Parathyroid hormone PTH(1-34) increases the volume, mineral content, and mechanical properties of regenerated mineralizing tissue after distraction osteogenesis in rabbits

The effect of intermittent parathyroid hormone on bone lengthening: current evidence to inform future effective interventions

PURPOSE

Recent studies have demonstrated the positive effects of parathyroid hormone (PTH) on bone healing, and findings support the use of PTH to accelerate bone healing following distraction osteogenesis. The goal of this review was to compile and discuss the mechanisms potentially underlying the effects of PTH on newly formed bone following a bone-lengthening procedure incorporating all relevant evidence in both animal and clinical studies.

METHODS

This review summarized all evidence from in vivo to clinical studies regarding the effects of PTH administration on a bone-lengthening model. In addition, a comprehensive evaluation of what is currently known regarding the potential mechanisms underlying the potential benefits of PTH in bone lengthening was presented. Some controversial findings regarding the optimal dosage and timing of administration of PTH in this model were also discussed.

RESULTS

The findings demonstrated that the potential mechanisms associated with the action of PTH on the acceleration of bone regeneration after distraction osteogenesis are involvement in mesenchymal cell proliferation and differentiation, endochondral bone formation, membranous bone formation, and callus remodeling.

CONCLUSIONS

In the last 20 years, a number of animal and clinical studies have indicated that there is a prospective role for PTH treatment in human bone lengthening as an anabolic agent that accelerates the mineralization and strength of the regenerated bone. Therefore, PTH treatment can be viewed as a potential treatment to increase the amount of new calcified bone and the mechanical strength of the bone in order to shorten the consolidation stage after bone lengthening.

Mechanical Characterization at the Microscale of Mineralized Bone Callus after Bone Lengthening

Distraction osteogenesis (DO) involves several processes to form an organized distracted callus. While bone regeneration during DO has been widely described, no study has yet focused on the evolution profile of mechanical properties of mineralized tissues in the distracted callus. The aim of this study was therefore to measure the elastic modulus and hardness of calcified cartilage and trabecular and cortical bone within the distracted callus during the consolidation phase. We used a microindentation assay to measure the mechanical properties of periosteal and endosteal calluses; each was subdivided into two regions. Histological sections were used to localize the tissues. The results revealed that the mechanical properties of calcified cartilage did not evolve over time. However, trabecular bone showed temporal variation. For elastic modulus, in three out of four regions, a similar evolution profile was observed with an increase and decrease over time. Concerning hardness, this evolves differently depending on the location in the distracted callus. We also observed spatial changes in between regions. A first duality was apparent between regions close to the native cortices and the central area, while latter differences were seen between periosteal and endosteal calluses. Data showed a heterogeneity of mechanical properties in the distracted callus with a specific mineralization profile.

Experimental Modeling of Combined and Sequential Use of Transosseous and Intramedullary Blocking Osteosynthesis

Background. The introduction of the combined and sequential application of transosseous and intramedullary blocked osteosynthesis in limb lengthening requires an experimental study of the features of distraction regenerate. For small animals (in particular rabbits), special models are required.

Aims. To develop experimental models of sequential and combined use of transosseous and intramedullary osteosynthesis in limb lengthening and substantiate their effectiveness.

Materials and methods. A comparative study was carried out on 30 rabbits of the Soviet Chinchilla breed. Experimental models of sequential (EM-1) and combined (EM-2) application of transosseous and intramedullary osteosynthesis with preservation of the apparatus during the fixation period to simulate blockage were studied in the main groups. For comparison, sequential (comparison model 1 – CM-1) and combined (comparison model 2 – CM-2) use of transosseous and intramedullary osteosynthesis with dismantling of the apparatus at the end of distraction were modeled. The control was a regenerate formed according to the classical Ilizarov method. Radiographs were performed in dynamics, CT and morphological studies – at the end of the fixation period.

Results. It was noted that regenerates of the same type in structure were formed in the EM-1 and CM-1 groups, as in the EM-2 and CM-2 groups. With successive methods, the spindle-shaped form of the regenerate prevailed, the formation of a pronounced periosteal component was noted. Powerful cortical plates, according to morphological studies, are formed from the periosteal and intermediate zones. With combined techniques, the cortical plates are formed thinner and predominantly from the periosteal component, the shape of the regenerate is closer to fusiform. In the comparison groups, the total time of surgical interventions was 25–50 % longer, in 50 % of cases there was a loss of length or deformation of the regenerate.

Conclusions. The developed models of sequential and combined use of transosseous and intramedullary osteosynthesis for limb lengthening with preservation of fixation with an apparatus to simulate blocking have proven to be reliable in terms of fixation and easy to use on small laboratory animals.. 

