Angiogenesis in fracture repair

Coupling of angiogenesis and osteogenesis by a specific vessel subtype in bone

The mammalian skeletal system harbours a hierarchical system of mesenchymal stem cells, osteoprogenitors and osteoblasts sustaining lifelong bone formation. Osteogenesis is indispensable for the homeostatic renewal of bone as well as regenerative fracture healing, but these processes frequently decline in ageing organisms, leading to loss of bone mass and increased fracture incidence. Evidence indicates that the growth of blood vessels in bone and osteogenesis are coupled, but relatively little is known about the underlying cellular and molecular mechanisms. Here we identify a new capillary subtype in the murine skeletal system with distinct morphological, molecular and functional properties. These vessels are found in specific locations, mediate growth of the bone vasculature, generate distinct metabolic and molecular microenvironments, maintain perivascular osteoprogenitors and couple angiogenesis to osteogenesis. The abundance of these vessels and associated osteoprogenitors was strongly reduced in bone from aged animals, and pharmacological reversal of this decline allowed the restoration of bone mass.

Histopathological features of bone regeneration in a canine segmental ulnar defect model

Background

Today, finding an ideal biomaterial to treat the large bone defects, delayed unions and non-unions remains a challenge for orthopaedic surgeions and researchers. Several studies have been carried out on the subject of bone regeneration, each having its own advantages. The present study has been designed in vivo to evaluate the effects of cellular auto-transplantation of tail vertebrae on healing of experimental critical bone defect in a dog model.

Methods

Six indigenous breeds of dog with 32 ± 3.6 kg average weight from both sexes (5 males and 1 female) received bilateral critical-sized ulnar segmental defects. After determining the health condition, divided to 2 groups: The Group I were kept as control I (n = 1) while in Group II (experimental group; n = 5) bioactive bone implants were inserted. The defects were implanted with either autogeneic coccygeal bone grafts in dogs with 3-4 cm diaphyseal defects in the ulna. Defects were stabilized with internal plate fixation, and the control defects were not stabilized. Animals were euthanized at 16 weeks and analyzed by histopathology.

Results

Histological evaluation of this new bone at sixteen weeks postoperatively revealed primarily lamellar bone, with the formation of new cortices and normal-appearing marrow elements. And also reformation cortical compartment and reconstitution of marrow space were observed at the graft-host interface together with graft resorption and necrosis responses. Finally, our data were consistent with the osteoconducting function of the tail autograft.

Conclusions

Our results suggested that the tail vertebrae autograft seemed to be a new source of autogenous cortical bone in order to supporting segmental long bone defects in dogs. Furthermore, cellular autotransplantation was found to be a successful replacement for the tail vertebrae allograft bone at 3-4 cm segmental defects in the canine mid- ulna. Clinical application using graft expanders or bone autotransplantation should be used carefully and requires further investigation.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2028232688119271.

Impaired angiogenesis during fracture healing in GPCR kinase 2 interacting protein-1 (GIT1) knock out mice

G protein coupled receptor kinase 2 (GRK2) interacting protein-1 (GIT1), is a scaffold protein that plays an important role in angiogenesis and osteoclast activity. We have previously demonstrated that GIT1 knockout (GIT1 KO) mice have impaired angiogenesis and dysregulated osteoclast podosome formation leading to a reduction in the bone resorbing ability of these cells. Since both angiogenesis and osteoclast-mediated bone remodeling are involved in the fracture healing process, we hypothesized that GIT1 participates in the normal progression of repair following bone injury. In the present study, comparison of fracture healing in wild type (WT) and GIT1 KO mice revealed altered healing in mice with loss of GIT1 function. Alcian blue staining of fracture callus indicated a persistence of cartilagenous matrix in day 21 callus samples from GIT1 KO mice which was temporally correlated with increased type 2 collagen immunostaining. GIT1 KO mice also showed a decrease in chondrocyte proliferation and apoptosis at days 7 and 14, as determined by PCNA and TUNEL staining. Vascular microcomputed tomography analysis of callus samples at days 7, 14 and 21 revealed decreased blood vessel volume, number, and connection density in GIT1 KO mice compared to WT controls. Correlating with this, VEGF-A, phospho-VEGFR2 and PECAM1 (CD31) were decreased in GIT1 KO mice, indicating reduced angiogenesis with loss of GIT1. Finally, calluses from GIT1 KO mice displayed a reduced number of tartrate resistant acid phosphatase-positive osteoclasts at days 14 and 21. Collectively, these results indicate that GIT1 is an important signaling participant in fracture healing, with gene ablation leading to reduced callus vascularity and reduced osteoclast number in the healing callus.

Amifostine protects vascularity and improves union in a model of irradiated mandibular fracture healing

BACKGROUND

Pathologic fractures of the mandible can be devastating to cancer patients and are due in large part to the pernicious effects of irradiation on bone vascularity. The authors' aim was to ascertain whether amifostine, a radioprotective drug, will preserve vascularity and improve bone healing in a murine model of irradiated mandibular fracture repair.

METHODS

Rats were randomized into three groups: nonirradiated fracture (n = 9), irradiation/fracture (n = 5), and amifostine/irradiation/fracture (n = 7). Animals in the irradiation groups underwent a human equivalent dose of radiation directed at the left hemimandible. Animals treated in the amifostine group received amifostine concomitantly with radiation. All animals underwent unilateral left mandibular osteotomy with external fixation set to a 2.1-mm fracture gap. Fracture healing was allowed for 40 days before perfusion with Microfil. Vascular radiomorphometrics were quantified with micro-computed tomography.

RESULTS

When compared with the irradiated/fractured group, amifostine treatment more than doubled the rate of fracture unions to 57 percent. Amifostine treatment also resulted in an increase in vessel number (123 percent; p < 0.05) and a corresponding decrease in vessel separation (55.5 percent; p < 0.05) there was no statistical difference in the vascularity metrics between the amifostine/irradiation/fracture group and the nonirradiated/fracture group.

CONCLUSIONS

Amifostine prophylaxis during radiation maintains mandibular vascularity at levels observed in nonirradiated fracture specimens, corresponding to improved unions. These results set the stage for clinical exploration of this targeted therapy alone and in combination with other treatments, to mitigate the effects of irradiation on bone healing and fracture repair.

Dimethyloxaloylglycine increases the bone healing capacity of adipose-derived stem cells by promoting osteogenic differentiation and angiogenic potential

Hypoxia inducible factor-1α (HIF-1α) plays an important role in angiogenesis-osteogenesis coupling during bone regeneration, which can enhance the bone healing capacity of mesenchymal stem cells (MSCs) by improving their osteogenic and angiogenic activities. Previous studies transduced the HIF-1α gene into MSCs with lentivirus vectors to improve their bone healing capacity. However, the risks due to lentivirus vectors, such as tumorigenesis, should be considered before clinical application. Dimethyloxaloylglycine (DMOG) is a cell-permeable prolyl-4-hydroxylase inhibitor, which can activate the expression of HIF-1α in cells at normal oxygen tension. Therefore, DMOG is expected to be an alternative strategy for enhancing HIF-1α expression in cells. In this study, we explored the osteogenic and angiogenic activities of adipose-derived stem cells (ASCs) treated with different concentrations of DMOG in vitro, and the bone healing capacity of DMOG-treated ASCs combined with hydrogels for treating critical-sized calvarial defects in rats. The results showed that DMOG had no obvious cytotoxic effects on ASCs and could inhibit the death of ASCs induced by serum deprivation. DMOG markedly increased vascular endothelial growth factor production in ASCs in a dose-dependent manner and improved the osteogenic differentiation potential of ASCs by activating the expression of HIF-1α. Rats with critical-sized calvarial defects treated with hydrogels containing DMOG-treated ASCs had more bone regeneration and new vessel formation than the other groups. Therefore, we believe that DMOG enhanced the angiogenic and osteogenic activity of ASCs by activating the expression of HIF-1α, thereby improving the bone healing capacity of ASCs in rat critical-sized calvarial defects.

