementation was able to improve stiffness, strain and modulus of elasticity in degarelix-induced groups, while stress parameter was significantly improved in orchidectomized groups (p <  0.05).

CONCLUSION

Quassinoid-rich EL extract enables to protect against bone loss due to testosterone deficiency. The protective effect on cortical thickness and biomechanical parameters is comparable to testosterone group.

The local administration of parathyroid hormone encourages the healing of bone defects in the rat calvaria: Micro-computed tomography, histological and histomorphometric evaluation

OBJECTIVE

To evaluate the effect of a single-dose local administration of PTH on bone healing in rat calvarial bone defects by means of micro-computed tomography, histological and histomorphometric analysis.

DESIGN

Critical-size cranial osteotomy defects were created in 42 male rats. The animals were randomly divided into 3 groups. In the C Group, the bone defect was only filled with a blood clot. In the S Group, it was filled with a collagen sponge and covered with bovine cortical membrane. In the PTH Group, the defect was filled with a collagen sponge soaked with PTH and covered with bovine cortical membrane. The groups were further split in two for euthanasia 15 and 60days post-surgery. Data was statistically analyzed with t-tests for independent samples or the nonparametric Mann-Whitney test when applicable. Intragroup comparisons were analyzed with paired t-tests (p<0.05).

RESULTS

Micro-CT analysis results did not demonstrate statistically significant intergroup differences. At 15days post-surgery, the histomorphometric analysis showed that the PTH Group exhibited a significantly higher percentage of bone formation compared with the S Group. At 60days post-surgery, a higher percentage of new bone was observed in the PTH group.

CONCLUSION

The results suggest that the local administration of PTH encouraged the bone healing in critical-size calvarial defects in rats.

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

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

Effect of Combined Teriparatide and Monthly Risedronate Therapy on Cancellous Bone Mass in Orchidectomized Rats: A Bone Histomorphometry Study

This study investigated the effects of combined teriparatide (an anabolic agent) and monthly risedronate (an anti-resorptive agent) therapy on cancellous bone mass in orchidectomized (ORX) rats. Fifty 14-week-old male Sprague-Dawley rats were randomized into five groups of ten animals each: sham-operation + vehicle; ORX + vehicle; ORX + risedronate (90 μg/kg subcutaneous, every 4 weeks); ORX + teriparatide (30 μg/kg subcutaneous, three times per week); and ORX + risedronate + teriparatide. After the 12-week experimental period, cancellous bone in the tibial proximal metaphysis was examined by static and dynamic histomorphometric analyses. ORX decreased bone volume per total volume (BV/TV) and trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). Risedronate increased BV/TV and Tb.N above the sham control values, while teriparatide prevented the ORX-induced decrease in BV/TV and increased trabecular width (Tb.Wi) above sham control levels. Risedronate decreased Tb.Sp below control values, while teriparatide prevented the ORX-induced increase in Tb.Sp. The combination of teriparatide and risedronate further increased BV/TV and Tb.N and decreased Tb.Sp as a result of suppression of bone remodeling, compared with teriparatide alone. These results suggest that teriparatide and monthly risedronate exert different effects on cancellous bone structure and thus have additive effects on cancellous bone mass in ORX rats.

Promotion of peri-implant bone healing by systemically administered parathyroid hormone (1-34) and zoledronic acid adsorbed onto the implant surface

The effect of human parathyroid hormone 1-34 (PTH) and zoledronic acid (ZA) alone or in combination on bone healing in osteoporotic settings was tested using implants inserted in tibiae of ovariectomized (OVX) rats. Combination therapy promoted bone healing more than each treatment alone 12 weeks after implant insertion.

INTRODUCTION

PTH and ZA have been demonstrated to be effective on implant fixation. However, reports about the combined use of PTH and ZA for promotion of bone healing around implant in osteoporotic settings are still limited. This study aims to investigate effects of PTH+ZA on implant stabilization in OVX rats.