The Effect of Parathyroid Hormone Analogues When Added to Mineralized Bone Xenografts

Implants can be a treatment option when there is sufficient quantity and quality of bone to provide support for long-term success. In the reconstruction of defects, autogenous bone remains the gold standard for its osteogenic and compatibility properties. However, the disadvantage of secondary surgery and the associated donor site morbidity prompts researchers to develop the ideal bone substitute for optimum bone reconstruction. Parathyroid hormone (PTH1-34) has provided a new option for improvement in bone regeneration. This study used a pig model to evaluate the effectiveness of parathyroid hormone when added to a xenograft, Bio-Oss, in reconstructing mandible defects. Six domestic pigs were used to create 3 posterior mandibular defects measuring 2 × 1-cm bilaterally with a total of 36 defects to simulate tooth extraction sites in humans. The defects were grafted in random order and divided into 3 groups as follows: control (no graft), Bio-Oss without PTH, and Bio-Oss with PTH. Defects were assessed with cone beam computerized tomography (CBCT), micro computerized tomography (microCT), nanoindentation, and histology. Results showed that adding PTH1-34 significantly enhanced the graft construct. CBCT showed a significant increase in the degree of bone mineralization. Nanoindentation showed increased hardness of regenerated bone and accelerated bone mineralization with PTH. MicroCT analysis revealed a trend toward higher bone regeneration and mineralization. The histological analysis showed a positive trend of the increase in cortical bone thickness and mineral apposition rate. In conclusion, the local addition of PTH1-34 to a xenograft has shown promising results to enhance bone regeneration in the reconstruction of mandibular defects.

Daily subcutaneous Teriparatide injection increased bone mineral density of newly formed bone after tibia distraction osteogenesis, a randomized study

Long bone defects are often treated by bone segment transport with the Ilizarov method requiring months spent with fixator mounted until bony consolidation of the newly formed bone. Shortening of consolidation would allow earlier fixator removal and earlier return to work. In pre-clinical studies parathyroid hormone, increased bone mineral density and mechanical properties of regenerate bone formed during distraction osteogenesis. Clinical studies showed that Teriparatide accelerated fracture healing in patients with osteoporotic fracture of the pelvis, hip, wrist and shoulder. We hypothesized that rhPTH(1-34) (Teriparatide) administered to patients who had undergone distraction osteogenesis, would increase mineralization of the regenerate formed during the consolidation phase. Sixteen patients with tibial defects after infection, underwent bone segment transport and at the time of docking the transport segment, were randomized to 8 weeks treatment with daily subcutaneous 0.20-μg Teriparatide injection followed by 8 weeks with no treatment, or to 8 weeks with no treatment followed by 8 weeks with daily subcutaneous 0.20 μg Teriparatide injection. Bone mineral density (BMD) of the regenerate was measured at the time of docking, 8 weeks after docking and 16 weeks after docking with DEXA. Functional evaluation was performed after one year. The design was a cross-over study. Overall BMD increased 0.14 g/cm² in 8 weeks without treatment and 0.33 g/cm² under Teriparatide treatment. After adjustment for a potential phase difference, 8 weeks of Teriparatide treatment led to an additional 0.19 g/cm² BMD increase (95%-CI:[0.11,0.28], p < 0.001). The ratio of the BMD increase between the two treatments was 0.33/0.14 = 2.43 (CI: [1.21,3.65]). Teriparatide treatment during the consolidation phase of distraction osteogenesis doubled the mineralization rate of the regenerate when compared to no treatment.

Oral dosing of pentoxifylline, a pan-phosphodiesterase inhibitor restores bone mass and quality in osteopenic rabbits by an osteogenic mechanism: A comparative study with human parathyroid hormone

The non-selective phosphodiesterase inhibitor pentoxifylline (PTX) is used for the treatment of intermittent claudication due to artery occlusion. Previous studies in rodents have reported salutary effects of the intraperitoneal administration of PTX in segmental bone defect and fracture healing, as well as stimulation of bone formation. We determined the effect of orally dosed PTX in skeletally mature ovariectomized (OVX) rabbits with osteopenia. The half-maximal effective concentration (EC₅₀) of PTX in rabbit bone marrow stromal cells was 3.07 ± 1.37 nM. The plasma PTX level was 2.05 ± 0.522 nM after a single oral dose of 12.5mg/kg, which was one-sixth of the adult human dose of PTX. Four months of daily oral dosing of PTX at 12.5 mg/kg to osteopenic rabbits completely restored bone mineral density, bone mineral content (BMC), microarchitecture and bone strength to the level of the sham-operated (ovary intact) group. The bone strength to BMC relationship between PTX and sham was similar. The bone restorative effect of PTX was observed in both axial and appendicular bones. In osteopenic rabbits, PTX increased serum amino-terminal propeptide, mineralized nodule formation by stromal cells and osteogenic gene expression in bone. PTX reversed decreased calcium weight percentage and poor crystal packing found in osteopenic rabbits. Furthermore, similar to parathyroid hormone (PTH), PTX had no effect on bone resorption. Taken together, our data show that PTX completely restored bone mass, bone strength and bone mineral properties by an anabolic mechanism. PTX has the potential to become an oral osteogenic drug for the treatment of post-menopausal osteoporosis.

