Stimulation of bone formation by intraosseous application of recombinant basic fibroblast growth factor in normal and ovariectomized rabbits

Implantable Electrical Stimulation at Dorsal Root Ganglions Accelerates Osteoporotic Fracture Healing via Calcitonin Gene-Related Peptide

The neuronal engagement of the peripheral nerve system plays a crucial role in regulating fracture healing, but how to modulate the neuronal activity to enhance fracture healing remains unexploited. Here it is shown that electrical stimulation (ES) directly promotes the biosynthesis and release of calcitonin gene-related peptide (CGRP) by activating Ca2+ /CaMKII/CREB signaling pathway and action potential, respectively. To accelerate rat femoral osteoporotic fracture healing which presents with decline of CGRP, soft electrodes are engineered and they are implanted at L3 and L4 dorsal root ganglions (DRGs). ES delivered at DRGs for the first two weeks after fracture increases CGRP expression in both DRGs and fracture callus. It is also identified that CGRP is indispensable for type-H vessel formation, a biological event coupling angiogenesis and osteogenesis, contributing to ES-enhanced osteoporotic fracture healing. This proof-of-concept study shows for the first time that ES at lumbar DRGs can effectively promote femoral fracture healing, offering an innovative strategy using bioelectronic device to enhance bone regeneration.

Acceleration of Bone Healing by In Situ-Forming Dextran-Tyramine Conjugates Containing Basic Fibroblast Growth Factor in Mice

An enzymatic crosslinking strategy using hydrogen peroxide (H₂O₂) and horseradish peroxidase (HRP) has been receiving increasing attention for use with in situ-formed hydrogels (IFHs). Several studies have reported the application of IFHs in cell delivery and tissue engineering. IFHs may also be ideal carrier materials for bone repair, although their potential as a carrier for basic fibroblast growth factor (bFGF) has yet to be evaluated. Here, we examined the effect of an IFH made of dextran (Dex)-tyramine (TA) conjugates (IFH-Dex-TA) containing bFGF in promoting bone formation in a fracture model in mice. Immediately following a fracture procedure, animals either received no treatment (control) or an injection of IFH-Dex-TA/phosphate-buffered saline (IFH-Dex-TA/PBS) or IFH-Dex-TA containing 1 μg bFGF (IFH-Dex-TA/bFGF) into the fracture site (n=10, each treatment). Fracture sites injected with IFH-Dex-TA/bFGF showed significantly greater bone volume, mineral content, and bone union than sites receiving no treatment or treated with IFH-Dex-TA/PBS alone (each n=10). This Dex-TA gel may be an effective drug delivery system for optimizing bFGF therapy.

Autologous bone grafts with MSCs or FGF-2 accelerate bone union in large bone defects

BACGROUND

Although the contribution of fibroblast growth factor (FGF)-2 and mesenchymal stromal cells (MSCs) to bone formation is well known, few studies have investigated the combination of an autologous bone graft with FGF-2 or MSCs for large bone defects.

METHODS

We studied an atrophic non-union model with a large bone defect, created by resecting a 10-mm section from the center of each femoral shaft of 12-week-old Sprague-Dawley rats. The periosteum of the proximal and distal ends of the femur was cauterized circumferentially, and excised portions were used in the contralateral femur as autologous bone grafts. The rats were randomized to three groups and given no further treatment (group A), administered FGF-2 at 20 μg/20 μL (group B), or 1.0 × 10⁶ MSCs (group C). Radiographs were taken every 2 weeks up to 12 weeks, with CT performed at 12 weeks. Harvested femurs were stained with toluidine blue and evaluated using radiographic and histology scores.

RESULTS

Radiographic and histological evaluation showed that bone union had been achieved at 12 weeks in group C, while group B showed callus formation and bridging callus but non-union, and in group A, callus formation alone was evident. Both radiographic and histological scores were significantly higher at 2, 4, 6, 8, 10, and 12 weeks in groups B and C than group A and also significantly higher in group C than group B at 12 weeks.

CONCLUSIONS

These data suggest that autologous bone grafts in combination with MSCs benefit difficult cases which cannot be treated with autologous bone grafts alone.

Long-term Observation of Regenerated Periodontium Induced by FGF-2 in the Beagle Dog 2-Wall Periodontal Defect Model

The long-term stability and qualitative characteristics of periodontium regenerated by FGF-2 treatment were compared with normal physiological healing tissue controls in a Beagle dog 2-wall periodontal defect model 13 months after treatment by assessing tissue histology and three-dimensional microstructure using micro-computed tomography (μCT). After FGF-2 (0.3%) or vehicle treatment at the defect sites, serial changes in the bone mineral content (BMC) were observed using periodic X-ray imaging. Tissues were harvested at 13 months, evaluated histomorphometrically, and the cortical bone volume and trabecular bone structure of the newly formed bone were analyzed using μCT. FGF-2 significantly increased the BMC of the defect area at 2 months compared with that of the control group, and this difference was unchanged through 13 months. The cortical bone volume was significantly increased by FGF-2, but there was no difference between the groups in trabecular bone structure. Bone maturation was occurring in both groups because of the lower cortical volume and denser trabecular bone than what is found in intact bone. FGF-2 also increased the area of newly formed bone as assessed histomorphometrically, but the ratios of trabecular bone in the defect area were similar between the control and FGF-2 groups. These results suggest that FGF-2 stimulates neogenesis of alveolar bone that is of similar quality to that of the control group. The lengths of the regenerated periodontal ligament and cementum, measured as the distance from the defect bottom to the apical end of the gingival epithelium, and height and area of the newly formed bone in the FGF-2 group were larger than those in the control group. The present study demonstrated that, within the limitation of artificial periodontal defect model, the periodontal tissue regenerated by FGF-2 was maintained for 13 months after treatment and was qualitatively equivalent to that generated through the physiological healing process.

FGF-2 promotes initial osseointegration and enhances stability of implants with low primary stability

OBJECTIVES

The aim of this study was to examine the effect of basic fibroblast growth factor (FGF-2) on osseointegration of dental implants with low primary stability in a beagle dog model.

MATERIALS AND METHODS

Customized titanium implants that were designed to have low contact with the existing bone were installed into the edentulous mandible of beagle dogs. To degrade the primary stability of the implants, the diameters of the bone sockets exceeded the implant diameters. FGF-2 (0.3%) plus vehicle (hydroxypropyl cellulose) or vehicle alone was topically applied to the sockets in the FGF-2 and control groups, respectively. In Study 1, the new bone area and length of new bone-to-implant contact (BIC) were evaluated at 4, 8, and 12 weeks after installation using histomorphometry and scanning electron microscopy. In Study 2, the implant stability quotient (ISQ) values were sequentially measured for 16 weeks using an Osstell system.

RESULTS

The histomorphometric analysis revealed that the new bone area and length of BIC in the FGF-2 group were significantly larger than those in the control group at 4 weeks. Electron microscopic observation showed intimate contact between the mature lamellar bone and the implant surfaces, osseointegration, in both groups. The ISQ values in the FGF-2 group were significantly increased from 6 to 16 weeks compared with those in the control group.

CONCLUSIONS

Taken together, our study demonstrates that FGF-2 promoted new bone formation around the dental implants and subsequent osseointegration, resulting in promotion of stability of implants with low primary stability.