METHODS

Twelve weeks after bilateral ovariectomy, OVX rats randomly received implants without or with ZA (by immersion in 1 mg/ml ZA solution for 24 h). Subsequently, half of the animals from each group also received subcutaneous injections of PTH (60 μg/kg, three times a week) for 12 weeks. Thus, there were four groups: control, PTH, ZA, and PTH+ZA.

RESULTS

All treatments promoted bone healing around implant compared to control, but PTH+ZA treatment showed significantly stronger effects than PTH or ZA alone in histological, micro-CT, and biomechanical tests.

CONCLUSION

The results indicated the additive effects of PTH and ZA on implant fixation in OVX rats; it was suggested that the anabolic effect of PTH was potent and not blunted by ZA during bone healing around implant when used concurrently.

Teriparatide vs. alendronate as a treatment for osteoporosis: changes in biochemical markers of bone turnover, BMD and quality of life

Background

We studied the use of teriparatide in postmenopausal women with severe osteoporosis.

Material/Methods

Two groups (A and B) of patients affected by severe osteoporosis (T-score ⩽−2.5 at bone mineral density were analyzed and 2 vertebral fractures on radiograph).

Group A was treated for 18 months with 20 μg/day of teriparatide. Group B was treated with bisphosphonates 70 mg/week. Every woman assumed 1 g of calcium and 800 IU of vitamin D3 daily. We evaluated the effects of therapy after 18 months (T18) from the beginning with bone turnover markers (alkaline phosphatase, procollagen type 1 N-terminal propeptide, and N-telopeptide cross-links) and dual-energy X-ray absorptiometry.

Results

Group A, at T18 procollagen type 1 N-terminal propeptide levels, increased 127%; bone alkaline phosphatase levels increased to 65%; N-telopeptide cross-links levels increased to 110%.

Group B, at T18 procollagen type 1 N-terminal propeptide levels, decreased to 74%; bone alkaline phosphatase levels decreased to 41%; N-telopeptide cross-links levels decreased to 72%.

After 18 months, lumbar bone mineral density increased to 12.4% and femoral bone mineral density increased to 5.2% in group A. Group B lumbar bone mineral density increased to 3.85% and femoral bone mineral density increased to 1.99%. Only a new vertebral fracture occurred in group A (2.4%), whereas 6 fractures occurred in group B (15.7%).

The quality of life questionnaire of the European Foundation for Osteoporosis (QUALEFFO) revealed a significant improvement in daily living, performed domestic jobs, and locomotor function in groups A and B.

Conclusions

The use of rhPTH in patients with severe osteoporosis offers more protection against fractures and improves the QoL more than bisphosphonates.

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

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

Effect of parathyroid hormone on hypogonadism induced bone loss of proximal femur of orchiectomized rat

Purpose

Management of hypogonadism-induced osteoporosis in elderly men is still a challenge. We investigated the short-term effects of parathyroid hormone (PTH) treatments on strength, micro-architecture, and mineral density of trochanteric region of orchiectomized rat femur.

Methods

Eight-month-old male Sprague–Dawley rats (n = 44) were divided into two groups: (1) orchiectomized (ORX) and (2) sham group. Twelve weeks after orchiectomy, half of the orchiectomized animals were treated with daily subcutaneously injected PTH (0.040 mg/kg/BW) (ORX-PTH) for 5 weeks. The other half remained untreated (ORX). The sham-operated group was divided and treated in the same way (sham, sham-PTH). After 5 weeks, both femurs were excised for biomechanical and histomorphometric analysis, trabecular measurements, mineral content assessment, and immunofluorescence analysis.

Results

The femoral trochanteric strength after PTH treatment was enhanced in the breaking test (ORX-F_max = 158.7 N vs. ORX + PTH-F_max = 202 N). Stiffness of treated ORX animals reached nearly the levels observed in untreated sham rats. PTH therapy improved the trabecular connectivity, width, and area (ORX-Tb.Ar = 47.79% vs. ORX + PTH-Tb.Ar = 68.47%, P < 0.05) in the proximal femur. The treated rats showed significantly improved mineral content in ashed femurs (ORX-mineral content = 43.73% vs. ORX + PTH-mineral content = 49.49%) when compared to the untreated animals. A comparison of widths of fluorescence bands in cortical bone of the subtrochanteric cross-sections showed a significant increase in oppositions after the PTH therapy.