Nitric oxide-mediated vasodilation increases blood flow during the early stages of stress fracture healing

Despite the strong connection between angiogenesis and osteogenesis in skeletal repair conditions such as fracture and distraction osteogenesis, little is known about the vascular requirements for bone formation after repetitive mechanical loading. Here, established protocols of damaging (stress fracture) and nondamaging (physiological) forelimb loading in the adult rat were used to stimulate either woven or lamellar bone formation, respectively. Positron emission tomography was used to evaluate blood flow and fluoride kinetics at the site of bone formation. In the group that received damaging mechanical loading leading to woven bone formation (WBF), (15)O water (blood) flow rate was significantly increased on day 0 and remained elevated 14 days after loading, whereas (18)F fluoride uptake peaked 7 days after loading. In the group that received nondamaging mechanical loading leading to lamellar bone formation (LBF), (15)O water and (18)F fluoride flow rates in loaded limbs were not significantly different from nonloaded limbs at any time point. The early increase in blood flow rate after WBF loading was associated with local vasodilation. In addition, Nos2 expression in mast cells was increased in WBF-, but not LBF-, loaded limbs. The nitric oxide (NO) synthase inhibitor N(ω)-nitro-l-arginine methyl ester was used to suppress NO generation, resulting in significant decreases in early blood flow rate and bone formation after WBF loading. These results demonstrate that NO-mediated vasodilation is a key feature of the normal response to stress fracture and precedes woven bone formation. Therefore, patients with impaired vascular function may heal stress fractures more slowly than expected.

Controlled multiple growth factor delivery from bone tissue engineering scaffolds via designed affinity

It is known that angiogenesis plays an important role in bone regeneration and that release of angiogenic and osteogenic growth factors can enhance bone formation. Multiple growth factors play key roles in processes that lead to tissue formation/regeneration during natural tissue development and repair. Therefore, treatments aiming to mimic tissue regeneration can benefit from multiple growth factor release, and there remains a need for simple clinically relevant approaches for dual growth factor release. We hypothesized that mineral coatings could be used as a platform for controlled incorporation and release of multiple growth factors. Specifically, mineral-coated scaffolds were "dip coated" in multiple growth factor solutions, and growth factor binding and release were dictated by the growth factor-mineral binding affinity. Beta tricalcium phosphate (β-TCP) scaffolds were fabricated using indirect solid-free form fabrication techniques and coated with a thin conformal mineral layer. Mineral-coated β-TCP scaffolds were sequentially dipped in recombinant human vascular endothelial growth factor (rhVEGF) and a modular bone morphogenetic peptide, a mineral-binding version of bone morphogenetic protein 2 (BMP2), solutions to allow for the incorporation of each growth factor. The dual release profile showed sustained release of both growth factors for over more than 60 days. Scaffolds releasing either rhVEGF alone or the combination of growth factors showed an increase in blood vessel ingrowth in a dose-dependent manner in a sheep intramuscular implantation model. This approach demonstrates a "modular design" approach, in which a controllable biologics carrier is integrated into a structural scaffold as a thin surface coating.

Immunohistochemial study on the expression of von Willebrand factor (vWF) after onlay autogenous iliac grafts for lateral alveolar ridge augmentation

INTRODUCTION

The main problems of autogenous bone transplants are their unpredictable atrophy and their loss of structure. One key factor lies in the poor revascularization of simple onlay grafts. The the aim of this study was to evaluate the revascularization processes in autogenous bone grafts from the iliac crest to the alveolar ridge.

METHODS

In a sheep model, autogenous bone grafts were harvested from the iliac crest. A combination of a resorbable collagen membrane (CM) and deproteinized bovine bone material (DBBM) was used to modify the bone graft (experiment 2). This was compared with a simple onlay bone graft (control group, experiment 1). The amount of vessels in bone and connective tissue (CT), and the amount of CT were analyzed. The expression of von Willebrand factor (vWF) was compared between the two experimental groups using immunohistochemical analysis.

RESULTS

The ratio of the amount of vessels in bone and CT changed over time, and more vessels could be detected in bone at 12-16 weeks of graft healing. The number of vessels were significantly higher in experiment 2 than in experiment 1. More CT was found in experiment 1, whereas the amount of CT in both experiments decreased over time.

CONCLUSION

This study shows a more intensive and extensive revascularization in experiment 2, as significantly more vessels were detected. The decreased amount of CT in experiment 2 clarifies its clinical superiority.

Basic science of bone healing

Bone healing is a complex process that can be influenced by both host and environmental factors. In this article, we review the biology involved in the regeneration of new bone after fracture, and factors influencing bone healing, including diabetes, smoking, NSAID use, and bisphosphonates.

Bone regeneration in rat calvarial defects implanted with fibrous scaffolds composed of a mixture of silicate and borate bioactive glasses

Previous studies have evaluated the capacity of porous scaffolds composed of a single bioactive glass to regenerate bone. In the present study, scaffolds composed of a mixture of two different bioactive glasses (silicate 13-93 and borate 13-93B3) were created and evaluated for their response to osteogenic MLO-A5 cells in vitro and their capacity to regenerate bone in rat calvarial defects in vivo. The scaffolds, which have similar microstructures (porosity=58-67%) and contain 0, 25, 50 and 100 wt.% 13-93B3 glass, were fabricated by thermally bonding randomly oriented short fibers. The silicate 13-93 scaffolds showed a better capacity to support cell proliferation and alkaline phosphatase activity than the scaffolds containing borate 13-93B3 fibers. The amount of new bone formed in the defects implanted with the 13-93 scaffolds at 12 weeks was 31%, compared to values of 25, 17 and 20%, respectively, for the scaffolds containing 25, 50 and 100% 13-93B3 glass. The amount of new bone formed in the 13-93 scaffolds was significantly higher than in the scaffolds containing 50 and 100% 13-93B3 glass. While the 13-93 fibers were only partially converted to hydroxyapatite at 12 weeks, the 13-93B3 fibers were fully converted and formed a tubular morphology. Scaffolds composed of an optimized mixture of silicate and borate bioactive glasses could provide the requisite architecture to guide bone regeneration combined with a controllable degradation rate that could be beneficial for bone and tissue healing.

