Continuous administration of basic fibroblast growth factor (FGF-2) accelerates bone induction on rat calvaria--an application of a new drug delivery system

Single metal-organic framework-embedded nanopit arrays: A new way to control neural stem cell differentiation

Stable and continuous supply of essential biomolecules is critical to mimic in vivo microenvironments wherein spontaneous generation of various cell types occurs. Here, we report a new platform that enables highly efficient neuronal cell generation of neural stem cells using single metal-organic framework (MOF) nanoparticle-embedded nanopit arrays (SMENA). By optimizing the physical parameters of homogeneous periodic nanopatterns, each nanopit can confine single nMOFs (UiO-67) that are specifically designed for long-term storage and release of retinoic acid (RA). The SMENA platform successfully inhibited physical interaction with cells, which contributed to remarkable stability of the nMOF (RA⊂UiO-67) structure without inducing nanoparticle-mediated toxicity issues. Owing to the continuous and long-term supply of RA, the neural stem cells showed enhanced mRNA expressions of various neurogenesis-related activities. The developed SMENA platform can be applied to other stem cell sources and differentiation lineages and is therefore useful for various stem cell-based regenerative therapies.

VEGF and FGF-2 Released In Palatal Suture after Rapid Maxillary Expansion (RME)

Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2) have the ability to increase vascular proliferation and permeability. The aim of this study was to quantify the release of two diffusible angiogenic growth factors (VEGF and FGF-2) after rapid maxillary expansion (RME). Thirty animals were randomly assigned to two groups. Control group (5 rats - intact suture) and Experimental groups (25 rats with RME) which were evaluated in different periods of treatment. Five animals were euthanized in different periods of healing at 0, 1, 2, 3, 5 and 7 days after RME. RT-PCR was used to evaluate the gene expression of angiogenic growth factors released on different periods of study. Data were submitted to statistical analysis using ANOVA followed by Tukey test and significance was assumed at a=0.05. RT-PCR showed that mRNAs of VEGF and FGF-2 were expressed in intact palatal suture tissue. mRNAs of VEGF and FGF-2 was upregulated in early periods (24 h) after RME (p<0.001 and p<0.01, respectively). The molecular levels of VEGF never returned to its original baseline values, and FGF-2 expression decreased up to day 5 (p<0.001) and suddenly increased at day 7, returning to its original level. RME increased VEGF secretion, but decreased FGF-2 secretion when compared to intact tissue. The results showed that these angiogenic growth factors are released and regulated in the palatal suture tissue after RME and could make an important contribution to the knowledge of overall reparative response of the suture tissue during the bone remodeling process.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

Release kinetics of the model protein FITC-BSA from different polymer-coated bovine bone substitutes

Background

Controlled release of proteins bound to conventional bone substitutes is still insufficient. Therefore, this study evaluates in-vitro release kinetics of the model protein FITC-BSA (fluorescein conjugated bovine serum albumine) from insoluble bovine collagenous bone matrices (ICBM) with different polymer coatings. Analyzes aim at comparing FITC-BSA release from uncoated versus coated ICBM over time to find bone substitute coatings with consistent release profiles.

Methods

Release kinetics of FITC-BSA from uncoated as well as coated ICBM with five different polymers (RESOMER R 203 H, RG 503 H, RG 504 H, RG 505, L 206 S) were measured over a period of 11 days (d). Measurements were conducted after 6 h (h), 12 h, 24 h, 3 d, 5 d, 7 d, 9 d and 11 d with six samples for each coated ICBM. Two groups were formed (1) with and (2) without medium change at times of measurement. For each group ANOVA with post-hoc Bonferroni testing was used. Scanning electron microscopy assessed morphologic differences between ICBM coating.

Results

In group 1 approx. 70% of FITC-BSA release from uncoated ICBM occurred after 6 h compared to approx. 50% in group 2. Only polymers with medium inherent viscosity, i.e. RESOMER RG 503 H, constantly showed significantly more FITC-BSA release throughout 11 d than uncoated ICBM (p = 0.007). The same was found for group 2 (p = 0.005). No significant differences between PLA and PLGA polymers were found. Scanning electron microscopy results indicate a weak adhesion of polymer coatings to ICBM explaining its rather weak retentive effect on overall FITC-BSA release.

Conclusions

Medium molecular size polymers reduce the overall released FITC-BSA from ICBM over time. In clinical practice these polymers may prove ideal for bone substitute materials.

