Mechanisms for the enhancement of fracture healing in rats treated with intermittent low-dose human parathyroid hormone (1-34)

Cellular and molecular mechanisms of accelerated fracture healing by COX2 gene therapy: studies in a mouse model of multiple fractures

This study sought to determine the cellular and molecular mechanisms of cyclooxygenase-2 (COX2) gene therapy to accelerate fracture repair in a mouse multiple tibial fractures model. The lenti-COX2 (or lenti-gfp control vector) was injected into fractures on day 1 post-fracture. At days 3-7, the COX2 treatment increased Sdf1-, Cxcr4-, Nes-, and Podxl-expressing mesenchymal stem cells (MSCs) within fracture calluses, suggesting an enhanced MSC recruitment or expansion. The COX2-treated mice formed smaller cartilaginous calluses that had less cartilage tissues than control mice. The expression of Sox9 mRNA was 7-fold less in COX2-treated than in control calluses at day 14, implying that COX2 reduces chondrocytic differentiation of MSCs. The therapy also enhanced angiogenesis as reflected by increased immunostaining of CD31, vWF, and α-SMA over controls in the cartilaginous callus at day 14-21. At which time, the COX2 gene therapy promoted bony remodeling of the cartilaginous callus to bridge the fracture gap that was accompanied by 2-fold increase in osteoclasts along the surface of the woven bone and an onset of osteogenesis. Blocking angiogenesis with daily injection of endostatin from day 4 to day 10 into fracture sites blocked the COX2-mediated reduction of callus size that was associated with an increase in hypertrophic chondrocytes and concomitant reduction in osteoclasts. In conclusion, COX2 accelerates fracture healing in part through three biological actions: 1) increased recruitment/expansion of MSCs; 2) decreased cartilaginous callus formation; and 3) increased angiogenesis-dependent cartilage remodeling. These effects were associated with an earlier onset of bony bridging of the fracture gap.

PTH-enhanced structural allograft healing is associated with decreased angiopoietin-2-mediated arteriogenesis, mast cell accumulation, and fibrosis

Recombinant parathyroid hormone (rPTH) therapy has been evaluated for skeletal repair in animal studies and clinical trials based on its known anabolic effects, but its effects on angiogenesis and fibrosis remain poorly understood. We examined the effects of rPTH therapy on blood vessel formation and osseous integration in a murine femoral allograft model, which caused a significant increase in small vessel numbers, and decreased large vessel formation (p < 0.05). Histology showed that rPTH also reduced fibrosis around the allografts to similar levels observed in live autografts, and decreased mast cells at the graft-host junction. Similar effects on vasculogenesis and fibrosis were observed in femoral allografts from Col1caPTHR transgenic mice. Gene expression profiling revealed rPTH-induced angiopoietin-1 (8-fold), while decreasing angiopoietin-2 (70-fold) at day 7 of allograft healing. Finally, we show anti-angiopoietin-2 peptibody (L1-10) treatment mimics rPTH effects on angiogenesis and fibrosis. Collectively, these findings show that intermittent rPTH treatment enhances structural allograft healing by two processes: (1) anabolic effects on new bone formation via small vessel angiogenesis, and (2) inhibition of angiopoietin-2-mediated arteriogenesis. The latter effect may function as a vascular sieve to limit mast cell access to the site of tissue repair, which decreases fibrosis around and between the fractured ends of bone. Thus, rPTH therapy may be generalizable to all forms of tissue repair that suffer from limited biointegration and excessive fibrosis.

The effect of therapies for osteoporosis on spine fusion: a systematic review

BACKGROUND CONTEXT

Fusion of the spine requires de novo bone formation and remodeling, processes that rely heavily on the action of the osteoblast and osteoclast. Bisphosphonate drugs and intermittent parathyroid hormone (PTH) therapy are widely prescribed to treat osteoporosis and act on the osteoblast/osteoclast complex. The impact of these medications on spine fusion is not known.

PURPOSE

To evaluate the available evidence on the potential impact of bisphosphonates and PTH on fusion rate and fusion quality in spinal arthrodesis.

STUDY DESIGN

A systematic review of the literature.

PATIENT SAMPLE

All available literature regarding the impact of bisphosphonates and PTH on spinal fusion.

OUTCOME MEASURES

Fusion rate and histologic, microstructural, or biomechanical measures of fusion quality.

METHODS

A systematic review of the literature published between 1980 and 2011 was conducted using major electronic databases. The results of studies meeting criteria for inclusion were then aggregated and examined for consensus on the effect of these medications on spine fusion.

RESULTS

The literature contained 18 animal studies and one clinical trial investigating the impact of these medications on spine fusion. Most animal studies evaluating the impact of bisphosphonates on fusion rate have not found statistically significant changes with treatment, although this fact may be attributable to low statistical power. The animal literature does suggest that bisphosphonate therapy results in a less histologically mature fusion mass; however, the impact of these changes on fusion mass biomechanics is unclear. The only available human study suggests that these bisphosphonates may increase the radiographically defined fusion rate but did not demonstrate an impact on clinical outcome. In animals, PTH improves the fusion rate and fusion mass microstructure, but data on its effect on fusion mass biomechanics are lacking. No studies have evaluated the impact of PTH on spine fusion in humans.

CONCLUSIONS

In animals, bisphosphonate therapy appears to impede maturation of the fusion mass, with an unclear effect on mechanical strength. This effect was not seen in the lone human study, which suggested that these medications improved the radiographically defined fusion rate. The available animal studies on intermittent PTH treatment suggest that it may improve fusion rate and fusion mass microstructure. Given the widespread use of these agents, further investigation into their impact on human spine fusion is necessary to inform the care of patients with osteoporosis who are undergoing spine surgery.

Prevention of atrophic nonunion by the systemic administration of parathyroid hormone (PTH 1-34) in an experimental animal model

OBJECTIVES

Recombinant human parathyroid hormone (PTH 1-34) has been previously shown to enhance fracture healing in animal models. Here, we sought to determine whether the systemic administration of PTH 1-34 is effective in preventing atrophic fracture nonunion in a murine, surgical nonunion model.

METHODS

We used an established reproducible long-bone murine fracture nonunion model by generating a midshaft femur fracture, followed by fracture distraction using an intramedullary pin and custom metallic clip to maintain a fracture gap of 1.7 mm. Mice were randomized to receive either daily intraperitoneal injections of 30 μg/kg PTH 1-34 for 14 days or saline injections. At 6 weeks after the procedure, radiographic and histologic assessment of fracture healing was performed.

RESULTS

At 6 weeks after surgery, the group treated with PTH showed higher rates of bony union (50% vs 8%; P < 0.05) as assessed by radiographic analysis. Mean gap size was also significantly lower in the PTH group (1.42 vs 0.36 mm in the control group; P < 0.05). Histologic analysis of atrophic nonunions in the control group revealed a persistent fracture gap with intervening fibrous tissue. In contrast, healed subjects in the PTH-treated group had cortical bridging with mature bone and relatively little callus, which is consistent with primary intramembranous ossification.

CONCLUSIONS

Daily systemic administration of recombinant PTH 1-34 increased the rate of union in a mouse atrophic nonunion model. This may have important implications for the potential clinical role of PTH 1-34 in the treatment of atrophic fracture nonunions.

Biomimetic CaP coating incorporated with parathyroid hormone improves the osseointegration of titanium implant

Parathyroid hormone (PTH) is a well-known therapeutic agent for osteoporosis treatment, however, the inconvenience of daily administration and side effect from systematic administration severely limits its application in clinic. PTH has been incorporated into a biomimetic calcium phosphate (CaP) coating via a co-precipitation method in a modified simulated body fluid. The aim of the current study is to evaluate the osseointegration response of PTH incorporated CaP coating on titanium implants. Implants with different doses of PTH were inserted into tibiae of mice and evaluated by X-ray, micro-CT, histology and back-scattered scanning electron microscopy. Improved osseointegration of the implants loaded with PTH was observed compared to CaP coating only after 28 days of implantation in mouse tibiae. Micro-CT analysis showed better bone integration around the implant incorporated with PTH. Bone area and bone contact evaluations have demonstrated that peri-implant bone regeneration is highly dependent on the dosage of PTH incorporated. The higher the PTH content, the more bone formed surrounding the implant. Therefore, our results suggest that biomimetic CaP coating could be a useful a carrier for PTH local delivery, which results in improved bone-to-implant integration.

