Temporospatial expression of vascular endothelial growth factor and basic fibroblast growth factor during mandibular distraction osteogenesis

The effect of Hypoxia-Inducible Factor-1a stabilization on bone regeneration during distraction osteogenesis: A systematic review of animal studies

OBJECTIVE

This systematic review described Hypoxia-Inducible Factor-1a stabilization or upregulation approaches along with underlying signaling pathways and assessed bone regeneration, angiogenesis, and consolidation time during DO in animal models.

DESIGN

A comprehensive and systematic search of electronic databases including PubMed, Scopus, and ScienceDirect was performed till December 26, 2023. The search was limited to English articles, and no time restrictions were applied.

RESULTS

A total of 14 studies met the inclusion criteria and were included for final review. Four methods have been shown to activate the HIF pathway including genetic, pharmacological, mechanical, and cell preconditioning approaches. Deferoxamine (DFO) was administered as a pharmacological hypoxia-mimicking agent in many studies reporting acceptable outcomes on bone regeneration and acceleration of bone consolation. Applying mechanical loads at the optimal rate and amplitude serves as a minimally invasive approach with acceptable results. HIF-related signaling pathways increase osteogenesis and angiogenesis during DO, potentially through VHL/HIF-1a/VEGF, Wnt/β-catenin, and Mesenchymal-Epithelial transition (MET) signaling pathways.

CONCLUSION

Activation of HIF-related signaling pathways enhances and accelerates bone regeneration during the consolidation phase of distraction osteogenesis. The most feasible approach with the least side effects must be selected for further clinical studies.

Effects of fibrous collagen/CDHA/hUCS biocomposites on bone tissue regeneration

Collagen- and bioceramic-based composites have been widely used in hard tissue engineering because they are analogous to the organic/inorganic constituents of native bones. However, biocomposites based on collagen and bioceramics show low mechanical stiffness and limited osteogenic activities. To elevate the low biophysical and biological activities, we have introduced a new biocomposite structure. Herein, we propose a biocomposite mimicking not only the physical structure of the extracellular matrix (ECM) structure but also the biochemical components of native bone tissues. Several components including fibrillated collagen, calcium-deficient hydroxyapatite (CDHA) obtained from α-tricalcium phosphate hydrolysis, and human umbilical cord serum (hUCS) were used to generate a unique structure of the biocomposite. The 3D-printed composites were topographically similar to the nanofibrous ECM and exhibited a mechanically stable structure. We also evaluated the in vitro biocompatibilities of the biocomposite using human adipose stem cells and found that the collagen/hUCS/CDHA scaffold accelerated the in vitro osteogenic differentiation of human adipose-derived stem cells and in vivo osteogenesis in a mastoid obliterated rat model.

Craniofacial and Long Bone Development in the Context of Distraction Osteogenesis

BACKGROUND

Bone retains regenerative potential into adulthood, and surgeons harness this plasticity during distraction osteogenesis. The underlying biology governing bone development, repair, and regeneration is divergent between the craniofacial and appendicular skeleton. Each type of bone formation is characterized by unique molecular signaling and cellular behavior. Recent discoveries have elucidated the cellular and genetic processes underlying skeletal development and regeneration, providing an opportunity to couple biological and clinical knowledge to improve patient care.

METHODS

A comprehensive literature review of basic and clinical literature regarding craniofacial and long bone development, regeneration, and distraction osteogenesis was performed.

RESULTS

The current understanding in craniofacial and long bone development and regeneration is discussed, and clinical considerations for the respective distraction osteogenesis procedures are presented.

CONCLUSIONS

Distraction osteogenesis is a powerful tool to regenerate bone and thus address a number of craniofacial and appendicular skeletal deficiencies. The molecular mechanisms underlying bone regeneration, however, remain elusive. Recent work has determined that embryologic morphogen gradients constitute important signals during regeneration. In addition, striking discoveries have illuminated the cellular processes underlying mandibular regeneration during distraction osteogenesis, showing that skeletal stem cells reactivate embryologic neural crest transcriptomic processes to carry out bone formation during regeneration. Furthermore, innovative adjuvant therapies to complement distraction osteogenesis use biological processes active in embryogenesis and regeneration. Additional research is needed to further characterize the underlying cellular mechanisms responsible for improved bone formation through adjuvant therapies and the role skeletal stem cells play during regeneration.

[Application of femoral-femoral artery bypass grafting combined with transverse tibial bone transporting for lower extremity arteriosclerosis obliterans or combined with diabetic foot]

Objective

To discuss the effectiveness of femoral-femoral artery bypass grafting combined with transverse tibial bone transporting in treatment of lower extremity arteriosclerosis obliterans (ASO) or combined with diabetic foot.

Methods

Between March 2014 and June 2016, 9 patients with lower extremity ASO or combined with diabetic feet were treated with femoral-femoral artery bypass grafting and transverse tibial bone transporting. All patients were male, aged from 63 to 82 years with an average of 74.2 years. The disease duration of ASO was 1.5-22.0 months (mean, 10.5 months). All cases were severe unilateral iliac arterial occlusion, including 5 cases of the left side and 4 cases of the right side. There were 7 cases with superficial femoral and/or infrapopliteal artery disease. There were 7 cases of ASO and 2 cases of ASO combined with diabetic foot (Wagner grade 4); all the ASO were grade Ⅳ according to Fontaine criteria. All patients had rest pain before operation, and the ankle brachial index was 0.24±0.12. In femoral-femoral artery bypass grafting operations, artificial blood vessels were used in 7 cases and autologous saphenous vein were used in the other 2 cases. The tibial bone transverse transporting began on the 8th day after operation by 1 mm per day and once per 6 hours; after transported for 2-3 weeks, it was moved back. The whole course of treatment was 10-14 weeks.