Extracellular matrix-inspired growth factor delivery systems for bone regeneration

Growth factors are very promising molecules to enhance bone regeneration. However, their translation to clinical use has been seriously limited, facing issues related to safety and cost-effectiveness. These problems derive from the vastly supra-physiological doses of growth factor used without optimized delivery systems. Therefore, these issues have motivated the development of new delivery systems allowing better control of the spatiotemporal release and signaling of growth factors. Because the extracellular matrix (ECM) naturally plays a fundamental role in coordinating growth factor activity in vivo, a number of novel delivery systems have been inspired by the growth factor regulatory function of the ECM. After introducing the role of growth factors during the bone regeneration process, this review exposes different issues that growth factor-based therapies have encountered in the clinic and highlights recent delivery approaches based on the natural interaction between growth factor and the ECM.

Preclinical testing of drug delivery systems to bone

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

Synthetic bone mimetic matrix-mediated in situ bone tissue formation through host cell recruitment

Advances in tissue engineering have offered new opportunities to restore anatomically and functionally compromised tissues. Although traditional tissue engineering approaches that utilize biomaterials and cells to create tissue constructs for implantation or biomaterials as a scaffold to deliver cells are promising, strategies that can activate endogenous cells to promote tissue repair are more clinically attractive. Here, we demonstrate that an engineered injectable matrix mimicking a calcium phosphate (CaP)-rich bone-specific microenvironment can recruit endogenous cells to form bone tissues in vivo. Comparison of matrix alone with that of bone marrow-soaked or bFGF-soaked matrix demonstrates similar extent of neo-bone formation and bridging of decorticated transverse processes in a posterolateral lumbar fusion rat model. Synthetic biomaterials that stimulate endogenous cells without the need for biologics to assist tissue repair could circumvent limitations associated with conventional tissue engineering approaches, including ex vivo cell processing and laborious efforts, thereby accelerating the translational aspects of regenerative medicine.

Biofunctional porous anodized titanium implants for enhanced bone regeneration

Efficient osseointegration is a key factor in dental implants to reduce the total time-course of therapy. Titanium implants with anodized surface gained much interest for their enhanced osseointegration. Anodized implant combined with bioactive drugs is an ideal candidate for enhance bone regeneration. Previously delivery of drugs from the metal implants has been attempted by utilizing a polymeric dip-coating method. However, the entire surface coating with polymer can diminish the advantageous surface roughness of anodized implants and cause contact inhibition between bone and implant surface. In this study, fibroblast growth factor-2 (FGF-2) loaded poly(lactide-co-glycolide) nanoparticles were partially coated on anodized Ti discs by an electrospray deposition. Nanoparticle coated anodized discs maintained their native porous structure and provided a sustained release of FGF-2 for more than 2 weeks with 40% initial burst. In vitro study confirmed the influence of polymeric nanoparticles and the release of growth factors from the Ti disc. Nanoparticle-coated groups significantly enhanced cell spreading and differentiation. For in vivo evaluation, the anodized titanium implants were applied to rabbit tibia model. The osseointegration was estimated by bone to implant contact of best three consecutive threads at the border of the implant. The mean osteointegration value of FGF-2 releasing implant groups (70.1%) was significantly higher than that of untreated implants (47.1%). We believe that the electrospray deposition technique is a particularly attractive approach for the coating of medical devices with porous surface to maintain their surface topography while allowing a sustained delivery of growth factors for bone regeneration. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3639-3648, 2014.

The influence of environmental factors on bone tissue engineering

Bone repair and regeneration are dynamic processes that involve a complex interplay between the substrate, local and systemic cells, and the milieu. Although each constituent plays an integral role in faithfully recreating the skeleton, investigators have long focused their efforts on scaffold materials and design, cytokine and hormone administration, and cell-based therapies. Only recently have the intangible aspects of the milieu received their due attention. In this review, we highlight the important influence of environmental factors on bone tissue engineering.

Biomaterial delivery of morphogens to mimic the natural healing cascade in bone

Complications in treatment of large bone defects using bone grafting still remain. Our understanding of the endogenous bone regeneration cascade has inspired the exploration of a wide variety of growth factors (GFs) in an effort to mimic the natural signaling that controls bone healing. Biomaterial-based delivery of single exogenous GFs has shown therapeutic efficacy, and this likely relates to its ability to recruit and promote replication of cells involved in tissue development and the healing process. However, as the natural bone healing cascade involves the action of multiple factors, each acting in a specific spatiotemporal pattern, strategies aiming to mimic the critical aspects of this process will likely benefit from the usage of multiple therapeutic agents. This article reviews the current status of approaches to deliver single GFs, as well as ongoing efforts to develop sophisticated delivery platforms to deliver multiple lineage-directing morphogens (multiple GFs) during bone healing.