Sustained release of PTH(1-34) from PLGA microspheres suppresses osteoarthritis progression in rats

We previously reported that PTH(1-34) inhibits the terminal differentiation of articular chondrocytes and, in turn, suppresses the progression of osteoarthritis (OA). However, this treatment requires an injection of PTH(1-34) once every 3 days over the treatment period. In this study, we studied the effect of sustained administration of PTH(1-34) in a papain-induced OA rat model. We developed an effective controlled-release system for prolonging the treatment duration of an intra-articular injection for OA treatment in rats. The effects of released PTH(1-34) from PLGA(65:35)-encapsulated PTH(1-34) microspheres (PTH/PLGA) on papain-induced OA in rat knees were studied. Microsphere morphology was observed in vitro by scanning electron microscopy, and microsphere size was determined with a particle size analyzer. The PTH(1-34) encapsulation efficiency and release profile, as well as the toxicity of PTH/PLGA, were examined. The bioactivity of released PTH(1-34) was tested by examining cAMP levels in MC3T3E1 cells. In vivo, we evaluated the changes of localized GAG, Col II, and Col X in the articular cartilage of rat knees. Our results demonstrated that the surface of the PLGA microspheres was smooth, and the size of the microspheres was in the range of 51-127 μm. PTH/PLGA microspheres sustainably released PTH(1-34) for 19 days with a concentration range of 0.01-100 nM that covered the expected concentration of 10nM at 37°C. The cAMP levels of MC3T3E1 cells were elevated in the response to released PTH(1-34) from PTH/PLGA microspheres, indicating that the released PTH(1-34) is bioactive. Most importantly, intra-articular treatment with either PTH(1-34) (0.1-100 nM) 3 days/injection or PTH/PLGA microspheres (15 days/injection) for 5 weeks revealed the similar effect on suppressing papain-induced OA changes (decreasing GAG and Col II and increasing Col X) in rat knee cartilage. The effect of PTH/PLGA microspheres on suppressing OA progression was similar to that of a once-every-three-day injection of PTH(1-34), indicating that both the sustained and intermittent action of PTH(1-34) effectively suppress OA progression. The developed PLGA microspheres with sustained release and long-term effect may be potent carriers for PTH(1-34) used to treat early OA.

The effect of rhPTH on the healing of tendon to bone in a rat model

Successful rotator cuff tendon repair depends on secure tendon-to-bone healing. Recombinant human parathyroid hormone (rhPTH) has been shown in multiple studies to accelerate bone healing. Recent studies have also shown that rhPTH is chondrogenic by increasing chondrocyte recruitment and differentiation. We hypothesized that rhPTH would improve tendon-to-bone healing in a rat rotator cuff repair model. One hundred and fourteen Sprague Dawley rats underwent division and repair of the supraspinatus tendon. Fifty seven rats received daily subcutaneous injections of 10 µg/kg of rhPTH. Rats were sacrificed at 3, 7, 14, 28, and 56 days for histologic and immunohistochemical analysis. In addition, rats in each group were sacrificed at 14, 28, and 56 days for biomechanical testing and micro CT analysis. At 2 weeks the controls had a significantly higher load to failure than the rhPTH group. At 28 and 56 days there were no differences in load to failure. rhPTH specimens had significantly higher stiffness at 56 days. MicroCT analysis showed that the rhPTH group had significantly greater total mineral content at all time points, as well as significantly higher bone volume (BV) at 14 and 28 days. Histologically, the rhPTH specimens had more fibrocartilage, osteoblasts, and blood vessels at all timepoints, with significantly better collagen fiber orientation at 28 and 56 days. Although treatment with rhPTH resulted in an increase in bone and mineralized fibrocartilage formation, as well as better collagen fiber organization, this did not translate into improved biomechanical properties.

Implications for fracture healing of current and new osteoporosis treatments: an ESCEO consensus paper

Osteoporotic fracture healing is critical to clinical outcome in terms of functional recovery, morbidity, and quality of life. Osteoporosis treatments may affect bone repair, so insights into their impact on fracture healing are important. We reviewed the current evidence for an impact of osteoporosis treatments on bone repair. Treatment with bisphosphonate in experimental models is associated with increased callus size and mineralization, reduced callus remodeling, and improved mechanical strength. Local and systemic bisphosphonate treatment may improve implant fixation. No negative impact on fracture healing has been observed, even after major surgery or when administered immediately after fracture. Experimental data for denosumab and raloxifene suggest no negative implications for bone repair. The extensive experimental results for teriparatide indicate increased callus formation, improved biomechanical strength, and greater external callus volume and total bone mineral content and density. Case reports and a randomized trial have produced mixed results but are consistent with a positive impact of teriparatide on clinical fracture healing. Studies with strontium ranelate in models of fracture healing indicate that it is associated with improved bone microstructure, callus volume, and biomechanical properties. Finally, there is experimental evidence for a beneficial effect of some of the agents currently being developed for osteoporosis, notably sclerostin antibody and DKK1 antibody. There is currently no evidence that osteoporosis treatments are detrimental for bone repair and some promising experimental evidence for positive effects on healing, notably for agents with a bone-forming mode of action, which may translate into therapeutic applications.

Amelioration of type I diabetes-induced osteoporosis by parathyroid hormone is associated with improved osteoblast survival

Type 1 diabetic osteoporosis results from impaired osteoblast activity and death. Therefore, anti-resorptive treatments may not effectively treat bone loss in this patient population. Intermittent parathyroid hormone (PTH) treatment stimulates bone remodeling and increases bone density in healthy subjects. However, PTH effects may be limited in patients with diseases that interfere with its signaling. Here, we examined the ability of 8 and 40 µg/kg intermittent PTH to counteract diabetic bone loss. PTH treatment reduced fat pad mass and blood glucose levels in non-diabetic PTH-treated mice, consistent with PTH-affecting glucose homeostasis. However, PTH treatment did not significantly affect general body parameters, including the blood glucose levels, of type 1 diabetic mice. We found that the high dose of PTH significantly increased tibial trabecular bone density parameters in control and diabetic mice, and the lower dose elevated trabecular bone parameters in diabetic mice. The increased bone density was due to increased mineral apposition and osteoblast surface, all of which are defective in type 1 diabetes. PTH treatment suppressed osteoblast apoptosis in diabetic bone, which could further contribute to the bone-enhancing effects. In addition, PTH treatment (40 µg/kg) reversed preexisting bone loss from diabetes. We conclude that intermittent PTH may increase type 1 diabetic trabecular bone volume through its anabolic effects on osteoblasts.

Locally administrated perindopril improves healing in an ovariectomized rat tibial osteotomy model

Angiotensin-converting enzyme inhibitors are widely prescribed to regulate blood pressure. High doses of orally administered perindopril have previously been shown to improve fracture healing in a mouse femur fracture model. In this study, perindopril was administered directly to the fracture area with the goal of stimulating fracture repair. Three months after being ovariectomized (OVX), tibial fractures were produced in Sprague–Dawley rats and subsequently stabilized with intramedullary wires. Perindopril (0.4 mg/kg/day) was injected locally at the fractured site for a treatment period of 7 days. Vehicle reagent was used as a control. Callus quality was evaluated at 2 and 4 weeks post-fracture. Compared with the vehicle group, perindopril treatment significantly increased bone formation, increased biomechanical strength, and improved microstructural parameters of the callus. Newly woven bone was arranged more tightly and regularly at 4 weeks post-fracture. The ultimate load increased by 66.1 and 76.9% (p<0.01), and the bone volume over total volume (BV/TV) increased by 29.9% and 24.3% (p<0.01) at 2 and 4 weeks post-fracture, respectively. These findings suggest that local treatment with perindopril could promote fracture healing in ovariectomized rats.