Sclerostin antibody enhances bone formation in a rat model of distraction osteogenesis

Neutralizing monoclonal sclerostin antibodies are effective in promoting bone formation at a systemic level and in orthopedic scenarios including closed fracture repair. In this study we examined the effects of sclerostin antibody (Scl-Ab) treatment on regenerate volume, density, and strength in a rat model of distraction osteogenesis. Surgical osteotomy was performed on 179 Sprague Dawley rats. After 1 week, rats underwent distraction for 2 weeks, followed by 6 weeks for consolidation. Two treatment groups received biweekly subcutaneous Scl-AbIII (a rodent form of Scl-Ab; 25 mg/kg), either from the start of distraction onward or restricted to the consolidation phase. These groups were compared to controls receiving saline. Measurement modalities included longitudinal DXA, ex vivo QCT, and microCT, tissue histology, and biomechanical four-point bending tests. Bone volume was increased in both Scl-Ab treatments regimens by the end of consolidation (+26-38%, p < 0.05), as assessed by microCT. This was associated with increased mineral apposition. Importantly, Scl-Ab led to increased strength in united bones, and this reached statistical significance in animals receiving Scl-Ab during consolidation only (+177%, p < 0.01, maximum load to failure). These data demonstrate that Scl-Ab treatment increases bone formation, leading to regenerates with higher bone volume and improved strength. Our data also suggest that the optimal effects of Scl-Ab treatment are achieved in the latter stages of distraction osteogenesis. These findings support further investigation into the potential clinical application of sclerostin antibody to augment bone distraction, such as limb lengthening, particularly in the prevention of refracture. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1106-1113, 2018.

Effect of intermittent administration of teriparatide on the mechanical and histological changes in bone grafted with β-tricalcium phosphate using a rabbit bone defect model

Grafting β-tricalcium phosphate (TCP) is a well-established method for restoring bone defects; however, there is concern that the mechanical stability of the grafted β-TCP is not maintained during bone translation. Teriparatide has an anabolic effect, stimulating bone formation and increasing bone mineral density for the treatment of osteoporosis. The aim of the present study was to evaluate the effect of intermittent teriparatide treatment on changes in bone grafted with β-TCP using a rabbit bone defect model. Bone defects (5×15 mm) were created in the distal femoral condyle of Japanese white rabbits, and β-TCP granules of two different total porosities were manually grafted. Teriparatide (40 µg/kg) or 0.2% rabbit serum albumin solution as a vehicle control was subcutaneously injected three times per week following the surgery. At 4 or 8 weeks post-surgery, serum samples were obtained and the levels of γ-carboxylated osteocalcin (Gla-OC) were quantified using ELISA. Histomorphometry was also performed using sections of graft sites following staining for tartrate resistant acid phosphatase. Activity and mechanical strength (maximum shear strength, maximum shear stiffness and total energy absorption) were evaluated using an axial push-out load to failure test. Teriparatide treatment significantly increased (P<0.05) the serum levels of Gla-OC, a specific marker for bone formation, suggesting that teriparatide enhances bone formation in β-TCP-grafted rabbits. Furthermore teriparatide increased the degradation of β-TCP by bone remodeling (P<0.05) and promoted the formation of new bone following application of the graft compared with the control group (P<0.01). Furthermore, teriparatide suppressed the reduction in mechanical strength (P<0.05) during bone translation in bone defects grafted with β-TCP. The results of the present study demonstrate that teriparatide is effective in maintaining the mechanical stability of grafted β-TCP, possibly by promoting new bone formation.

The biology of bone lengthening

Distraction osteogenesis biologically resembles fracture healing with distinctive characteristics notably in the distraction phase of osteogenesis. In the latency phase of bone lengthening, like in the inflammatory phase of fracture repair, interleukines are released and act with growth factors released from platelets in the local haematoma, leading to attraction, proliferation and differentiation of mesenchymal stem cells into osteoblasts and other differentiated mesenchymal cells. These in turn produce matrix, collagen fibers and growth factors. A callus containing cells, collagen fibers, osteoid and cartilage matrix is formed. Provided stable fixation, distraction will trigger intramembranous bone formation. As distraction proceeds, the distraction gap develops five distinctive zones with unmineralized bone in the middle, remodelling bone peripherally, and mineralizing bone in between. During consolidation, the high concentration of anabolic growth factors in the regenerate diminishes with time as remodelling takes over to form mature cortical and cancellous bone. Systemic disease, congenital bone deficiencies, medications and substance abuse can influence the quality and quantity of regenerate bone, usually in a negative way. The regenerate bone can be manipulated when needed by using injection of mesenchymal stem cells and platelets, growth factors (BMP-2 and -7), and systemic medications (bisphosphonates and parathyroid hormone). Growth factors and systemic anabolic and antiresorptive drugs are prescribed on special indications, while distraction osteogenesis is not an authorized indication. To some extent, however, these compounds can be used off-label. Use in children presents special problems since growth factors and specific anabolic medications may involve a risk of inducing cancer.