Demineralized bone matrix as a vehicle for delivering endogenous and exogenous therapeutics in bone repair

As a unique human bone extract approved for implant use, demineralized bone matrix (DBM) retains substantial amounts of endogenous osteoconductive and osteoinductive proteins. Commercial preparations of DBM represent a clinically accessible, familiar, widely used and degradable bone-filling device, available in composite solid, strip/piece, and semi-solid paste forms. Surgically placed and/or injected, DBM releases its constituent compounds to bone sites with some evidence for inducing new bone formation and accelerating healing. Significantly, DBM also has preclinical history as a drug carrier by direct loading and delivery of several important classes of therapeutics. Exogenous bioactive agents, including small molecule drugs, protein and peptide drugs, nucleic acid drugs and transgenes and therapeutic cells have been formulated within DBM and released to bone sites to enhance DBM's intrinsic biological activity. Local release of these agents from DBM directly to surgical sites in bone provides improved control of dosing and targeting of both endogenous and exogenous bioactivity in the context of bone healing using a clinically familiar product. Given DBM's long clinical track record and commercial accessibility in standard forms and sources, opportunities to formulate DBM as a versatile matrix to deliver therapeutic agents locally to bone sites in orthopedic repair and regenerative medicine contexts are attractive.

Silica-chitosan hybrid coating on Ti for controlled release of growth factors

A hybrid material composed of a silica xerogel and chitosan was coated on Ti for the delivery of growth-factors. Fibroblast growth factor (FGF) and green fluorescence protein were incorporated into the coatings for hard tissue engineering. Silica was chosen as a coating material because of its high surface area as well as its good bioactivity. Chitosan provides mechanical stability and contributes to the control of the release rate of the growth factors. When the chitosan composition was 30% or more, the hybrid coating was stable physically and mechanically. The release of the growth-factors, observed in phosphate buffer solution at 37°C, was strongly dependent on the coating material. The hybrid coating containing FGF showed significantly improved osteoblast cell responses compared to the pure xerogel coating with FGF or the hybrid coating without FGF. These results indicate that the hybrid coating is potentially very useful in enhancing the bioactivity of metallic implants by delivering growth-factors in a controlled manner.

Alveolar bone regeneration using poly-(lactic acid-co-glycolic acid-co-ε-caprolactone) porous membrane with collagen sponge containing basic fibroblast growth factor: An experimental study in the dog

The aim of this study was to evaluate the effects of combining porous poly-lactic acid-co-glycolic acid-co-ε-caprolactone (PLGC) as a barrier membrane and collagen sponge containing basic fibroblast growth factor (bFGF) to promote bone regeneration in the canine mandible. In six beagle dogs, two lateral bone defects per side were created in the mandible. The lateral bone defects on the left side were treated with a PLGC membrane plus a collagen sponge containing bFGF. In half of these, the collagen sponge contained 50 µg of bFGF. In the other half, it contained 250 µg of bFGF. As a control, we treated the right-side bone defects in each animal with the same PLGC membrane but with a collagen sponge containing phosphate buffered saline. Computed tomography (CT) images were recorded at 3 and 6 months post-op to evaluate regeneration of the bone defects. After a healing period of 6 months, whole mandibles were removed for micro-CT and histological analyses. The post-op CT images showed that more bone had formed at all experimental sites than at control sites. At 3 months post-op, the volume of bone at defect sites covered with PLGC membrane plus 250 µg of bFGF was significantly greater than it was at defect sites covered with PLGC membrane plus 50 µg of bFGF. At 6 months post-op, however, this difference was smaller and not statistically significant. Micro-CT measurement showed that the volume of new bone regenerated at bone-defect sites, covered with PLGC membrane plus bFGF, was significantly greater than that of control sites. However, the presence or absence of bFGF in the collagen sponge did not significantly affect the bone density of new bone. These results suggest that the macroporous bioresorbable PLGC membrane plus collagen sponge containing bFGF effectively facilitates healing in GBR procedures.