A fracture does not adversely affect bone mineral density responses after teriparatide treatment

BACKGROUND

Fracture leads to local and systemic catabolic physiologic changes. As teriparatide is an agent used to treat osteoporosis in patients with fragility fractures, it is unclear whether teriparatide treatment alters bone mineral density (BMD) and bone markers when given to patients with fractures.

QUESTIONS/PURPOSES

We asked whether BMD and bone marker responses would be blunted in patients with fractures placed on teriparatide after fracture compared with patients without fractures on teriparatide.

PATIENTS AND METHODS

We retrospectively collected data from 141 patients treated with teriparatide for osteoporosis. Seventy-seven patients received teriparatide after fractures (fracture group), whereas 64 were treated for other indications (nonfracture group). We determined BMD at the lumbar spine and at the proximal femur before and 12 and 24 months posttreatment. Bone markers (urine N-telopeptide [urine NTX], bone-specific alkaline phosphatase [BALP]) were measured at baseline and 3, 12, and 24 months posttreatment.

RESULTS

Mean lumbar spine and hip BMDs at last followup increased from baseline with no differences between groups to approximately 9% and 4% at 24 months, respectively. Both bone markers increased from baseline in the nonfracture group, peaking at 12 months. For the fracture group, only urine NTX increased at 3 and 12 months posttreatment. Although the peak levels of both bone markers in the nonfracture group were greater, there was no difference between the two groups.

CONCLUSIONS

Fracture does not have a negative effect on the BMD and bone marker responses to teriparatide treatment. Clinicians should anticipate comparable BMD responses when treating patients with teriparatide for osteoporotic fractures and for other indications.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

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.

Parathyroid hormone treatment improves the cortical bone microstructure by improving the distribution of type I collagen in postmenopausal women with osteoporosis

Although an important index, the level of bone mineral density (BMD) does not completely describe fracture risk. Another bone structural parameter, the orientation of type I collagen, is known to add to risk determination, independently of BMD, ex vivo. We investigated the Haversian system of transiliac crest biopsies from postmenopausal women before and after treatment with parathyroid hormone (PTH). We used the birefringent signal of circularly polarized light and its underlying collagen arrangements by confocal and electron microscopy, in conjunction with the degree of calcification by high-resolution micro-X-ray. We found that PTH treatment increased the Haversian system area by 11.92 ± 5.82 mm² to 12.76 ± 4.50 mm² (p = 0.04); decreased bright birefringence from 0.45 ± 0.02 to 0.40 ± 0.01 (scale zero to one, p = 0.0005); increased the average percent area of osteons with alternating birefringence from 48.15% ± 10.27% to 66.33% ± 7.73% (p = 0.034); and nonsignificantly decreased the average percent area of semihomogeneous birefringent osteons (8.36% ± 10.63% versus 5.41% ± 9.13%, p = 0.40) and of birefringent bright osteons (4.14% ± 8.90% versus 2.08% ± 3.36%, p = 0.10). Further, lamellar thickness significantly increased from 3.78 ± 0.11 µm to 4.47 ± 0.14 µm (p = 0.0002) for bright lamellae, and from 3.32 ± 0.12 µm to 3.70 ± 0.12 µm (p = 0.045) for extinct lamellae. This increased lamellar thickness altered the distribution of birefringence and therefore the distribution of collagen orientation in the tissue. With PTH treatment, a higher percent area of osteons at the initial degree of calcification was observed, relative to the intermediate-low degree of calcification (57.16% ± 3.08% versus 32.90% ± 3.69%, p = 0.04), with percentage of alternating osteons at initial stages of calcification increasing from 19.75 ± 1.22 to 80.13 ± 6.47, p = 0.001. In conclusion, PTH treatment increases heterogeneity of collagen orientation, a starting point from which to study the reduction in fracture risk when PTH is used to treat osteoporosis.

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.

Delayed short-course treatment with teriparatide (PTH(1-34)) improves femoral allograft healing by enhancing intramembranous bone formation at the graft-host junction

Clinical management of critical bone defects remains a major challenge. Despite preclinical work demonstrating teriparatide (PTH(1-34)) effectiveness in small animals, inconclusive data from clinical trials have raised questions of dose and regimen. To address this, we completed a comprehensive study in the murine femoral allograft model, to assess the effects of dose (0.4, 4, and 40 µg/kg/day) and various treatment regimens on radiographic, histologic, and biomechanical healing at 2, 4, and 9 weeks. Only the high dose (40 µg/kg) of PTH(1-34) demonstrated significant effects when given daily over 9 weeks. Remarkably, equivalent biomechanical results were obtained with delayed, short treatment from 2 to 6 weeks that did not induce a significant increase in endochondral bone formation and callus volume. In contrast, PTH(1-34) treatment from 1 to 5 weeks postop demonstrated similar osteogenic effects as immediate daily treatment for 9 weeks, but failed to achieve a significant increase in biomechanics at 9 weeks. MicroCT and histologic analyses demonstrated that the 2-week delay in treatment allowed for timely completion of the endochondral phase, such that the prominent effects of PTH(1-34) were enhanced intramembranous bone formation and remodeling at the graft-host junction. These findings support the potential use of PTH(1-34) as an adjuvant therapy for massive allograft healing, and suggest that there may be an ideal treatment window in which a short course is administered after the endochondral phase to promote osteoblastic bone formation and remodeling to achieve superior union with modest callus formation.

Experimental stimulation of bone healing with teriparatide: histomorphometric and microhardness analysis in a mouse model of closed fracture

Fracture consolidation is a crucial goal to achieve as early as possible, but pharmacological stimulation has been neglected so far. Teriparatide has been considered for this purpose for its anabolic properties. We set up a murine model of closed tibial fracture on which different doses of teriparatide were tested. Closed fracture treatment avoids any bias introduced by surgical manipulations. Teriparatide's effect on callus formation was monitored during the first 4 weeks from fracture. Callus evolution was determined by histomorphometric and microhardness assessment. Daily administration of 40 μg/kg of teriparatide accelerated callus mineralization from day 9 onward without significant increase of sizes, and at day 15 the microhardness properties of treated callus were similar to those of bone tissue. Teriparatide considerably improved callus consolidation in the very early phases of bone healing.

Anabolic agents and bone quality

BACKGROUND

The definition of bone quality is evolving particularly from the perspective of anabolic agents that can enhance not only bone mineral density but also bone microarchitecture, composition, morphology, amount of microdamage, and remodeling dynamics.

QUESTIONS/PURPOSES

This review summarizes the molecular pathways and physiologic effects of current and potential anabolic drugs.

METHODS

From a MEDLINE search (1996-2010), articles were identified by the search terms "bone quality" (1851 articles), "anabolic agent" (5044 articles), "PTH or parathyroid hormone" (32,229 articles), "strontium" or "strontium ranelate" (283 articles), "prostaglandin" (77,539 articles), and "statin" or "statins" (14,233 articles). The search strategy included combining each with the phrase "bone quality." Another more limited search aimed at finding more novel potential agents.

RESULTS

Parathyroid hormone is the only US Food and Drug Administration-approved bone anabolic agent in the United States and has been the most extensively studied in in vitro animal and human trials. Strontium ranelate is approved in Europe but has not undergone Food and Drug Administration trials in the United States. All the studies on prostaglandin agonists have used in vivo animal models and there are no human trials examining prostaglandin agonist effects. The advantages of statins include the long-established advantages and safety profile, but they are limited by their bioavailability in bone. Other potential pathways include proline-rich tyrosine kinase 2 (PYK2) and sclerostin (SOST) inhibition, among others.

CONCLUSIONS

The ongoing research to enhance the anabolic potential of current agents, identify new agents, and develop better delivery systems will greatly enhance the management of bone quality-related injuries and diseases in the future.

Endogenous PTH deficiency impairs fracture healing and impedes the fracture-healing efficacy of exogenous PTH(1-34)

Background

Although the capacity of exogenous PTH1-34 to enhance the rate of bone repair is well established in animal models, our understanding of the mechanism(s) whereby PTH induces an anabolic response during skeletal repair remains limited. Furthermore it is unknown whether endogenous PTH is required for fracture healing and how the absence of endogenous PTH would influence the fracture-healing capacity of exogenous PTH.