Local drug delivery for enhancing fracture healing in osteoporotic bone

Fragility fractures can cause significant morbidity and mortality in patients with osteoporosis and inflict a considerable medical and socioeconomic burden. Moreover, treatment of an osteoporotic fracture is challenging due to the decreased strength of the surrounding bone and suboptimal healing capacity, predisposing both to fixation failure and non-union. Whereas a systemic osteoporosis treatment acts slowly, local release of osteogenic agents in osteoporotic fracture would act rapidly to increase bone strength and quality, as well as to reduce the bone healing period and prevent development of a problematic non-union. The identification of agents with potential to stimulate bone formation and improve implant fixation strength in osteoporotic bone has raised hope for the fast augmentation of osteoporotic fractures. Stimulation of bone formation by local delivery of growth factors is an approach already in clinical use for the treatment of non-unions, and could be utilized for osteoporotic fractures as well. Small molecules have also gained ground as stable and inexpensive compounds to enhance bone formation and tackle osteoporosis. The aim of this paper is to present the state of the art on local drug delivery in osteoporotic fractures. Advantages, disadvantages and underlying molecular mechanisms of different active species for local bone healing in osteoporotic bone are discussed. This review also identifies promising new candidate molecules and innovative approaches for the local drug delivery in osteoporotic bone.

Sustained delivery of biomolecules from gelatin carriers for applications in bone regeneration

Local delivery of therapeutic biomolecules to stimulate bone regeneration has matured considerably during the past decades, but control over the release of these biomolecules still remains a major challenge. To this end, suitable carriers that allow for tunable spatial and temporal delivery of biomolecules need to be developed. Gelatin is one of the most widely used natural polymers for the controlled and sustained delivery of biomolecules because of its biodegradability, biocompatibility, biosafety and cost–effectiveness. The current study reviews the applications of gelatin as carriers in form of bulk hydrogels, microspheres, nanospheres, colloidal gels and composites for the programmed delivery of commonly used biomolecules for applications in bone regeneration with a specific focus on the relationship between carrier properties and delivery characteristics.

The dual face of parathyroid hormone and prostaglandins in the osteoimmune system

The microenvironment of bone marrow, an extraordinarily heterogeneous and dynamic system, is populated by bone and immune cells, and its functional dimension has been at the forefront of recent studies in the field of osteoimmunology. The interaction of both marrow niches supports self-renewal, differentiation, and homing of the hematopoietic stem cells and provides the essential regulatory molecules for osteoblast and osteoclast homeostasis. Impaired signaling within the niches results in a pathological tableau and enhances disease, including osteoporosis and arthritis, or the rejection of hematopoietic stem cell transplants. Discovering the anabolic players that control these mechanisms has become warranted. In this review, we focus on parathyroid hormone (PTH) and prostaglandins (PGs), potent molecular mediators, both of which carry out a multitude of functions, particularly in bone lining cells and T cells. These two regulators proved to be promising therapeutic agents when strictly clinical protocols on dose treatments were applied.

Acceleration of periosteal bone formation by human basic fibroblast growth factor containing a collagen-binding domain from Clostridium histolyticum collagenase

Basic fibroblast growth factor 2 (bFGF) is a potent mitogen for mesenchymal cells, and the local application of recombinant bFGF accelerates bone union and defect repair. However, repeated dosing is required for sustained therapeutic effect as the efficacy of bFGF decreases rapidly following its diffusion from bone defect sites. Here, we attempted to develop a collagen-based bone formation system using a fusion protein (collagen binding-bFGF, CB-bFGF) consisting of bFGF and the collagen-binding domain (CBD) of Clostridium histolyticum collagenase. The addition of the CBD to bFGF did not modify its native biological activity, as shown by the capacity of the fusion protein to promote the in vitro proliferation of periosteal mesenchymal cells. The affinity of the fusion protein towards collagen and demineralized bone matrix (DBM) was also confirmed by collagen-binding assays. Moreover, in vivo periosteal bone formation assays showed that the combination of CB-bFGF with a collagen sheet induced periosteal bone formation at protein concentrations lower than those required for bFGF alone. In addition, grafts of DBM loaded with CB-bFGF accelerated new bone formation in rat femurs compared to the same concentration of bFGF administered alone. Taken together, these properties suggest that the CB-bFGF/collagen composite is a promising material for bone repair in the clinical setting.

Erythroid promoter confines FGF2 expression to the marrow after hematopoietic stem cell gene therapy and leads to enhanced endosteal bone formation

Fibroblast growth factor-2 (FGF2) has been demonstrated to be a promising osteogenic factor for treating osteoporosis. Our earlier study shows that transplantation of mouse Sca-1(+) hematopoietic stem/progenitor cells that are engineered to express a modified FGF2 leads to considerable endosteal/trabecular bone formation, but it also induces adverse effects like hypocalemia and osteomalacia. Here we report that the use of an erythroid specific promoter, β-globin, leads to a 5-fold decrease in the ratio of serum FGF2 to the FGF2 expression in the marrow cavity when compared to the use of a ubiquitous promoter spleen focus-forming virus (SFFV). The confined FGF2 expression promotes considerable trabeculae bone formation in endosteum and does not yield anemia and osteomalacia. The avoidance of anemia in the mice that received Sca1(+) cells transduced with FGF2 driven by the β-globin promoter is likely due to attenuation of high-level serum FGF2-mediated stem cell mobilization observed in the SFFV-FGF2 animals. The prevention of osteomalacia is associated with substantially reduced serum Fgf23/hypophosphatemia, and less pronounced secondary hyperparathyroidism. Our improved stem cell gene therapy strategy represents one step closer to FGF2-based clinical therapy for systemic skeletal augmentation.

Dynamic compressive loading of image-guided tissue engineered meniscal constructs

This study investigated the hypothesis that dynamic compression loading enhances tissue formation and increases mechanical properties of anatomically shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were seeded in 2%w/v alginate, crosslinked with CaSO(4), injected into μCT based molds, and post crosslinked with CaCl(2). Samples were loaded via a custom bioreactor with loading platens specifically designed to load anatomically shaped constructs in unconfined compression. Based on the results of finite element simulations, constructs were loaded under sinusoidal displacement to yield physiological strain levels. Constructs were loaded 3 times a week for 1 h followed by 1 h of rest and loaded again for 1 h. Constructs were dynamically loaded for up to 6 weeks. After 2 weeks of culture, loaded samples had 2-3.2 fold increases in the extracellular matrix (ECM) content and 1.8-2.5 fold increases in the compressive modulus compared with static controls. After 6 weeks of loading, glycosaminoglycan (GAG) content and compressive modulus both decreased compared with 2 week cultures by 2.3-2.7 and 1.5-1.7 fold, respectively, whereas collagen content increased by 1.8-2.2 fold. Prolonged loading of engineered constructs could have altered alginate scaffold degradation rate and/or initiated a catabolic cellular response, indicated by significantly decreased ECM retention at 6 weeks compared with 2 weeks. However, the data indicates that dynamic loading had a strikingly positive effect on ECM accumulation and mechanical properties in short term culture.