Endostatin inhibits Callus remodeling during fracture healing in mice

Information on the impact of endogenous anti-angiogenic factors on bone repair is limited. The hypothesis of the present study was endostatin, an endogenous inhibitor of angiogenesis, disturbs fracture healing. We evaluated this hypothesis in a closed femoral fracture model studying two groups of mice, one that was treated by a daily injection of 10 µg recombinant endostatin subcutaneously (n = 38) and a second one that received the vehicle for control (n = 37). Histomorphometric analysis showed a significantly increased callus formation in endostatin-treated animals at 2 and 5 weeks post-fracture. This was associated with a significantly higher callus tissue fraction of cartilage and fibrous tissue at 2 weeks and a significantly higher fraction of bone at 5 weeks post-fracture. Biomechanical testing revealed a significantly higher torsional stiffness in the endostatin group at 2 weeks. For both groups, we could demonstrate the expression of the endostatin receptor unit integrin alpha5 in endothelial cells, osteoblasts, osteoclasts, and chondrocytes at 2 weeks. Immunohistochemical fluorescence staining of CD31 showed a lower number of blood vessels in endostatin-treated animals compared to controls. The results of the present study indicate endostatin promotes soft callus formation but inhibits callus remodeling during fracture healing most probably by an inhibition of angiogenesis.

Deferoxamine expedites consolidation during mandibular distraction osteogenesis

BACKGROUND

A limitation of mandibular distraction osteogenesis (DO) is the length of time required for consolidation. This drawback subjects patients to possible pin-site infections, as well as a prolonged return to activities of normal daily living. Developing innovative techniques to abridge consolidation periods could be immensely effective in preventing these problematic morbidities. Deferoxamine (DFO) is an angiogenic activator that triggers the HIF-1α pathway through localized iron depletion. We previously established the effectiveness of DFO in enhancing regenerate vascularity at a full consolidation period (28 days) in a murine mandibular DO model. To investigate whether this augmentation in vascularity would function to accelerate consolidation, we progressively shortened consolidation periods prior to μCT imaging and biomechanical testing (BMT).

MATERIALS AND METHODS

Three time points (14d, 21d and 28d) were selected and six groups of Sprague-Dawley rats (n = 60) were equally divided into control (C) and experimental (E) groups for each time period. Each group underwent external fixator placement, mandibular osteotomy, and a 5.1 mm distraction. During distraction, the experimental groups were treated with DFO injections into the regenerate gap. After consolidation, mandibles were imaged and tension tested to failure. ANOVA was conducted between groups, and p < 0.05 was considered statistically significant.

RESULTS

At 14 days of consolidation the experimental group demonstrated significant increases in bone volume fraction (BVF), bone mineral density (BMD) and ultimate load (UL) in comparison to non-treated controls. The benefit of treatment was further substantiated by a striking 100% increase in the number of bony unions at this early time-period (C:4/10 vs. E:8/10). Furthermore, metrics of BVF, BMD, Yield and UL at 14 days with treatment demonstrated comparable metrics to those of the fully consolidated 28d control group.

CONCLUSION

Based on these findings, we contend that augmentation of vascular density through localized DFO injection delivers an efficient means for accelerating bone regeneration without significantly impacting bone quality or strength.

Recovery from hind limb ischemia enhances rhBMP-2-mediated segmental bone defect repair in a rat composite injury model

Although severe extremity trauma is often inclusive of skeletal and vascular damage in combination, segmental bone defect repair with concomitant vascular injury has yet to be experimentally investigated. To this end, we developed a novel rat composite limb injury model by combining a critically-sized segmental bone defect with surgically-induced hind limb ischemia (HLI). Unilateral 8mm femoral defects were created alone (BD) or in combination with HLI (BD + HLI), and all defects were treated with rhBMP-2 via a hybrid biomaterial delivery system. Based on reported clinical and experimental observations on the importance of vascular networks in bone repair, we hypothesized that HLI would impair bone regeneration. Interestingly, the BD+HLI group displayed improved radiographic bridging, and quantitative micro-CT analysis revealed enhanced bone regeneration as early as week 4 (p < 0.01) that was sustained through week 12 (p < 0.001) and confirmed histologically. This effect was observed in two independent studies and at two different doses of rhBMP-2. Micro-CT angiography was used to quantitatively evaluate vascular networks at week 12 in both the thigh and the regenerated bone defect. No differences were found between groups in total blood vessel volume in the thigh, but clear differences in morphology were present as the BD+HLI group possessed a more interconnected network of smaller diameter vessels (p < 0.001). Accordingly, while the overall thigh vessel volume was comparable between groups, the contributions to vessel volume based on vessel diameter differed significantly. Despite this evidence of a robust neovascular response in the thigh of the BD + HLI group, differences were not observed between groups for bone defect blood vessel volume or morphology. In total, our results demonstrate that a transient ischemic insult and the subsequent recovery response to HLI significantly enhanced BMP-2-mediated segmental bone defect repair, providing additional complexity to the relationship between vascular tissue networks and bone healing. Ultimately, a better understanding of the coupling mechanisms may reveal important new strategies for promoting bone healing in challenging clinical scenarios.

Deferoxamine restores callus size, mineralization, and mechanical strength in fracture healing after radiotherapy

BACKGROUND

Therapeutic augmentation of fracture-site angiogenesis with deferoxamine has proven to increase vascularity, callus size, and mineralization in long-bone fracture models. The authors posit that the addition of deferoxamine would enhance pathologic fracture healing in the setting of radiotherapy in a model where nonunions are the most common outcome.

METHODS

Thirty-five Sprague-Dawley rats were divided into three groups. Fracture, irradiated fracture, and irradiated fracture plus deferoxamine. The irradiated fracture and irradiated fracture plus deferoxamine groups received a human equivalent dose of radiotherapy [7 Gy/day for 5 days, (35 Gy)] 2 weeks before mandibular osteotomy and external fixation. The irradiated fracture plus deferoxamine group received injections of deferoxamine into the fracture callus after surgery. After a 40-day healing period, mandibles were dissected, clinically assessed for bony union, imaged with micro-computed tomography, and tension tested to failure.

RESULTS

Compared with irradiated fractures, metrics of callus size, mineralization, and strength in deferoxamine-treated mandibles were significantly increased. These metrics were restored to a level demonstrating no statistical difference from control fractures. In addition, the authors observed an increased rate of achieving bony unions in the irradiated fracture plus deferoxamine-treated group when compared with irradiated fracture (67 percent and 20 percent, respectively).

CONCLUSIONS

The authors' data demonstrate nearly total restoration of callus size, mineralization, and biomechanical strength, and a threefold increase in the rate of union with the use of deferoxamine. The authors' results suggest that the administration of deferoxamine may have the potential for clinical translation as a new treatment paradigm for radiation-induced pathologic fractures.

Evaluation of bone healing in canine tibial defects filled with cortical autograft, commercial-DBM, calf fetal DBM, omentum and omentum-calf fetal DBM

The present study was conducted to compare the effects of xenogenic bovine fetal demineralized bone matrix (DBM), commercial DBM, omentum, omentum-calf fetal DBM, cortical autograft and xenogenic cartilage powder on the healing of tibial defects in a dog model to determine the best material for bone healing. Seven male adult mongrel dogs, weighing 26.2 ± 2.5 kg, were used in this study. Seven holes with a diameter of 4-mm were created and then filled with several biomaterials. Radiographs were taken postoperatively on day 1 and weeks 2, 4, 6, 8. The operated tibias were removed on the 56th postoperative day and histopathologically evaluated. On postoperative days 14, 42 and 56, the lesions of the control group were significantly inferior to those in the other group (p < 0.05). On the 28th postoperative day, the autograft group was significantly superior to the control and omentum groups (p < 0.05). Moreover, calf fetal DBM was significantly superior to the control group. There was no significant difference between the histopathological sections of all groups. Overall, the omentum and omentum-DBM groups were superior to the control group, but inferior to the autograft, commercial-DBM, calf fetal DBM and calf fetal cartilage groups.

