Homologous growth hormone accelerates healing of segmental bone defects

In situ bone tissue engineering via ultrasound-mediated gene delivery to endogenous progenitor cells in mini-pigs

More than 2 million bone-grafting procedures are performed each year using autografts or allografts. However, both options carry disadvantages, and there remains a clear medical need for the development of new therapies for massive bone loss and fracture nonunions. We hypothesized that localized ultrasound-mediated, microbubble-enhanced therapeutic gene delivery to endogenous stem cells would induce efficient bone regeneration and fracture repair. To test this hypothesis, we surgically created a critical-sized bone fracture in the tibiae of Yucatán mini-pigs, a clinically relevant large animal model. A collagen scaffold was implanted in the fracture to facilitate recruitment of endogenous mesenchymal stem/progenitor cells (MSCs) into the fracture site. Two weeks later, transcutaneous ultrasound-mediated reporter gene delivery successfully transfected 40% of cells at the fracture site, and flow cytometry showed that 80% of the transfected cells expressed MSC markers. Human bone morphogenetic protein-6 (BMP-6) plasmid DNA was delivered using ultrasound in the same animal model, leading to transient expression and secretion of BMP-6 localized to the fracture area. Micro-computed tomography and biomechanical analyses showed that ultrasound-mediated BMP-6 gene delivery led to complete radiographic and functional fracture healing in all animals 6 weeks after treatment, whereas nonunion was evident in control animals. Collectively, these findings demonstrate that ultrasound-mediated gene delivery to endogenous mesenchymal progenitor cells can effectively treat nonhealing bone fractures in large animals, thereby addressing a major orthopedic unmet need and offering new possibilities for clinical translation.

Recipient-derived angiogenesis with short term immunosuppression increases bone remodeling in bone vascularized composite allotransplantation: A pilot study in a swine tibial defect model

Current vascularized composite allotransplantation (VCA) transplantation protocols rely upon life-long immune modulation to maintain tissue perfusion. Alternatively, bone-only VCA viability may be maintained in small animal models using surgical angiogenesis from implanted autogenous vessels to develop a neoangiogenic bone circulation that will not be rejected. This study tests the method's efficacy in a large animal model as a bridge to clinical practice, quantifying the remodeling and mechanical properties of porcine tibial VCAs. A segmental tibial defect was reconstructed in Yucatan miniature swine by transplantation of a matched tibia segment from an immunologically mismatched donor. Microsurgical repair of nutrient vessels was performed in all pigs, with simultaneous intramedullary placement of an autogenous arteriovenous (AV) bundle in Group 2. Group 1 served as a no-angiogenesis control. All received 2 weeks of immunosuppression. After 16 weeks, micro-CT and histomorphometric analyses were used to evaluate healing and remodeling. Axial compression and nanoindentation studies evaluated bone mechanical properties. Micro-CT analysis demonstrated significantly more new bone formation and bone remodeling at the distal allotransplant/recipient junction and on the endosteal surfaces of Group 2 tibias (p = 0.03). Elastic modulus and hardness were not adversely affected by angiogenesis. The combination of 2 weeks of immunosuppression and autogenous AV-bundle implantation within a microsurgically transplanted tibial allotransplant permitted long-term allotransplant survival over the study period of 16 weeks in this large animal model. Angiogenesis increased bone formation and remodeling without adverse mechanical effects. The method may allow future composite-tissue allotransplantation of bone without the risks associated with long-term immunosuppression. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1242-1249, 2017.

Preclinical testing of drug delivery systems to bone

Bone defects do not heal in 5-10% of the fractures. In order to enhance bone regeneration, drug delivery systems are needed. They comprise a scaffold with or without inducing factors and/or cells. To test these drug delivery systems before application in patients, they finally need to be tested in animal models. The choice of animal model depends on the main research question; is a functional or mechanistic evaluation needed? Furthermore, which type of bone defects are investigated: load-bearing (i.e. orthopedic) or non-load-bearing (i.e. craniomaxillofacial)? This determines the type of model and in which type of animal. The experiments need to be set-up using the 3R principle and must be reported following the ARRIVE guidelines.