Influence of internal fixator stiffness on murine fracture healing: two types of fracture healing lead to two distinct cellular events and FGF-2 expressions

This study aimed to clarify the relationship between the mechanical environment at the fracture site and endogenous fibroblast growth factor-2 (FGF-2). We compared two types of fracture healing with different callus formations and cellular events using MouseFix(TM) plate fixation systems for murine fracture models. Left femoral fractures were induced in 72 ten-week-old mice and then fixed with a flexible (Group F) or rigid (Group R) Mouse Fix(TM) plate. Mice were sacrificed on days 3, 5, 7, 10, 14, and 21. The callus volumes were measured by 3D micro-CT and tissues were histologically stained with hematoxylin & eosin or safranin-O. Sections from days 3, 5, and 7 were immunostained for FGF-2 and Proliferating Cell Nuclear Antigen (PCNA). The callus in Group F was significantly larger than that in Group R. The rigid plate allowed bone union without a marked external callus or chondrogenesis. The flexible plate formed a large external callus as a result of endochondral ossification. Fibroblastic cells in the granulation tissue on days 5 and 7 in Group F showed marked FGF-2 expression compared with Group R. Fibroblastic cells showed ongoing proliferation in granulation tissue in group F, as indicated by PCNA expression, which explained the relative granulation tissue increase in group F. There were major differences in early phase endogenous FGF-2 expression between these two fracture healing processes, due to different mechanical environments.

A local application of recombinant human fibroblast growth factor 2 for tibial shaft fractures: A randomized, placebo-controlled trial

Fibroblast growth factor 2 (FGF-2) is a potent mitogen for mesenchymal cells, and a local application of recombinant human FGF-2 (rhFGF-2) in a gelatin hydrogel has been reported to accelerate bone union in our animal studies and preparatory dose-escalation trial on patients with surgical osteotomy. We have performed a randomized, double-blind, placebo-controlled trial in which patients with fresh tibial shaft fractures of transverse or short oblique type were randomly assigned to three groups receiving a single injection of the gelatin hydrogel containing either placebo or 0.8 mg (low-dosage group) or 2.4 mg (high-dosage group) of rhFGF-2 into the fracture gap at the end of an intramedullary nailing surgery. Of 194 consecutive patients over 2 years, 85 met the eligibility criteria, and 70 (24 in the placebo group and 23 each in low- and high-dosage groups) completed the 24-week study. The cumulative percentages of patients with radiographic bone union were higher in the rhFGF-2-treated groups (p = .031 and .009 in low- and high-dosage group, respectively) compared with the placebo group, although there was no significant difference between low- and high-dosage groups (p = .776). At 24 weeks, 4, 1, and 0 patients in the placebo, low-dosage, and high-dosage groups, respectively, continued to show delayed union. No patient underwent a secondary intervention, and the time to full weight bearing without pain was not significantly different among the three groups (p = .567). There also was no significant difference in the profiles of adverse events among the groups. In conclusion, a local application of the rhFGF-2 hydrogel accelerated healing of tibial shaft fractures with a safety profile.

Different endogenous threshold levels of Fibroblast Growth Factor-ligands determine the healing potential of frontal and parietal bones

In the skull vault, neural crest derived frontal bones have an increased healing capacity and higher expression levels of Fibroblast Growth Factor-ligands as compared to mesoderm-derived parietal bones. Thus, we asked whether Fibroblast Growth Factor-ligands are responsible for the superior healing potential of frontal bones. Parietal defects in juvenile and adult mice treated with Fibroblast Growth Factor-2, -9 and -18 showed increased bone regeneration, comparable to frontal defects. Immunohistochemistry revealed increased recruitment of osteoprogenitors and activation of FGF-signaling pathways in FGF-treated parietal defects. Conversely, calvarial defects in Fgf-9(+/-) and Fgf-18(+/-) mice showed impaired calvarial healing which could be rescued by exogenous Fibroblast Growth Factor-ligands. Moreover, by utilizing Wnt1Cre/R26R mice, the migration and contribution of dura mater and pericranium cells to calvarial healing could be demonstrated. Taken together our results demonstrated that different endogenous threshold levels of Fibroblast Growth Factor-ligands in frontal and parietal bones have a profound impact on calvarial regeneration. The present study thereby opens new avenues for translational medicine.

Effect of media mixing on ECM assembly and mechanical properties of anatomically-shaped tissue engineered meniscus

This study investigated the hypothesis that controlled media mixing will enhance tissue formation and increase mechanical properties of anatomically-shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were seeded in 2% w/v alginate, cross-linked with 0.02 g/mL CaSO(4), and injected into molds of menisci. Engineered menisci were incubated for up to 6 weeks. A mixing media bioreactor was designed to ensure proper mixing of culture medium while protecting constructs from the spinning impeller. Impeller speeds were calibrated to produce Reynolds number (Re) of 0.5, 2.9, 5.8, 10.2, and 21.8. Constructs were divided a tested in confined compression and in tension to determine the equilibrium and tensile moduli, respectively. Media stimulation resulted in a 2-5 fold increase in mechanical properties and a 2-3 fold increase in matrix accumulation in constructs over 6 weeks in culture. Benefits from mixing stimulation for collagen accumulation and compressive modulus appeared to peak near Re 2.9, and decreased with increased mixing intensity. This study suggests that fluid mixing can be optimized to enhance mechanical properties of anatomically-shaped engineered constructs.

Craniofacial surgery, from past pioneers to future promise

OBJECTIVES

As a surgical subspecialty devoted to restoration of normal facial and calvarial anatomy, craniofacial surgeons must navigate the balance between pathologic states of bone excess and bone deficit. While current techniques employed take root in lessons learned from the success and failure of early pioneers, craniofacial surgery continues to evolve, and novel modalities will undoubtedly arise integrating past and present experiences with future promise to effectively treat craniofacial disorders.

METHODS

This review provides an overview of current approaches in craniofacial surgery for treating states of bone excess and deficit, recent advances in our understanding of the molecular and cellular processes underlying craniosynostosis, a pathological state of bone excess, and current research efforts in cellular-based therapies for bone regeneration.

RESULTS

The surgical treatment of bone excess and deficit has evolved to improve both the functional and morphological outcomes of affected patients. Recent progress in elucidating the molecular and cellular mechanisms governing bone formation will be instrumental for developing improved therapies for the treatment of pathological states of bone excess and deficit.

CONCLUSIONS

While significant advances have been achieved in craniofacial surgery, improved strategies for addressing states of bone excess and bone deficit in the craniofacial region are needed. Investigations on the biomolecular events involved in craniosynostosis and cellular-based bone tissue engineering may soon be added to the armamentarium of surgeons treating craniofacial dysmorphologies.

Image-guided tissue engineering of anatomically shaped implants via MRI and micro-CT using injection molding

This study demonstrates for the first time the development of engineered tissues based on anatomic geometries derived from widely used medical imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI). Computer-aided design and tissue injection molding techniques have demonstrated the ability to generate living implants of complex geometry. Due to its complex geometry, the meniscus of the knee was used as an example of this technique's capabilities. MRI and microcomputed tomography (microCT) were used to design custom-printed molds that enabled the generation of anatomically shaped constructs that retained shape throughout 8 weeks of culture. Engineered constructs showed progressive tissue formation indicated by increases in extracellular matrix content and mechanical properties. The paradigm of interfacing tissue injection molding technology can be applied to other medical imaging techniques that render 3D models of anatomy, demonstrating the potential to apply the current technique to engineering of many tissues and organs.