Wrapped omentum with periosteum concurrent with adipose derived adult stem cells for bone tissue engineering in dog model

Adipose derived adult stem cells (ASCs) are multipotent cells that are able to differentiate into osteoblasts in presence of certain factors. The histological characteristics of periosteum makes it a specific tissue with a unique capacity to be engineered. Higher flexibility of the greater omentum is useful for reconstructive surgery. These criteria make it suitable for tissue engineering. The present study was designed to evaluate bone tissue engineering with periosteal free graft concurrent with ASCs and pedicle omentum in dog model. Twelve young female indigenous dogs were used in this experiment. In omental group (n = 4), end of omentum was wrapped by periosteum of the radial bone in abdomen of each dog. In omental-autogenously ASCs group (n = 4), 1 ml of ASCs was injected into the wrapped omentum with periosteum while in omental-allogenously ASCs group (n = 4), 1 ml of allogenous ASCs was injected. Lateral view radiographs were taken from the abdominal cavity postoperatively at the 2nd, 4th, 6th and 8th weeks post-surgery. Eight weeks after operation the dogs were re-anesthetized and the wrapped omenum by periosteum in all groups was found and removed for histopathological evaluation. Our results showed that omentum-periosteum, omental-periosteum-autogenous ASCs and omental-periosteum-allogenous ASCs groups demonstrated bone tissue formation in the abdominal cavity in dog model. The radiological, macroscopical and histological findings of the present study by the end of 8 weeks post-surgery indicate bone tissue engineering in all three groups in an equal level. The present study has shown that the wrapped omentum with periosteum concurrent with ASCs (autogenous or allogenous ASCs) lead to a favorable bone tissue formation. We suggested that it may be useful when pedicle graft omentum used concurrent with periosteum in the bone defect reconstruction, and this phenomenon should be studied in future.

Enhanced reconstruction of long bone architecture by a growth factor mutant combining positive features of GDF-5 and BMP-2

Non healing bone defects remain a worldwide health problem and still only few osteoinductive growth factors are available for clinical use in bone regeneration. By introducing BMP-2 residues into growth and differentiation factor (GDF)-5 we recently produced a mutant GDF-5 protein BB-1 which enhanced heterotopic bone formation in mice. Designed to combine positive features of GDF-5 and BMP-2, we suspected that this new growth factor variant may improve long bone healing compared to the parent molecules and intended to unravel functional mechanisms behind its action. BB-1 acquired an increased binding affinity to the BMP-IA receptor, mediated enhanced osteogenic induction of human mesenchymal stem cells versus GDF-5 and higher VEGF secretion than BMP-2 in vitro. Rabbit radius defects treated with a BB-1-coated collagen carrier healed earlier and with increased bone volume compared to BMP-2 and GDF-5 according to in vivo micro-CT follow-up. While BMP-2 callus often remained spongy, BB-1 supported earlier corticalis and marrow cavity formation, showing no pseudojoint persistence like with GDF-5. Thus, by combining positive angiogenic and osteogenic features of GDF-5 and BMP-2, only BB-1 restored a natural bone architecture within 12 weeks, rendering this promising growth factor variant especially promising for long bone regeneration.

Increased presence of capillaries next to remodeling sites in adult human cancellous bone

Vascularization is a prerequisite for osteogenesis in a number of situations, including bone development, fracture healing, and cortical bone remodeling. It is unknown whether a similar link exists between cancellous bone remodeling and vascularization. Here, we show an association between remodeling sites, capillaries, proliferative cells, and putative osteoblast progenitors. Iliac crest biopsies from normal human individuals were subjected to histomorphometry and immunohistochemistry to identify the respective positions of bone remodeling sites, CD34-positive capillaries, smooth muscle actin (SMA)-positive putative osteoblast progenitors, including pericytes, Ki67-positive proliferative cells, and bone remodeling compartment (BRC) canopies. The BRC canopy is a recently described structure separating remodeling sites from the bone marrow, consisting of CD56-positive osteoblasts at an early differentiation stage. We found that bone remodeling sites were associated with a significantly increased presence of capillaries, putative osteoblast progenitors, and proliferative cells in a region within 50 µm of the bone or the canopy surface. The increases were the highest above eroded surfaces and at the level of the light-microscopically assessed contact of these three entities with the bone or canopy surfaces. Between 51 and 100 µm, their densities leveled to that found above quiescent surfaces. Electron microscopy asserted the close proximity between BRC canopies and capillaries lined by pericytes. Furthermore, the BRC canopy cells were found to express SMA. These ordered distributions support the existence of an osteogenic-vascular interface in adult human cancellous bone. The organization of this interface fits the current knowledge on the mode of action of vasculature on osteogenesis, and points to the BRC canopy as a central player in this mechanism. We propose a model where initiation of bone remodeling coincides with the induction of proximity of the vasculature to endosteal surfaces, thereby allowing capillary-BRC canopy interactions that activate marrow events, including recruitment of osteoblast progenitors to bone remodeling sites.

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.

Intraarticular injection of platelet-rich plasma reduces inflammation in a pig model of rheumatoid arthritis of the knee joint

OBJECTIVE

Treatment options for rheumatoid arthritis range from symptomatic approaches to modern molecular interventions such as inhibition of inflammatory mediators. Inhibition of inflammation by platelet-rich plasma (PRP) has been proposed as a treatment for tendinitis and osteoarthritis. The present study was undertaken to investigate the effect of PRP on antigen-induced arthritis (AIA) of the knee joint in a large animal model.

METHODS

Six-month-old pigs (n = 10) were systemically immunized by bovine serum albumin (BSA) injection, and arthritis was induced by intraarticular BSA injection. PRP was injected into the knee joints of 5 of the animals after 2 weeks. An additional 5 animals received no systemic immunization (controls). Signs of arthritis were documented by plain histologic analysis, Safranin O staining, and immunohistochemistry analysis for type II collagen (CII), interleukin-6 (IL-6), and vascular endothelial growth factor (VEGF). Interleukin-1β (IL-1β), IL-6, tumor necrosis factor α (TNFα), VEGF, and insulin-like growth factor 1 (IGF-1) protein content was measured by Luminex assay.

RESULTS

In the pigs with AIA, plain histologic analysis revealed severe arthritic changes in the synovium. Safranin O and CII staining showed decreased proteoglycan and CII content in cartilage. Immunohistochemistry analysis revealed increased levels of IL-6 and VEGF in synovium and cartilage, and protein concentrations of IL-6, VEGF, IL-1β, and IGF-1 in synovium and cartilage were elevated as well; in addition, TNFα protein was increased in cartilage. Treatment with PRP led to attenuation of these arthritic changes in the synovium and cartilage.

CONCLUSION

We have described a porcine model of AIA. Experiments using this model demonstrated that PRP can attenuate arthritic changes as assessed histologically and based on protein synthesis of typical inflammatory mediators in the synovial membrane and cartilage.