An Examination of Differences in the New Bone Formation Promoted by Different Doses of Recombinant Human Parathyroid Hormone during Mandibular Distraction Osteogenesis

BACKGROUND

The administration of different doses of parathyroid hormone to promote mandibular distraction osteogenesis remains unclear. The objective of the present study was to examine the effects of recombinant human parathyroid hormone on new bone formation during mandibular distraction osteogenesis and to investigate the dose-effect relationship associated with this phenomenon.

METHODS

A total of 45 rabbits were used to establish the mandibular distraction osteogenesis model. The rabbits were divided into a control group (that received a subcutaneous injection of 1 ml of saline every other day) and experimental groups A, B, C, and D (that received subcutaneous injections of 10, 20, 30, and 40 μg/kg of recombinant human parathyroid hormone, respectively, every other day). On days 1, 7, and 14 of the consolidation period after the distraction had been completed, new bone in the distraction region was examined through histomorphometric investigation and bone mineral density testing.

RESULTS

On days 1, 7, and 14 of the fixation period, the number of osteoblasts, trabecular bone area, and bone mineral density were greater in each experimental group than in the control group. On day 1 of the consolidation period, group C featured the highest average number of osteoblasts. On day 14 of the consolidation period, group C exhibited the highest bone mineral densities and largest trabecular bone areas.

CONCLUSIONS

Intermittent subcutaneous injections of recombinant human parathyroid hormone can promote new bone formation during mandibular distraction osteogenesis. Different doses of recombinant human parathyroid hormone promoted mandibular distraction osteogenesis to differing extents.

[Osteoprotegerin/receptor activator of nuclear factor-κB ligand expression in mandibular distraction osteogenesis regulated by parathyroid hormone]

OBJECTIVE

This research aimed to investigate the expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in mandibular distraction osteogenesis (DO) regulated by parathyroid hormone (PTH) and to explore the mechanism by which PTH promotes DO.

METHODS

A rabbit mandibular DO model was established. The rabbits were randomly divided into experimental group and control group. The former were subcutaneously injected with different doses of PTH on alternate days, the latter was injected with normal saline every other day. Serum OPG levels were detected through enzyme-linked immunosorbent assay. The OPG and RANKL expression levels in the DO-induced formation of a new bone tissue were examined through immunohistochemistry staining.

RESULTS

The serum OPG levels gradually increased during distraction. At the end of the stretch, the OPG expression in the experimental group was significantly stronger than that in the control group. As the fixed period was extended, the OPG expression in the new bone gradually decreased, but the RANKL expression increased.

CONCLUSION

Intermittent subcutaneous PTH injection can upregulate the OPG expression and accelerate bone metabolism. Thus, this procedure promotes the early generation of a new bone in the mandible through DO.

A New Way to Accelerate the Distraction of the Transpalatal Suture in Growing Dogs Using Recombinant Human Bone Morphogenetic Protein-2

OBJECTIVE

The purpose of this study was to evaluate the administration of recombinant human bone morphogenetic protein-2 (rhBMP-2) on trans-sutural distraction osteogenesis (TSDO) of the transverse palatal suture in growing dogs.

STUDY DESIGN

A total of 36 growing dogs were used in this study. The experimental animals were treated with different elastic force and rhBMP-2. The bone regeneration was determined with X-ray, histology, and clinical evaluation. The computed values underwent statistical analyses using analysis of variance.

RESULTS

The maxillary complex was most noticeably advanced with an applied elastic force of 600 g (22.4 ± 5.0 mm) and 800 g + rhBMP-2 (24 ± 5.1 mm). Immunohistochemical staining showed that the expression of bone morphogenetic protein-2 and bone morphogenetic protein-4 varied with different elastic force. These changes were statistically significant when 600 g and 800 g + rhBMP-2 were applied within 2 weeks of distraction when compared with controls (P < .05).

CONCLUSIONS

The results of this study suggest that TSDO in the growing dog should be safe and well tolerated when inducing bony lengthening of the maxilla. rhBMP-2 plays an important role in bone regeneration using TSDO.