Results

The incision of tibial bone transverse transporting was necrotic in 1 case, and healed after dressing change. There was no obvious complication at the orifice of the needle. The other patients had no incision complication. The granulation tissue of foot wound was growing quickly after tibial bone transverse transporting, and the wound was reduced after 2-3 weeks. All the 9 patients were followed up 12-32 months (mean, 19 months). The ankle brachial index was 0.67±0.09 at 2 months postoperatively, which was significantly higher than that before operation ( t=17.510, P=0.032). All the feet ulcer wounds healed and the healing time was 6.7-9.4 weeks (mean, 7.7 weeks). During follow-up, color Doppler ultrasound or CT examination revealed grafted blood vessel patency. The external fixator was removed at 12-14 weeks after operation. One case died of sudden myocardial infarction at 14 months after operation, and there was no lymphatic leakage. The patency rate of femoral-femoral bypass was 100% at 1 year after operation. The tibial transverse bone grafting healed with tibia at 4-6 months after operation. At last follow-up, the effective rate was 100%.

Conclusion

Femoral-femoral artery bypass grafting combined with transverse tibial bone transporting is an effective method in the treatment of lower extremity ASO or combined with diabetic foot.

A Simple Mandibular Distraction Protocol to Avoid Tracheostomy in Patients with Pierre Robin Sequence

Objective

Recent treatment goals for Pierre Robin sequence (PRS) focus on avoiding tracheostomy through modalities such as mandibular distraction osteogenesis (MDO). We primarily evaluated the efficacy of our straightforward MDO treatment protocol for resolution of PRS-associated airway obstruction while secondarily analyzing patient characteristics associated with success or failure of MDO.

Design

A retrospective chart review before and after treatment.

Setting

Tertiary institutional center and private practice setting.

Patients

All patients were diagnosed with PRS and treated with MDO, according to the MDO treatment protocol, by a single surgeon with the same operative technique from 1999 to 2013. A sample size of n = 38 met the inclusion criteria. Data assessed included tracheostomy status (pre-MDO, post-MDO, or none), microlaryngoscopy and bronchoscopy (MLB) findings, multipositional airway study results, clinical resolution of airway obstruction following MDO, and patient characteristics.

Main Outcome Measure

Resolution of airway obstruction with avoidance of a tracheostomy.

Results

Prior to referral for MDO, five patients required urgent tracheostomy. Of patients without a pre-MDO tracheostomy (n = 33), two patients required tracheostomy post-MDO, while 94% avoided tracheostomy with clinical resolution of airway obstruction (n = 31). On secondary analysis, anatomic abnormalities diagnosed by MLB were associated with a higher rate of tracheostomy ( P = .037), confirming the utility of preoperative evaluation with MLB; otherwise, no patient characteristics demonstrated significance in patient selection. Follow-up ranged from 6 months to 10 years (mean = 6.45 years, median = 7.61 years).

Conclusions

Our treatment protocol demonstrates MDO is highly effective for resolving severe airway obstruction related to PRS. Based on secondary analysis, our simplified protocol does not require amendment.

Periosteal Distraction Osteogenesis: An Effective Method for Bone Regeneration

The treatment of bone defects is challenging and controversial. As a new technology, periosteal distraction osteogenesis (PDO) uses the osteogenicity of periosteum, which creates an artificial space between the bone surface and periosteum to generate new bone by gradually expanding the periosteum with no need for corticotomy. Using the newly formed bone of PDO to treat bone defects is effective, which can not only avoid the occurrence of immune-related complications, but also solve the problem of insufficient donor. This review elucidates the availability of PDO in the aspects of mechanisms, devices, strategies, and measures. Moreover, we also focus on the future prospects of PDO and hope that PDO will be applied to the clinical treatment of bone defects in the future.

NPNT is Expressed by Osteoblasts and Mediates Angiogenesis via the Activation of Extracellular Signal-regulated Kinase

Angiogenesis plays an important role in bone development and remodeling and is mediated by a plethora of potential angiogenic factors. However, data regarding specific angiogenic factors that are secreted within the bone microenvironment to regulate osteoporosis is lacking. Here, we report that Nephronectin (NPNT), a member of the epidermal growth factor (EGF) repeat superfamily proteins and a homologue of EGFL6, is expressed in osteoblasts. Intriguingly, the gene expression of NPNT is reduced in the bone of C57BL/6J ovariectomised mice and in osteoporosis patients. In addition, the protein levels of NPNT and CD31 are also found to be reduced in the tibias of OVX mice. Exogenous addition of mouse recombinant NPNT on endothelial cells stimulates migration and tube-like structure formation in vitro. Furthermore, NPNT promotes angiogenesis in an ex vivo fetal mouse metatarsal angiogenesis assay. We show that NPNT stimulates the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated kinase (MAPK) in endothelial cells. Inhibition of ERK1/2 impaired NPNT-induced endothelial cell migration, tube-like structure formation and angiogenesis. Taken together, these results demonstrate that NPNT is a paracrine angiogenic factor and may play a role in pathological osteoporosis. This may lead to new targets for treatment of bone diseases and injuries.

A case of mandible hypoplasia treated with autologous bone graft from mandibular symphysis: Expression of VEGF and receptors in bone regeneration

The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) system plays an important role in angiogenesis and osteogenesis during both skeletal development and postnatal bone growth and repair. Indeed, protein expression changes of this system could contribute to craniofacial defects commonly associated with a variety of congenital syndromes. Similarly to other craniofacial bones, mandible arises from neural crest cells of the neuroectodermal germ layer, and undergoes membranous ossification. Here, we report a case of left mandibular hypoplasia in a 42-year-old man treated with autologous bone graft from mandibular symphysis. After 3 months from surgical reconstruction, the protein expression of VEGF and receptors (VEGFR-1, -2 and -3) in regenerated bone tissue was evaluated by immunohistochemistry. At variance with the mandibular symphysis bone harvested for graft surgery, we observed de novo expression of VEGF and VEGFRs in osteoblasts and osteocytes from post-graft regenerating mandible bone tissue. In particular, while VEGFR-1 and VEGFR-3 immunopositivity was widespread in osteoblasts, that of VEGFR-2 was scattered. Among the three receptors, VEGFR-3 was the more intensively expressed both in osteoblasts and osteocytes. These findings suggest that VEGFR-2 might be produced during the early period of regeneration, while VEGFR-1 might participate in bone cell maintenance during the middle or late consolidation period. VEGFR-3 might, instead, represent a specific signal for ectomesenchymal lineage differentiation during bone regeneration. Modulation of VEGF/VEGFR signaling could contribute to graft integration and new bone formation during mandibular regeneration.