Continuous local infusion of fibroblast growth factor-2 enhances consolidation of the bone segment lengthened by distraction osteogenesis in rabbit experiment

Experimental tibial lengthening was achieved in 61 rabbits to examine the effect of continuous local infusion of recombinant human fibroblast growth factor-2 (rhFGF-2) on bone healing of the lengthened segment. The tibial diaphysis was separated by osteotomy and was subjected to slow progressive distraction (rate: 0.35 mm/12 h) using a monolateral external fixator. There were a lag phase for 1 week, a distraction phase for 2 weeks, and a consolidation phase for 5 weeks in this experiment. At various stages of distraction, rhFGF-2 was infused continuously for 2 weeks into the lengthened segment (rate: 14.28 microg/60 microl/day) using an osmotic pump implanted under the skin. Bone healing was significantly accelerated when rhFGF-2 was infused in the beginning of consolidation phase, but not in the distraction phase or in the lag phase. Infusion of normal saline (N/S) using the same osmotic pump had no effect. Dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computerized tomography (pQCT) studies demonstrated that rhFGF-2-treated tibia had increased bone mineral density (BMD), bone mineral content (BMC) and cortical bone thickness (CBT) when compared with N/S-treated tibia. Three-point bending test demonstrated that rhFGF-2-treated bone had significantly stronger mechanical properties than N/S-treated bone. Finally, distribution of the infused materials was checked by using Indian ink or radio-opaque. The dyes distributed widely but exclusively in the lengthened segment. Based on these results, we conclude that direct delivery of rhFGF-2 into the lengthened segment can shorten the consolidation phase of limb lengthening and the method is applicable to the clinical treatment.

Local application of recombinant human fibroblast growth factor-2 on bone repair: a dose-escalation prospective trial on patients with osteotomy

Based on preclinical evidence in animal models, the present study examined the clinical efficacy and safety of recombinant human fibroblast growth factor-2 (rhFGF-2) to accelerate bone repair in a dose-escalation prospective trial. One of three dosages (200, 400 or 800 microg) of rhFGF-2 in a biodegradable gelatin hydrogel was injected during surgery into the osteotomy site of 59 knee osteoarthritis patients undergoing high tibial osteotomy, and 57 of them were monitored for 16 weeks. The rhFGF-2 dose dependently increased the percentage of patients with radiographic bone union, and decreased the average time needed for such union. The percentages of patients with an absence of pain and full-weight bearing were also greater in the higher dosage groups than in the low dosage group, especially in the clinically critical periods 6, 8, and 10 weeks. Neither blood chemistries nor clinical adverse events were associated with the rhFGF-2 dosages. We therefore conclude that the rhFGF-2 in gelatin hydrogel dose dependently accelerated radiographic bone union of a surgical osteotomy with a safety profile at least at the dosages used, suggesting the clinical efficacy of this agent for bone repair.

Expression of bone morphogenetic protein 2 and fibroblast growth factor 2 during bone regeneration using different implant materials as an onlay bone graft in rabbit mandibles

OBJECTIVES

The purpose of this study was to histologically and immunohistochemically evaluate bone regeneration using 3 different implant materials in rabbit mandibles and to compare the bone regenerative capability of these materials in an animal model.

STUDY DESIGN

Adult male Japanese white rabbits (n = 48; 12-16 wks old; 2.5-3.0 kg) were divided into 4 groups, consisting of 12 animals each. The implant materials were beta-tricalcium phosphate (beta-TCP), autologous bone derived from the radius, and recombinant human bone morphogenetic protein 2 (rhBMP-2) with polylactic acid/polyglycolic acid copolymer and gelatin sponge (PGS) complex. After incising along the inferior border of the mandible, the materials were implanted as only grafts and covered by titanium mesh with screws. No material was implanted into the control group. The rabbits were killed at 2, 4, 8, 12, and 24 wks postoperatively, and formalin-fixed specimens containing titanium mesh were embedded in acrylic resin. The specimens were stained with hematoxylin and eosin. For immunohistochemical analysis, the specimens were treated with BMP-2 and fibroblast growth factor 2 (FGF-2) antibodies. Finally, they were examined microscopically.

RESULTS

The autologous bone induced substantially more new bone formation compared with beta-TCP at 4 wks postoperatively. However, rhBMP-2/PGS induced new bone formation at 8 wks postoperatively. No growth of bony tissue was observed in the control group at any period. In the autologous bone and rhBMP-2/PGS groups, both BMP-2 and FGF-2 were observed later in the beta-TCP group than in other groups.

CONCLUSION

This study suggests that autologous bone as well as rhBMP-2/PGS implants induce expression of both BMP-2 and FGF-2 specifically at the operated sites, even at early stages.

Repair of segmental bone defects in rabbit tibiae using a complex of beta-tricalcium phosphate, type I collagen, and fibroblast growth factor-2

The objective of this study was to evaluate the effects of a complex of beta-tricalcium phosphate (beta-TCP) granules, collagen, and fibroblast growth factor-2 (FGF-2) on cortical bone repair in rabbits. Segmental bone defects of 5 mm in length were created in the middle of the tibial shaft. The defect was stabilized with a plate and screws, and was filled with 0.3 ml of a complex of beta-TCP granules and 5% collagen, with or without 200 microg of recombinant human fibroblast growth factor-2 (rhFGF-2). Bone regeneration and beta-TCP resorption were assessed by X-ray and micro-CT scanner. A three-point bending test was also performed. The results showed that the segmental bone defect was not only radiologically, but also mechanically healed with cortical bone 12 weeks after implantation of the complex with rhFGF-2. In contrast, after implantation of the complex without rhFGF-2, most of the defect was filled with beta-TCP and only a small amount of bone formation was found. These results suggest that resorption of beta-TCP is important for bone formation and may be promoted by FGF-2 in the beta-TCP implantation site. In addition, the complex of beta-TCP granules and collagen combined with rhFGF-2 provides a paste-like material that is easy to handle. This material may be of considerable use in the treatment of cortical bone defects.

Efficacy of bone marrow-derived stem cells in strengthening osteoporotic bone in a rabbit model

Osteoporosis might be due to defects in mesenchymal stem cells (MSCs) that lead to reduced proliferation and osteoblast differentiation. We hypothesized that transplantation of MSCs into sites at risk for developing osteoporotic bone could improve bone structure and biomechanics. The aim of this study was to establish an osteoporosis rabbit model by ovariectomy (OVX), characterize the autologous MSCs from the OVX rabbits, and transplant the autologous MSCs into the OVX rabbits. MSCs harvested from bone marrow of normal and OVX rabbits were culture expanded and differentiated in osteogenic medium. Phenotypes were evaluated by collagen I immunostaining, von Kossa staining, and quantitative assays of bone-specific alkaline phosphatase (B-ALP) and osteocalcin (OCN). MSCs were transfected with green fluorescence protein (GFP) and implanted in the gluteus muscle to trace their fate in vivo. Cultured autologous MSCs from OVX rabbits were constructed in calcium alginate gels and then transplanted in the distal femurs. At 4 and 8 weeks after implantation, histomorphometrical and biomechanical analyses were performed on the samples. MSCs from OVX rabbits displayed higher B-ALP activity, but had similar OCN levels as compared to those from sham rabbits. After 8 weeks of implantation, more bone apposition was found in the MSC-alginate-treated group. Histomorphometry indicated increased trabecular thickness. Histology also illustrated improved microstructures with newly formed osteoids and enhanced trabecular thickness. In addition, biomechanical testing revealed stronger stiffness in the MSC-alginate treatment group. Therefore, this study implies that transplantation of MSCs can help to strengthen osteoporotic bone in rabbits.