Influence of Parathyroid Hormone-Loaded PLGA Nanoparticles in Porous Scaffolds for Bone Regeneration

Biodegradable poly(lactide-co-glycolide) (PLGA) nanoparticles, containing human parathyroid hormone (PTH (1–34)), prepared by a modified double emulsion-solvent diffusion-evaporation method, were incorporated in porous freeze-dried chitosan-gelatin (CH-G) scaffolds. The PTH-loaded nanoparticles (NPTH) were characterised in terms of morphology, size, protein loading, release kinetics and in vitro assessment of biological activity of released PTH and cytocompatibility studies against clonal human osteoblast (hFOB) cells. Structural integrity of incorporated and released PTH from nanoparticles was found to be intact by using Tris-tricine SDS-PAGE. In vitro PTH release kinetics from PLGA nanoparticles were characterised by a burst release followed by a slow release phase for 3–4 weeks. The released PTH was biologically active as evidenced by the stimulated release of cyclic AMP from hFOB cells as well as increased mineralisation studies. Both in vitro and cell studies demonstrated that the PTH bioactivity was maintained during the fabrication of PLGA nanoparticles and upon release. Finally, a content of 33.3% w/w NPTHs was incorporated in CH-G scaffolds, showing an intermittent release during the first 10 days and, followed by a controlled release over 28 days of observation time. The increased expression of Alkaline Phosphatase levels on hFOB cells further confirmed the activity of intermittently released PTH from scaffolds.

Changes over time in callus formation caused by intermittently administering PTH in rabbit distraction osteogenesis models

Background

Changes over time in the callus during intermittent administration of parathyroid hormone (PTH) were studied in rabbit distraction osteogenesis models.

Method

Models of distraction osteogenesis in Japanese white rabbits were created, and distraction osteogenesis (total length: 10.5 mm) was performed for 2 weeks. Simultaneously with the start of distraction, 30 rabbits received 4 weeks of subcutaneous administration of 30 μg/kg of PTH(1–34), teriparatide, (P-group: n = 15) or saline (N-group: n = 15) every other day. The tibias of five rabbits were dissected at 6, 8, and 10 weeks after surgery to perform bone mineral density (BMD), peripheral quantitative computed tomography (pQCT), and mechanical testing.

Results

The mean BMD had no significant differences over time at 6, 8, and 10 weeks after surgery between the P-group and the N-group. On pQCT, the P-group had significant increases in total bone cross-sectional area of the callus compared to the N-group at 8 and 10 weeks after surgery. On mechanical testing, the P-group’s absorption energy had not changed at 6 weeks after surgery compared to the N-group, but it had significantly increased at 8 weeks. At 10 weeks after surgery, the N-group’s absorption energy rapidly increased, and the difference between the two groups disappeared.

Conclusion

The intermittent administration of PTH(1–34), teriparatide, for 4 weeks every other day from the start of distraction had the potential to shorten the callus maturation period in the rabbit distraction osteogenesis models.

Bone marrow aspirate concentrate and platelet-rich plasma enhanced bone healing in distraction osteogenesis of the tibia

BACKGROUND

During lower limb lengthening, poor bone regeneration is a devastating complication. Several local or systemic applications have been used to promote osteogenesis, and biologic stimulations are gaining attention, but their utility has not been proven in this setting.

QUESTIONS/PURPOSES

In patients undergoing bilateral tibial lengthening, we compared those receiving an osteotomy site injection of autologous bone marrow aspirate concentrate (BMAC) plus platelet-rich plasma (PRP) with those not receiving such an injection in terms of external fixator index (time in external fixation divided by amount of lengthening), full weightbearing index (time until a patient was permitted to do full weightbearing divided by amount of lengthening), four cortical healing indexes (time until each cortical union divided by amount of lengthening), and callus shape and type.

METHODS

Twenty-two patients (44 tibias) undergoing bilateral tibial lengthening enrolled in this randomized trial. Two patients were excluded, one due to insufficient radiographic evaluation and one who was lost to followup, leaving 20 patients (40 segments) for inclusion. Ten patients (20 segments) received BMAC combined with PRP injection (treatment group) and 10 patients (20 segments) received no injection (control group). All patients underwent stature lengthening for familial short stature with the lengthening over nail technique. Autologous BMAC combined with PRP was injected at the tibial osteotomy site at the end of the index surgery. Mean distraction rates were similar between groups (0.75 mm/day in the treatment group versus 0.72 mm/day in the control group; p = 0.24). Full weightbearing was permitted when we observed radiographic evidence of healing at two cortices; this assessment was made by the surgeon who was blinded to the treatment each patient received. Minimum followup was 24 months (mean, 28 months; range, 24-34 months).

RESULTS

There was no difference in mean external fixator index between groups. However, mean cortical healing indexes (anterior/posterior/medial/lateral) were 1.14/0.81/0.96/0.88 months/cm in the treatment group and 1.47/1.26/1.42/1.22 months/cm in the control group (all p < 0.001), showing faster healing in the treatment group at each cortex. Full weightbearing was permitted earlier in the treatment group than in the control group (index: 0.99 months/cm and 1.38 months/cm, respectively, p < 0.001). Callus shape and type were not different between groups.