Magnetic poly(ε-caprolactone)/iron-doped hydroxyapatite nanocomposite substrates for advanced bone tissue engineering

In biomedicine, magnetic nanoparticles provide some attractive possibilities because they possess peculiar physical properties that permit their use in a wide range of applications. The concept of magnetic guidance basically spans from drug delivery and hyperthermia treatment of tumours, to tissue engineering, such as magneto-mechanical stimulation/activation of cell constructs and mechanosensitive ion channels, magnetic cell-seeding procedures, and controlled cell proliferation and differentiation. Accordingly, the aim of this study was to develop fully biodegradable and magnetic nanocomposite substrates for bone tissue engineering by embedding iron-doped hydroxyapatite (FeHA) nanoparticles in a poly(ε-caprolactone) (PCL) matrix. X-ray diffraction analyses enabled the demonstration that the phase composition and crystallinity of the magnetic FeHA were not affected by the process used to develop the nanocomposite substrates. The mechanical characterization performed through small punch tests has evidenced that inclusion of 10 per cent by weight of FeHA would represent an effective reinforcement. The inclusion of nanoparticles also improves the hydrophilicity of the substrates as evidenced by the lower values of water contact angle in comparison with those of neat PCL. The results from magnetic measurements confirmed the superparamagnetic character of the nanocomposite substrates, indicated by a very low coercive field, a saturation magnetization strictly proportional to the FeHA content and a strong history dependence in temperature sweeps. Regarding the biological performances, confocal laser scanning microscopy and AlamarBlue assay have provided qualitative and quantitative information on human mesenchymal stem cell adhesion and viability/proliferation, respectively, whereas the obtained ALP/DNA values have shown the ability of the nanocomposite substrates to support osteogenic differentiation.

Localized deferoxamine injection augments vascularity and improves bony union in pathologic fracture healing after radiotherapy

BACKGROUND

Medically based efforts and alternative treatment strategies to prevent or remediate the corrosive effects of radiotherapy on pathologic fracture healing have failed to produce clear and convincing evidence of success. Establishing an effective pharmacologic option to prevent or treat the development of non-unions in this setting could have immense therapeutic potential. Experimental studies have shown that deferoxamine (DFO), an iron-chelating agent, bolsters vascularity and subsequently enhances normal fracture healing when injected locally into a fracture callus in long bone animal models. Since radiotherapy is known to impede angiogenesis, we hypothesized that the pharmacologic addition of DFO would serve to mitigate the effects of radiotherapy on new vessel formation in vitro and in vivo.

MATERIALS AND METHODS

In vitro investigation of angiogenesis was conducted utilizing HUVEC cells in Matrigel. Endothelial tubule formation assays were divided into four groups: Control, Radiated, Radiated+Low-Dose DFO and Radiated+High-Dose DFO. Tubule formation was quantified microscopically and video recorded for the four groups simultaneously during the experiment. In vivo, three groups of Sprague-Dawley rats underwent external fixator placement and fracture osteotomy of the left mandible. Two groups received pre-operative fractionated radiotherapy, and one of these groups was treated with DFO after fracture repair. After 40 days, the animals were perfused and imaged with micro-CT to calculate vascular radiomorphometrics.

RESULTS

In vitro, endothelial tubule formation assays demonstrated that DFO mitigated the deleterious effects of radiation on angiogenesis. Further, high-dose DFO cultures appeared to organize within 2h of incubation and achieved a robust network that was visibly superior to all other experimental groups in an accelerated fashion. In vivo, animals subjected to a human equivalent dose of radiotherapy (HEDR) and left mandibular fracture demonstrated quantifiably diminished μCT metrics of vascular density, as well as a 75% incidence of associated non-unions. The addition of DFO in this setting markedly improved vascularity as demonstrated with 3D angiographic modeling. In addition, we observed an increased incidence of bony unions in the DFO treated group when compared to radiated fractures without treatment (67% vs. 25% respectively).

CONCLUSION

Our data suggest that selectively targeting angiogenesis with localized DFO injections is sufficient to remediate the associated severe vascular diminution resulting from a HEDR. Perhaps the most consequential and clinically relevant finding was the ability to reduce the incidence of non-unions in a model where fracture healing was not routinely observed.

Angiogenesis is required for stress fracture healing in rats

Although angiogenesis and osteogenesis are critically linked, the importance of angiogenesis for stress fracture healing is unknown. In this study, mechanical loading was used to create a non-displaced stress fracture in the adult rat forelimb. Fumagillin, an anti-angiogenic agent, was used as the water soluble analogue TNP-470 (25mg/kg) as well as incorporated into lipid-encapsulated α(v)β(3) integrin targeted nanoparticles (0.25mg/kg). In the first experiment, TNP-470 was administered daily for 5 days following mechanical loading, and changes in gene expression, vascularity, and woven bone formation were quantified. Although no changes in vascularity were detected 3 days after loading, treatment-related downregulation of angiogenic (Pecam1) and osteogenic (Bsp, Osx) genes was observed at this early time point. On day 7, microCT imaging of loaded limbs revealed diminished woven bone formation in treated limbs compared to vehicle treated limbs. In the second experiment, α(v)β(3) integrin targeted fumagillin nanoparticles were administered as before, albeit with a 100-fold lower dose, and changes in vascularity and woven bone formation were determined. There were no treatment-related changes in vessel count or volume 3 days after loading, although fewer angiogenic (CD105 positive) blood vessels were present in treated limbs compared to vehicle treated limbs. This result manifested on day 7 as a reduction in total vascularity, as measured by histology (vessel count) and microCT (vessel volume). Similar to the first experiment, treated limbs had diminished woven bone formation on day 7 compared to vehicle treated limbs. These results indicate that angiogenesis is required for stress fracture healing, and may have implications for inducing rapid repair of stress fractures.

Stimulated angiogenesis for fracture healing augmented by low-magnitude, high-frequency vibration in a rat model-evaluation of pulsed-wave doppler, 3-D power Doppler ultrasonography and micro-CT microangiography

This study aimed to investigate the mechanism of low-magnitude high-frequency vibration (LMHFV) treatment on angiogenesis and blood flow for enhancement of fracture healing. Nine-month-old ovariectomized (OVX) and sham-operated (Sham) rats received closed fractures creation at the femora and were randomized into LMHFV treatment (Sham-V, OVX-V) or control (Sham-C, OVX-C) groups. Pulsed-wave Doppler indicated an increase in blood flow velocity of the femoral artery at weeks 2 (OVX pair: p = 0.030) and 4 (OVX pair: p = 0.012; Sham pair: p = 0.020) post-treatment. Significantly enhanced vascular volume (VV) at the fracture site in the vibration groups was demonstrated by 3-D high-frequency power Doppler at week 2 (Sham pair: p = 0.021) and micro-computed tomography (microCT) microangiography at weeks 2 (OVX pair: p = 0.009) and 4 (OVX pair: p = 0.034), which echoed the osteogenesis findings by radiographic and microCT analysis. VV in the OVX groups was inferior to the Sham groups. However, OVX-V showed higher percentages of angiogenic enhancement than Sham-V. Despite impaired neo-angiogenesis in osteoporotic fractures, LMHFV could increase blood flow and angiogenesis in both normal and osteoporotic fractures, thus enhancing fracture healing.