Proliferation and Differentiation of Rat Bone Marrow Stromal Cells on Poly(glycolic acid)–Collagen Sponge

We studied the effects of dexamethasone (Dex) and basic fibroblast growth factor (bFGF) on proliferation and differentiation of rat bone marrow stromal cells (RBMSCs), using three scaffolds: collagen sponge, poly(glycolic acid) (PGA)-collagen sponge, and PGA-collagen (UV) sponge. RBMSCs were seeded into the sponges, and cultured in primary medium, primary medium with Dex, and primary medium with bFGF and Dex. Three weeks after cultivation, we examined alkaline phosphatase (ALP) activity and cell number in the sponges, and also performed macroscopic, light microscopic, and scanning electron microscopic (SEM) observations. Collagen sponge shrank considerably, but PGA-collagen and PGA-collagen (UV) sponges maintained most of their original shape. PGA-collagen (UV) sponge supplemented with bFGF and Dex together had the highest ALP activity and cell number, followed by PGA-collagen sponge. Although collagen sponge showed cell proliferation only on the surface, the other two sponges showed cell proliferation in the interior. SEM showed the best cell attachment to PGA-collagen (UV) sponge in the presence of bFGF and Dex, followed by PGA-collagen sponge. In conclusion, PGA-collagen (UV) and PGA-collagen sponges proved to be much more useful as scaffolding for bone regeneration when combined with bFGF and Dex.

Gene Expression Profiling in the Rat Cranial Suture

Although many theories have attempted to explain the etiopathogenesis of premature cranial suture fusion, which results in craniosynostosis, recent studies have focused on the role of growth factors and receptors. Using a well-established model of cranial suture biology, the authors developed a novel approach to quantitatively analyze the gene expression profiles of candidate cranial suture growth factors and their receptors. We collected suture mesenchyme and adjacent osteogenic fronts from Sprague-Dawley rats at postnatal days 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 35. RNA was extracted from posterior frontal (PF) and sagittal (SAG) sutures, and reverse transcription-polymerase chain reaction (RT-PCR) was performed for cranial suture candidate cytokines BMP2, BMP3, BMP4, FGF-2, FGFR1, FGFR2, FGFR4, TGF-betaRI, TGF-betaRII, and TGF-betaRIII. The authors confirmed quantitative RT-PCR results with Southern and dot blot analyses. Suture growth factor and receptor expression levels changed significantly with time. Expression levels decreased toward baseline in the SAG suture by day 35. There was a marked difference in FGFR1, FGF-2, TGF-betaRI, and TGF-betaRII expression levels when comparing the fusing PF and nonfusing SAG sutures. Although FGF-2 ligand expression was low, FGF receptor 1 (FGFR1) levels were markedly elevated with a bimodal expression pattern in both PF and SAG similar to that of BMP2, BMP3, and BMP4. Although there were statistically significant differences in TGF-betaRI and TGF-betaRII expression in the PF and SAG sutures, TGF-betaRIII levels were unchanged. The authors report a novel approach to cranial suture growth factor/receptor profiling and confirm their results with standard analytic tools. The data confirm, quantify, and extend the results of previously published studies. By quantifying the gene expression profiles of normal cranial suture biology, we may begin to understand the aberrant growth factor cascades of craniosynostosis and devise targeted therapeutic interventions that can alter the course of this malady.

Uncaria rhynchophylla Induces Angiogenesis in Vitro and in Vivo

Angiogenesis consists of the proliferation, migration, and differentiation of endothelial cells, and angiogenic factors and matrix protein interactions modulate this process. The aim of this study was to determine the angiogenic properties of Uncaria rhynchophylla. Uncaria rhynchophylla significantly enhanced human umbilical vein endothelial cells (HUVECs) proliferation in a dose-dependent manner. Neutralization of vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) by monoclonal antibody suppressed the Uncaria rhynchophylla stimulatory effect on proliferation. In addition, Uncaria rhynchophylla significantly increased chemotactic-migration on gelatin and tubular structures on Matrigel of HUVECs in a dose-dependent manner. Interestingly, Uncaria rhynchophylla dose-dependently increased VEGF, and bFGF gene expression and protein secretion of HUVEC. The angiogenic activity of Uncaria rhynchophylla was confirmed using an in vivo Matrigel angiogenesis model, showing promotion of blood vessel formation. These results suggest that Uncaria rhynchophylla could potentially used to accelerate vascular wound healing or to promote the growth of collateral blood vessel in ischemic tissues.

Tendon injury and tendinopathy: healing and repair

Tendon disorders are frequent and are responsible for substantial morbidity both in sports and in the workplace. Tendinopathy, as opposed to tendinitis or tendinosis, is the best generic descriptive term for the clinical conditions in and around tendons arising from overuse. Tendinopathy is a difficult problem requiring lengthy management, and patients often respond poorly to treatment. Preexisting degeneration has been implicated as a risk factor for acute tendon rupture. Several physical modalities have been developed to treat tendinopathy. There is limited and mixed high-level evidence to support the, albeit common, clinical use of these modalities. Further research and scientific evaluation are required before biological solutions become realistic options.

Fibroblast growth factor 2 in synovial fluid from an osteoarthritic knee with cartilage regeneration

The levels of fibroblast growth factor 2 (FGF2) in synovial fluid of osteoarthritic knees were measured. The correlation between FGF2 and the severity of cartilage degeneration in varus-deformed knees with medial compartmental osteoarthritis or the articular cartilage regeneration that occurs after high tibial osteotomy (HTO) were investigated. Knees that underwent total knee arthroplasty (TKA) were categorized as either mildly or severely degenerated according to a modified Outerbridge's grading system for degeneration of articular cartilage. Regeneration of articular cartilage was observed in a biopsy specimen from the medial femoral condyle removed with the patient's consent during hardware removal approximately 2 years after HTO. The joint fluid FGF2 level was measured at that time using an enzyme-linked immunosorbent assay. Cartilage regeneration was classified as immature or mature according to the staging for regeneration of articular cartilage. The histological findings were analyzed using Pineda's evaluation method for cartilage regeneration. The mean concentration of FGF2 was 57.4 +/- 17.6 pg/ml in the joint fluid from knees with severely degenerated cartilage. This was higher than the FGF2 concentration found in the mildly degenerated group. Approximately 2 years after HTO the FGF2 level in synovial fluid was lower in knees with mature regenerated cartilage than in those with immature regeneration. Osteoarthritic knees at a more mature regeneration stage had a lower Pineda's histological score. This result suggested that the FGF2 concentration in knees with osteoarthritis was influenced by articular cartilage degeneration and regeneration, and it correlated with the histological evaluation.

Local infusion of FGF-2 enhances bone ingrowth in rabbit chambers in the presence of polyethylene particles

Osseointegration of porous-coated implants during revision arthroplasty procedures is often impeded due to the presence of residual granuloma, particulate debris, and a sclerotic, dysvascular bone bed. We hypothesized that local infusion of recombinant fibroblast growth factor (FGF-2) would increase bone ingrowth in an in vivo model of tissue differentiation in the rabbit tibia in the presence of phagocytosable polyethylene particles. A drug test chamber (DTC) was implanted in the proximal medial tibial metaphysis of mature rabbits unilaterally. The chamber contained a 1x 1 x 5-mm tunnel for tissue ingrowth, and was connected to an osmotic diffusion pump. FGF-2 was infused at dosages of 0, 0.5, 5, 50, or 500 ng/day for a 3-week period, with subsequent harvesting of the ingrown tissue after each 3-week treatment. The effects of ultrahigh molecular weight polyethylene particles (0.5-microm diameter) on tissue ingrowth were determined by adding particles to the chamber at concentrations of 5.8 x 10(11) (low dose) or 1.7 x 10(12) (high dose) particles/mL, with and without infusion of 50 ng/day of FGF for 3 weeks. The tissue forming in the chamber was harvested after each treatment for histologic processing and morphometric analysis of bone ingrowth. Statistical analysis was performed using parametric tests (ANOVA), nonparametric tests (Kruskal-Wallis test) and post hoc tests. In the absence of particles, infusion of 50 ng FGF-2 per day yielded the greatest amount of bone ingrowth. The high dose of particles suppressed bone ingrowth into the chamber, but the low dose particles did not (p = 0.0002, 95% confidence limits = 9.19-18.80). Infusion of 50 ng FGF-2 per day significantly increased net bone formation in the presence of high-dose UHMWPE particles (p = 0.039, 95% confidence limits = 1.41-6.79). There was a trend for decreased numbers of vitronectin-receptor positive (osteoclast-like) cells with the addition of FGF-2, compared to particles alone (p = 0.08). Local delivery of FGF-2 may prove useful in mitigating the adverse effects of wear debris (e.g., in treating early osteolytic lesions), and facilitating osseointegration of revision total joint replacements in situations where the bone bed is suboptimal and residual particles and granulomatous tissue are present.