Conclusions

Our finding supports the hypothesis that PTH therapy seems to be a rational therapy in patients with hypogonadism induced bone loss and improves the bone strength of trochanteric region of rat femur.

Inhibition of sclerostin by monoclonal antibody increases bone formation, bone mass, and bone strength in aged male rats

The purpose of this study was to evaluate the effects of sclerostin inhibition by treatment with a sclerostin antibody (Scl-AbII) on bone formation, bone mass, and bone strength in an aged, gonad-intact male rat model. Sixteen-month-old male Sprague-Dawley rats were injected subcutaneously with vehicle or Scl-AbII at 5 or 25 mg/kg twice per week for 5 weeks (9-10/group). In vivo dual-energy X-ray absorptiometry (DXA) analysis showed that there was a marked increase in areal bone mineral density of the lumbar vertebrae (L(1) to L(5) ) and long bones (femur and tibia) in both the 5 and 25 mg/kg Scl-AbII-treated groups compared with baseline or vehicle controls at 3 and 5 weeks after treatment. Ex vivo micro-computed tomographic (µCT) analysis demonstrated improved trabecular and cortical architecture at the fifth lumbar vertebral body (L(5) ), femoral diaphysis (FD), and femoral neck (FN) in both Scl-AbII dose groups compared with vehicle controls. The increased cortical and trabecular bone mass was associated with a significantly higher maximal load of L(5) , FD, and FN in the high-dose group. Bone-formation parameters (ie, mineralizing surface, mineral apposition rate, and bone-formation rate) at the proximal tibial metaphysis and tibial shaft were markedly greater on trabecular, periosteal, and endocortical surfaces in both Scl-AbII dose groups compared with controls. These results indicate that sclerostin inhibition by treatment with a sclerostin antibody increased bone formation, bone mass, and bone strength in aged male rats and, furthermore, suggest that pharmacologic inhibition of sclerostin may represent a promising anabolic therapy for low bone mass in aged men.

The effectiveness of intermittent rat parathyroid hormone (1-34) treatment on low bone mass due to oestrogen or androgen depletion in skeletally mature rats

Rat parathyroid hormone (PTH) 1-34 (4 microg/kg/day) was applied for 2.5 months to 9 month-old rats immediately after ovariectomy or orchidectomy or to 15 month-old rats with low bone mass which had been castrated 6 months before in order to know the effects on serum biochemistry parameters, lumbar and femoral bone mineral density, histology, cancellous and cortical bone histomorphometry, mineralisation content profile in cortical bone by backscattered-electron microscopy, and femoral torsion biomechanical testing. In ovariectomised rats, preventive PTH treatment avoided cancellous bone loss in tibial metaphysis and partially in lumbar vertebra, while in cortical bone, PTH increased endosteal resorption and periosteal formation. In intervention study, PTH did not restore cancellous bone but a strong endosteal and periosteal new bone formation was detected. In orchidectomised rats, PTH, in preventive study, avoided cancellous bone loss in metaphysis and lumbar vertebra, and a mild new bone formation in cortical bone was found. In intervention study, PTH maintained baseline cancellous bone mass, but in cortical bone a strong endosteal and periosteal new bone formation was detected. The PTH-induced new bone formation was confirmed by histology and by mineral content profiles. After castration, biomechanical properties were affected in females but not in male rats and PTH reverted this effect.