Effect of Recombinant Human Growth Hormone on Osseointegration of Titanium Implants: A Histologic and Biomechanical Study in Rabbits

To evaluate the action of recombinant human growth hormone (rhGH) on osseointegration of titanium implants in rabbits. Fourteen adult New Zealand rabbits, aged 30 weeks, were used in the study, and randomly divided into 2 groups. In each animal, 2 (2.2 mm × 6 mm) pure titanium implants were placed in the left tibia. In one group (test group), 1 IU (0.3 mg) of rhGH as a lyophilized powder was applied to each osteotomy site prior to implant placement. Only titanium implants were placed in osteotomy sites of the other group (control). Animals were humanely killed at 14 and 42 days after surgery, and samples were then prepared for histologic analysis and biomechanical test. The biomechanical test showed tensile pull-out stress values of 33.88 N/cm2 for controls and 59.26 N/cm2 for the rhGH group at 14 days and 25.99 N/cm2 and 29.69 N/cm2 for the control and the test group, respectively, at 42 days. Scanning electron microscope analysis showed more uniform and abundant bone tissue in contact with the implants for the test group at 14 days, and no differences between groups at 42 days. Furthermore, histologic analysis also showed accelerated bone repair in 14 days and a more advanced stage of bone remodeling for the rhGH-treated group when compared to controls after 42 days of repair. Such results show that the topical use of rhGH induces new bone formation in the early stages of bone repair and hence accelerates osseointegration of titanium dental implants.

Use of localized human growth hormone and testosterone injections in addition to manual therapy and exercise for lower back pain: a case series with 12-month follow-up

Objective

The objective of this case series was to investigate the feasibility and safety of a novel method for the management of chronic lower back pain. Injections of recombinant human growth hormone and testosterone to the painful and dysfunctional areas in individuals with chronic lower back pain were used. In addition, the participants received manual therapies and exercise addressing physical impairments such as motor control, strength, endurance, pain, and loss of movement. Pain ratings and self-rated functional outcomes were assessed.

Study design

This is a case series involving consecutive patients with chronic lower back pain who received the intervention of injections of recombinant human growth hormone and testosterone, and attended chiropractic and/or physical therapy. Outcomes were measured at 12 months from the time of injection.

Setting

A community based hospital affiliated office, and a private practice block suite.

Participants

A total of 60 consecutive patients attending a pain management practice for chronic lower back pain were recruited for the experimental treatment. Most participants were private pay.

Interventions

Participants who provided informed consent and were determined not to have radicular pain received diagnostic blocks. Those who responded favorably to the diagnostic blocks received injections of recombinant human growth hormone and testosterone in the areas treated with the blocks. Participants also received manipulation- and impairment-based exercises.

Outcome measures

Outcomes were assessed at 12 months through pain ratings with the Mankowski Pain Scale and the Oswestry Disability Index.

Results

Of the 60 patients recruited, 49 provided informed consent, and 39 completed all aspects of the study. Those patients receiving the intervention reported a significant decrease in pain ratings (P<0.01) and a significant improvement in self-rated Oswestry Disability Index scores (P<0.01). In addition, in the Oswestry Disability Index results, 41% of the patients demonstrated a 50% or greater change in their disability score. Of the subjects who withdrew from the study, one was due to the pain created by the injections and nine were for nonstudy factors.

Conclusion

The intervention appeared to be safe and the results provide a reasonable expectation that the intervention would be beneficial for a population of individuals with chronic nonradicular lower back pain. Due to the design of the study, causality cannot be inferred, but the results do indicate that further study of the intervention may be warranted.

Cellular and morphological aspects of fibrodysplasia ossificans progressiva. Lessons of formation, repair, and bone bioengineering

Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disease that causes bone formation within the muscles, tendons, ligaments and connective tissues. There is no cure for this disorder and only treatment of the symptoms is available. The purpose of this study was to review the literature and describe the clinical, cellular and molecular aspects of FOP. The material used for the study was obtained by reviewing scientific articles published in various literature-indexed databases. In view of its rarity and of the lack of insightful information and the unpredictability of its course, FOP is a challenging disorder for professionals who are confronted by it. However, this rare disease raises a great deal of interest because understanding the mechanism of mature bone formation can encourage research lines related to bone regeneration and the prevention of heterotopic ossification.