The molecular biology of distraction osteogenesis

Distraction osteogenesis has become a mainstay in bone tissue engineering and has significantly improved our armamentarium for reconstructive craniomaxillofacial procedures. However, although the biomechanical, histological, and ultrastructural changes associated with distraction osteogenesis have been widely described, the molecular mechanisms governing the formation of new bone in the interfragmental gap of gradually distracted bone segments remain largely unclear. Recently, a rat model of mandibular distraction was described that provides an excellent environment for deciphering the molecular mechanisms that mediate distraction osteogenesis. This article presents the hypotheses and current research that have furthered knowledge of the molecular mechanisms that govern distraction osteogenesis. Recent studies have implicated a growing number of cytokines that are intimately involved in the regulation of bone synthesis and turnover. The gene regulation of numerous cytokines (transforming growth factor-beta1, -beta2, -beta3, bone morphogenetic proteins, insulin-like growth factor-1, fibroblast growth factor-2) and extracellular matrix proteins (osteonectin, osteopontin) during distraction osteogenesis have been best characterized and are discussed in this article. It is believed that understanding the biomolecular mechanisms that mediate membranous distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone healing.

Co-culture of osteoblasts with immature dural cells causes an increased rate and degree of osteoblast differentiation

For decades surgeons have exploited the ability of infants to reossify large calvarial defects. To demonstrate the role of dura mater-osteoblast communication during the process of calvarial reossification, the authors used a novel in vitro system that recapitulates the in vivo anatomic relationship of these cell populations. Primary cultures of osteoblast cells from 2-day-old Sprague-Dawley rat pups were grown on six-well plates, and cultures of immature, non-suture-associated dura mater cells from 6-day-old Sprague-Dawley rat pups were grown on Transwell inserts. When the osteoblast and dura mater cell cultures reached confluence, they were combined. This Transwell co-culture system permitted the two cell populations to grow together in the same well, but it prevented direct cell-to-cell contact. Therefore, the authors were able to determine, for the first time, whether paracrine signaling from immature, non-suture-associated dura mater could influence the biologic activity of osteoblasts. Osteoblasts co-cultured with dural cells proliferated significantly faster after 2 days (2.1 x 10(5) +/- 2.4 x 10(4) versus 1.4 x 10(5) +/- 2.2 x 10(4), p < or = 0.05) and 4 days (3.1 x 10(5) +/- 5 x 10(4) versus 2.2 x 10(5) +/- 4.0 x 10(4), p < or = 0.01) than did osteoblasts cultured alone. After 20 days, co-cultured osteoblasts expressed greater amounts of mRNA for several markers of osteoblast differentiation, including collagen I alpha I (4-fold), alkaline phosphatase (2.5-fold), osteopontin (3-fold), and osteocalcin (4-fold), than did osteoblasts cultured alone. After 30 days, co-cultured osteoblasts produced bone nodules that were significantly greater both in number (324 +/- 29 nodules versus 252 +/- 29 nodules per well, p , < or = 0.04) and total area of nodules (65 +/- 11 mm(2) versus 24 +/- 1.6 mm(2), p < or = 0.003) than osteoblasts cultured alone. To begin to understand how dural cells effect changes in osteoblast gene expression, the authors compared the expression of candidate genes, transforming growth factor beta 1 and fibroblast growth factor 2, in dural cells and osteoblasts before and after 5 days of culture. Interestingly, the dura mater produced marked amounts of these osteogenic cytokines compared with osteoblasts.The described co-culture system demonstrated that co-cultured osteoblasts proliferated more rapidly and experienced an increased rate and degree of cellular maturation than did osteoblasts cultured alone. The authors hypothesize that this effect was due to paracrine signaling (e.g., transforming growth factor beta 1 and fibroblast growth factor 2) from the dura mater, and they are investigating those mechanisms in ongoing experiments. Collectively these data verify that immature, non-suture-associated dura mater can influence the biologic activity of osteoblasts. Moreover, the production of cytokines derived from the dura mater (e.g., transforming growth factor beta 1 and fibroblast growth factor 2), and they may begin to explain why immature animals and infants with intact dura mater can reossify large calvarial defects.

Regulation of osteoclast differentiation by fibroblast growth factor 2: stimulation of receptor activator of nuclear factor kappaB ligand/osteoclast differentiation factor expression in osteoblasts and inhibition of macrophage colony-stimulating factor function in osteoclast precursors

This study investigated the mechanism of direct and indirect actions of fibroblast growth factor 2 (FGF-2) on osteoclast differentiation using two mouse cell culture systems. In the coculture system of osteoblasts and bone marrow cells, FGF-2 stimulated osteoclast formation. This effect was decreased markedly by osteoprotegerin (OPG) or NS-398, a selective cyclo-oxygenase 2 (COX-2) inhibitor. FGF-2 (> or = 10(-9) M) stimulated receptor activator of nuclear factor kappaB ligand/osteoclast differentiation factor (RANKL/ODF) messenger RNA (mRNA) expression from 2 h to 7 days in cultured osteoblasts. NS-398 did not affect the early induction but decreased the later one, indicating that the later effect is mediated by COX-2 induction in osteoblasts. To study the direct action of FGF-2 on osteoclast precursors, we used mouse macrophage-like cell line C7 cells that can differentiate into osteoclasts in the presence of soluble RANKL/ODF (sRANKL/ODF) and macrophage colony-stimulating factor (M-CSF). Although osteoblasts expressed all FGF receptors (FGFR-1 to -4), only FGFR-1 was detected in C7 cells at various differentiation stages. FGF-2 alone or in combination with sRANKL/ODF did not induce osteoclastogenesis from C7 cells; however, FGF-2 from lower concentrations (> or = 10(-11) M) significantly decreased osteoclast formation induced by M-CSF in the presence of sRANKL/ODF. FGF-2 did not alter mRNA levels of M-CSF receptor (Fms) or RANK in C7 cells. Immunoprecipitation/ immunoblotting analyses revealed that tyrosine phosphorylation of several cellular proteins including Fms in C7 cells induced by M-CSF was inhibited by FGF-2 in the presence of sRANKL/ODF. We conclude that FGF-2 regulates osteoclast differentiation through two different mechanisms: (1) an indirect stimulatory action via osteoblasts to induce RANKL/ODF partly through COX-2 induction and prostaglandin production and (2) a direct inhibitory action on osteoclast precursors by counteracting M-CSF signaling.