Effect of lactoferrin-embedded collagen membrane on osteogenic differentiation of human osteoblast-like cells

Lactoferrin (LF) has the ability to promote the proliferation and differentiation of osteoblasts, suggesting its potential utility as an osteogenic growth factor in bone tissue engineering. However, this type of application requires improved drug delivery system (DDS) technology at the target site. In this study, we report enhanced calcium deposition and alkaline phosphatase (ALP) activity using the type I collagen membrane during osteogenic differentiation of MG63 human osteoblast-like cells, indicating that type I collagen not only acts as a site for calcification but also promotes the expression of differentiated phenotypes. We also used this membrane as a drug delivery carrier for bovine LF. Approximately 27% of LF embedded on the type I collagen membrane was released within the first hour in cell-free condition. This initial burst release of LF was followed by a slower release from the collagen membrane. Bovine LF embedded in the type I collagen membrane promoted its calcification during osteogenic differentiation of MG63 cells without the loss of LF bioactivity. Taken together, ALP activity and osteocalcin production were enhanced in the MG63 cells plated on the LF-embedded collagen membrane, suggesting that LF incorporated in the collagen membrane promoted bone-like tissue formation by MG63 cells. These observations suggest that the type I collagen membrane is useful as a drug delivery carrier for LF in bone tissue engineering.

Effect of combined application of bFGF and inorganic polyphosphate on bioactivities of osteoblasts and initial bone regeneration

Basic fibroblast growth factor (bFGF) and inorganic polyphosphate (poly(P)) have been recognized as therapeutic agents that enhance bone regeneration. It has also been shown that poly(P) may enhance the mitogenic activity of bFGF. The purpose of this study is to evaluate the combined effect of bFGF and poly(P) on bioactivities of osteoblasts and initial bone regeneration in vitro and in vivo. MC3T3-E1 cells were treated with bFGF, poly(P) or bFGF+poly(P), then subjected to cell proliferation assay, alkaline phosphatase (ALP) activity measurement, quantitative real-time reverse transcription-polymerase chain reaction and Alizarin S Red staining. In an in vivo study, bFGF-, poly(P)- and bFGF+poly(P)-modified interconnected porous hydroxyapatite (IPHA) complexes were fabricated, and placed into the femurs of rabbits to evaluate new bone formation histologically and histomorphometrically. The highest enhancement of cell proliferation were observed in those treated with bFGF+poly(P) on days 5 and 7. Cells treated with bFGF+poly(P) also exhibited increased ALP activity on days 5 and 10, up-regulated mRNA levels of osteocalcin and osteopontin, and enhanced calcification when compared to the non-treated cells. In vivo, the highest bone formation ratio was observed in bFGF+poly(P)-modified IPHA complexes. This study indicated that co-application of bFGF and poly(P) may provide enhanced bone formation by modulating cell proliferation and the mineralization process. It is anticipated that a combined application of bFGF and poly(P) can provide a novel method for bone regeneration in clinical use.

Collagen vitrigel membrane useful for paracrine assays in vitro and drug delivery systems in vivo

We previously succeeded in converting a soft and turbid disk of type-I collagen gel into a strong and transparent vitrigel membrane utilizing a concept for the vitrification of heat-denatured proteins and have demonstrated its protein-permeability and advantage as a scaffold for reconstructing crosstalk models between two different cell types. In this study, we observed the nano-structure of the type-I collagen vitrigel membrane and verified its utility for paracrine assays in vitro and drug delivery systems in vivo. Scanning electron microscopic observation revealed that the vitrigel membrane was a dense network architecture of typical type-I collagen fibrils. In the crosstalk model between PC-12 pheochromocytoma cells and L929 fibroblasts, nerve growth factor (NGF) secreted from L929 cells passed through the collagen vitrigel membrane and induced the neurite outgrowth of PC-12 cells by its paracrine effect. Also, the collagen vitrigel membrane containing vascular endothelial growth factor (VEGF) showed sustained-release of VEGF in vitro and its subcutaneous transplantation into a rat resulted in remarkable angiogenesis. These data suggest that the collagen vitrigel membrane is useful for paracrine assays in vitro and drug delivery systems in vivo.