Quantification of skeletal blood flow and fluoride metabolism in rats using PET in a pre-clinical stress fracture model

PURPOSE

Blood flow is an important factor in bone production and repair, but its role in osteogenesis induced by mechanical loading is unknown. Here, we present techniques for evaluating blood flow and fluoride metabolism in a pre-clinical stress fracture model of osteogenesis in rats.

PROCEDURES

Bone formation was induced by forelimb compression in adult rats. (15)O water and (18)F fluoride PET imaging were used to evaluate blood flow and fluoride kinetics 7 days after loading. (15)O water was modeled using a one-compartment, two-parameter model, while a two-compartment, three-parameter model was used to model (18)F fluoride. Input functions were created from the heart, and a stochastic search algorithm was implemented to provide initial parameter values in conjunction with a Levenberg-Marquardt optimization algorithm.

RESULTS

Loaded limbs are shown to have a 26% increase in blood flow rate, 113% increase in fluoride flow rate, 133% increase in fluoride flux, and 13% increase in fluoride incorporation into bone as compared to non-loaded limbs (p < 0.05 for all results).

CONCLUSIONS

The results shown here are consistent with previous studies, confirming this technique is suitable for evaluating the vascular response and mineral kinetics of osteogenic mechanical loading.

Perfusion flow enhances osteogenic gene expression and the infiltration of osteoblasts and endothelial cells into three-dimensional calcium phosphate scaffolds

Maintaining cellular viability in vivo and in vitro is a critical issue in three-dimensional bone tissue engineering. While the use of osteoblast/endothelial cell cocultures on three-dimensional constructs has shown promise for increasing in vivo vascularization, in vitro maintenance of cellular viability remains problematic. This study used perfusion flow to increase osteogenic and angiogenic gene expression, decrease hypoxic gene expression, and increase cell and matrix coverage in osteoblast/endothelial cell co-cultures. Mouse osteoblast-like cells (MC3T3-E1) were cultured alone and in co-culture with mouse microvascular endothelial cells (EOMA) on three-dimensional scaffolds for 1, 2, 7, and 14 days with or without perfusion flow. mRNA levels were determined for several osteogenic, angiogenic, and hypoxia-related genes, and histological analysis was performed. Perfusion flow downregulated hypoxia-related genes (HIF-1α, VEGF, and OPN) at early timepoints, upregulated osteogenic genes (ALP and OCN) at 7 days, and downregulated RUNX-2 and VEGF mRNA at 14 days in osteoblast monocultures. Perfusion flow increased cell number, coverage of the scaffold perimeter, and matrix area in the center of scaffolds at 14 days. Additionally, perfusion flow increased the length of endothelial cell aggregations within co-cultures. These suggest perfusion stimulated co-cultures provide a means of increasing osteogenic and angiogenic activity.

The treatment of segmental bone defects in rabbit tibiae with vascular endothelial growth factor (VEGF)-loaded gelatin/hydroxyapatite "cryogel" scaffold

The aim of this study was to investigate the effectiveness of a novel hydroxyapatite containing gelatin scaffold--with and without local vascular endothelial growth factor (VEGF) administration--as the synthetic graft material in treatment of critical-sized bone defects. An experimental nonunion model was established by creating critical-sized (10 mm. in length) bone defects in the proximal tibiae of 30 skeletally mature New Zealand white rabbits. Following tibial intramedullary fixation, the rabbits were grouped into three: The defects were left empty in the first (control) group, the defects were grafted with synthetic scaffolds in the second group, and synthetic scaffolds loaded with VEGF were administered at bone defects in the third group. Five rabbits in each group were killed on 6th and 12th weeks, and new bone growth was assessed radiologically, histologically and with dual-energy X-ray absorptiometry (DEXA). At 6 weeks, VEGF-administered group had significantly better scores than the other two groups. The second group also had significantly better scores than the control group. At 12 weeks, while no significant difference was noted between the second and third groups, these two groups both had significantly better scores in all criteria compared with the control group. There were no signs of complete fracture healing in the control group. The administration of hydroxyapatite containing gelatin scaffold yielded favorable results in grafting the critical-sized bone defects in this experimental model. The local administration of VEGF on the graft had a positive effect in the early phase of fracture healing.

Leader genes in osteogenesis: a theoretical study

Little is still known about the molecular mechanisms involved in the process of osteogenesis. In this paper, the leader genes approach, a new bioinformatics method which has already been experimentally validated, is adopted in order to identify the genes involved in human osteogenesis. Interactions among genes are then calculated and genes are ranked according to their relative importance in this process. In total, 167 genes were identified as being involved in osteogenesis. Genes were divided into 4 groups, according to their main function in the osteogenic processes: skeletal development; cell adhesion and proliferation; ossification; and calcium ion binding. Seven genes were consistently identified as leader genes (i.e. the genes with the greatest importance in osteogenesis), while 14 were found to have slightly less importance (class B genes). It was interesting to notice that the larger part of leader and class B genes belonged to the cell adhesion and proliferation or to the ossification sub-groups. This finding suggested that these two particular sub-processes could play a more important role in osteogenesis. Moreover, among the 7 leader genes, it is interesting to notice that RUNX2, BMP2, SPARC, PTH play a direct role in bone formation, while the 3 other leader genes (VEGF, IL6, FGF2) seem to be more connected with an angiogenetic process. Twenty-nine genes have no known interactions (orphan genes). From these results, it may be possible to plan an ad hoc experimentation, for instance by microarray analyses, focused on leader, class B and orphan genes, with the aim to shed new light on the molecular mechanisms underlying osteogenesis.

Angiogenic microRNA-210 is present in cells surrounding osteonecrosis

A role of microRNAs (miRNAs), which are ≈ 22-nucleotide non-coding RNAs, has recently been recognized in human diseases. The objective of this study was to identify the expression pattern of miRNA (miR)-210, known to be associated with angiogenesis, in bone from patients with osteonecrosis (ON) of the femoral head. The expression of miR-210 in bone from 10 patients with osteoarthritis (OA) of the hip and ten with ON was analyzed by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and by in situ hybridization. In addition, immunohistochemical staining for von Willebrand factor (vWF) and vascular endothelial growth factor (VEGF) was performed to identify the miR-210 expressing cells. We found that in ON samples, the expression of mature, primary miR-210, VEGF, matrix metalloproteinase (MMP)-2, and MMP-7 was significantly higher than that of OA samples. Section in situ hybridization of mature miR-210 revealed that mature miR-210 is expressed around the necrotic area. vWF and VEGF were also strongly expressed in the miR-210 expressing cells. This study shows that miR-210 is intensely expressed in ON, and might play a role in ON pathogenesis. The present study provides a solid basis for further functional analyses of miRNAs in ON.

An emerging cell-based strategy in orthopaedics: endothelial progenitor cells

PURPOSE

The purpose of this article was to analyze the results of studies in the literature, which evaluated the use of endothelial progenitor cells (EPCs) as a cell-based tissue engineering strategy.

METHODS

EPCs have been successfully used in regenerative medicine to augment neovascularization in patients after myocardial infarction and limb ischemia. EPCs' important role as vasculogenic progenitors presents them as a potential source for cell-based therapies to promote bone healing.

RESULTS

EPCs have been shown to have prominent effects in promoting bone regeneration in several animal models. Evidence indicates that EPCs promote bone regeneration by stimulating both angiogenesis and osteogenesis through a differentiation process toward endothelial cell lineage and formation of osteoblasts. Moreover, EPCs increase vascularization and osteogenesis by increased secretion of growth factors and cytokines through paracrine mechanisms.