Recombinant human acidic fibroblast growth factor and fibrin carrier regenerates bone

Bone regeneration promoted by acidic recombinant human fibroblast growth factor (rhFGF-1), rabbit demineralized bone matrix (rDBM), and a fibrin (f) delivery system was measured in critical-sized defects in rabbits' radii. A unilateral segmental defect 20 mm in length was prepared in radii of 48 skeletally mature New Zealand White rabbits divided equally between 4- and 8-week cohorts. The temporal cohorts were divided equally among four treatment groups: rDBM, rDBM/f, rDBM/rhFGF-1/f, and rhFGF-1/f. Data for the fifth group, untreated critical-sized defects, were exploited from previous published reports from this laboratory. In response to experimental treatments, radiomorphometric and histomorphometric methods were used to derive quantitative outcome data that were tested by analysis of variance and post hoc multiple comparison tests (significance p </= 0.05). Radiomorphometric data (percentage of radiopacity of defect) were acquired at the day of the operation and every 2 weeks thereafter, whereas histomorphometric data (square millimeters of new bone formation) were determined at term. The objective for the study was to develop candidate bone regenerative therapies. Therefore, the hypotheses were that experimental treatments would promote bone formation within critical-sized defects and that one treatment would be superior to the rest. Testing hypotheses was achieved with quantitative methodology, and data were subjected to statistical models. Radiopacity at each 2-week period was greater in treated defects than in untreated critical-sized defects. The amount of radiopacity promoted by rDBM/f and rhFGF-1/f at 8 weeks was equivalent and was greater than antecedent times. Histomorphometric data analyses indicated that rDBM/f and rDBM evoked the same quantity of new bone formation at 4 weeks; by 8 weeks, all treatments except rDBM/f had more new bone within the critical-sized defects in comparison to untreated defects. That rDBM/f promoted less new bone than rDBM alone may suggest fibrin decreases bone formation, perhaps by impeding local solubility of endogenous and rDBM-containing signaling molecules. However, rhFGF-1/f promoted a significant and unexpected increase in bone formation response that could refute the previous notion. In conclusion, the combination of rDBM/rhFGF-1/f may represent a significant, new osteogenic therapeutic regimen. Additional assessments in higher order species must be accomplished to corroborate efficacy.

Regional differentiation of cranial suture-associated dura mater in vivo and in vitro: implications for suture fusion and patency

Despite its prevalence, the etiopathogenesis of craniosynostosis is poorly understood. To better understand the biomolecular events that occur when normal craniofacial growth development goes awry, we must first investigate the mechanisms of normal suture fusion. Murine models in which the posterior frontal (PF) suture undergoes programmed sutural fusion shortly after birth provide an ideal model to study these mechanisms. In previous studies, our group and others have shown that sutural fate (i.e., fusion vs. patency) is regulated by the dura mater (DM) directly underlying a cranial suture. These studies have led to the hypothesis that calvarial DM is regionally differentiated and that this differentiation guides the development of the overlying suture. To test this hypothesis, we evaluated the messenger RNA (mRNA) expression of osteogenic cytokines (transforming growth factor beta1 [TGF-beta1] and TGF-beta3) and bone-associated extracellular matrix (ECM) molecules (collagen I, collagen III, osteocalcin, and alkaline phosphatase) in freshly isolated, rat dural tissues associated with the PF (programmed to fuse) or sagittal (SAG; remains patent) sutures before histological evidence of sutural fusion (postnatal day 6 [N6]). In addition, osteocalcin protein expression and cellular proliferation were localized using immunohistochemical staining and 5-bromo-2'deoxyuridine (BrdU) incorporation, respectively. We showed that the expression of osteogenic cytokines and bone-associated ECM molecules is potently up-regulated in the DM associated with the PF suture. In addition, we showed that cellular proliferation in the DM associated with the fusing PF suture is significantly less than that found in the patent SAG suture just before the initiation of sutural fusion N6. Interestingly, no differences in cellular proliferation rates were noted in younger animals (embryonic day 18 [E18] and N2). To further analyze regional differentiation of cranial suture-associated dural cells, we established dural cell cultures from fusing and patent rat cranial sutures in N6 rats and evaluated the expression of osteogenic cytokines (TGF-beta1 and fibroblast growth factor 2 [FGF-2]) and collagen I. In addition, we analyzed cellular production of proliferating cell nuclear antigen (PCNA). These studies confirmed our in vivo findings and showed that dural cell cultures derived from the fusing PF suture expressed significantly greater amounts of TGF-beta1, FGF-2, and collagen I. In addition, similar to our in vivo findings, we showed that PF suture-derived dural cells produced significantly less PCNA than SAG suture-derived dural cells. Finally, coculture of dural cells with fetal rat calvarial osteoblastic cells (FRCs) revealed a statistically significant increase in proliferation (*p < 0.001) in FRCs cocultured with SAG suture-derived dural cells as compared with FRCs cocultured alone or with PF suture-derived dural cells. Taken together, these data strongly support the hypothesis that the calvarial DM is regionally differentiated resulting in the up-regulation of osteogenic cytokines and bone ECM molecules in the dural tissues underlying fusing but not patent cranial sutures. Alterations in cytokine expression may govern osteoblastic differentiation and ECM molecule deposition, thus regulating sutural fate. Elucidation of the biomolecular events that occur before normal cranial suture fusion in the rat may increase our understanding of the events that lead to premature cranial suture fusion.

Fibroblast growth factor (FGF)-2 directly stimulates mature osteoclast function through activation of FGF receptor 1 and p42/p44 MAP kinase

We previously reported that fibroblast growth factor-2 (FGF-2) acts not only on osteoblasts to stimulate osteoclastic bone resorption indirectly but also on mature osteoclasts directly. In this study, we investigated the mechanism of this direct action of FGF-2 on mature osteoclasts using mouse and rabbit osteoclast culture systems. FGF-2 stimulated pit formation resorbed by isolated rabbit osteoclasts moderately from low concentrations (>/=10(-12) m), whereas at high concentrations (>/=10(-9) m) it showed stimulation on pit formation resorbed by unfractionated bone cells very potently. FGF-2 (>/=10(-12) m) also increased cathepsin K and MMP-9 mRNA levels in mouse and rabbit osteoclasts. Among FGF receptors (FGFR1 to 4) only FGFR1 was detected on isolated mouse osteoclasts, whereas all FGFRs were identified on mouse osteoblasts. FGF-2 (>/=10(-12) m) up-regulated the phosphorylation of cellular proteins, including p42/p44 mitogen-activated protein (MAP) kinase, and increased the kinase activity of immunoprecipitated FGFR1 in mouse osteoclasts. The stimulation of FGF-2 on mouse and rabbit osteoclast functions was abrogated by PD-98059, a specific inhibitor of p42/p44 MAP kinase. These results strongly suggest that FGF-2 acts directly on mature osteoclasts through activation of FGFR1 and p42/p44 MAP kinase, causing the stimulation of bone resorption at physiological or pathological concentrations.