Critical size bone defect reconstruction by an autologous 3D osteogenic-like tissue derived from differentiated adipose MSCs

For critical size bone defects and bone non-unions, bone tissue engineering using osteoblastic differentiated adipose mesenchymal stem cells (AMSCs) is limited by the need for a biomaterial to support cell transplantation. An osteoblastic three-dimensional autologous graft made of AMSCs (3D AMSC) was developed to solve this issue. This autograft was obtained by supplementing the osteoblastic differentiation medium with demineralized bone matrix. Two surgical models were developed to assess the potential of this 3D osteogenic AMSC autograft. A four-level spinal fusion using polyetheretherketone cages was designed in six pigs to assess the early phase of ossification (8-12 weeks postimplantation). In each pig, four groups were compared: cancellous bone autograft, freeze-dried irradiated cancellous pig bone, 3D AMSC, and an empty cage. A critical size femoral defect (n = 4, bone non-union confirmed 6 months postoperatively) was used to assess the 3D AMSCs' ability to achieve bone fusion. Pigs were followed by CT scan and explanted specimens were analyzed for bone tissue remodeling by micro-CT scan, micro-radiography, and histology/histomorphometry. In the spine fusion model, bone formation with the 3D AMSC was demonstrated by a significant increase in bone content. In the critical-size femoral defect model, the 3D AMSC achieved new bone formation and fusion in a poorly vascularized fibrotic environment. This custom-made 3D osteogenic AMSC autograft is a therapeutic solution for bone non-unions and for critical-size defects.

Treatment of long bone defects and non-unions: from research to clinical practice

The treatment of long bone defects and non-unions is still a major clinical and socio-economical problem. In addition to the non-operative therapeutic options, such as the application of various forms of electricity, extracorporeal shock wave therapy and ultrasound therapy, which are still in clinical use, several operative treatment methods are available. No consensus guidelines are available and the treatments of such defects differ greatly. Therefore, clinicians and researchers are presently investigating ways to treat large bone defects based on tissue engineering approaches. Tissue engineering strategies for bone regeneration seem to be a promising option in regenerative medicine. Several in vitro and in vivo studies in small and large animal models have been conducted to establish the efficiency of various tissue engineering approaches. Neverthelsss, the literature still lacks controlled studies that compare the different clinical treatment strategies currently in use. However, based on the results obtained so far in diverse animal studies, bone tissue engineering approaches need further validation in more clinically relevant animal models and in clinical pilot studies for the translation of bone tissue engineering approaches into clinical practice.

Growth hormone: does it have a therapeutic role in fracture healing?

BACKGROUND

The role of growth hormone (GH) in augmenting fracture healing has been postulated for over half a century. GH has been shown to play a role in bone metabolism and this can be mediated directly or indirectly through IGF-I.

OBJECTIVES

The use of GH was evaluated as a possible therapeutic agent in augmenting fracture healing.

METHOD

A literature search was undertaken on GH and its effect on bone fracture healing primarily using MEDLINE/OVID (1950 to January 2009). Key words and phrases including 'growth hormone', 'insulin like growth factor', 'insulin like growth factor binding protein', 'insulin like growth factor receptor', 'fracture repair', 'bone healing', 'bone fracture', 'bone metabolism', 'osteoblast' and 'osteoclast' were used in different combinations. Manual searches of the bibliography of key papers were also undertaken.

RESULTS

Current evidence suggests a positive role of GH on fracture healing as demonstrated by in vitro studies on osteoblasts, osteoclasts and the crosstalk between the two. Animal studies have demonstrated a number of factors influencing the effect of GH in vivo such as dose, timing and method of administration. Application of this knowledge in humans is limited but clearly demonstrates a positive effect on fracture healing. Concern has been raised in the past regarding the safety profile of the pharmacological use of GH when used in critically ill patients.

CONCLUSION

The optimal dose and method of administration is still to be determined, and the safety profile of this novel use of GH needs to be investigated prior to establishing its widespread use as a fracture-healing agent.

The challenge of establishing preclinical models for segmental bone defect research

A considerable number of international research groups as well as commercial entities work on the development of new bone grafting materials, carriers, growth factors and specifically tissue-engineered constructs for bone regeneration. They are strongly interested in evaluating their concepts in highly reproducible large segmental defects in preclinical and large animal models. To allow comparison between different studies and their outcomes, it is essential that animal models, fixation devices, surgical procedures and methods of taking measurements are well standardized to produce reliable data pools and act as a base for further directions to orthopaedic and tissue engineering developments, specifically translation into the clinic. In this leading opinion paper, we aim to review and critically discuss the different large animal bone defect models reported in the literature. We conclude that most publications provide only rudimentary information on how to establish relevant preclinical segmental bone defects in large animals. Hence, we express our opinion on methodologies to establish preclinical critically sized, segmental bone defect models used in past research with reference to surgical techniques, fixation methods and postoperative management focusing on tibial fracture and segmental defect models.