Methodology/Principal Findings

Closed mid-diaphyseal femur fractures were created and stabilized with an intramedullary pin in 8-week-old wild-type and Pth null (Pth^−/−) mice. Mice received daily injections of vehicle or of PTH1-34 (80 µg/kg) for 1–4 weeks post-fracture, and callus tissue properties were analyzed at 1, 2 and 4 weeks post-fracture. Cartilaginous callus areas were reduced at 1 week post-fracture, but were increased at 2 weeks post-fracture in vehicle-treated and PTH-treated Pth^−/− mice compared to vehicle-treated and PTH-treated wild-type mice respectively. The mineralized callus areas, bony callus areas, osteoblast number and activity, osteoclast number and surface in callus tissues were all reduced in vehicle-treated and PTH-treated Pth^−/− mice compared to vehicle-treated and PTH-treated wild-type mice, but were increased in PTH-treated wild-type and Pth^−/− mice compared to vehicle-treated wild-type and Pth^−/− mice.

Conclusions/Significance

Absence of endogenous PTH1-84 impedes bone fracture healing. Exogenous PTH1-34 can act in the absence of endogenous PTH but callus formation, including accelerated endochondral bone formation and callus remodeling as well as mechanical strength of the bone are greater when endogenous PTH is present. Results of this study suggest a complementary role for endogenous PTH1-84 and exogenous PTH1-34 in accelerating fracture healing.

Atypical subtrochanteric femoral fractures in patients with skeletal malignant involvement treated with intravenous bisphosphonates

BACKGROUND

Atypical subtrochanteric femoral fractures have been identified as a potential complication of long-term bisphosphonate therapy for the treatment of osteoporosis. Patients with skeletal malignant involvement, who receive much higher cumulative doses of bisphosphonates than do patients with osteoporosis, may be at higher risk for the development of these fractures.

METHODS

A retrospective review of the imaging studies and case notes was done for patients with skeletal malignant involvement who received a minimum of twenty-four doses of intravenous bisphosphonates between 2004 and 2007 and were followed until death or the time of the latest review. Patients were classified as having an atypical subtrochanteric femoral fracture if they had a transverse subtrochanteric fracture following low-energy trauma or an impending fracture, together with radiographic findings of diffuse diaphyseal cortical thickening and cortical beaking at the subtrochanteric area.

RESULTS

In the study cohort of 327 patients, we identified four patients who developed an atypical subtrochanteric femoral fracture. All four patients were female, three had breast cancer, and one had myeloma. There was no significant difference between patients who developed an atypical subtrochanteric femoral fracture and those who did not with regard to the doses of intravenous bisphosphonates or the duration of treatment.

CONCLUSIONS

The prevalence of atypical subtrochanteric femoral fractures in patients with skeletal malignant involvement who are managed with high doses of intravenous bisphosphonates is low. All patients in our study who had development of these fractures had prodromal symptoms of thigh pain.

Topical and intermittent application of parathyroid hormone recovers alveolar bone loss in rat experimental periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is characterized by periodontal tissue inflammation and alveolar bone loss. The intermittent administration of parathyroid hormone (PTH), a major regulator of bone remodeling, has been demonstrated to stimulate osteoblastic activity. Although the systemic administration of PTH has been reported to protect against periodontitis-associated bone loss, the effect of the topical administration of PTH is unclear. In this study, the effect of intermittent administration of PTH on osteoblastic differentiation was examined in cultured calvaria cells and then the effect of topical and intermittent administration of PTH was determined by measuring the recovery of alveolar bone loss after inducing experimental periodontitis in rats.

MATERIAL AND METHODS

Alkaline phosphatase activity and bone nodule formation were measured in fetal rat calvaria cells. Experimental periodontitis was induced by placing nylon ligature around rat maxillary molars for 20 d. After ligature removal (day 0), PTH was topically injected into buccal gingiva three times a week for 10 wk. Micro-computed tomography analysis and histological examination were performed on days 35 and 70.

RESULTS

Intermittent exposure of PTH in calvaria cells increased alkaline phosphatase activity and bone nodule formation by 1.4- and 2.4-fold, respectively. Ligature procedures induced marked alveolar bone loss around the molars on day 0 and greater bone recovery was observed in the PTH-treated rats on day 70. An increase in osteoid formation on the surface of alveolar bone was detected in the PTH-treated rats.

CONCLUSION

Intermittent treatment with PTH stimulated osteoblastic differentiation in fetal rat calvaria cell cultures, and topical and intermittent administration of PTH recovered alveolar bone loss in rat experimental periodontitis.

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.

Inhibition of sclerostin by monoclonal antibody enhances bone healing and improves bone density and strength of nonfractured bones

Therapeutic enhancement of fracture healing would help to prevent the occurrence of orthopedic complications such as nonunion and revision surgery. Sclerostin is a negative regulator of bone formation, and treatment with a sclerostin monoclonal antibody (Scl-Ab) results in increased bone formation and bone mass in animal models. Our objective was to investigate the effects of systemic administration of Scl-Ab in two models of fracture healing. In both a closed femoral fracture model in rats and a fibular osteotomy model in cynomolgus monkeys, Scl-Ab significantly increased bone mass and bone strength at the site of fracture. After 10 weeks of healing in nonhuman primates, the fractures in the Scl-Ab group had less callus cartilage and smaller fracture gaps containing more bone and less fibrovascular tissue. These improvements at the fracture site corresponded with improvements in bone formation, bone mass, and bone strength at nonfractured cortical and trabecular sites in both studies. Thus the potent anabolic activity of Scl-Ab throughout the skeleton also was associated with an anabolic effect at the site of fracture. These results support the potential for systemic Scl-Ab administration to enhance fracture healing in patients.

Preparation and evaluation of parathyroid hormone incorporated CaP coating via a biomimetic method

Parathyroid hormone (PTH) is a potent bone growth stimulator used for osteoporosis treatment. However, the inconvenience of daily administration and side effect of systemic exposure severely limit its use in clinical applications. Local, controlled delivery is a promising approach which can maintain therapeutic concentration locally for a long period. In this study, PTH was incorporated into a biomimetic calcium phosphate (CaP) coating via a coprecipitation process in a modified simulated body fluid (m-SBF). It was found that PTH was successfully incorporated into biomimetic CaP coating on titanium surface with a high incorporation efficiency. The incorporation of PTH into coatings had significantly changed the coating morphology, but the composition of the coating remained unchanged. Localized release of PTH had occurred in vitro, and was accompanied with partial dissolution of CaP coatings. Cell culture study demonstrated that the PTH released from CaP coatings fully retained its bioactivity. It had improved substantially MC3T3-E1 cell proliferation but slightly delayed the expression of alkaline phosphatase (ALP) of the cells. In summary, our results have shown that CaP coatings incorporated with PTH may be a promising approach for osteoporosis and other bone-related disease treatment in the future.

Teriparatide therapy enhances devitalized femoral allograft osseointegration and biomechanics in a murine model

Despite the remarkable healing potential of long bone fractures, traumatic injuries that result in critical defects require challenging reconstructive limb sparing surgery. While devitalized allografts are the gold standard for these procedures, they are prone to failure due to their limited osseointegration with the host. Thus, the quest for adjuvants to enhance allograft healing remains a priority for this unmet clinical need. To address this, we investigated the effects of daily systemic injections of 40 μg/kg teriparatide (recombinant human parathyroid hormone) on the healing of devitalized allografts used to reconstruct critical femoral defects (4mm) in C57Bl/6 mice. The femurs were evaluated at 4 and 6 weeks using micro CT, histology, and torsion testing. Our findings demonstrated that teriparatide induced prolonged cartilage formation at the graft-host junction at 4 weeks, which led to enhanced trabeculated bone callus formation and remarkable graft-host integration at 6-weeks. Moreover, we observed a significant 2-fold increase in normalized callus volume (1.04 ± 0.3 vs. 0.54 ± 0.14 mm³/mm; p < 0.005), and Union Ratio (0.28 ± 0.07 vs. 0.13 ± 0.09; p < 0.005), compared to saline treated controls at 6-weeks. Teriparatide treatment significantly increased the torsional rigidity (1175 ± 311 versus 585 ± 408 N.mm²) and yield torque (10.5 ± 4.2 versus 6.8 ± 5.5 N.mm) compared to controls. Interestingly, the Union Ratio correlated significantly with the yield torque and torsional rigidity (R²=0.59 and R²=0.77, p < 0.001, respectively). These results illustrate the remarkable potential of teriparatide as an adjuvant therapy for allograft repair in a mouse model of massive femoral defect reconstruction, and warrant further investigation in a larger animal model at longer time intervals to justify future clinical trials for PTH therapy in limb sparing reconstructive procedures.