Distraction histogenesis of the maxillofacial region

The changes in the surrounding soft tissues during long bone distraction in orthopedic surgery have been the subject of several reports, studies on changes in the craniofacial region, in which various tissues, including the skin, muscle, tendon, blood vessel, and gingiva are rare. Therefore, there is a need for studies on the soft tissue aspects of bone lengthening of the craniofacial region. The aim of this review was to address this issue by reviewing the literature about the distraction histogenesis of various tissues, including skin, muscle, blood vessel, nerve, and gingiva.

In-vivo functional study on the involvement of CFTR, SLC26A6, NHE-1 and CA isoenzymes II and XII in uterine fluid pH, volume and electrolyte regulation in rats under different sex-steroid influence

Precise control of uterine fluid pH, volume and electrolytes is important for the reproductive processes. In this study, we examined the functional involvement of multiple proteins including Cystic Fibrosis Transmembrane Regulator (CFTR), Cl(-)/HCO3 (-) exchanger (SLC26A6), sodium-hydrogen exchanger-1 (NHE-1) and carbonic anhydrase (CA) in the regulation of these uterine fluid parameters.

METHODS

Adult female WKY rats were divided into intact, non-ovariectomised at different oestrous cycle phases and ovariectomised treated with sex-steroids. Following oestrous phase identification or sex-steroid treatment, in-vivo uterine perfusion was performed with and without the presence of these inhibitors: glibenclamide, DIDS, ACTZ and EIPA. The pH, volume, Cl(-), HCO3 (-) and Na(+) concentrations of the perfusate from different groups were then analyzed. Meanwhile, the expression of CFTR, SLC26A6, NHE-1, CAII and CAXII was visualized by immunohistochemistry (IHC).

RESULTS

Parallel increase in the pH, volume, Cl(-), HCO3 (-) and Na(+) concentrations was observed at estrus (Es), proestrus (Ps) and following 17β-oestradiol (E) treatment, which was inhibited by glibenclamide, DIDS and ACTZ while parallel reduction in these parameters was observed at diestrus (Ds) and following progesterone (P) treatment which was inhibited by ACTZ and EIPA. CFTR and SLC26A6 expression were up-regulated under E dominance, while NHE-1 expression was up-regulated under P dominance. Meanwhile, CA isoenzymes were expressed under both E and P influence.

CONCLUSION

CFTR, SLC26A6 and CA were involved in mediating parallel increase in the uterine fluid volume, pH and electrolyte concentration under E while NHE and CA were involved in mediating the reduction of these parameters under P.

The effect of bone morphogenic protein-2-coated tri-calcium phosphate/hydroxyapatite on new bone formation in a rat model of femoral distraction osteogenesis

BACKGROUND AIMS

Distraction osteogenesis (DO) is an increasingly popular technique used to stimulate new bone formation to treat orthopedic disorders resulting from bone defects and deficits. Because of various possible complications that can occur during the long consolidation period, the development of procedures to accelerate regenerated ossification is clearly desirable. The purpose of this study was to evaluate the effect of single insertions of bone morphogenic protein-2 (BMP-2), delivered by tri-calcium phosphate (TCP)/hydroxyapatite (HA), administered at osteotomy sites, on the rate of new bone formation during DO in a rat model.

METHODS

Thirty-six male Sprague-Dawley rats, aged 12 weeks and weighing a mean (± standard deviation) of 401 ± 14 g, were used in this study. The animals were randomized into three groups of 12 rats each. Group I served as a control, group II was treated with only TCP/HA, and group III was treated with recombinant human (rh) BMP-2-coated TCP/HA. Materials were inserted into the medullary canal at the femoral osteotomy site at the end of the lengthening period. After a 7-day latent phase, distraction was commenced on day 0 at a rate of 0.50 mm every 6 h for 5 days (2 mm daily), resulting in a total of 10 mm of lengthening by day 5. At two different time-points [at 4 weeks (day 33) and 8 weeks (day 61) after cessation of distraction], the progress of bone formation was determined with microcomputed tomography (micro-CT), histology and real-time polymerase chain reaction (PCR). The mean and standard deviation of the values obtained from the experiment were computed and statistical analyses performed using anova. Statistical significance was established at P < 0.05. Results. Radiographically, all group III rat femurs exhibited bridging callus formation 8 weeks after cessation of distraction, whereas group II rat femurs demonstrated non-bridging callus formation. None of the group I rat femurs showed callus in the central zone of the distraction gap. For micro-CT, bone formation and remodeling of the distraction regeneration with beta-TCP/HA coated with rhBMP-2 had greater values than the control sides at all time-points. Two-dimensional quantitative analysis of the distraction regeneration showed that the bone volume of group III had higher values than groups I and II at 4 weeks (P < 0.05). This difference was also evident at 8 weeks. With hematoxylin and eosin (H&E) staining, the control group (group I) did not show any bone tissue at the distraction site. In group II at 4 weeks, abundant fibrous tissue surrounding the particles was visible with some areas of woven bone. At 8 weeks, the woven bone covered the particles but not the whole circumference. In group III at 4 weeks, much of the woven bone surrounded the particle with some fibrocartilagenous materials. At 8 weeks, woven bone covering the whole circumference of the particles was visible.