Anabolic agents and the bone morphogenetic protein pathway

A major unmet need in the medical field today is the availability of suitable treatments for the ever-increasing incidence of osteoporosis and the treatment of bone deficit conditions. Although therapies exist which prevent bone loss, the options are extremely limited for patients once a substantial loss of skeletal bone mass has occurred. Patients who have reduced bone mass are predisposed to fractures and further morbidity. The FDA recently approved PTH (1-34) (Teriparatide) for the treatment of postmenopausal osteoporosis after both preclinical animal and clinical human studies indicated it induces bone formation. This is the only approved bone anabolic agent available but unfortunately it has limited use, it is relatively expensive and difficult to administer. Consequently, the discovery of low cost orally available bone anabolic agents is critical for the future treatment of bone loss conditions. The intricate process of bone formation is co-ordinated by the action of many different bone growth factors, some stored in bone matrix and others released into the bone microenvironment from surrounding cells. Although all these factors play important roles, the bone morphogenetic proteins (BMPs) clearly play a central role in both bone cartilage formation and repair. Recent research into the regulation of the BMP pathway has led to the discovery of a number of small molecular weight compounds as candidate bone anabolic agents. These agents may usher in a new wave of more innovative and versatile treatments for osteoporosis as well as orthopedic and dental indications.

Development of New Drug Delivery System for Implant Bone Augmentation Using a basic Fibroblast Growth Factor-gelatin Hydrogel Complex

This study sought to clarify the effectiveness of bFGF-gelatin hydrogel complex on bone regeneration around implants for the development of a new drug delivery system for bone augmentation. Twenty-four titanium implants (03.3 mmX 10 mm) were placed into edentulous areas of the mandibles of four beagle dogs with the upper four screw threads exposed at buccal side. bFGF-gelatin hydrogel complex with 0, 0.1, 1, 10, 100 microg bFGF or autogenous bone (as control) then filled the bone defect site to cover the exposed screw threads. After eight weeks, tissue specimens including implants were evaluated histologically and histomorphometrically. Histological observation showed new bone formation around exposed screw threads in the groups with 1, 10, 100 microg bFGF and autogenous bone-a striking contrast to the groups with contents of 0 and 0.1 microg bFGF. These results thus suggested that bFGF-gelatin hydrogel complex using an optimum amount of bFGF was useful for bone augmentation around implants.

Coordinated fibroblast growth factor and heparan sulfate regulation of osteogenesis

Growth and lineage-specific differentiation constitute crucial phases in the development of stem cells. Control over these processes is exerted by particular elements of the extracellular matrix, which ultimately trigger a cascade of signals that regulate uncommitted cells, by modulating their survival and cell cycle progression, to shape developmental processes. Uncontrolled, constitutive activation of fibroblast growth factor receptors (FGFR) results in bone abnormalities, underlining the stringent control over fibroblast growth factor (FGF) activity that must be maintained for normal osteogenesis to proceed. Mounting evidence suggests that FGF signalling, together with a large number of other growth and adhesive factors, is controlled by the extracellular glycosaminoglycan sugar, heparan sulfate (HS). In this review, we focus on FGF activity during osteogenesis, their receptors, and the use of HS as a therapeutic adjuvant for bone repair.

Fibroblast Growth Factor-2 Augments Recombinant Human Bone Morphogenetic Protein-2-Induced Osteoinductive Activity

The osteoinductive activity induced by recombinant human BMP-2 (rhBMP-2) blunts proportionately as the recipient ages. In order to compensate for this bluntness administration of fibroblast growth factor-2 (FGF-2) has been considered. The aim of this study was to determine whether FGF-2 administration augments osteoinductive activity caused by rhBMP-2 and to evaluate the effect of aging on bone formation induced by coadministration of rhBMP-2 and FGF-2. Sixty-four Wistar strain male rats of 8-week-old (prepubertal) and 16-week-old (postpubertal) received bone defects bilaterally in the parietal bone and the defects were filled by a polylactic acid polyglycolic acid copolymer/gelatin sponge (PGS) impregnated with rhBMP-2 plus 0 ng, 25 ng, and 250 ng FGF-2 (n=10 in each). At 2 weeks after grafting, the new bone volume seemed to be larger in the rhBMP-2+FGF-2 groups than in the rhBMP-2 alone group. At 4 weeks, the new bone formation was linked to the adjacent original bone. In the prepubertal rats, all newly formed bone was similarly calcified. In the postpubertal rats, only the rhBMP-2+25 ng FGF-2 group showed this higher degree of calcification. At 2 weeks, alkaline phosphatase (ALP) activity in the rhBMP-2+25 ng FGF-2 group was significantly (p<0.05) larger than that in the rhBMP-2 group in both prepubertal and postpubertal rats. This result shows that low-dose administration of FGF-2 enhanced the degree of calcification and ALP activity in the rhBMP-2 grafting site especially in the postpubertal rats. Therefore, FGF-2 would be a candidate to compensate for the reduction of osteoinductive activity of rhBMP-2 with aging.