CONCLUSIONS

Autologous BMAC combined with PRP injection at the osteotomy site helped improve bone healing in distraction osteogenesis of the tibia, although the effect size was small.

LEVEL OF EVIDENCE

Level I, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.

Intermittent parathyroid hormone administration improves periodontal healing in rats

BACKGROUND

Intermittent administration of parathyroid hormone (PTH) promotes new bone formation in patients with osteoporosis and bone fractures. It was shown previously that PTH also reduces periodontitis-related bone loss. The aim of this study is to evaluate the effect of treatment with PTH on periodontal healing in rats.

METHODS

Fenestration defects were created at the buccal surface of the distal root of the mandibular first molars, and both periodontal ligament (PDL) and cementum were removed. Animals were then assigned to two groups (eight animals per group): group 1: control, placebo administration; and group 2: test, human PTH (hPTH) 1-34 administration at a concentration of 40 μg/kg. For both groups, the animals were injected every 2 days, and the animals were sacrificed at 14 and 21 days after surgery. Specimens were harvested and processed for routine decalcified histologic sections. The following parameters were assessed: 1) remaining bone defect extension (RBDE); 2) newly formed bone density (NFBD); 3) total callus area (TCA); 4) osteoclast number (ON) in the callus region; and 5) newly formed dental cementum-like tissue (NFC). Birefringence of root PDL reattachment was also evaluated.

RESULTS

Birefringence analysis showed root PDL reattachment for both groups 21 days after treatment. Intermittent hPTH 1-34 administration decreased RBDE (P <0.01) and increased NFBD (P <0.01), TCA (P <0.01), area of NFC (P <0.01), and ON in the callus region (P <0.01).

CONCLUSION

Within the limits of the present study, intermittent administration of hPTH 1-34 led to an enhanced periodontal healing process compared with non-treated animals.

Transsutural distraction and tissue regeneration of the midfacial skeleton: experimental studies in growing dogs

Objective : The purpose of this study was to evaluate the effect of different mechanical forces on the expansion of the palatine suture using transsutural distraction osteogenesis. Methods : A total of 48 dogs were used in this study. The experimental groups were treated with a custom-designed internal distractor. Bone regeneration was determined with x-rays and histology. The computed values underwent statistical analyses using analysis of variance. Results : The maxillary complex was most noticeably advanced with an applied mechanical force of 600 g (20.15 ± 1.36 mm), compared with forces of 400 g (19.88 ± 1.41 mm) and 800 g (2.24 ± 0.93 mm). Immunohistochemical staining showed that the expression of bone morphogenetic protein-2 and bone morphogenetic protein-4 fluctuated with different mechanical forces. These changes were statistically significant when 600 g of force was applied within 30 days of distraction (P < .05). Conclusions : Transsutural distraction osteogenesis in the growing dog should be safe and well tolerated in inducing bony lengthening of the maxilla, and the optimal force is 600 × g. Bone morphogenetic protein-2 and bone morphogenetic protein-4 may play an important roles in the signaling pathways that link mechanical forces and biological responses.

Parathyroid hormone applications in the craniofacial skeleton

Parathyroid hormone (PTH) is known for its ability to 'build' bone, with research in this area centered on its use as an osteoporosis therapeutic. Recent interest has developed regarding its potential for regenerative applications such as fracture healing and osseous defects of the oral cavity. Many years of investigation using murine gene-targeted models substantiate a role for signaling at the PTH/PTH-related protein (PTHrP) receptor (PPR) in intramembranous bone formation in the craniofacial region as well as in tooth development. Pre-clinical studies clearly support a positive role of intermittent PTH administration in craniofacial bones and in fracture healing and implant integration. A few human clinical studies have shown favorable responses with teriparatide (the biologically active fragment of PTH) administration. Favorable outcomes have emerged with teriparatide administration in patients with osteonecrosis of the jaw (ONJ). New delivery strategies are in development to optimize targeted application of PTH and to help maximize local approaches. The promising host-modulating potential of PTH requires more information to further its effectiveness for craniofacial regeneration and osseous wound-healing, including a better delineation of cellular targets, temporal effects of PTH action, and improved approaches for local/targeted delivery of PTH.

Systemic intermittent parathyroid hormone treatment improves osseointegration of press-fit inserted implants in cancellous bone

BACKGROUND AND PURPOSE

Intermittent administration of parathyroid hormone (PTH) has an anabolic effect on bone, as confirmed in human osteoporosis studies, distraction osteogenesis, and fracture healing. PTH in rat models leads to improved fixation of implants in low-density bone or screw insertion transcortically.