Intermittent parathyroid hormone fails to stimulate osseointegration in diabetic rats

OBJECTIVES

Diabetes is considered a risk factor in the osseointegration of dental implants, which suggests that these patients might benefit from anabolic therapies. Preclinical studies, including investigations by this research group, revealed that intermittent administration of parathyroid hormone (PTH) stimulates bone formation on the surface of titanium implants under physiological conditions. However, the anabolic effect of PTH on osseointegration under the hyperglycemic condition of diabetes is unknown.

METHODS

The ability of PTH to stimulate osseointegration was investigated in 40 female Wistar rats that were randomly divided into the following treatment groups: diabetes, diabetes plus PTH, control, and control plus PTH. Diabetes was induced by intraperitoneal injection of streptozotocin (45 mg/kg) at 1 week before implantation. Rats received PTH at a dose of 60 μg/kg or a vehicle by subcutaneous injection starting at the day of implant insertion into the tibia. Histomorphometric analysis was performed after 4 weeks.

RESULTS

The medullary peri-implant bone area significantly increased in rats receiving PTH in comparison with the control group (41±12% to 20±12%; P<0.01). Moreover, there was an increased bone-to-implant contact (BIC) area in animals treated with PTH (47±18% to 27±16%; P<0.05). In contrast, diabetic rats failed to benefit from the anabolic treatment. A similar peri-implant bone area occurred in the diabetes group, independent of treatment with PTH (13±9% to 15±6%; P>0.05). Moreover, PTH did not affect the BIC area under hyperglycemic conditions (16±12% to 16±8%; P>0.05). No significant changes were observed in the cortical compartment of all groups.

CONCLUSION

These results demonstrate that the metabolic characteristics of the diabetic rats produced a condition that was unable to respond to PTH treatment. These findings led us to hypothesize that metabolic control of diabetes might be a critical determinant when diabetic patients are undergoing anabolic therapy to enhance osseointegration.

Management of osteoporosis in patients hospitalized for hip fractures

Hip fracture is associated with high morbidity, mortality, and economic burden worldwide. It is also a major risk factor for a subsequent fracture. A literature search on the management of osteoporosis in patients with hip fracture was performed on the Medline database. Only one clinical drug trial was conducted in patients with a recent hip fracture. Further studies that specifically address post-fracture management of hip fracture are needed. The efficacy of anti-osteoporosis medication in older individuals and those at high risk of fall is reviewed in this paper. Adequate nutrition is vital for bone health and to prevent falls, especially in malnourished patients. Protein, calcium, and vitamin D supplementation is associated with increased hip BMD and a reduction in falls. Fall prevention, exercise, and balance training incorporated in a comprehensive rehabilitation program are essential to improve functional disability and survival. Exclusion of secondary causes of osteoporosis and treatment of coexistent medical conditions are also vital. Such a multidisciplinary team approach to the management of hip fracture patients is associated with a better clinical outcome. Although hip fracture is the most serious of all fractures, osteoporosis management should be prioritized to prevent deterioration of health and occurrence of further fracture.

Intermittent weekly administration of human parathyroid hormone (1-34) improves bone-hydroxyapatite block bonding in ovariectomized rats

Hydroxyapatite (HA) blocks have been widely used for the reconstruction of bone defects and as a bone substitute. Bone-implant bonding depends on both implant-related factors and patient variables. Intermittent human parathyroid hormone (h-PTH) has a strong anabolic effect on bone formation. The purpose of the present study is to evaluate whether intermittent h-PTH administration enhances bone-HA block bonding in normal versus ovariectomized (OVX) rats. Cancellous bone osteotomy and HA-block implantation were performed on the proximal left tibia in both OVX and sham-operated 7-month-old female Sprague-Dawley rats. Newly formed cancellous bone around the HA block and bone-HA block bonding were evaluated by bone histomorphometry at 8 weeks after the administration of h-PTH (100 μg/kg/week) or its vehicle. The administration of h-PTH significantly increased cancellous bone volume by stimulating bone formation in OVX rats (p < 0.01). Although bone-HA block bonding was significantly decreased in OVX rats compared to that of sham-operated rats (p < 0.01), h-PTH improved the bone-HA block bonding in OVX rats (p < 0.01). These results suggest that intermittent h-PTH treatment may improve bone-HA bonding in osteoporosis by restoring cancellous bone volume and enhancing cancellous bone formation around the HA block.

Teriparatide therapy and beta-tricalcium phosphate enhance scaffold reconstruction of mouse femoral defects

To investigate the efficacy of endocrine parathyroid hormone treatment on tissue-engineered bone regeneration, massive femoral defects in C57Bl/6 mice were reconstructed with either 100:0 or 85:15 poly-lactic acid (PLA)/beta-tricalcium phosphate (β-TCP) scaffolds (hereafter PLA or PLA/βTCP, respectively), which were fabricated with low porosity (<30%) to improve their structural rigidity. Experimental mice were treated starting at 1 week postop with daily subcutaneous injections of 40 μg/kg teriparatide until sacrifice at 9 weeks, whereas control mice underwent the same procedure but were injected with sterile saline. Bone regeneration was assessed longitudinally using planar X-ray and quantitative microcomputed tomography, and the reconstructed femurs were evaluated at 9 weeks either histologically or biomechanically to determine their torsional strength and rigidity. Teriparatide treatment increased bone volume and bone mineral content significantly at 6 weeks and led to enhanced trabeculated bone callus formation that appeared to surround and integrate with the scaffold, thereby establishing union by bridging bone regeneration across the segmental defect in 30% of the reconstructed femurs, regardless of the scaffold type. However, the bone volume and mineral content in the PLA reconstructed femurs treated with teriparatide was reduced at 9 weeks to control levels, but remained significantly increased in the PLA/βTCP scaffolds. Further, bridged teriparatide-treated femurs demonstrated a prototypical brittle bone torsion behavior, and were significantly stronger and stiffer than control specimens or treated specimens that failed to form bridging bone union. Taken together, these observations suggest that intermittent, systemic parathyroid hormone treatment can enhance bone regeneration in scaffold-reconstructed femoral defects, which can be further enhanced by mineralized (βTCP) particles within the scaffold.

Long bone fracture repair in mice harboring GFP reporters for cells within the osteoblastic lineage

GFP reporter mice previously developed to assess levels of osteoblast differentiation were employed in a tibial long bone fracture model using a histological method that preserves fluorescent signals in non-decalcified sections of bone. Two reporters, based on Col1A1 (Col3.6GFPcyan) and osteocalcin (OcGFPtpz) promoter fragments, were bred into the same mice to reflect an early and late stage of osteoblast differentiation. Three observations were apparent from this examination. First, the osteoprogenitor cells that arise from the flanking periosteum proliferate and progress to fill the fracture zone. These cells differentiate to osteoblasts, chondrocytes, to from the outer cortical shell. Second, the hypertrophic chondrocytes are dispersed and the cartilage matrix mineralized by the advancing Col3.6+ osteoblasts. The endochondral matrix is removed by the following osteoclasts. Third, a new cortical shell develops over the cartilage core and undergoes a remodeling process of bone formation on the inner surface and resorption on the outer surface. The original fractured cortex undergoes resorption as the outer cortical shell remodels inward to become the new diaphyseal bone. The fluorescent microscopy and GFP reporter mice used in this study provide a powerful tool for appreciating the molecular and cellular processes that control these fundamental steps in fracture repair, and may provide a basis for understanding fracture nonunion.