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.

Vascular endothelial growth factor, fibroblast growth factor 2, platelet derived growth factor and transforming growth factor beta released in human dental pulp following orthodontic force

OBJECTIVE

The release of four diffusible angiogenic growth factors in human dental pulp following orthodontic force was investigated by using neutralising growth factor antibodies (NAs), individually and in four different combinations to block their effects. This study investigated if increasing the number of NAs (anti h vascular endothelial growth factor (VEGF), anti h fibroblast growth factor (FGF2), anti h platelet derived growth factor (PDGF) and anti Transforming growth factor beta (TGFbeta)) in combination resulted in a progressive reduction of the angiogenic response of the pulp.

MATERIALS AND METHODS

The dental pulps from two groups of 40 premolar teeth, four teeth from each of 20 patients treated with fixed appliances for 2 weeks, were divided vertically, and sections from each half pulp co-cultured with sections of rat aorta in collagen. In one group, one of each of the four NAs, and in the other group, one of the four different NA combinations were added to the media of the co-cultures from one half of the pulp from each of the four teeth of each patient; the other half pulp co-cultures were controls. Cultures were examined daily by light microscopy for growth and number of microvessels.

RESULTS

NAs significantly reduced microvessel numbers in the co-cultures when added individually (P<0.004), and in each of the four combinations (P<0.002), with a trend to progressively reduced microvessel numbers with increasing number of NAs in combination.

CONCLUSIONS

Results indicated that all four angiogenic growth factors examined were released following orthodontic force application and play a role in the angiogenic response of the pulp, and that these factors may be more effective in combination.

Denatured collagen as support for a FGF-2 delivery system: physicochemical characterizations and in vitro release kinetics and bioactivity

Collagen-based materials have scaffold properties to support bioactive molecules such as growth factor (GF). Gelatin, a denatured collagen, may have also some potential to interact with GF. An alternative process to denature collagen using trifluoroacetic acid (TFA) was investigated. Physicochemical characterization (XPS, DSC, isoelectric point, water uptake) of TFA-denatured collagen was comparable to regular gelatin, except a significant hydrophilicity and a pH sensitivity. FGF-2 was mixed with either regular gelatin or TFA-denatured collagen, then incorporated to a collagen sponge. Autoradiography revealed a relatively homogenous distribution of radiolabeled FGF-2 within the sponge. In vitro release kinetic of radiolabeled FGF-2 was investigated as well as the bioactivity of FGF-2 towards endothelial cell growth. The mixture was also sorbed to hydrogels made of ethylene vinyl acetate co-polymer and poly(2-hydroxyethyl methacrylate), and to cell culture insert membranes as control. Release of FGF-2 from collagen was progressive in the presence of TFA-denatured collagen, and cell growth was stimulated (significant peak at 8 and 10 days) by TFA-denatured collagen and FGF-2 eluted particularly from collagen sponges. Whereas control hydrogels, and those with regular gelatin showed a early stimulation of cell growth (1-5 days). Thus, the combination of both FGF-2 and an acid-denatured collagen in collagen sponges allows to sustain in vitro endothelial cell activity.

Hybrid Constructs for Craniofacial Reconstruction: Sustained Gene Delivery Using Demineralized Bone Matrix Putty

These experiments evaluate the efficacy of a demineralized bone matrix putty engineered as a hybrid construct for sustained, site-directed gene transfer using an adenoviral vector. In vitro experiments were performed to evaluate the optimal dosing for gene transfer to fetal calvarial osteoblasts and dural cells and for the sustainability of gene transfer from the hybrid constructs. In the dosing experiments, hybrid constructs were created by combining 0.5 mL of demineralized bone matrix putty (DBX; SYNTHES Maxillofacial, Monument, CO) with 1 x 10(8), 1 x 10(7), or 1 x 10(6) particle-forming units (PFU) of an adenoviral vector carrying the gene encoding green fluorescent protein (AdGFP). These constructs were then placed in direct contact, or in transwell coculture, with fetal murine calvarial osteoblasts or dural cells at a multiplicity of infection (MOI = viral particle/cell ratio) of 1000, 100, and 10. The sustainability of gene transfer was tested through transfer of the hybrid construct to wells containing untransfected cells every 24 hours for 30 days. In both experiments, gene transfer was determined through the visualization of GFP using fluorescence light microscopy 24 hours after the onset of transfection. Optimal dosing for gene transfer occurred at an MOI of 10 for calvarial osteoblasts and 100 for dural cells. At greater concentrations, toxicity was observed in the majority of samples. Gene transfer to fetal dural cells and calvarial osteoblasts was sustained throughout the 30-day period. These experiments suggest that adenoviral vectors could be successfully incorporated within demineralized bone matrix to provide effective, sustained, site-directed gene transfer.