MATERIAL AND METHODS

We examined the effect of human PTH (1-34) on the cancellous osseointegration of unloaded implants inserted press-fit in intact bone of higher animal species. 20 dogs were randomized to treatment with human PTH (1-34), 5 μg/kg/day subcutaneously, or placebo for 4 weeks starting on the day after insertion of a cylindrical porous coated plasma-sprayed titanium alloy implant in the proximal metaphyseal cancellous bone of tibia. Osseointegration was evaluated by histomorphometry and fixation by push-out test to failure.

RESULTS

Surface fraction of woven bone at the implant interface was statistically significantly higher in the PTH group by 1.4 fold with (median (interquartile range) 15% (13-18)) in the PTH group and 11% (7-13) in control. The fraction of lamellar bone was unaltered. No significant difference in bone or fibrous tissue was observed in the circumferential regions of 0-500, 500-1,000, and 1,000-2,000 μm around the implant. Mechanically, the implants treated with PTH showed no significant differences in total energy absorption, maximum shear stiffness, or maximum shear strength.

INTERPRETATION

Intermittent treatment with PTH (1-34) improved histological osseointegration of a prosthesis inserted press-fit at surgery in cancellous bone, with no additional improvement of the initial mechanical fixation at this time point.

Effects of intermittent parathyroid hormone treatment on new bone formation during distraction osteogenesis in the rat mandible

OBJECTIVE

The effect of intermittent parathyroid hormone (PTH[1-34]) treatment on bone regeneration in a rat model of mandibular distraction was evaluated using microcomputed tomography.

STUDY DESIGN

After a 5-day latency period, mandibles of 18 rats were distracted at 0.2 mm/12 hours for 10 days, and rats in the PTH and control groups received subcutaneous injections of PTH(1-34) at a dosage of 60 μg/kg body weight or a vehicle only, respectively, 3 times a week. The animals were humanely killed after 10 days of distraction and after 1 week and 3 weeks of consolidation.

RESULTS

In reconstructed 3-dimensional images of the distracted mandible, mean bone volumes of the desired region of interest in the PTH group were significantly larger than those in the control group at all time points.

CONCLUSIONS

Intermittent PTH(1-34) treatment enhances new bone formation during mandibular distraction in a rat model, and it may be effective for shortening the consolidation period.

The effect of bisphosphonate and intermittent human parathyroid hormone 1-34 treatments on cortical bone allografts in rabbits

AIM

This study compares the effect of bisphosphonate and intermittent PTH administration on haversian remodeling in cortical bone allografts in rabbits.

MATERIALS AND METHODS

An intercalary heat-treated cortical bone allograft was applied to a segment skeletal defect in the left femur of Japanese white rabbits. The rabbits were randomly assigned to one of three groups: the vehicle control group (CNT); the bisphosphonate group (B group); and the intermittent PTH treatment group (P group). Periodic radiographic evaluation was performed and peripheral quantitative computerized tomography (pQCT) was used to evaluate the total bone area (Area), bone mineral density (BMD), and bone mineral content (BMC). The allografts also underwent histological examination.

RESULTS

The P group was radiographically superior in the latter stage, compared with the other groups. pQCT analysis of the allografts showed that the B group had a significantly higher Area and BMC. These parameters in the latter stage were significantly lower in the P group than in the other groups. The allograft of the B group was histologically mostly necrotic bone, whereas allograft of the P group showed abundant newly formed bone.

CONCLUSION

In rabbits, bisphosphonate prevents resorption, but suppresses remodeling and incorporation; by contrast, PTH increases resorption and accelerates allograft remodeling and incorporation. Based on our preliminary data, we suggest that further research on the manner of administration of bisphosphonate and PTH - which have contrasting effects - can be beneficial in maintaining bone strength and in regulating remodeling and allograft incorporation.

Potent anti-inflammatory agent escin does not affect the healing of tibia fracture and abdominal wound in an animal model

Escin, a potent anti-inflammatory and anti-edematous agent, has been widely used clinically in preventing inflammatory edema after trauma, such as fracture and surgery. The aim of this study was to investigate whether escin has an inhibitory effect on fracture healing, and whether escin has an inhibitory effect on wound healing after surgery. Male New Zealand white rabbits underwent tibial mid-diaphyseal osteotomy, and were administered escin once per day for 10 days. At weeks 2, 4 and 6, bone fracture healing and bone mineral density were measured. The histologic examination of callus, osteocalcin, alkaline phosphatase, calcium and phosphate in the serum were also assayed. In another experiment, the rats underwent midline laparotomy, and received escin once prior to or after the operation. Six days later, the abdominal incision wounds were excised for measuring hydroxyproline levels. The results showed that there were no significant differences in fracture healing between the model and rabbits administered escin, and escin did not affect the hydroxyproline levels in the abdominal incision wounds of the rats. These findings suggest that escin has no inhibitory effect on fracture and wound healing in animal models.