CONCLUSIONS

Application of rhBMP-2, at the end of the rather rapid distraction period, as a single bolus significantly increased the osteogenic process, while beta-TCP/HA behaved effectively as a sustained delivery system for this osteoinductive protein.

Local application of VEGF compensates callus deficiency after acute soft tissue trauma--results using a limb-shortening distraction procedure in rabbit tibia

Acute soft tissue trauma influences callus formation and fracture healing. Several studies showed a relationship between angiogenesis and bone formation during distraction osteogenesis. The purpose of this study was to investigate the influence of controlled release of vascular endothelial growth factor (VEGF) on callus formation in a limb-shortening distraction procedure after acute compartment syndrome. Acute soft tissue trauma with critical increased compartment pressure was generated in 22 rabbits, and the limb was shortened simulating fracture site debridement. In the test group (n=11), a VEGF-coated collagen matrix was locally applied around the fracture, while no collagen was applied in the control group (n=11). Following 10 days in limb shortening, a gradual distraction of 0.5 mm/12 h was performed using an external fixation device and followed up for 40 days. Osseous consolidation occurred in all animals. Average callus diameter (1.54 ± 0.8 vs. 1.27 ± 0.14 mm) and torsional strength (72% vs. 46% of normal) were significantly higher in the test versus the control group. Blood vessel formation increased with a significantly higher number of vessels (6.3 vs. 3.81/mm2 ) and larger cross-sectional area (>40 µm, 90.5% vs. 86%) in the test versus control group. The results showed that locally applied VEGF stimulates fracture healing after acute soft tissue trauma and might be an option for fracture treatment in cases with severe soft tissue damage.

bFGF-Modified BMMSCs enhance bone regeneration following distraction osteogenesis in rabbits

Distraction osteogenesis (DO), which induces new bone formation along the vector of pull without requiring the use of bone graft, has become a valuable surgical method for patients with limb discrepancy or craniofacial microsomia. However, the long treatment period and possible fibrous union or nonunion hampers its further clinical application. Bone marrow mesenchymal stem cells (BMMSCs) have been widely used as a source of cell therapy or a vector for gene transfer. Basic fibroblast growth factor (bFGF) has high potential for promotion of bone regeneration. However, bFGF has a short half value period in vivo. In this study, osteodistraction was applied in craniofacial bone of rabbit to observe the effects of BMMSCs with or without bFGF gene transfected on bone regeneration in the distracted zone. Mandibular lengthening (10 mm) was performed in 42 New Zealand white rabbits using a rapid distraction rate (2 mm/day). The animals were then randomly divided into group A, group B and group C (n=14 for each group). At the end of distraction, physiological saline, autologous BMMSCs and BMMSCs transfected with bFGF were injected into the distraction gaps in groups A, B, and C, respectively. Eight weeks after DO, the rabbits were sacrificed, and the distracted mandibles were harvested and processed for radiography, dual energy x-ray absorptiometry (DXA), micro-CT, histology and three-point bend testing. Under a rapid distraction, immature or poor bone healing was observed in the distracted callus from group A. However, better bone formation and higher bone mineral density (BMD) and bone mineral content (BMC) in the distracted callus were observed in group B and group C, the latter showed excellent bone formation and highest BMD and BMC. Such finding was confirmed by histological and micro-CT examinations. The values of BT/TV in group C were highest and the micro-architecture presented more mature characteristics. The mechanical strength in group C was 1.63-fold and 1.28-fold greater than that in group A and B by three-point bending testing. The results of this study suggest that BMMSCs transplantation can promote bone formation in DO, and bFGF-modified BMMSCs were more effective in this enhancement.

Histomorphometric comparison between continuous and discontinuous distraction osteogenesis

INTRODUCTION

Experimental research on optimising the distraction protocol has been performed extensively in the past. However, relatively little research has been done on the rhythm of distraction. Findings in the orthopaedic literature showed that the outcome of distraction osteogenesis (DO) is positively influenced by increasing the rhythm of distraction. The aim of this study is to quantitatively compare continuous with discontinuous rhythms of distraction in rabbits.

MATERIALS AND METHODS

Tissue blocks of regenerated bone were harvested from thirty-eight young adult female New-Zealand White rabbits. After a latency period of three days, rabbits were subjected for eleven days to either single daily activation of the distractor at a rate of 0.9 mm/d, or triple daily activation at a rate of 0.9 mm/d, or continuous activation at a rate of 0.9 mm/d. After three weeks of consolidation, bone regenerates were analysed using histomorphometry.

RESULTS

The continuous DO group showed significantly (p<.01) more regenerate bone volume in the central part of the regenerate than the discontinuous DO groups. Higher osteoblastic activity was seen, as well as more blood vessels (p<.05). Bone volume and the number of blood vessels correlated significantly in the central part of the regenerate (p<.05). Also, the early mineral apposition rate (MAR) was higher than the late MAR (p<.05).

CONCLUSIONS

Continuous DO significantly accelerates bone formation when compared with discontinuous DO.

The effect of periosteal injury and masticatory micromovement on the healing of a mandibular distraction osteogenesis site

OBJECTIVES

Surgical periosteal injury and masticatory loading are likely factors affecting the healing of a mandibular DO site. This study is aimed to characterize the healing features of an early-phase mandibular DO site and assess the effects of these factors.

DESIGN

Eighteen 3-6-month-old miniature pigs received a right mandibular osteotomy and were distracted for 5 days (1 mm/day) and consolidated for 0, 1 or 2 weeks (Groups A, B and C, respectively). Bone formation, chondrogenesis and vascular structure of the distraction site were measured using histological methods and their changes with consolidation time were characterized. The effect of periosteal injury was assessed by comparing the more severely injured lateral side with the less disturbed medial side. The effect of masticatory loading was evaluated by relating the healing features to the interfragmentary micromovement caused by soft-diet mastication.