Endosseous implant anchorage is critically dependent on mechanostructural determinants of peri-implant bone trabeculae

Low bone mass is highly prevalent among patients receiving endosseous implants. In turn, the implantation prognosis in low-density skeletal sites is poor. However, little is known about the mechanostructural determinants of implant anchorage. Using metabolic manipulations that lead to low bone density and to its rescue, we show here that anchorage is critically dependent on the peri-implant bone (PIB). Titanium implants were inserted horizontally into the proximal tibial metaphysis of adult rats 6 weeks after orchiectomy (ORX) or sham ORX. Systemic intermittent administration of human parathyroid hormone (1-34) [iahPTH(1-34)] or vehicle commenced immediately thereafter for 6 weeks. The bone-implant apparatus was then subjected to image-guided failure assessment, which assesses biomechanical properties and microstructural deformation concomitantly. Anchorage failure occurred mainly in PIB trabeculae, 0.5 to 1.0 mm away from the implant. Mechanically, the anchorage performed poorly in ORX-induced low-density bone, attributable mainly to decreased trabecular number. iahPTH(1-34) rescued the PIB density and implant mechanical function by augmenting trabecular thickness (Tb.Th). However, implant biomechanical properties in low-density bone were relatively insensitive to implant surface treatment that affected only the osseointegration (%bone-implant contact). These results support a model wherein anchorage failure involves buckling of the weakest trabecular struts followed by sequential failure of the stronger trabeculae. Treatment with iahPTH(1-34) induced thicker struts, which were able to delay and even prevent failure of individual elements, thus implicating trabecular thickness as a prime target for enhancing implant anchorage by systemic bone anabolic therapy.

Expression of Rho GDIalpha in rat osteoblasts intermittently exposed to parathyroid hormone in vitro and in vivo

AIM

To investigate the mechanism of the bone-forming effects of intermittent parathyroid hormone (PTH) administration and to search for novel molecules of bone anabolism via the PTH signaling pathway.

METHODS

Primary cultures of rat osteoblasts (ROBs) were divided into an intermittent PTH-treated group (Itm) and a control group (Ctr). Imitating the pharmacokinetics of intermittent PTH administration in vivo, the ROBs in the Itm group were exposed to PTH for 6 h in a 24-h incubation cycle, and the ROBs in the Ctr group were exposed to vehicle for the entire incubation cycle. The cells were collected at 6 h and 24 h of the final cycle, and the proteins in the Itm and Ctr groups were analyzed by two-dimensional electrophoresis (2-DE) coupled with peptide mass fingerprinting and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to detect proteins that were differentially expressed. The proteins with the most significant changes in vitro were validated by immunohistochemistry (IHC) in a rat model.

RESULTS

The proteomics analysis indicated that a total of 26 proteins were up- or down-regulated in the Itm group compared with the Ctr group at 6 h and 24 h; among these, 15 proteins were successfully identified. These proteins mainly belong to the cytoskeleton and molecular chaperone protein families, and most of these have anti-apoptotic effects in various cells. Rho GDP-dissociation inhibitor alpha (RhoGDIalpha) and vimentin were the most significantly changed proteins. Further studies by IHC showed that the expression of RhoGDIalpha in ROBs was significantly higher in PTH-treated sham-operated rats than in vehicle-treated sham-operated rats, but the difference was not significant between PTH-treated and vehicle-treated OVX rats. Vimentin expression was not changed in either PTH-treated sham-operated rats or PTH-treated OVX rats.

CONCLUSION

Our research suggests that intermittent PTH treatment induces changes in expression of many proteins in ROBs in vitro, and it results in RhoGDIalpha up-regulation in ROBs both in vitro and in vivo when estrogen is present. This up-regulation of RhoGDIalpha may be one of the mechanisms underlying the synergistic bone-forming effect of PTH and estrogen.Acta Pharmacologica Sinica (2009) 30: 1001-1007; doi: 10.1038/aps.2009.60.