Effect of human parathyroid hormone hPTH (1-34) applied at different regimes on fracture healing and muscle in ovariectomized and healthy rats

Three experiments were conducted to investigate the effect of intermittent administration of parathyroid hormone (PTH) (1-34) applied at different regimes on fracture healing and muscle in healthy and ovariectomized (Ovx at 3 months of age) rats. Five-month old rats underwent bilateral transverse metaphyseal osteotomy of tibia and were divided into groups (12 rats each). In Exp 1, Ovx rats were either treated with PTH (7x/w, 1-35d), with oral estradiol-17beta-benzoate (0.4 mg/kg BW, 1-35d) or untreated. In Exp. 2, there were 3 groups: healthy untreated or treated with PTH (5x/w, 1-35d or 7-35d). In Exp. 3, there were 7 groups: healthy, Ovx, "healthy PTH 5x/w 7-35d", "Ovx PTH 5x/w 7-35d, 14-35d or 14-28d", "Ovx PTH every other day 7-35d". Single dosage of PTH was 40 microg/kg BW. After 35 days of healing one tibia was analyzed by computed tomographical, biomechanical, histological analyses. The other tibia was used in analyses of Alp, Oc, Trap 1, Igf-1, Rankl, Opg genes (Exp.2, 3). Serum Oc and Alp were measured. Body, uterus weight was recorded. M. gastrocnemius was analyzed for weight (Exp. 2), fiber size and mitochondrial respiratory activity (MRA) (Exp.3). Estrogen enhanced uterus weight, prevented body increase, however, did not improve bone healing in Ovx rats (Exp. 1). PTH administration from days 1 and 7 improved bone parameters in all rats regardless of the application frequency (7, 5x/w or every other day) (Exp. 1, stiffness Ovx: 118+13 N/mm, Ovx PTH: 250+/-20 N/mm) being more effective in healthy rats (Exp. 3, stiffness improvement Healthy: 59 to 174 N/mm, Ovx: 52 to 98 N/mm). Serum Oc level was elevated in PTH treated rats. Application from day 14 proved to be less effective (Exp. 3). PTH had no effect (P>0.05) on body, uterus and muscle weight, muscle fiber size, MRA and expression of bone markers. PTH promoted bone healing in Ovx and healthy rats, when it is applied during early stage of healing without having any adverse systemic effect. In perspective, PTH may represent a treatment for enhancement of fracture healing. The findings need to be confirmed by follow-up studies on other animals.

Back pain during different sequential treatment regimens of teriparatide: results from EUROFORS

OBJECTIVE

To investigate changes in back pain in postmenopausal women with severe osteoporosis who received teriparatide for 24 months or switched at 12 months to raloxifene or no active treatment.

STUDY DESIGN AND METHODS

This prospective, controlled, randomised, open-label, 2-year study enrolled 868 postmenopausal women with osteoporosis and a recent fragility fracture. After 12 months of teriparatide (20 microg/day), 507 patients were randomised to further teriparatide (n = 305), raloxifene 60 mg/day (n = 100), or no active treatment (n = 102) for another 12 months (substudy 1); in substudy 2, 199 patients continued teriparatide. All received calcium and vitamin D supplementation. Back pain was self-assessed by patients using a visual analogue scale (0-100 mm). Changes in back pain were analysed using a mixed model for repeated measures.

RESULTS

During year 1, back pain decreased from a mean (SD) of 48.9 mm (24.0) at baseline by 11.5 mm (p < 0.001) in the total study population. In substudy 1, mean change in back pain from month 12 (randomisation) to 24 months was -2.2, -4.4 and +0.7 mm in the teriparatide (p = 0.076), raloxifene (p = 0.041), and no active treatment groups (p = 0.751). There were no between-group differences from randomization to 18 or 24 months. In a sensitivity analysis excluding patients with low baseline back pain (VAS < 30 mm), mean change from randomisation to endpoint was significant for teriparatide (-3.9 mm, p = 0.006) and raloxifene (-6.3 mm, p = 0.018) groups. Subgroup analyses of 503 patients who received teriparatide for up to 2 years showed that patients with a recent vertebral fracture had a greater decrease in back pain than those without (p < 0.05). Those with and without mild back pain (>or=30 mm), and those with and without severe back pain (>or=60 mm) at baseline all had a statistically significant reduction in back pain after 24 months (p < 0.05).

CONCLUSIONS

Teriparatide treatment is associated with significant reductions in back pain regardless of the presence of recent vertebral fracture. These results need to be considered with caution due to the open-label design of the study.

Parathyroid hormone and bisphosphonate have opposite effects on stress fracture repair

This study was aimed to investigate the effects of Parathyroid hormone (PTH) and alendronate (ALN) on stress fracture repair. Stress fractures were induced in the ulnae of female adult rats. Animals were treated daily with vehicle, PTH (40 microg/kg) or alendronate (2 microg/kg), respectively. Bone mineral content (BMC) and bone mineral density (BMD) of bilateral ulnae were measured at two, four and eight weeks following induction of stress fracture. Histology at the ulna midshaft was undertaken at 2 and 4 weeks and mechanical testing was done at 8 weeks after stress fracture. PTH increased BMC significantly by 7% at 4 weeks and BMD and BMC significantly by 10% and 7% at 8 weeks compared to the control. Alendronate did not change BMD or BMC in comparison with the control. PTH significantly stimulated bone formation by 114% at 2 weeks, increased intracortical resorption area by 23% at 4 weeks, and enhanced the ultimate force of the affected ulnae by 15% at 8 weeks compared to the control. Alendronate significantly suppressed bone formation rate by 44% compared to the control at 4 weeks. These data indicate that PTH may accelerate intracortical bone remodeling induced by microdamage and alendronate may delay intracortical bone remodeling during stress fracture repair in rats. This study suggests that PTH may be used to facilitate stress fracture repair whereas bisphosphonates may delay tissue level repair of stress fractures.

Glucocorticoid attenuates the anabolic effects of parathyroid hormone on fracture repair

Long-term use of glucocorticoid (GC) not only reduces bone mass and strength, which leads to a greater risk of fracture, but also hinders fracture repair. In this study, we produced open fractures in GC-treated mice and investigated the effects of human parathyroid hormone 1-34 (hPTH) on fracture repair. Swiss-Webster mice were randomly divided into five groups. Three groups of GC-treated mice were given prednisolone, which was slowly released from subcutaneously implanted pellets at the rate of 1.4 mg/kg/day. Placebo pellets were implanted into the animals in two placebo groups. Three weeks later, osteotomies at the midshaft femora were performed and intramedullary pins were inserted to stabilize the fracture site under general anesthesia. Following fracture surgery, three GC groups were treated subcutaneously with vehicle, PTH at a low dose (40 ug/kg/day), and PTH at a high dose (80 ug/kg/day), respectively. Two placebo groups were given vehicle and PTH at a dose of 40 ug/kg/day, respectively. Radiographs, dual-energy X-ray absorptiometry, and mechanical testing (four-point bending) were used to evaluate fracture repair at 4 weeks after fracture surgery. Callus development, endochondral ossification, and recovery of mechanical strength at the fracture sites in GC animals treated with vehicle were significantly suppressed compared to placebo animals. Normally, PTH accelerates fracture repair. In GC-treated mice, PTH fails to improve endochondral ossification and mechanical properties compared to vehicle treatment, suggesting that the anabolic effect of PTH on fracture healing can be attenuated by GC administration in mice.