CONCLUSION

EPCs offer the potential to emerge as a new strategy among other cell-based therapies to promote bone regeneration. Further investigations and human trials are required to address current questions with regard to biology and mechanisms of action of EPCs in bone tissue engineering.

Difference in intraosseous blood vessel volume and number in osteoporotic model mice induced by spinal cord injury and sciatic nerve resection

In the present study, we examined intraosseous blood vessel parameters of the tibial metaphysis in mice using microcomputed tomography (µCT) to investigate the relationship between post-nerve-injury osteoporosis and local intraosseous blood vessel volume and number. Mice were randomly divided into groups receiving spinal cord injury (SCI), sciatic nerve resection group (NX), or intact controls (30 mice/group). Four weeks after surgery, mice were perfused with silicone and the distribution of intraosseous blood vessels analyzed by μCT. The bone density, μCT microstructure, biomechanical properties, and the immunohistochemical and biochemical indicators of angiogenesis were also measured. The SCI group showed significantly reduced tibial metaphysis bone density, μCT bone microstructure, tibial biomechanical properties, indicators of angiogenesis, and intraosseous blood vessel parameters compared to the NX group. Furthermore, the spinal cord-injured mice exhibited significantly decreased intraosseous blood vessel volume and number during the development of osteoporosis. In conclusion, these data suggest that decreased intraosseous blood vessel volume and number may play an important role in the development of post-nerve-injury osteoporosis.

Dental implant failure associated with bacterial infection and long-term bisphosphonate usage: a case report

Although the risk of developing osteonecrosis of the jaw for oral implants in patients using oral bisphosphonates (BPs) is low, the devastating complications still require caution. We document a case of severe periimplant infection that developed after the patient had used oral BPs for 3 years. Exposed bone and osteonecrosis persisted for more than 2 months after 1 infected implant was explanted by a dentist unaware that the patient was taking BPs. After oral BPs had been stopped, another involved implant was explanted, sequestra were removed, a primary closure was sutured, and the antibiotic was changed; then the wound was finally under control. The explanted implant with attached bone was processed for undecalcified ground sections, and specimens from the bony lesion were sent to pathology for examination. Osteonecrosis, severe inflammatory osteolysis, and heavy bacterial colonization were found. Patients at risk must be alerted about the potential risks of implant failure and developing BP-related osteonecrosis of the jaw.

Deferoxamine enhances the vascular response of bone regeneration in mandibular distraction osteogenesis

BACKGROUND

Bone regeneration during distraction osteogenesis is intricately associated with an enhanced vascular response. Augmenting this response may offer considerable clinical advantages such as optimizing the quality of regenerate formation, decreasing lengthy consolidation periods, or increasing regenerate size and distance. Using deferoxamine, an angiogenic transcriptional activator, the authors posit that substantial increases in vascular volume beyond the normal response to mechanical distraction can be quantified with micro-computed tomography after vessel perfusion during mandibular distraction osteogenesis.

METHODS

Two groups of Sprague-Dawley rats (n = 12) underwent external fixator placement, mandibular osteotomy, and 5.1-mm distraction. During distraction, the experimental group (n = 6) was treated with deferoxamine injections into the distraction gap. After consolidation, the animals were perfused and imaged with micro-computed tomography. Vascular radiomorphometrics were calculated and statistical comparison was conducted with the independent samples t test. A value of p ≤ 0.05 was considered statistically significant.

RESULTS

A 40 percent statistically significant increase in the number of vessels (0.82 vessels/mm versus 1.15 vessels/mm; p < 0.012) and a complementary decrease in the space between vessels (1.18 mm versus 0.86 mm; p < 0.012) were calculated in the experimental regenerate when compared with controls. This robust increase in vascularity could also be readily observed with micro-computed tomographic image reconstruction. Gross examination revealed a denser regenerate in the deferoxamine-injected group that is clearly illustrated with Faxitron radiography.

CONCLUSION

The authors' study quantifies the ability of deferoxamine to augment the vascular response of mandibular distraction osteogenesis and establishes correlations between this therapeutic enrichment and enhanced regenerate formation.

Increased exercise after stable closed fracture fixation does not affect fracture healing in mice

PURPOSE

The aim of the present study was to evaluate the systemic biological effect of increased exercise on bone repair after stable fracture fixation.

METHODS

Two groups of SKH-1h mice were studied. Animals of the first group (n=36) were housed in cages supplied with a running wheel, while mice of the second group (n=37) were housed in standard cages for control. Using a closed femur fracture model, bone repair was analysed by histomorphometry and biomechanical testing at 2 and 5 weeks. At 2 weeks, we additionally evaluated the expression of the proliferation marker PCNA (proliferating cell nuclear antigen) and the angiogenic and osteogenic growth factor VEGF (vascular endothelial growth factor). To standardise the mechanical conditions in the fracture gap, we used an intramedullary compression screw for stable fracture fixation.

RESULTS

Each mouse of the exercise group run a mean total distance of 23.5 km after 2 weeks and 104.3 km after 5 weeks. Histomorphometric analysis of the size and tissue composition of the callus could not reveal significant differences between mice undergoing exercise and controls. Accordingly, biomechanical testing showed a comparable torsional stiffness, peak rotation angle, and load at failure of the healing bones in the two groups. The expression of PCNA and VEGF did also not differ between mice of the exercise group and controls.

CONCLUSION

We conclude that increased exercise does not affect bone repair after stable fracture fixation.

Bone Substitute Effect on Vascularization and Bone Remodeling after Application of phVEGF165 Transfected BMSC

VEGF (vascular endothelial growth factor) promotes vascularization and remodeling of bone substitutes. The aim of this study was to examine the effect of distinct resorbable ceramic carriers on bone forming capacities of VEGF transfected bone marrow stromal cells (BMSC). A critical size defect of the radius in rabbits was filled either by a low surface scaffold called beta-TCP (tricalciumphsphate) or the high surface scaffold CDHA (calcium deficient hydroxy-apatite) loaded with autologous BMSC, which were either transfected with a control plasmid or a plasmid coding for phVEGF165. They were compared to unloaded scaffolds. Thus, six treatment groups (n = 6 in each group) were followed by X-ray over 16 weeks. After probe retrieval, the volume of new bone was measured by micro-CT scans and vascularization was assessed in histology. While only minor bone formation was found in both carriers when implanted alone, BMSC led to increased osteogenesis in both carriers. VEGF promoted vascularization of the scaffolds significantly in contrast to BMSC alone. Bone formation was increased in the beta-TCP group, whereas it was inhibited in the CDHA group that showed faster scaffold degradation. The results indicate that the interaction of VEGF transfected BMSC with resorbable ceramic carrier influences the ability to promote bone healing.

Micro-CT observation of angiogenesis in bone regeneration

OBJECTIVES

Restoration of an adequate blood supply is essential for the bone healing process and is key to the success of bone augmentation procedures. In this study, we evaluated angiogenesis in rat calvarial flat bone defects using in vivo microfocus computed tomography (micro-CT).

MATERIALS AND METHODS

Twenty rats were used. The calvarium was exposed and calvarial bone defects of critical (5-mm diameter) and non-critical (2.7-mm diameter) sizes were prepared. Bone regeneration and angiogenesis were evaluated by image analysis using micro-CT and histological examination.