Cannabinoids and the skeleton: from marijuana to reversal of bone loss

The active component of marijuana, Delta(9)-tetrahydrocannabinol, activates the CB1 and CB2 cannabinoid receptors, thus mimicking the action of endogenous cannabinoids. CB1 is predominantly neuronal and mediates the cannabinoid psychotropic effects. CB2 is predominantly expressed in peripheral tissues, mainly in pathological conditions. So far the main endocannabinoids, anandamide and 2-arachidonoylglycerol, have been found in bone at 'brain' levels. The CB1 receptor is present mainly in skeletal sympathetic nerve terminals, thus regulating the adrenergic tonic restrain of bone formation. CB2 is expressed in osteoblasts and osteoclasts, stimulates bone formation, and inhibits bone resorption. Because low bone mass is the only spontaneous phenotype so far reported in CB2 mutant mice, it appears that the main physiologic involvement of CB2 is associated with maintaining bone remodeling at balance, thus protecting the skeleton against age-related bone loss. Indeed, in humans, polymorphisms in CNR2, the gene encoding CB2, are strongly associated with postmenopausal osteoporosis. Preclinical studies have shown that a synthetic CB2-specific agonist rescues ovariectomy-induced bone loss. Taken together, the reports on cannabinoid receptors in mice and humans pave the way for the development of 1) diagnostic measures to identify osteoporosis-susceptible polymorphisms in CNR2, and 2) cannabinoid drugs to combat osteoporosis.

Beneficial effects of combined administration of alendronate and alfacalcidol on cancellous bone mass of the tibia in orchidectomized rats: a bone histomorphometry study

The purpose of the present study was to examine the effects of combined administration of alendronate (ALN) and alfacalcidol (ALF) on the cancellous and cortical bone mass of the tibia in orchidectomized rats. Fifty male Sprague-Dawley rats, 3 mo of age, were randomized by the stratified weight method into five groups: age-matched control, orchidectomy, and orchidectomy with administration of ALN (2.5 mug/kg, s.c., 5 times a week), ALF (0.05 microg/kg, p.o., 5 times a week), or ALN+ALF. The total experimental period was 12 wk. Orchidectomy reduced the cancellous bone mass of the proximal tibial metaphysis and maturation-related cortical bone gain of the tibial diaphysis as a result of increased trabecular bone resorption and decreased periosteal bone formation and also increased endocortical bone erosion and formation. ALN suppressed trabecular bone resorption and endocortical bone erosion and formation and increased periosteal bone formation, while ALF increased the number of osteoblasts and suppressed trabecular bone resorption and markedly increased periosteal and endocortical bone formation. Thus, both ALN and ALF prevented the orchidectomy-induced reduction in the cancellous bone mass and maturation-related cortical bone gain. Combined administration of ALN and ALF increased the cancellous bone mass as compared with the values observed in age-matched controls by causing more marked suppression of trabecular bone resorption. The present study showed the beneficial effects of combined administration of ALN and ALF on the cancellous bone mass of the tibia in orchidectomized rats.

Human parathyroid hormone 1-34 prevents bone loss in experimental biliary cirrhosis in rats

BACKGROUND & AIMS

Reduced bone mass and increased fracture rate are complications of primary biliary cirrhosis (PBC). The effect of intermittent administration of human parathyroid hormone (hPTH) 1-34 on bone mass and architecture in bile duct-ligated (BDL) rats was studied.

METHODS

Six-month-old male rats were subjected to BDL or sham operation (SO) and were treated from the second postoperative week intermittently with either hPTH 1-34 40 microg/kg per day, 80 microg/kg per day, or a vehicle for 4 weeks. Femoral and tibial bones were evaluated ex vivo by dual x-ray absorptiometry, microcomputed tomography, and histomorphometry. Serum osteocalcin and urinary deoxypyridinoline cross-links (DPD) were determined.

RESULTS

BDL rats had decreased bone mass compared with SO rats as indicated by a 6% decrease in femoral and tibial bone mineral density (BMD), 18% reduction in femoral trabecular bone volume (bone volume/total volume [BV/TV]), 17% decrease in trabecular thickness, and 10% decrease in tibial cortical thickness. The administration of hPTH 1-34 at 40 microg/kg per day increased femoral and tibial BMD (9% and 9%), femoral trabecular BV/TV (50%), trabecular thickness (50%), tibial cortical thickness (17%), and serum osteocalcin (82%). On the other hand, hPTH 1-34 80 microg/kg per day had no effect on BMD and tibial cortical thickness, was associated with a smaller increase in trabecular BV/TV (24%), and had a higher osteoclast number and DPD compared with untreated BDL rats and the lower hPTH 1-34 dose treatment group.