Parathyroid hormone and bone healing

Fracture healing is a complex process, and a significant number of fractures are complicated by impaired healing and non-union. Impaired healing is prevalent in certain risk groups, such as the elderly, osteoporotics, people with malnutrition, and women after menopause. Currently, no pharmacological treatments are available. There is therefore an unmet need for medications that can stimulate bone healing. Parathyroid hormone (PTH) is the first bone anabolic drug approved for the treatment of osteoporosis, and intriguingly a number of animal studies suggest that PTH could be beneficial in the treatment of fractures and could thus be a potentially new treatment option for induction of fracture healing in humans. Furthermore, fractures in animals with experimental conditions of impaired healing such as aging, estrogen withdrawal, and malnutrition can heal in an expedited manner after PTH treatment. Interestingly, fractures occurring at both cancellous and cortical sites can be treated successfully, indicating that both osteoporotic and nonosteoporotic fractures can be the target of PTH-induced healing. Finally, the data suggest that PTH partly prevents the delay in fracture healing caused by aging. Recently, the first randomized, controlled clinical trial investigating the effect of PTH on fracture healing was published, indicating a possible clinical benefit of PTH treatment in inducing fracture healing. The aim of this article is therefore to review the evidence for the potential of PTH in bone healing, including the underlying mechanisms for this, and to provide recommendations for the clinical testing and use of PTH in the treatment of impaired fracture healing in humans.

Inhibition of angiotensin-converting enzyme stimulates fracture healing and periosteal callus formation - role of a local renin-angiotensin system

BACKGROUND AND PURPOSE

The renin-angiotensin system (RAS) regulates blood pressure and electrolyte homeostasis. In addition, 'local' tissue-specific RAS have been identified, regulating regeneration, cell growth, apoptosis, inflammation and angiogenesis. Although components of the RAS are expressed in osteoblasts and osteoclasts, a local RAS in bone has not yet been described and there is no information on whether the RAS is involved in fracture healing. Therefore, we studied the expression and function of the key RAS component, angiotensin-converting enzyme (ACE), during fracture healing.

EXPERIMENTAL APPROACH

In a murine femur fracture model, animals were treated with the ACE inhibitor perindopril or vehicle only. Fracture healing was analysed after 2, 5 and 10 weeks using X-ray, micro-CT, histomorphometry, immunohistochemistry, Western blotting and biomechanical testing.

KEY RESULTS

ACE was expressed in osteoblasts and hypertrophic chondrocytes in the periosteal callus during fracture healing, accompanied by expression of the angiotensin type-1 and type-2 receptors. Perindopril treatment reduced blood pressure and bone mineral density in unfractured femora. However, it improved periosteal callus formation, bone bridging of the fracture gap and torsional stiffness. ACE inhibition did not affect cell proliferation, but reduced apoptotic cell death. After 10 week treatment, a smaller callus diameter and bone volume after perindopril treatment indicated an advanced stage of bone remodelling.

CONCLUSIONS

Our study provides evidence for a local RAS in bone that influenced the process of fracture healing. We show for the first time that inhibition of ACE is capable of accelerating bone healing and remodelling.

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.

Parathyroid hormone: is there a role in fracture healing?

Parathyroid hormone is a well-known regulator of calcium metabolism in the body. It binds to osteoblasts and assists in the regulation of bone turnover. Changes in parathyroid hormone levels have been documented in pathologic states such as osteoporosis, and fluxes are also noted during healing of fractures. Because fracture healing requires time and is sometimes unreliable, a search for fracture-healing adjuvants that accelerate the healing rate and improve reliability of healing is compelling. Parathyroid hormone, as a systemic mediator of calcium and bone metabolism, is a good candidate. Much research has been accomplished in animal models examining the role of parathyroid hormone in fracture healing. Although further research is required, especially in human fracture patients, early indicators are that parathyroid hormone may play a role in accelerating fracture healing in healthy patients and in reducing rates of fracture nonunion in compromised patients or tissue beds.

Intermittent PTH(1-34) does not increase union rates in open rat femoral fractures and exhibits attenuated anabolic effects compared to closed fractures

Intermittent Parathyroid Hormone (PTH)((1-34)) has an established place in osteoporosis treatment, but also shows promising results in models of bone repair. Previous studies have been dominated by closed fracture models, where union is certain. One of the major clinical needs for anabolic therapies is the treatment of open and high energy fractures at risk of non-union. In the present study we therefore compared PTH((1-34)) treatment in models of both open and closed fractures. 108 male Wistar rats were randomly assigned to undergo standardized closed fractures or open osteotomies with periosteal stripping. 27 rats in each group were treated s.c. with PTH((1-34)) at a dose of 50 mug/kg 5 days a week, the other 27 receiving saline. Specimens were harvested at 6 weeks for mechanical testing (n=17) or histological analysis (n=10). In closed fractures, union by any definition was 100% in both PTH((1-34)) and saline groups at 6 weeks. In open fractures, the union rate was significantly lower (p<0.05), regardless of treatment. In open fractures the mechanically defined union rate was 10/16 (63%) in saline and 11/17 (65%) in PTH((1-34)) treated fractures. By histology, the union rate was 3/9 (33%) with saline and 5/10 (50%) with PTH((1-34)). Radiological union was seen in 13/25 (52%) for saline and 15/26 (58%) with PTH((1-34)). Open fractures were associated with decreases in bone mineral content (BMC) and volumetric bone mineral density (vBMD) on quantitative computerized tomography (QCT) analysis compared to closed fractures. PTH((1-34)) treatment in both models led to significant increases in callus BMC and volume as well as trabecular bone volume/total volume (BV/TV), as assessed histologically (p<0.01). In closed fractures, PTH((1-34)) had a robust effect on callus size and strength, with a 60% increase in peak torque (p<0.05). In the open fractures that united and could be tested, PTH((1-34)) treatment also increased peak torque by 49% compared to saline (p<0.05). In conclusion, intermittent PTH((1-34)) produced significant increases in callus size and strength in closed fractures, but failed to increase the rate of union in an open fracture model. In the open fractures that did unite, a muted response to PTH was seen compared to closed fractures. Further research is required to determine if PTH((1-34)) is an appropriate anabolic treatment for open fractures.

Effect of intermittent systemic administration of recombinant parathyroid hormone (1-34) on mandibular fracture healing in rats

PURPOSE

To establish a rat mandibular fracture model and investigate the short- and long-term effects of recombinant parathyroid hormone (PTH 1-34) on mandibular fracture healing in rats.

MATERIALS AND METHODS

A controlled unilateral mandibular fracture was created surgically in 29 male Sprague-Dawley rats and then stabilized using an external fixation device. The rats were divided into 2 groups: 1 group received daily subcutaneous injections of 10 microg/kg of PTH(1-34) and 1 group served as the vehicle control. The rats were killed on postoperative days 7 and 21, and radiographic densitometry and histologic evaluation of new bone formation were performed.

RESULTS

A novel unilateral mandibular fracture model was established that has significant differences from previously published models, both in the location of the osteotomy site and in the rigid external stabilization device. The PTH(1-34) treated rats showed a statistically significant difference (P < .05) in callous formation compared with the control animals. Radiographic densitometry evaluation of the injury site revealed an increase in bone density, apparent at day 7 in the experimental group. Visual inspection of the histologic sections stained with Masson's trichrome blue showed an apparent increase in new bone formation at 21 days in the PTH-treated group compared with the control group.

CONCLUSIONS

Intermittent systemic administration of PTH(1-34) might enhance the healing of mandibular fractures in the early phase (7-day period). Long-term administration (21-day period) showed no statistically significant differences between the control and experimental group by radiographic densitometry.

Estrogen and raloxifene improve metaphyseal fracture healing in the early phase of osteoporosis. A new fracture-healing model at the tibia in rat

BACKGROUND

Fracture healing in osteoporosis is delayed. Quality and speed of fracture healing in osteoporotic fractures are crucial with regard to the outcome of patients. The question arises whether established antiosteoporotic drugs can further improve fracture healing.

MATERIALS AND METHODS

Osteoporosis manifests predominantly in the metaphyseal bone. Nevertheless, an established metaphyseal fracture model is lacking. A standardized metaphyseal fracture-healing model with stable plate fixation was developed for rat tibiae. The healing process was analyzed by biomechanical, gene expression, and histomorphometric methods in ovariectomized (OVX) and sham-operated rats (SHAM), compared to standardized estrogen (E)- and raloxifene (R)-supplemented diets.