Increased marrow-derived osteoprogenitor cells and endosteal bone formation in mice lacking thrombospondin 2

The phenotype of thrombospondin 2 (TSP2)-null mice includes abnormalities in collagen fibrils and increases in ligamentous laxity, vascular density, and bleeding time. In this study, analyses by computerized tomography (CT) revealed that cortical density was increased in long bones of TSP2-null mice. Histomorphometric analysis showed that the mid-diaphyseal endosteal bone formation rate (BFR) of TSP2-null mice was increased in comparison with that of wild-type (WT) animals. Although microgeometric analysis showed that periosteal and endosteal radii were reduced, the mechanical properties of femurs from TSP2-null mice were not significantly different from those of controls, presumably because of the concomitant increase in endosteal bone mass. Bone loss in ovariectomized mice was equivalent for WT and mutant mice, a finding that indicates that TSP2-null animals are capable of normal bone resorption. To further explore the cellular basis for the increased endosteal BFR in TSP2-null mice, marrow stromal cells (MSCs) were isolated and examined in vitro. These cells were found to be present in increased numbers in a colony forming unit (CFU) assay and showed an increased rate of proliferation in vitro. We conclude that TSP2 regulates the proliferation of osteoblast progenitors, directly or indirectly, and that in its absence endosteal bone formation is increased.

Direct and indirect actions of fibroblast growth factor 2 on osteoclastic bone resorption in cultures

Fibroblast growth factor 2 (FGF-2 or basic FGF) is known to show variable actions on bone formation and bone resorption. This study was undertaken to elucidate the mechanisms whereby FGF-2 affects bone metabolism, especially bone resorption, using three different culture systems. FGF-2 at 10(-9) M and higher concentrations induced osteoclastic cell formation in the coculture system of mouse osteoblastic cells and bone marrow cells, and this induction was abrogated by nonsteroidal anti-inflammatory drugs (NSAIDs). 45Ca release from prelabeled cultured mouse calvariae stimulated by FGF-2 (10(-8) M) was also inhibited by NSAIDs, and the inhibition was stronger by NSAIDs, which are more selective for inhibition of cyclooxygenase 2 (COX-2) than COX-1, suggesting the mediation of COX-2 induction. COX-2 was highly expressed and its messenger RNA (mRNA) level was stimulated by FGF-2 in osteoblastic cells whereas it was undetectable or not stimulated by FGF-2 in cells of osteoclast lineage. To further investigate the direct actions of FGF-2 on osteoclasts, resorbed pit formation was compared between cultures of purified osteoclasts and unfractionated bone cells from rabbit long bones. FGF-2 (> or = 10(-12) M) stimulated resorbed pit formation by purified osteoclasts with a maximum effect of 2.0-fold at 10(-11) M, and no further stimulation was observed at higher concentrations. However, FGF-2 at 10(-9) M - 10(-8) M stimulated resorbed pit formation by unfractionated bone cells up to 9.7-fold. NS-398, a specific COX-2 inhibitor, did not affect the FGF-2 stimulation on purified osteoclasts but inhibited that on unfractionated bone cells. We conclude that FGF-2 at low concentrations (> or =10(-12) M) acts directly on mature osteoclasts to resorb bone moderately, whereas at high concentrations (> or = 10(-9) M) it acts on osteoblastic cells to induce COX-2 and stimulates bone resorption potently.

Bioactive factors for bone tissue engineering

Orthopaedic surgery is currently in the midst of a transformation from bone grafting and the use of bone graft substitutes to bone tissue engineering. Bioactive bone growth factors likely will play a particularly important role in this emerging field. This article will review the three leading strategies for using bioactive factors for bone tissue engineering: extraction and partial purification of growth factors, recombinant protein synthesis, and gene therapy. Preclinical and early clinical trial results with bone morphogenetic protein-2, bone morphogenetic protein-7 (osteogenic protein-1), and NeOsteo bovine bone protein extract will be reviewed. In addition, the current obstacles to clinical implementation of bone tissue engineering will be reviewed.

Involvement of fibroblast growth factor-2 in joint destruction of rheumatoid arthritis patients

OBJECTIVE

To investigate the effect of the synovial fluid from knee joints of rheumatoid arthritis (RA) patients with different severities of joint destruction on osteoclastogenesis and bone resorption.

METHODS

Synovial fluid was harvested from the knee joints of 59 RA patients and 37 ostcoarthritis (OA) patients. RA patients with Larsen's knee grade 1-3 were classified as mild RA (n = 30) and those with grade 4 or 5 as severe RA (n = 29). Cytokine concentrations in synovial fluid were measured by ELISA. Osteoclastogenesis was measured by tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cell (MNC) formation in a co-culture of mouse osteoblastic cells and bone marrow cells, and bone resorption by 45Ca release from pre-labelled cultured neonatal mouse calvariae.

RESULTS

The synovial fluid of severe RA patients significantly stimulated TRAP-positive MNC formation and 45Ca release compared to those of mild RA and OA patients. Among the bone-resorptive cytokines fibroblast growth factor-2 (FGF-2), tumour necrosis factor alpha (TNF-alpha), interleukin-1alpha (IL-1alpha), IL-6 and soluble IL-6 receptor (sIL-6R), only FGF-2 concentration in the synovial fluid was positively correlated to Larsen's grade, and severe RA patients showed significantly higher FGF-2 concentrations than mild RA patients. Osteoclastogenesis in a co-culture system which was stimulated by the synovial fluid of severe RA patients was significantly inhibited by a neutralizing antibody against FGF-2 and this inhibition was stronger than antibodies against other cytokines.

CONCLUSION

The increase in endogenous FGF-2 levels in the synovial fluid of RA patients may play a role in the joint destruction by inducing osteoclastogenesis.

Novel formulation of fibroblast growth factor-2 in a hyaluronan gel accelerates fracture healing in nonhuman primates

Recent advances in understanding the biology of fracture healing and the availability of specific macromolecules has resulted in the development of novel treatments for injuries to bone. Fibroblast growth factor-2 or basic fibroblast growth factor (4 mg/ml), a potent mitogen, and hyaluronan (20 mg/ml), an extracellular matrix component, were combined into a viscous gel formulation intended for direct, percutaneous injection into fresh fractures. In an experimental primate fracture model, a bilateral 1-mm-gap osteotomy was surgically created in the fibulae of baboons. A single direct administration of this hyaluronan/fibroblast growth factor-2 formulation to the defect site significantly promoted local fracture healing as evidenced by increased callus formation and mechanical strength. Radiographic analysis showed that the callus area was statistically significantly larger at the treated sites than at the untreated sites. Specimens treated with 0.1, 0.25, and 0.75 ml hyaluronan/fibroblast growth factor-2 demonstrated a 48, 50, and 34% greater average load at failure and an 82, 104, and 66% greater energy to failure than the untreated controls, respectively. By histologic analysis, the callus size, periosteal reaction, vascularity, and cellularity were consistently more pronounced in the treated osteotomies than in the untreated controls. These results suggest that hyaluronan/fibroblast growth factor-2 may provide a significant advance in the treatment of fractures.

Single local injection of recombinant fibroblast growth factor-2 stimulates healing of segmental bone defects in rabbits

The effects of a single local injection of recombinant human fibroblast growth factor-2 on the healing of segmental bone defects were evaluated in rabbits. One month after the external fixator originally designed for this experiment was installed in the tibia of the rabbit, a 3-mm bone defect was created by an osteotomy in the middle of the tibia and 0, 50, 100, 200, or 400 microg of fibroblast growth factor-2 in 100 microl of saline solution was injected into the defect. Injection of the growth factor increased the volume and mineral content of newly made bone at the defect in a dose-dependent manner with significant effects at concentrations of 100 microg or greater. These significant effects were observed at 5 weeks and later. One hundred micrograms of the growth factor increased the volume and mineral content of newly made bone by 95 and 36%, respectively, at 5 weeks. These results indicate that a single local injection of fibroblast growth factor-2 stimulates the healing of segmental defects. We speculate that such an injection could be clinically useful for the healing of fractures even when the fracture gap is rather large.