CONCLUSIONS

BDL rats exhibit loss of bone mass and structure, which can be prevented by the intermittent administration of hPTH 1-34, a potential therapy for osteoporosis in PBC.

Trabecular bone gradient in rat long bone metaphyses: mathematical modeling and application to morphometric measurements and correction of implant positioning

The distribution of trabecular structures in mammalian long bone metaphyses has been insufficiently explored. We show in rats that the trabecular bone structural parameters display a decreasing gradient, toward the diaphysis, that can be defined mathematically. This gradient is applicable for optimizing the reference volume in metabolic studies and for retrospective correction of implant positioning.

INTRODUCTION

The mammalian metaphyseal trabecular bone is unevenly distributed. Hence, defining a standard reference volume is critical for morphometric analyses in metaphyseal sites.

MATERIALS AND METHODS

The distal femoral and proximal tibial metaphyses of adult orchietomized (ORX) or sham-ORX rats were scanned by microCT 6 wk postoperatively. Morphometric analysis based on 3D image data was performed in 450-microm-thick transversal segments defined consecutively from the primary spongiosa toward the diaphysis. The results were subjected to curve-fit analysis. A similar approach was used for proximal tibial metaphyseal sites carrying titanium implants inserted horizontally 6 wk post-ORX and examined 2-12 wk after implantation.

RESULTS

The respective curve-fit analysis in both femur and tibia revealed decreasing linear/quadratic and logarithmic gradients for all morphometric parameters in the sham-ORX animals. The ORX animals showed similar gradients with roughly similar slopes but lower values. For the bone volume (BV/TV) and connectivity (Conn.D) densities, the magnitude of the ORX effect vastly increased toward the diaphysis. The trabecular number was unaffected in ORX femora and tibias. The trabecular thickness showed a constant decrease in the femur and was unchanged in the tibia. These findings are useful for the determination and reporting of reference volumes in morphometric studies. Implementing the curve-fit analysis for retrospective correction of implant positioning revealed differences in BV/TV, Tb.N, Conn.D, and percent implant surface in contact with bone (%OI) between the sham-ORX and ORX rats. These differences were otherwise undisclosed. In addition, a temporal increase in %OI was shown only for the corrected measurements.

CONCLUSIONS

We show the feasibility of modeling trabecular bone structures using mathematical tools. Such modeling may be used as an experimental tool. Moreover, if proven applicable to human skeletal structures, it may be further developed for the diagnosis of metabolic bone diseases and evaluation of therapeutic measures.

Cannabinoid receptors and the regulation of bone mass

A functional endocannabinoid system is present in several mammalian organs and tissues. Recently, endocannabinoids and their receptors have been reported in the skeleton. Osteoblasts, the bone forming cells, and osteoclasts, the bone resorbing cells, produce the endocannabinoids anandamide and 2-arachidonoylglycerol and express CB2 cannabinoid receptors. Although CB2 has been implicated in pathological processes in the central nervous system and peripheral tissues, the skeleton appears as the main system physiologically regulated by CB2. CB2-deficient mice show a markedly accelerated age-related bone loss and the CNR2 gene (encoding CB2) in women is associated with low bone mineral density. The activation of CB2 attenuates ovariectomy-induced bone loss in mice by restraining bone resorption and enhancing bone formation. Hence synthetic CB2 ligands, which are stable and orally available, provide a basis for developing novel anti-osteoporotic therapies. Activation of CB1 in sympathetic nerve terminals in bone inhibits norepinephrine release, thus balancing the tonic sympathetic restrain of bone formation. Low levels of CB1 were also reported in osteoclasts. CB1-null mice display a skeletal phenotype that is dependent on the mouse strain, gender and specific mutation of the CB1 encoding gene, CNR1.