RESULTS

With consolidation time, bone formation and chondrogenesis became stronger whilst vascular structure became more mature. Compared to the medial side, bone formation and chondrogenesis on the lateral side were significantly delayed in Groups A and B, but not in Group C, in which periosteal recovery had occurred. No difference was found for vascular measurements between the medial and lateral sides. In Group B, bone formation, but not chondrogenesis or vascular structures, tended to be negatively correlated with the magnitude of masticatory micromovement during the distraction phase.

CONCLUSION

The results suggest that periosteal injury inhibits early mandibular DO site healing, whereas micromovement from soft-diet mastication mechanics has a negligible effect.

VEGF facilitates periosteal distraction-induced osteogenesis in rabbits: a micro-computerized tomography study

BACKGROUND AND PURPOSE

Distraction osteogenesis is routinely used for reconstruction of bone. Conversely, it was hypothesized that mechanical traction of the periosteum would induce bone formation, and hence the use of periosteal distraction for induction of osteogenesis has been proposed. Further, it was postulated that intracallus administration of vascular endothelial growth factor (VEGF) would facilitate osteogenesis. To investigate this hypothesis, formation of newly synthesized bone was evaluated using micro-computerized tomography (microCT) and histomorphometry.

MATERIALS AND METHODS

Periosteal distractors were placed subperiosteally in one side of the mandible of rabbits, whereas the contralateral served as control. One group of animals received VEGF into the forming callus. Formation of bone was measured using microCT and histological analysis.

RESULTS

The results demonstrate formation of new bone following periosteal distraction. Addition of VEGF to the distraction site increased bone synthesis.

CONCLUSIONS

microCT and histological analysis validate the hypothesis that mechanical distraction of the periosteum induces osteogenesis and that VEGF has a positive effect on osteogenesis. Periosteal distraction is emerging as a reliable technique for bone regeneration.

OP-1 injection increases VEGF expression but not angiogenesis in a rabbit model of distraction osteogenesis

We have previously shown that a single injection of rhBMP-7 (OP-1) applied to the regenerate early during distraction accelerates bone consolidation in a rabbit model of distraction osteogenesis. In the present study, we hypothesised that the injection of OP-1 improves bone consolidation by increasing blood flow to the distracted site. Blood flow into the regenerate of a rabbit model was measured and vascular endothelial growth factor (VEGF) expression was tested using semi-quantitative PCR. Immunohistochemistry was used for assessing the temporal and spatial expression of platelet endothelial cell adhesion molecule (PECAM), VEGF and its receptors following OP-1 injection. We observed a higher expression of VEGF and its receptors in the regenerate with OP-1 treatment. However, there was no difference in the increase in bone blood flow nor PECAM expression between the treated and control groups of animals. Interestingly, the increased expression of VEGF and its receptors was associated with chondrocyte and fibroblast-like cells, but not with endothelial cells. These results suggest that accelerated ossification by OP-1 may depend on a non-vascular mechanism, possibly involving a non-angiogenic function of VEGF signalling.

Mobilization of endothelial progenitor cells in fracture healing and distraction osteogenesis

INTRODUCTION

Fracture healing and distraction osteogenesis (DO) are unique postnatal bone formation processes, and neovascularization is critically required for successful bone regeneration. We investigated endothelial progenitor cell (EPC) mobilization during bone regeneration, and the possible contribution of EPCs to increased vascularization and new bone formation, especially in DO.

METHODS

Mouse tibia fracture and rat tibia DO models were used in this study. The proportion of EPCs among the peripheral and splenic mononuclear cells (MNCs) was determined by examining the endothelial lineage staining characteristics and EPC cell surface markers. Messenger RNA expression of molecules related to EPC mobilization and homing at the fracture site were analyzed by ribonuclease protection assay and reverse-transcription polymerase chain reaction. In the rat tibia DO model, we measured blood flow during DO, and determined the distribution of ex vivo-expanded and intravenously-infused EPCs.

RESULTS

The proportion of EPCs among the peripheral and splenic MNCs increased after fracture, peaked on post-fracture day 3, and returned to basal levels during the healing period. Messenger RNA expression of EPC mobilizing cytokines such as vascular endothelial growth factor (VEGF), stem cell factor, monocyte chemoattractant protein-1, and stromal cell-derived factor-1, were upregulated at the fracture callus. The plasma VEGF levels peaked prior to the increase in the EPC proportion. Adhesion molecules involved in EPC homing were expressed at the fracture callus. In the DO model, the temporal pattern of the increase in the EPC proportion was similar to that in the fracture healing model, but the EPC proportion increased again during the distraction and consolidation phases. The distraction gap was relatively ischemic during the distraction phase and blood flow increased profusely later in the consolidation phase. The number of EPCs homing to the bone regeneration site in the DO model correlated with the number of transplanted EPCs in a dose-dependent manner.

CONCLUSIONS

These findings suggest that signals from the bone regeneration site mobilize EPCs from the bone marrow into the peripheral circulation. Increased EPC mobilization and homing may contribute to neovascularization and thus to new bone formation in fracture healing and DO.

Increased lengthening rate decreases expression of fibroblast growth factor 2, platelet-derived growth factor, vascular endothelial growth factor, and CD31 in a rat model of distraction osteogenesis

BACKGROUND

The rate of lengthening has a profound impact on bone regeneration during distraction osteogenesis. Rapid distraction can delay or completely inhibit union, whereas distracting too slowly may lead to premature consolidation. However, the mechanisms responsible for retardation of healing due to rapid distraction have not been elucidated. This study explored whether rapid distraction alters the expression of certain angiogenic growth factors, in particular, fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF-AA), and subsequent new vessel formation as evidenced by platelet endothelial cellular adhesion marker expression (CD31), an indicator of vascular budding.

METHODS

Unilateral femoral lengthenings were performed in 60 male Sprague-Dawley rats using a protocol that involved a 7-day latency period and distraction rates of either 0.5 (slow distraction) or 1.5 mm/d (fast distraction) for a total of 7.0 mm of lengthening. Animals were euthanized on postoperative days 8, 10, 12, 14, and 21 (n = 6 per time point and distraction rate). Expression of FGF-2, VEGF, PDGF-AA, and CD31 was characterized immunohistochemically.