Osteoporotic fracture and parathyroid hormone

Osteoporosis and age-related bone loss is associated with changes in bone remodeling characterized by decreased bone formation relative to bone resorption, resulting in bone fragility and increased risk of fractures. Stimulating the function of bone-forming osteoblasts, is the preferred pharmacological intervention for osteoporosis. Recombinant parathyroid hormone (PTH), PTH(1-34), is an anabolic agent with proven benefits to bone strength and has been characterized as a potential therapy for skeletal repair. In spite of PTH's clinical use, safety is a major consideration for long-term treatment. Studies have demonstrated that intermittent PTH treatment enhances and accelerates the skeletal repair process via a number of mechanisms. Recent research into the molecular mechanism of PTH action on bone tissue has led to the development of PTH analogs to control osteoporotic fractures. This review summarizes a number of advances made in the field of PTH and bone fracture to combat these injuries in humans and in animal models. The ultimate goal of providing an alternative to PTH, currently the sole anabolic therapy in clinical use, to promote bone formation and improve bone strength in the aging population is yet to be achieved.

Teriparatide Therapy as an Adjuvant for Tissue Engineering and Integration of Biomaterials

Critically sized large bone defects commonly result from trauma, radical tumor resections or infections. Currently, massive allografting remain as the clinical standard to treat these critical defects. Unfortunately, allograft healing is limited by the lack of osteogenesis and bio-integration of the graft to the host bone. Based on its widely studied anabolic effects on the bone, we have proposed that teriparatide [recombinant parathyroid hormone (PTH(1-34))] could be an effective adjuvant for massive allograft healing. In support of this theory, here we review studies that have demonstrated that intermittent PTH(1-34) treatment enhances and accelerates the skeletal repair process via a number of mechanisms including: effects on mesenchymal stem cells (MSC), angiogenesis, chondrogenesis, bone formation and remodeling. We also review the current literature on the effects of PTH(1-34) therapy on bone healing, and discuss this drug's long term potential as an adjuvant for endogenous tissue engineering.

Endogenous tissue engineering: PTH therapy for skeletal repair

Based on its proven anabolic effects on bone in osteoporosis patients, recombinant parathyroid hormone (PTH(1-34)) has been evaluated as a potential therapy for skeletal repair. In animals, the effect of PTH(1-34) has been investigated in various skeletal repair models such as fractures, allografting, spinal arthrodesis and distraction osteogenesis. These studies have demonstrated that intermittent PTH(1-34) treatment enhances and accelerates the skeletal repair process via a number of mechanisms, which include effects on mesenchymal stem cells, angiogenesis, chondrogenesis, bone formation and resorption. Furthermore, PTH(1-34) has been shown to enhance bone repair in challenged animal models of aging, inflammatory arthritis and glucocorticoid-induced bone loss. This pre-clinical success has led to off-label clinical use and a number of case reports documenting PTH(1-34) treatment of delayed-unions and non-unions have been published. Although a recently completed phase 2 clinical trial of PTH(1-34) treatment of patients with radius fracture has failed to achieve its primary outcome, largely because of effective healing in the placebo group, several secondary outcomes are statistically significant, highlighting important issues concerning the appropriate patient population for PTH(1-34) therapy in skeletal repair. Here, we review our current knowledge of the effects of PTH(1-34) therapy for bone healing, enumerate several critical unresolved issues (e.g., appropriate dosing regimen and indications) and discuss the long-term potential of this drug as an adjuvant for endogenous tissue engineering.

Transcription factor osterix modified bone marrow mesenchymal stem cells enhance callus formation during distraction osteogenesis

This study was designed to investigate the effects of local delivery of bone marrow mesenchymal stem cells (BMMSCs) with or without osterix (OSX) gene transfected on bone regeneration in the distracted zone using a rabbit model of mandibular lengthening. Fifty-four New Zealand white rabbits underwent osteodistraction of the left mandible and were then randomly divided into group A, group B, and group C (n = 18 for each group). At the end of distraction BMMSCs transfected with OSX, autologous BMMSCs and physiological saline were injected into the distraction gaps in groups A, B, and C, respectively. Nine animals from each group were humanely killed at 2 and 6 weeks after completion of distraction. The distracted mandibles were harvested and processed for radiographic, histological, and immunohistochemical examination. Excellent bone formation in the distracted callus was observed in group A and group B; the former showed better bone formation and highest bone mineral density (BMD), thickness of new trabeculae (TNT, mm) and volumes of the newly formed bone area (NBV) in the distraction zones. Group C animals showed poor bone formation in the distracted callus when compared with groups A and B. Positive immunostaining of bone sialoprotein (BSP) was observed in the distracted callus in all groups; however, BSP expression was much stronger in group A than in groups B and C. The results of this study suggest transplantation of BMMSCs can promote bone formation in DO; OSX-mediated ex vivo gene therapy was more effective during bone deposition and callus formation in distraction osteogenesis.