Comparison of dried plum supplementation and intermittent PTH in restoring bone in osteopenic orchidectomized rats

Bone loss was confirmed after 90 days in 50 6-month-old male Sprague Dawley rats that were sham-operated or orchidectomized (ORX). In this study, we have shown that dried plum (DP) has potent effects on bone in terms of bone mass, microarchitecture, and strength in osteopenic male rats. Although these changes may be mediated through the suppression of bone resorption, the fact that the restoration in some of the bone structural and biomechanical parameter shares some similarities with parathyroid hormone (PTH) should not be overlooked. Further investigation is needed on a mechanistic level to clarify the influence of DP on bone metabolism.

INTRODUCTION

This study was designed to investigate the extent to which DP reverses bone loss in osteopenic ORX rats and to compare its effects to PTH.

MATERIALS AND METHODS

Fifty, 6-month-old male Sprague Dawley rats were sham-operated or ORX, and bone loss was confirmed after 90 days. The ORX groups were assigned to control (AIN-93M) diet, 25% DP diet, or PTH (80 microg/kg) for 90 days.

RESULTS

DP induced an 11% increase in vertebral and femoral BMD compared to ORX-controls. BMD in the PTH-treated group was increased by 20.7% (vertebra) and 17.9% (femur). Vertebral trabecular bone volume (BV/TV) and number were increased by DP and trabecular separation was decreased compared to controls, which were similar to PTH. Alterations in trabecular bone of the femur were similar to those in the vertebra, but DP did not restore BV/TV to the same extent. Cortical thickness was improved by DP and further enhanced by PTH. DP tended to decrease urinary deoxypyridinoline and calcium, but did not alter alkaline phosphatase or osteocalcin.

CONCLUSION

We conclude that though the degree of improvement was not equivalent to PTH with regard to all parameters, DP reverses bone loss due to ORX and the mechanisms should be further investigated.

Overexpression of the transcriptional factor Runx2 in osteoblasts abolishes the anabolic effect of parathyroid hormone in vivo

There is convincing evidence that Runx2 could be a regulator of the anabolic action of parathyroid hormone (PTH) in bone. We therefore decided to determine how Runx2 overexpression in osteoblasts affects the anabolic response to PTH. Transgenic osteoporotic female mice overexpressing Runx2 (TG) and their wild-type littermates (WT) were treated with PTH (100 microg/kg/day, 7 days a week) or with the vehicle for 6 weeks. Unexpectedly, Runx2 overexpression blunted the increase in the mineral density and volume of bone induced by intermittent PTH in WT mice. Our findings also indicate that PTH failed to increase bone formation in TG mice overexpressing Runx2. This abolition of the effect of PTH by Runx2 overexpression was attributable to a decrease in the differentiation of osteoblastic cells both in vivo and in vitro. Finally, we showed that less cAMP was induced by PTH and that there were fewer PTH binding sites in TG than WT osteoblasts. In conclusion, our findings demonstrate that in vivo a high level of Runx2 abolishes the anabolic effect of PTH, probably via a decrease in the sensitivity of TG osteoblasts to PTH, and that the level of expression of Runx2 is critical if PTH is to produce its anabolic effect on bone in vivo.

Dried plum prevents bone loss in a male osteoporosis model via IGF-I and the RANK pathway