RESULTS

Cellular staining of FGF-2, PDGF-AA, VEGF, and CD31 was reduced on days 8 to 12 in the regenerate of the fast-distraction animals compared with the slow-distraction animals. Staining of all growth factors was weak on days 14 and 21 at the slow rate and absent at the fast rate. Regardless of time point, a similar spatial localization of growth factor expression was observed at the 2 rates of distraction.

CONCLUSIONS

The reduced expression of angiogenic growth factors and CD31, a marker of new vessel formation, indicates that the angiogenic cascade and new vessel formation required for effective bone healing is disrupted at a distraction rate of 1.5 mm/d in a rat model of limb lengthening.

CLINICAL RELEVANCE

Delayed bone healing with rapid distraction may be due in part to decreased cellular signaling required for angiogenesis. It may be possible to improve bone healing at increased distraction rates with the appropriately timed administration of growth factors.

Evaluation of chemokine and cytokine profiles in osteoblast progenitors from umbilical cord blood stem cells by BIO-PLEX technology

We have used cytokine protein array to analyze the secretion of cytokines from an osteoblastic clone derived from human umbilical cord blood mesenchymal stem cells (MSCs) cultured in an osteogenic differentiation medium. The analysis demonstrated the unexpected ability of osteoblast committed cells and their early progenitors to produce significant amounts of a range of soluble immune mediators without in vitro exposure to clinically relevant bacterial pathogens. The cells were expanded and their osteogenic potential analyzed over 45 days of culture was revealed by the expression of osteoblast-specific markers (alkaline phosphatase and Runx2), and by matrix mineralization. Over this culture period, the cells secreted particularly high levels of IL-8, MCP-1 and VEGF, but did not express IL-2, IL-7, IL-17, eotaxin, G-CSF and IFN-gamma. These findings should encourage the use of human umbilical cord blood as a potential stem cells source for bone regeneration.

Temporal and spatial expression of osteoprotegerin and receptor activator of nuclear factor -kappaB ligand during mandibular distraction in rats

PURPOSE

The expression profiles of osteoprotegerin and receptor activator of nuclear factor-kappaB ligand (RANKL) were investigated in the distraction region to reveal bone remodelling characters during mandibular distraction osteogenesis.

MATERIAL AND METHODS

Osteotomies were performed and external distractors were used on the mandibles of 42 adult male SD rats. After a 5-day latency period, the distractors were activated at a rate of 0.4mm/day for 6 days, followed by a 4-week consolidation period. Radiographs were taken, and specimens were harvested at the end of the latency period, when distraction was completed, and at the end of 1, 2, 3 and 4 weeks of the consolidation period. Tartrate-resistant acid phosphatase staining was used to detect activated osteoclasts. Temporospatial expression of osteoprotegerin and RANKL was investigated by using immunohistochemistry, in situ hybridization and reverse transcription polymerase chain reaction. Semi-quantitative analysis was used to characterize osteoprotegerin (OPG). RANKL and RANKL/OPG ratio.

RESULTS

In all time points, osteoprotegerin and RANKL were co-localized in bone marrow lining cells, osteoblasts and newly embedded osteocytes. Osteoprotegerin mRNA expression increased to a peak when distraction was completed and maintained this level until the end of week 2 of the consolidation period. RANKL mRNA expression increased steadily until the end of week 1 of the consolidation period and maintained a peak level until the end of week 3, with a slight decrease at the end of week 2. The RANKL/OPG ratio increased continuously and reached its highest level at the end of weeks 3 and 4 of the consolidation period. Tartrate-resistant acid phosphatase staining positive osteoclasts were mainly detected at weeks 2, 3 and 4 of the consolidation period in bone marrow cavities and bone surfaces.

CONCLUSIONS

The temporospatial expression patterns of osteoprotegerin and RANKL suggest that the osteoblast lineage cell network orchestrates bone remodelling during distraction osteogenesis and most activated bone resorption takes place during weeks 3 and 4 of the consolidation phase.

Expression of vascular endothelial growth factor and its receptors after mandibular distraction osteogenesis

During distraction osteogenesis, angiogenic activity is essential for new bone formation. This study examined the expression of vascular endothelial growth factor (VEGF) and two of its receptors, Flt-1 (VEGFR-1) and Flk-1 (VEGFR-2), in cellular components after mandibular distraction osteogenesis. Unilateral mandibular distraction (0.5 mm twice per day for 10 days) was performed in six mongrel dogs. Two animals each were killed on days 7, 14 and 28 after completion of distraction. The distracted mandibular segments and contralateral undistracted control segments were harvested and processed for immunohistochemical examination. Seven days after distraction, there was a significant increase in the expression levels of VEGF and its receptors in the osteoblasts, osteocytes and immature fibroblast-like cells compared to control specimens. These levels were maintained for 14 days after distraction in the osteoblasts and fibroblast-like cells. Twenty-eight days after distraction, VEGF and VEGFR-1 were expressed only moderately/weakly in the osteoblasts, and no VEGFR-2 expression was detected in the cellular component of the distracted bone. Throughout the observation period, VEGFR-1 expression was stronger than that of VEGFR-2. The expression patterns of VEGF and its receptors suggest that it plays an important role in osteogenesis, and that osteoblasts and immature fibroblast-like cells of the distracted bone may have an autocrine growth effect during distraction osteogenesis.