Biologie moléculaire de la distraction osseuse

Distraction osteogenesis has become a mainstay in bone engineering and the recent application of this technique to the membranous craniofacial skeleton has significantly improved our armamentarium for reconstructive craniomaxillofacial procedures. However, if 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, our laboratory has described a rat mandibular distraction model that provides an excellent environment for deciphering the molecular mechanisms that mediate distraction osteogenesis. In this Article, we present the hypotheses and current research that have furthered our 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-B, Bone Morphogenetic Proteins, Insulin-like Growth Factor-1, Fibroblast Growth Factor-2) during distraction osteogenesis have been best characterized and will be discussed in this text. We believe that novel systems like the rat model will facilitate our understanding of the biomolecular mechanisms that mediate membranous distraction osteogenesis and will ultimately guide the development of targeted-strategies designed to accelerate bone healing.

FGF-4 and titanium implants: a pilot study in rabbit bone

AIM

To evaluate the effect of a local single injection of amino-terminally truncated recombinant human fibroblast growth factor-4 (rhFGF-4s) on titanium implant incorporation in a rabbit bone.

MATERIAL AND METHODS

Thirty-six threaded titanium implants were inserted into the femur and tibia of six rabbits. Three weeks prior to implant insertion 10 microg of FGF-4 in an altelocollagen carrier or the carrier alone was injected into the intended implant sites. Biomechanical evaluation by (i) resonance frequency analysis and (ii) peak removal torque measurements was performed after 6 weeks. The implants with surrounding tissue were processed to undecalcified ground sections followed by light-microscopic quantifications of the bone in threaded area and the apical parts of the implants.

RESULTS

A general trend, however not statistically significant, with higher mean values obtained in the above-mentioned tests was found. The FGF-4-treated implants revealed a significantly increased bone area in the apical part of the implants compared to the corresponding control implants.

CONCLUSION

A local single injection of rhFGF-4 may stimulate bone formation around titanium implants in bone. However, further research is required to confirm these results, understand the mechanisms of FGF, and establish optimal dose and delivery methods.

Bone tissue engineering: recent advances and promising therapeutic agents

Bone regeneration can be accomplished with growth factors, cells and delivery systems. This review is a summary of these components that may be used for tissue regeneration. Support for the potential therapeutic applications of transcription factors in bone tissue engineering will also be discussed.

Effects of simvastatin gels on murine calvarial bone

BACKGROUND

The cholesterol-lowering drug simvastatin has been shown to stimulate murine calvarial bone growth after multiple injections. The purpose of this study was to test if similar bone stimulation could be induced by 2 single-dose drug delivery systems appropriate to periodontal therapy.

METHODS

ICR Swiss mice were treated with the following protocols: 1) injection of methylcellulose gel alone, subcutaneously over the calvarium (INJ-GEL; n = 8); 2) injection of gel with simvastatin (INJ-SIM; 2.2 mg, n = 16); 3) polylactide membrane (PLA) containing gel alone implanted over calvarium (MEM-GEL; n = 10); 4) implanted PLA membrane containing gel and simvastatin (MEM-SIM; n = 10); and 5) untreated mice (n = 12). Animals were sacrificed after 22 or 44 days, calvaria decalcified and stained with hematoxylin and eosin, and images digitized and measured for bone thickness and area. Data were compared using analysis of variance.

RESULTS

INJ-SIM stimulated a 53% (P = 0.02) increase at the thickest point of calvarial bone, while MEM-SIM caused a highly significant (P < or = 0.0005) increase in bone thickness (159% to 172%) and bone area (144% to 180%) compared to gel controls. Simvastatin gels caused soft tissue inflammation, which appeared to be related to bone increases. If INJ-SIM animals showing leakage of gel and/or no inflammation were excluded from analysis, INJ-SIM resulted in more bone (58% to 83%) than gel controls. An insignificant amount of SIM-stimulated bone was lost over the long term (44 days).