RESULTS

Critical- and non-critical-sized calvarial bone defects showed bone regeneration and angiogenesis around the midsagittal suture. Critical-sized calvarial bone defects showed approximately 1.2% reossification of the original surgical defect, whereas the non-critical-sized defects showed approximately 43.3% reossification at day 28. Furthermore, angiogenesis was observed later in the critical-sized calvarial bone defects (about 38.2%), whereas angiogenesis was observed early in the non-critical-sized calvarial bone defects (about 75.5%) at day 28. New blood vessel networks were observed around defects of both sizes.

CONCLUSIONS

Angiogenesis preceded bone regeneration around critical- and non-critical-sized calvarial bone defects. Angiogenesis led to full bone formation in non-critical-sized defects.

Sonic Hedgehog-activated engineered blood vessels enhance bone tissue formation

Large bone defects naturally regenerate via a highly vascularized tissue which progressively remodels into cartilage and bone. Current approaches in bone tissue engineering are restricted by delayed vascularization and fail to recapitulate this stepwise differentiation toward bone tissue. Here, we use the morphogen Sonic Hedgehog (Shh) to induce the in vitro organization of an endothelial capillary network in an artificial tissue. We show that endogenous Hedgehog activity regulates angiogenic genes and the formation of vascular lumens. Exogenous Shh further induces the in vitro development of the vasculature (vascular lumen formation, size, distribution). Upon implantation, the in vitro development of the vasculature improves the in vivo perfusion of the artificial tissue and is necessary to contribute to, and enhance, the formation of de novo mature bone tissue. Similar to the regenerating callus, the artificial tissue undergoes intramembranous and endochondral ossification and forms a trabecular-like bone organ including bone-marrow-like cavities. These findings open the door for new strategies to treat large bone defects by closely mimicking natural endochondral bone repair.

Effects of adipose tissue stem cell concurrent with greater omentum on experimental long-bone healing in dog

Repair of large bone defects resulting from trauma, tumors, and osteitis is a current challenge to surgeons. Adipose-derived adult stem cells (ASCs) are multipotent cells that are able to differentiate into osteoblasts in the presence of certain factors. In this study, the role of greater omentum as a scaffold incorporation of ASCs was evaluated in long-bone defect healing in dog model. Sixteen 3-4-year-old, male adult mongrel dogs, weighing 25.2 ± 3.5 kg, were used in this study. In the control group (n = 4), the defect was left empty. In the omental group (n = 4), the defect was filled with harvested omentum. In the omental-ASCs group (n = 4), the defect was filled with omentum and 1 mL of ASCs was injected into the grafted omentum. In the omental-culture medium group (n = 4), 1 mL of culture medium was injected into the grafted omentum. Finally, the injured radial bones were fixed with plate and screw. Radiographs of each forelimb was taken postoperatively on the first day and at the second, fourth, sixth, and eighth weeks postinjury to evaluate bone formation, union, and remodeling of the defect. The operated radii were removed on the 56th postoperative day and were histopathologically evaluated. In this study, both omental-culture medium and omental-ASCs groups demonstrated superior osteogenic potential in healing the radial bone defect. Compared to those of the omental and control groups, more advanced bone healing criteria were present in the omental-culture medium and omental-ASCs groups at radiological and histopathological levels at 8 weeks postsurgery.

Rapid Heterotrophic Ossification with Cryopreserved Poly(ethylene glycol-) Microencapsulated BMP2-Expressing MSCs

Autologous bone grafting is the most effective treatment for long-bone nonunions, but it poses considerable risks to donors, necessitating the development of alternative therapeutics. Poly(ethylene glycol) (PEG) microencapsulation and BMP2 transgene delivery are being developed together to induce rapid bone formation. However, methods to make these treatments available for clinical applications are presently lacking. In this study we used mesenchymal stem cells (MSCs) due to their ease of harvest, replication potential, and immunomodulatory capabilities. MSCs were from sheep and pig due to their appeal as large animal models for bone nonunion. We demonstrated that cryopreservation of these microencapsulated MSCs did not affect their cell viability, adenoviral BMP2 production, or ability to initiate bone formation. Additionally, microspheres showed no appreciable damage from cryopreservation when examined with light and electron microscopy. These results validate the use of cryopreservation in preserving the viability and functionality of PEG-encapsulated BMP2-transduced MSCs.

Bone regeneration in distraction osteogenesis demonstrates significantly increased vascularity in comparison to fracture repair in the mandible

BACKGROUND

Tissue analysis of bone regenerate has suggested an intense vascular response after mandibular distraction osteogenesis (DO). Quantifying and three-dimensionally imaging this vascular response could be of immense clinical import in efforts to advance the utility of bone regeneration and repair. Conventional quantification of vascular responses has heretofore focused on inexact, cumbersome measurements of blood flow and histologic vessel counting. Using micro-computed tomography after vessel perfusion, we posit that quantitative vascular metrics will be significantly higher in mandibular DO compared with those observed in fracture repair (FxR) after bony union.

METHODS

Sprague-Dawley rats underwent mandibular osteotomy and external fixator placement. A DO group (n=9) underwent a 5.1-mm distraction, whereas a FxR group (n=12) had a 2.1-mm fixed gap set. Forty days after surgery, Microfil was perfused into the vasculature, and imaging ensued. Vascular radiomorphometrics were calculated for the regions of interest. Independent-samples t-test was performed for comparison, with statistical significance set at P≤0.05.

RESULTS

Stereological analysis demonstrated statistically significant increases in the distracted vasculature compared with fracture repair: vessel volume fraction (5.4% versus 2.8%, P=0.030) and vessel number (0.86 versus 0.50 mm, P=0.014).

CONCLUSIONS

We report robust and quantifiable increases in vascular density in DO compared with FxR. Our findings support a significant distinction between the regenerative processes of mandibular DO from the reparative mechanisms controlling fracture healing. A better understanding of the differences between the 2 types of bone formation may enable clinicians to selectively optimize therapeutic outcomes in the future.

Diabetes mellitus negatively affects peri-implant bone formation in the diabetic domestic pig

AIM

Diabetes mellitus is classified as a relative contraindication for implant treatment, and higher failure rates have been seen in diabetic patients. The aim of the present study was to investigate the effect of diabetes on peri-implant bone formation in an animal model of human bone repair.

MATERIALS AND METHODS

Diabetes was induced by an intra-venous application of streptozotocin (90 mg/kg) in 15 domestic pigs. Implants were placed after significant histopathological changes in the hard and soft tissues were verified. The bone-implant contact (BIC), peri-implant bone mineral density (BMD), and expression of collagen type-I and osteocalcin proteins were qualitatively evaluated 4 and 12 weeks after implantation. Fifteen animals served as healthy controls.

RESULTS

Diabetes caused pathological changes in the soft and hard tissues. The BIC and BMD were significantly reduced in the diabetic group after 4 and 12 weeks. Collagen type-I was increased in the diabetic group at both time points, whereas osteocalcin was reduced in the diabetic group.

CONCLUSIONS

Poorly controlled diabetes negatively affects peri-implant bone formation and bone mineralization. These findings have to be taken into consideration for diabetic patients with an indication for implant therapy.