Critical issues in translational and clinical research for the study of new technologies to enhance bone repair

Osteoporosis increases fracture risk, especially in metaphyseal bone. Fractures seriously impair function and quality of life and incur large direct and indirect costs. Although the prevention of fractures is certainly the option, a fast and uneventful healing process is optimal when fractures do occur. Many new therapeutic strategies have been developed to accelerate fracture-healing or to diminish the complication rate during the course of fracture-healing. However, widely accepted guidelines are needed to demonstrate the positive or negative interactions of bioactive substances, drugs, and other agents that are being used to promote fracture-healing. For each study design, the primary study goal should be indicated. Outcome variables should include both objective and subjective parameters. The guidelines should be harmonized between European and American regulatory authorities to ensure comparability of results of studies and to foster global harmonization of regulatory requirements.

The effect of locally applied vascular endothelial growth factor on meniscus healing: gross and histological findings

INTRODUCTION

Tears in the peripheral part of the menisci have a better healing potential than tears in the central part, because the central two-thirds of the menisci are avascular. We hypothesized that healing of meniscus tears in the avascular zone can be promoted by the local application of the angiogenic factor vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

A tear was created in the avascular zone of the medial meniscus in 18 merino sheep. The tear was then repaired with an uncoated suture (group 1), a suture coated with PDLLA (group 2), and by a suture coated with PDLLA/VEGF (group 3).

RESULTS

After 6 weeks, we observed increased immunostaining for factor VIII in the VEGF-treated group 3. However, in this treatment group no meniscus healed completely. In the uncoated suture group and in the PDLLA-coated-suture group, partial healing was observed in three animals and complete healing in three animals, respectively.

CONCLUSION

In this experiment the local application of VEGF via PDLLA-coated sutures did not promote meniscus healing. Growth factors might not always be a promising tool for tissue repair.

New technologies for the enhancement of skeletal repair

Although fracture healing is a well-optimized biological process that leads to healing, approximately 10-20% of fractures result in impaired or delayed healing and these fractures may benefit from the use of biotechnologies to enhance skeletal repair. Peptide signaling molecules such as the bone morphogenetic proteins have been shown to stimulate the healing of fresh fractures, nonunions, and spinal fusions and side effects from their use appear to be minimal. Other growth factors currently being studied for local application include growth and differentiation factor-5 (GDF-5), vascular endothelial growth factor (VEGF), transforming growth factor beta (TGFbeta), and platelet-derived growth factor (PDGF). Molecules such as prostaglandin E receptor agonists and the thrombin-related peptide, TP508, have shown promise in animal models of fracture repair. Gene therapy using various growth factors or combinations of factors might also aid in fracture repair, particularly as new methods for delivery that do not require viral vectors are developed. Systemic therapy with agents such as parathyroid hormone (PTH), growth hormone (GH), and the HMG-CoA reductase inhibitors are also under investigation. As these and other technologies are shown to be safe and effective, their use will become a part of the standard of care in managing skeletal injuries.

Homologous growth hormone accelerates bone healing--a biomechanical and histological study

The purpose of this study was to prove whether homologous growth hormone has a beneficial effect in the early phase of bone healing. Therefore the left tibias of 24 Yucatan micropigs were osteotomized and stabilized by plate fixation. The treatment group (12 animals) received 100 microg of recombinant porcine growth hormone (rpGH)/kg body w/day sc, whereas the control pigs (12 animals) received 1 ml sodium chloride as placebo. After a healing period of 4 weeks the animals were sacrificed and destructive torsional testing was performed. For histological evaluation 6 microm serial slices of the tibiae were stained with von Kossa. The total area of callus formation (CA) and the mineralized bone area (BA) were quantified by image analysis. The fraction of mineralized bone tissue within the callus area, the bone density (BD), was calculated as follows: BD = (BA/CA) x 100. Torsional failure load was 91% higher and torsional stiffness 61% higher in the treatment group than in the control group (P < 0.05). The histomorphometric measurements revealed an advance for the CA (GH: 127.6 +/- 38.9 mm(2); placebo: 75.9 +/- 50.7 mm(2); P < 0.005) as well as for the BA (GH: 89.3 +/- 25.8 mm(2); placebo: 55.9 +/- 38.5 mm(2); P < 0.001) for the GH-treated animals in comparison to the control animals. The BD was similar in both groups (GH: 70.6 +/- 8.4%; placebo: 74.0 +/- 6.24%; P = 0.28). These data indicate that administration of homologous GH stimulates callus formation and ossification in the early phase of bone healing, which consequently results in an increased mechanical strength and stiffness.