CONCLUSIONS

A single, high dose of simvastatin gel can stimulate murine cranial bone apposition, particularly when delivered under an occlusive membrane. Both approaches should be investigated further for possible development for periodontal therapy.

Modeling of drug release from collagen matrices

Drug release from collagen matrices is in most cases governed by diffusion from swollen matrices but also enzymatic matrix degradation or hydrophobic drug/collagen interactions may contribute. To reduce water uptake and to prolong the release, insoluble collagen matrices have been chemically or dehydrothermally crosslinked. Assuming Fickian diffusion a one-dimensional model was developed and tested that allows description of water penetration, swelling and drug release and that may be expanded considering a subsequent erosion process or interactions. Swelling is described by a volume balance. For dry collagen matrices crosslinked by thermal treatment the existence of a moving front separating the polymer from a gel phase was considered, and a convective term induced by the volume expansion was incorporated. The resulting moving boundary problem was solved using a method based on biquadratic finite elements in both space and time that is stable, shows high accuracy, and is suitable for solving problems with a singularity at the initial time point. The model was verified for insoluble collagen matrices at different crosslinking degrees for both chemical and thermal treatment. For constant diffusion coefficients a close form of the solution was derived yielding equivalent results to the numerical approach.

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.

Osteoinductive molecules in orthopaedics: basic science and preclinical studies

Osteoinductive molecules are characterized by their ability to promote the formation of bone. Most osteoinductive molecules are cytokines, which are extracellular proteins or peptides that mediate cell to cell signaling. Examples of osteoinductive cytokines are certain bone morphogenetic proteins and some growth and differentiation factors. Some osteoinductive molecules are not secreted molecules. LIM mineralization protein-1 is an example of an intracellular osteoinductive molecule. Significant advances have been made in characterizing the molecular composition and mechanism of action of these osteoinductive molecules. Preclinical studies with these molecules have provided better understanding of the doses, formulation, and delivery mechanism necessary for effective bone formation in model systems of spinal fusion and other orthopaedic problems. The current authors will review the most important basic science and preclinical studies involving these osteoinductive molecules.

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.

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.

Bone growth factors

Osteoblastic culture models, experimental, and clinical models have revealed that bone growth factors influence cellular activity. Growth factors including bone morphogenetic proteins, transforming growth factor beta, platelet-derived growth factor, insulin-like growth factors I and II, and acidic and basic fibroblast growth factors, are powerful tools for fracture healing and bone grafting. Understanding the role that bone growth factors play in bone repair is necessary to apply these factors in a clinical setting.

Effects of recombinant human fibroblast growth factor-2 on osteogenic cell populations during orthopic osteogenesis in vivo

The osteogenic effects of fibroblast growth factor-2 (FGF-2) in vivo on different cell populations of the osteoblastic cell lineage have not been fully elucidated. In this study, the efficacy of recombinant human fibroblast growth factor-2 (rhFGF-2) to stimulate orthopic bone formation in transosseous rat mandibular defects, with different cell populations allowed access to the defects, was investigated with the aim to further decipher FGF-2 effects. Three different doses of rhFGF-2 (10 ng, 100 ng, and 1 microg) were delivered in an absorbable collagen sponge carrier, whereas some defects were implanted with the carrier only, and some were left untreated. Barrier membranes, made of microporous expanded polytetrafluoroethylene, were simultaneously placed over half the number of defects in each treatment group, thus forcing osteogenic cells to be derived from intraosseous sources. Evaluation was made by light microscopy and computerized image analysis after 12 and 24 of days healing. Whereas no general stimulatory effect could be ascertained at 12 days, higher rhFGF-2 doses decreased bone formation by both intraosseously and periosteally derived cells. At 24 days, a clear, although rather limited, stimulatory effect on osteogenesis was observed, but again a decrease was observed with the 1 microg dose. At both observation periods, an increased number of osteocytes was found in the newly formed bone at sites treated with the lower rhFGF-2 doses, whereas the high-dose rhFGF-2 resulted in a return to control levels, irrespective of whether cells were intraosseously derived or from the periosteum also. Based on differential analysis of bone healing by cells from different sources as well as on bone cellularity, the results suggest that rhFGF-2 in vivo exerts a stimulatory effect on proliferation of committed osteoblastic cells. This effect is biphasic, in that higher doses are without effect or may even be inhibitory. No inductive effect on osteoblast recruitment could be found. These effects differ from those of, for instance, BMP-2 and TGF-beta1.