RESULTS

Estrogen and raloxifene improved the biomechanical properties of bone healing compared to OVX (Yield load: SHAM = 63.1 +/- 20.8N, E = 60.8 +/- 17.9N, R = 44.7+/-17.5N, OVX = 32:5 +/- 22.0N). Estrogen vs OVX was significant based on a denser trabecular network. Raloxifene greatly induced total callus formation ((R = 5.3 +/- 0.9 mm2, E = 4.7 +/- 0.5 mm2, SHAM = 4.51 +/- 0.61 mm2, OVX =4.1 +/- 0.6 mm2), whereas estrogen mainly enhanced new endosteal bone formation. There was no correlation between the gene expression (osteocalcin, collagen1alpha1, IGF-1, tartrate-resistant phosphatase) in the callus and the morphology and quality of callus formation.

CONCLUSION

Raloxifene and estrogen improve fracture healing in osteoporotic bone significantly with regard to callus formation, resistance, and elasticity. The biomechanically stable metaphyseal osteotomy model with T-plate fixation presented here has proven to be appropriate to investigate fracture healing in osteoporosis.

Evidence for anti-osteoporosis therapy in acute fracture situations--recommendations of a multidisciplinary workshop of the International Society for Fracture Repair

The International Society for Fracture Repair convened a multidisciplinary workshop to assess the current evidence around the interaction between anti-osteoporosis drugs and the healing of incident fractures, with a view to making recommendations for clinical practice. The consensus was that there is no evidence-based reason to withhold anti-resorptive therapy while a fracture heals, whether or not the patient was taking such therapy when the fracture occurred. The workshop also considered existing models of service provision for secondary prevention and concluded that the essential ingredient for reliable delivery is the inclusion of a dedicated coordinator role. Several unresolved issues were defined as subjects for further research, including the question of whether continuous long-term administration of anti-resorptives may impair bone quality. The rapidly changing area requires re-assessment of drugs and their interaction with fracture healing in the near future.

Teriparatide for acceleration of fracture repair in humans: a prospective, randomized, double-blind study of 102 postmenopausal women with distal radial fractures

Animal experiments show a dramatic improvement in skeletal repair by teriparatide. We tested the hypothesis that recombinant teriparatide, at the 20 microg dose normally used for osteoporosis treatment or higher, would accelerate fracture repair in humans. Postmenopausal women (45 to 85 years of age) who had sustained a dorsally angulated distal radial fracture in need of closed reduction but no surgery were randomly assigned to 8 weeks of once-daily injections of placebo (n = 34) or teriparatide 20 microg (n = 34) or teriparatide 40 microg (n = 34) within 10 days of fracture. Hypotheses were tested sequentially, beginning with the teriparatide 40 microg versus placebo comparison, using a gatekeeping strategy. The estimated median time from fracture to first radiographic evidence of complete cortical bridging in three of four cortices was 9.1, 7.4, and 8.8 weeks for placebo and teriparatide 20 microg and 40 microg, respectively (overall p = .015). There was no significant difference between the teriparatide 40 microg versus placebo groups (p = .523). In post hoc analyses, there was no significant difference between teriparatide 40 microg versus 20 microg (p = .053); however, the time to healing was shorter in teriparatide 20 microg than placebo (p = .006). The primary hypothesis that teriparatide 40 microg would shorten the time to cortical bridging was not supported. The shortened time to healing for teriparatide 20 microg compared with placebo still may suggest that fracture repair can be accelerated by teriparatide, but this result should be interpreted with caution and warrants further study.

Deleterious effects of intermittent recombinant parathyroid hormone on cartilage formation in a rabbit microfracture model: a preliminary study

Intermittent parathyroid hormone administration can enhance fracture healing in an animal model. Despite the success of exogenous parathyroid hormone on fracture healing and spine fusion, few studies have examined the role of parathyroid hormone on cartilage formation. We determined the effects of intermittent parathyroid hormone on cartilage formation in a rabbit microfracture model of cartilage regeneration. Twelve rabbits were divided into three equal groups: (1) microfracture alone, (2) microfracture + parathyroid hormone daily for 7 days, and (3) microfracture + parathyroid hormone for 28 days. Nonoperated contralateral knees were used as controls. The animals were sacrificed at 3 months and gross and histologic analysis was performed. The microfracture alone group demonstrated the most healing on gross and histologic analysis. Treatment with either 1 or 4 weeks of parathyroid hormone inhibited cartilage formation. Although discouraging from a cartilage repair point of view, this study suggests that the role parathyroid hormone administration has in clinical fracture healing must be examined carefully. Although parathyroid hormone is beneficial to promote healing in spine fusion and midshaft fractures, its deleterious effects on cartilage formation suggests that it may have adverse effects on the outcomes of periarticular fractures such as tibial plateau injuries that require cartilage healing for a successful clinical outcome.

Strontium ranelate enhances callus strength more than PTH 1-34 in an osteoporotic rat model of fracture healing

Treatment of an underlying disease is often initiated after the occurrence of an osteoporotic fracture. Our aim was to investigate whether teriparatide (PTH 1-34) and strontium ranelate affect fracture healing in ovariectomized (OVX) rats when provided for the first time after the occurrence of an osteoporotic fracture. We combined the model of an OVX rat with a closed diaphyseal fracture. Sixty Sprague Dawley rats were randomly assigned to four groups. Fracture healing in OVX rats after treatment with pharmacological doses of strontium ranelate and PTH 1-34 was compared with OVX and sham-treated control groups. After 28 days, the femur was excised and scanned by micro computed tomography and the callus evaluated, after which biomechanical torsional testing was performed and torque and toughness until reaching the yield point were analyzed. Only treatment with strontium ranelate led to a significant increase in callus resistance compared to the OVX control rats, whereas both PTH 1-34 and strontium ranelate increased the bone volume/tissue volume ratio of the callus. The PTH 1-34-increased trabecular bone volume within the callus was even higher compared to sham. As for the callus tissue volume, the increase induced by strontium ranelate was significant, contrary to the changes induced by PTH. Callus in strontium ranelate-treated animals is more resistant to torsion compared with OVX control rats. To our knowledge, this is the first report of the enhancement of fracture healing by strontium ranelate. Because both treatments enhance bone and tissue volume within the callus, there may be a qualitative difference between the calluses of PTH 1-34- and strontium ranelate-treated OVX rats. The superior results obtained with strontium ranelate compared to PTH in terms of callus resistance could be the consequence of a better quality of the new bone formed within the callus.

The effects of low-level laser therapy on bone in diabetic and nondiabetic rats

OBJECTIVE

The aim of the present study was to examine the effects of low-level laser therapy (LLLT) on the tibia of streptozotocin-induced diabetic (STZ-D) rats.

BACKGROUND DATA

LLLT has been found to accelerate fracture healing in animals. Diabetes mellitus decreases bone volume and its biomechanical parameters.

MATERIALS AND METHODS

Twenty rats were divided randomly into four groups. Rats in the first two groups were administrated a single injection of STZ to induce diabetes, while animals in groups 3 and 4 were given a sham injection of distilled water. The right tibia in groups 1 and 2 was treated with a He-Ne laser (632.8 nm, 10 mW) of 28.6 and 382.2 J/cm(2), respectively. LLLT was performed daily for 14 consecutive days. The right tibia of rats in group 3 was treated with LLLT the same as group 2. The right tibia of rats in group 4 was used for based line studies. After 14 d, right tibiae and left tibiae (control bone) were extracted and subjected to the three-point bending test and histological study.

RESULTS

Maximum force (N) was significantly greater in laser-treated bones of groups 2 and 3 compared with their relevant control groups (paired Student t test, p = 0.05 and p = 0.007, respectively). Density of the bone lamella meshwork of compact bone in group 2 was significantly greater in comparison with its control group (paired Student t test, p = 0.005).

CONCLUSION

LLLT on tibia of STZ-D rats increased the bone lamella meshwork density of compact bone and also increased its strength.