Systemic application of growth hormone enhances the early healing phase of osteochondral defects--a preliminary study in micropigs

Healing of osteochondral defects following trauma remains a significant clinical problem, often leading to osteoarthritis. Growth hormone (GH) has been shown to accelerate formation of bone and cartilage tissue in the growth plates and in cell cultures. To investigate the influence of systemically administered recombinant porcine growth hormone (r-pGH) on the healing of osteochondral defects we performed a histomorphometrical analysis of full-thickness cartilage defects in the femoral condyle of micropigs. Forty-eight mature female Yucatan micropigs were divided into two groups, one receiving a daily injection of r-pGH (100 microg/kg), the other receiving sodium chloride as placebo. A circular 6-mm-diameter full-thickness defect of the cartilage was created, extending 1.5 mm into the subchondral bone. The animals were sacrificed after 4 (n = 24) and 6 (n = 24) weeks. The von-Kossa stain was used to visualise the calcified structures; cartilage and the fibrous tissue were marked with a combined Safranin-O/light-green stain. The defect filling and the percentage of bone, cartilage, and fibrous tissue into the defect were evaluated using an image analysis system. Furthermore, histological grading was performed using the modified Wakitani score. After 4 weeks no differences were observed between both groups. The defect filling after 6 weeks with newly formed bone was significantly higher in the r-pGH-treated group. The formation of cartilage and fibrous tissue showed a trend towards better healing in the GH-treated group; however, there was no significant difference. In the r-pGH-treated group, the percentage of total defect filling was significantly higher. The evaluation of the vascularity showed a significantly lower number of vessels in the GH-treated group after 6 weeks. Histomorphological grading revealed a significantly lower total Wakitani score in the GH-treated group, which represents a better healing result compared to the controls. The results of the present study suggest that circulating r-pGH or one of its mediators may accelerate osteochondral defect healing by stimulating the formation of osseous and chondral tissue. The analysis of the vascularity leads to the assumption of an advanced maturation of the osteochondral defects under the influence of GH.

New strategies for craniofacial repair and replacement: a brief review

Craniofacial anomalies can severely affect the appearance, function, and psychosocial well being of patients; thus, tissue engineers are developing new techniques to functionally and aesthetically rebuild craniofacial structures. In the past decade, there have been tremendous advances in the field of tissue engineering that will substantially alter how surgeons approach craniofacial reconstruction. In this brief review, we highlight some of the preclinical recombinant protein, gene transfer, and cell-based strategies currently being developed to augment endogenous tissue repair or create structures for replacement. In addition, we discuss the importance of studying endogenous models of tissue induction and present some of the current in vitro and in vivo approaches to growing complex tissues/organs for craniofacial reconstruction.

Improvement of fracture healing by systemic administration of growth hormone and local application of insulin-like growth factor-1 and transforming growth factor-beta1

Fracture healing is influenced by numerous hormones, growth factors, and cytokines. The systemic administration of growth hormone (GH) has shown to accelerate bone regeneration. Local application of growth factors, such as insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta-1 (TGF-beta1), are known to stimulate bone metabolism. Until now, the exact local and systemic mechanisms that lead to improved bone regeneration remain unclear. In addition, the effect of systemic administration of GH as compared with locally delivered growth factors on fracture healing in rats is not known. A midshaft fracture of the right tibia of 5-month-old female Sprague-Dawley rats (n = 80) was intramedullary stabilized with IGF-1 and TGF-beta1 coated vs. uncoated titanium K-wires. The growth factors were incorporated in a poly(D,L-lactide) (PDLLA) coating and released continuously throughout the experiment. Recombinant species-specific (rat) GH was applied systemically (2 mg/kg body weight) by daily subcutaneous injection and compared with a placebo group. The healing process was radiologically monitored. Twenty-eight days after fracture biomechanical torsional testing was performed. The consolidation and callus composition, including quantification of cartilage and mineralized tissue, was traced in histomorphometrical investigations using an image analysis system. Both methods, the systemic administration of GH and the local application of growth factors, showed significant biomechanical and histological effects on fracture healing. The local growth factor application showed a stronger effect on fracture healing than the systemic GH injection. The combined application of both methods did not accelerate the effect on bone healing compared with the single application. It is therefore concluded that combining local and systemic stimulating methods does not provide further additive effects with regard to fracture healing.