Previously, dietary supplementation with dried plums, a rich source of polyphenolic compounds with antioxidant and anti-inflammatory properties, has been shown to improve bone density, microstructure and biomechanics in female animal models of osteopenia. We designed this study to determine the extent to which dried plum prevents skeletal deterioration in gonadal hormone deficient male animals and to begin to understand its mechanism of action. Sixty 6-month-old male Sprague-Dawley rats were either sham-operated (Sham = 1 group) or orchidectomized (ORX = 4 groups) and randomly assigned to dietary treatments: standard semi-purified diet (Control) with either LD = 5%, MD = 15%, or HD = 25% (w/w) dried plum for 90 days. At the end of the treatment period, both the MD and HD dried plum completely prevented the ORX-induced decrease in whole body, femur, and lumbar vertebra bone mineral density (BMD). Biomechanical testing indicated that the MD and HD of dried plum prevented the ORX-induced decrease in ultimate load of the cortical bone as well as the compressive force and stiffness of trabecular bone within the vertebrae. Analyses of trabecular microarchitecture of the distal femur metaphysis and vertebral body revealed that HD dried plum protected against the decrease in trabecular bone volume (BV/TV) induced by ORX. In the distal femur, all doses of dried plum improved trabecular number (TbN) and separation (TbSp) compared to the ORX-control group, while MD and HD dried plum prevented the ORX-induced changes in vertebral TbN and TbSp. At the end of the 90-day treatment, no remarkable changes in serum osteocalcin or alkaline phosphatase in any of the treatment groups were observed, while serum insulin-like growth factor (IGF)-I was increased by dried plum. The ORX-induced increase in urinary deoxypyridinoline (DPD) excretion was completely prevented by all doses of dried plum coinciding with down-regulation of gene expression for receptor activator of NFkappa-B ligand (RANKL) and osteoprotegerin (OPG) in the bone. We conclude that dried plum prevents osteopenia in androgen deficient male rats, and these beneficial effects may be attributed in part to a decrease in osteoclastogenesis via down-regulation of RANKL and stimulation of bone formation mediated by IGF-I.

Parathyroid hormone 1-34 enhances titanium implant anchorage in low-density trabecular bone: a correlative micro-computed tomographic and biomechanical analysis

The use of endosseous titanium implants is the standard of care in dentistry and orthopaedic surgery. Nevertheless, implantation in low-density bone has a poor prognosis and experimental studies show delayed implant anchorage following gonadectomy-induced bone loss. Intermittently administered human parathyroid hormone 1-34 [iahPTH(1-34)] is the leading bone anabolic therapy. Hence, this study assessed whether iahPTH(1-34) enhances titanium implant integration in low-density bone. Threaded titanium implants, 0.9 mm in diameter, were inserted horizontally into the proximal tibial metaphysis of 5-month-old rats, 7 weeks postorchiectomy (ORX). Subcutaneous administration of iahPTH(1-34), at 5, 25 and 75 microg/kg/day commenced immediately thereafter and lasted for 8 weeks. Quantitative micro-computed tomography (muCT) at the implantation site was carried out at 15 microm resolution using high energy and long integration time to minimize artifacts resulting from the high implant radiopacity. Osseointegration (OI) was calculated as percent implant surface in contact with bone (%OI) quantified as the ratio of "bone"-to-total voxels in contact with the implant. Additionally, the trabecular bone volume density (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N) and connectivity density (Conn.D) were measured in the peri-implant bone. All microCT parameters were stimulated by iahPTH(1-34) dose-dependently; the percent maximal enhancement was %OI = 143, BV/TV = 257, Tb.Th = 150, Tb.N = 140 and Conn.D = 193. The maximal values of %OI, BV/TV and Tb.Th in iahPTH(1-34)-treated ORX rats exceeded significantly those measured in the implantation site of untreated sham-ORX controls. The same specimens were then subjected to pullout biomechanical testing. The biomechanical parameters were also enhanced by iahPTH(1-34) dose-dependently, exceeding the values recorded in the sham-ORX controls. The percent iahPTH(1-34)-induced maximal enhancement was: ultimate force = 315, stiffness = 270 and toughness = 395. Except for the BV/TV and Tb.Th, there was no significant difference between the effect of the 25 and 75 microg/kg/day doses. There was a highly significant correlation between the morphometric and biomechanical parameters suggesting the use of quantitative CT as predictive of the implant mechanical properties. These findings demonstrate that iahPTH(1-34) effectively stimulates implant anchorage in low-density trabecular bone and thus the feasibility of administering iahPTH(1-34) to improve the clinical prognosis in low-density trabecular bone sites.