The distribution of the growth factors FGF-2 and VEGF, and their receptors, in growing red deer antler

The cellular distributions of the growth factors FGF-2 and VEGF, and their receptors FGFR1, FGFR2 and FGFR3, and VEGFR-2 respectively, were visualized by immunohistochemistry and light microscopy in sections of growing red deer antler. Both of these signalling systems were widely expressed in the integument and osteocartilaginous compartments. FGF-2 was found in the same cells as all three FGFRs, indicating that FGF signalling may be principally autocrine. The patterns of labelling for VEGF and its receptor were similar to those seen for FGF-2 and FGFR-3, in both compartments. Our data are consistent with the findings of others in suggesting that FGF-2 induces expression of VEGF, to stimulate and maintain high rates of neovascularisation and angiogenesis, thereby providing nutrients to both velvet and bone as they rapidly grow and develop. The presence of FGF and VEGF and their receptors in epithelial cells suggests that these signalling systems play a role in skin development, raising the possibility that one or both may be involved in the close coupling of the coordinated growth of the integument and osteocartilage of antler, a process which is poorly understood at present.

Craniofacial bone tissue engineering

Repair and reconstruction of the craniofacial skeleton represents a significant biomedical burden, with thousands of procedures per-formed annually secondary to injuries and congenital malformations. Given the multitude of current approaches, the need for more effective strategies to repair these bone deficits is apparent. This article explores two major modalities for craniofacial bone tissue engineering: distraction osteogenesis and cellular based therapies. Current understanding of the guiding principles for each of these modalities is elaborated on along with the knowledge gained from clinical and investigative studies. By laying this foundation, future directions for craniofacial distraction and cell-based bone engineering have emerged with great promise for the advancement of clinical practice.

Evaluation of delayed-image bone scintigraphy to assess bone formation after distraction osteogenesis in dogs

OBJECTIVE

To quantitatively assess distraction-induced bone formation in a crural lengthening model in dogs by use of delayed-image bone scintigraphy.

ANIMALS

12 mature Labrador Retrievers.

PROCEDURE

Dogs were randomly allocated to 1 of 3 groups. A circular external skeletal fixation system was mounted on the right crus of each dog. Osteotomy of the distal portion of the tibia and fibula was performed in groups 1 and 2 and was followed by a lengthening procedure of 10 mm in the first group only. The third group served as sham-operated controls. Delayed-image bone scintigraphy with technetium-99m hydroxy methylene diphosphonate was performed 2, 4, and 6 weeks after surgery. Delayed-image-to-region-of-interest, delayed-image-to-crural, and delayed-image-to-femoral scintigraphic activity ratios were calculated. New bone formation was quantified by use of densitometric image analysis, and values for the scintigraphic ratios were compared.

RESULTS

In the distraction and osteotomy groups, delayed-image-to-region-of-interest and delayed-image-to-crural ratios increased significantly. Although densitometric image analysis revealed increased bone formation after distraction, the region-of-interest ratios and crural ratios were similar in both groups. All dogs had increased delayed-image-to-femoral ratios.

CONCLUSIONS AND CLINICAL RELEVANCE

Delayed-image bone scintigraphy ratios were not effective at differentiating between the amounts of distraction-induced bone and osteotomy-induced bone. Metabolic bone activity in the adjacent femur was increased as a consequence of circular external skeletal fixator placement. Delayed-image bone scintigraphy was not adequately sensitive to quantitatively monitor bone formation but may be useful as an early predictor of bone healing.

Axial shortening during distraction osteogenesis leads to enhanced bone formation in a rabbit model through the HIF-1alpha/vascular endothelial growth factor system

Axial micromotion of bone fragments enhances callus formation during fracture repair or limb lengthening. To examine this, we used an axial-shortening model of the tibial callus in rabbits and performed histological analyses. After 10-mm lengthening of the left tibia with an external fixator, we shortened the callus by 2 mm. Radiographs and quantitative evaluation of corrected bone mineral density showed a significant increase in mineralization in the shortened callus (57.3 vs. 36.2%, p = 0.001). Histologically, greater osteoblast proliferation and more vigorous trabecular bone formation were noted in the shortened calluses than in the controls. Around the front of membranous bone formation in the shortened callus, there was a significant decrease in mean percentage area of vascular lumens (1.8 vs. 4.5%, p = 0.009), which seemed attributable to compressive force, and a significantly increased production of vascular endothelial growth factor (VEGF; 422.5 vs. 142.7 pg/mg protein, p = 0.007) and its receptors. There were also increased numbers of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts and proliferating cell nuclear antigen (PCNA)-positive cells. A marked increase of hypoxia inducible factor-1alpha (HIF-1alpha) expression in osteoblasts was also observed in this area. Thus, enhancement of membranous bone formation by static compression or axial dynamization may be at least partly attributable to HIF-1alpha-mediated VEGF induction following the local hypoxia caused by collapse of vascular lumens.

Growth factor expression following clinical mandibular distraction osteogenesis in humans and its comparison with existing animal studies

AIM

Lengthening the mandible by distraction osteogenesis (DO) is nowadays a well recognized technique in maxillofacial surgery. In this study growth factor expression profiles were examined in biopsies taken from six patients undergoing mandibular DO and compared with findings from a sheep model for mandibular DO.

STUDY DESIGN

In all patients (and sheep), the ascending ramus was distracted 10-15 mm at a rate of 1mm/day using an intraoral device. Biopsies were taken from the centre of the distraction zone 21 days after completion of distraction. Using standard immunohistochemical techniques, samples were stained for platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-beta), basic fibroblast growth factor (bFGF) and bone morphogenetic proteins-2, -4 and -7 (BMP-2, -4, -7), matrix metalloproteinases-1 and -3 (MMP-1, -3), the vascular endothelial growth factor (VEGF), a marker for endothelial cells (CD-31) and type IV collagen (Col IV).

RESULTS

Positive staining for PDGF, bFGF, TGF-beta, BMP-2, -4, and -7 was noted in cells and matrix components. There was intense staining for MMP-1. Strong staining for CD-31 and COL IV was observed adjacent to vessels. VEGF staining was less specific. Similar findings were noted in the sheep model.

CONCLUSION

Growth factor expression in the human distraction site is similar to that in the sheep model.

Effect of vascularity on canine distracted tibial callus consolidation

In the consolidation period of distraction osteogenesis, mineralization occurs before corticalization. We hypothesized that the increased rate of bone mineral density correlates to the density of vascularity in the callus. We unilaterally lengthened the tibia in eight adult beagles. After a waiting period of 7 days, tibiae were lengthened for 30 days. After a consolidation period of an additional 60 days, all animals were euthanized. Just before euthanasia, blood vessels were perfused with 50% w/v barium sulfate solution, and soft radiographs of the distracted callus and the control tibiae were taken. Bone mineral density of the regenerated bones was measured preoperatively by quantitative computed tomography on Days 37, 68, and 98. Increases of the percent bone mineral density (from Day 37 to Day 98 and from Day 68 to Day 98) correlated with the blood vessel volume density ratios on Day 98. Our results suggest that preservation of the higher density of blood vessels in the consolidation period could lead to the better mineralization of the distracted callus.

Histology of the porcine mandibular distraction wound

The purpose of this study was to document the progression and pattern of endosteal bone formation in a porcine mandibular distraction wound. Bone formation was assessed in a 0-day latency model (n=24 pigs) using distraction rates of 1, 2, or 4 mm/day to create a 12-mm gap. Macro-radiographs and sagittal histologic sections, from the center of the mandible, were evaluated by computer morphometrics (% bone fill) and by a semi-quantitative bone formation score. Mean percent area of new bone was 12.4% (0-25.9%), 7.5% (0-21.3%) and 3.8% (0-10.5%) in mandibles distracted at 1, 2 or 4 mm/day respectively. At all time points, percent area of new bone was highest in mandibles distracted at 1 mm/day. Bone was deposited from the margins of the osteotomy toward the center of the wound and occurred first around the inferior alveolar canal and tooth bud regions. New bone formed by intramembranous ossification alone. The results of this experiment document the contribution of endosteal bone formation in this model of distraction osteogenesis.

Effect of platelet-rich-plasma on cranial distraction osteogenesis in sheep: preliminary clinical and radiographic results

The purpose of this study was to investigate the effect of platelet-rich-plasma (PRP) on cranial distraction osteogenesis. Standardized calvaria critical size defects (6 cm x 5 cm) were created in 16 adult female sheep. Bifocal cranial transport distraction osteogenesis with autogenous free calvaria bone grafts (2 cm x 4 cm) was performed at a rate of 1mm once daily to a total of 30 mm. The 16 sheep involved in the experiment were randomly divided into four groups, four animals in each: Group 1 (no PRP, latency 5 days); Group 2 (no PRP, latency 0 day), Group 3 (PRP, latency 5 days) and Group 4 (PRP, latency 0 day). After a consolidation phase of 6 weeks, the animals were sacrificed and specimens harvested for conventional radiological and 3D quantitative computer tomographic (3D-QCT) assessment. New bone was generated in the distraction zone in all groups. There were significantly (P < 0.05) higher densities in the proximal region of the distraction regenerate in Group 4 (PRP, latency 0 day) compared to Group 2. However, no significant differences in mean density of the total distraction regenerate were found, neither in volume of the bony regenerate between the experimental groups. This study showed that PRP only had an effect on bone regeneration if active distraction was started immediately after application of PRP in the distraction gap.

An In Vitro Model for Dissecting Distraction Osteogenesis

Distraction osteogenesis (DO) is a mechanotransduction process capable of generating viable osseous tissue by the gradual separation of osteotomized bone edges. Several variables are implicated in DO: magnitude of mechanical strain, distraction rate, and type of distracted bone. The combination of these factors acts on different types of cells inducing apoptosis, cell proliferation, and differentiation. The elucidation of the molecular mechanisms has important clinical implications because it may facilitate the use of recombinant proteins or gene therapy to accelerate bone regeneration. Previous reports have analyzed several molecules such as extracellular matrix proteins, cytokines, bone morphogenetic proteins, hormones, and angiogenic factors. Moreover, a single protein can have multifunctional roles. With such a huge number of mechanical, histologic, cellular, and molecular variables, there is the need to have a cell culture model that enables the selection of the effect of a specific strength to a single cell type at different time points and with or without cytokines. The analysis of the genetic profiling of a cell line cultured on an equibiaxial stretch device has such characteristic. Because there is a recruitment and commitment of preosteoblastic cells during bone lengthening and no previous report has focus on them, the authors used a preosteoblast MC3T3-E1 cell line to detect the early molecular effects of distraction on mesenchymal cells. By using DNA microarrays containing 15,000 clones, the authors identified several genes the expression of which was significantly up- or down-regulated. The differentially expressed genes cover a broad range of biological processes: cell growth, metabolism, morphogenesis, cell communication, response to stress, and cell death. The data reported are the first genetic portrait of stretched preosteoblasts. They can be relevant in the better understanding of the molecular mechanism of DO and as a model for comparing the effect of distraction on different cell lines and primary cultures, rate and strength of distraction, and with or without cytokines.

Immunolocalization of Vascular Endothelial Growth Factor During Heterotopic Bone Formation Induced From Grafted Periosteum

Vessel invasion is an important step in cartilage replacement that leads to bone formation, and vascular endothelial growth factor (VEGF) has been implicated as a key player in this process. Although grafted periosteum undergoes endochondral ossification, little is known about the role of VEGF in this process. In the current study the authors investigated by immunohistochemical, histochemical, and ultrastructural techniques the localization of VEGF during bone formation in periosteal grafts. At day 14 after grafting the tibias of Japanese white rabbits, periosteal cells in the grafted tissue had differentiated into chondrocytes to form cartilage. Some chondrocytes were immunopositive for VEGF expression, and subsequent vessel invasion occurred predominantly in these VEGF-positive areas. At day 45, the cartilage invaded by blood vessels had been replaced by newly formed bone. These findings suggest that VEGF is associated with the process of blood vessel invasion into cartilage before bone replacement in endochondral ossification from grafted periosteum.