Novel glycidyl methacrylated dextran (Dex-GMA)/gelatin hydrogel scaffolds containing microspheres loaded with bone morphogenetic proteins: Formulation and characteristics

Novel thermomechanical hydrogel scaffolds containing our previously prepared microspheres loaded with bone morphogenetic proteins (BMP) were successfully generated by radical crosslinking and low dose gamma-irradiation from combination of two kind of biomaterials: glycidyl methacrylated dextran (Dex-GMA) and gelatin. The structure of those resulting smart hybrid hydrogels was evaluated by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) analyses, and as a function of the degree of Dex-GMA's substitution (DS), the proportion between Dex-GMA and gelatin, and the initial polyethyleneglycol (PEG) concentration used in the preparation of the hydrogels. The swelling and degradation properties and the temperature-sensitive drug release manner were determined by dynamic evaluation methods in vitro, and the gel content was also calculated. MIP analysis showed that by systematically altering the preparation parameters, the overall networks were clearly macroporous with pore sizes ranging from 5.6+/-4.2 to 37.7+/-13.7 microm. As expected, the pore size decreased as DS and initial PEG concentration increased, whereas the opposite was found for the gel content. Moreover, the porosity values ranged from 73.7+/-12.4% up to 89.6+/-6.3%. The SEM results also showed the inter-connective pores as well as microspheres encased into their porous structure of those hydrogels. The swelling and degradation properties of the resultant hydrogels varied according to the DS of Dex-GMA and initial PEG concentration, while the proportion between Dex-GMA and gelatin had no significant influence on those characterizations. By changing the composition ratio of the two precursors, the phase transition temperature (lower critical solution temperature, LSCT) of the hydrogel scaffolds could also be adjusted to be or near the body temperature, so BMP release from microsphere-hydrogel compounds could be accordingly controlled and the release period could be varied from 18 to more than 28 days. These results demonstrated that a novel temperature-sensitive and biodegradable Dex-GMA/gelatin scaffold containing microspheres loaded with BMP could be successfully developed from both dextran- and gelatin-based biomaterials, which could promisingly satisfy the need, desire, and expectation of both self-regulated drug delivery and tissue-engineering applications.

The regulatory role of TGF-beta in airway remodeling in asthma

Both structural and inflammatory cells are capable of secreting transforming growth factor (TGF)-beta and expressing TGF-beta receptors. TGF-beta can induce multiple cellular responses including differentiation, apoptosis, survival and proliferation, and has been implicated in the development of several pathogenic conditions including cancer and asthma. Elevated levels of TGF-beta have been reported in the asthmatic airway. TGF-beta binds to its receptor complex and activates multiple pathways involving proteins such as Sma and Mad homologues, phosphatidylinositol-3 kinase and the mitogen-activated protein kinases, leading to the transcription of several genes. Cell type, cellular condition, and microenvironment, all play a role in determining which pathway is activated, which, in turn, is an indication of which gene is to be transcribed. TGF-beta has been shown to induce apoptosis in airway epithelial cells. A possible role for TGF-beta in the regulation of epithelial cell adhesion properties has also been reported. Enhancement of goblet cell proliferation by TGF-beta suggests a role in mucus hyper-secretion. Elevated levels of TGF-beta correlate with subepithelial fibrosis. TGF-beta induces proliferation of fibroblast cells and their differentiation into myofibroblasts and extracellular matrix (ECM) protein synthesis during the development of subepithelial fibrosis. TGF-beta also induces proliferation and survival of and ECM secretion in airway smooth muscle cells (ASMCs), suggesting a possible cause of increased thickness of airway tissues. TGF-beta also induces the production and release of vascular endothelial cell growth factor and plasminogen activator inhibitor, contributing to the vascular remodeling in the asthmatic airway. Blocking TGF-beta activity inhibits epithelial shedding, mucus hyper-secretion, angiogenesis, ASMC hypertrophy and hyperplasia in an asthmatic mouse model. Reduction of TGF-beta production and control of TGF-beta effects would be beneficial in the development of therapeutic intervention for airway remodeling in chronic asthma.

Delivery mode and efficacy of BMP-2 in association with implants

Bone healing may be improved in implant patients by the administration of osteogenic agents, such as bone morphogenetic protein 2 (BMP-2). But the efficacy of BMP-2 depends upon its mode of application. We hypothesized that BMP-2 is capable of a higher osteogenic efficacy when delivered physiologically, viz., when incorporated into a calcium-phosphate carrier that mimics mineralized bone matrix, than when administered via simple pharmacological modes, such as by adsorption onto a carrier surface. Using an ectopic rat model, we compared the osteoinductive efficacies of calcium-phosphate implant-coatings bearing either incorporated, adsorbed, or incorporated and adsorbed BMP-2. When adsorbed directly onto the naked implant surface, BMP-2 was not osteogenic. When adsorbed onto a calcium-phosphate coating, it was osteoinductive, but not highly efficacious. When BMP-2 was incorporated into calcium-phosphate coatings, it was a potent bone-inducer, whose efficacy was compromised, not potentiated, by the additional deposition of an adsorbed pool.

Expression, purification, renaturation and activation of fish myostatin expressed in Escherichia coli: facilitation of refolding and activity inhibition by myostatin prodomain

Myostatin (growth and differentiation factor-8) is a member of the transforming growth factor-beta superfamily, is expressed mainly in skeletal muscle and acts as a negative growth regulator. Mature myostatin (C-terminal) is a homodimer that is cleaved post-translationally from the precursor myostatin, also yielding the N-terminal prodomain. We expressed in Escherichia coli three forms of fish myostatin: precursor, prodomain and mature. The three forms were over-expressed as inclusion bodies. Highly purified inclusion bodies were solubilized in a solution containing guanidine hydrochloride and the reducing agent DTT. Refolding (indicated by a dimer formation) of precursor myostatin, mature myostatin or a mixture of prodomain and mature myostatin was compared under identical refolding conditions, performed in a solution containing sodium chloride, arginine, a low concentration of guanidine hydrochloride and reduced and oxidized glutathione at 4 degrees C for 14 days. While precursor myostatin formed a reversible disulfide bond with no apparent precipitation, mature myostatin precipitated in the same refolding solution, unless CHAPS was included, and only a small proportion formed a disulfide bond. The trans presence of the prodomain in the refolding solution prevented precipitation of mature myostatin but did not promote formation of a dimer. Proteolytic cleavage of purified, refolded precursor myostatin with furin yielded a monomeric prodomain and a disulfide-linked, homodimeric mature myostatin, which remained as a latent complex. Activation of the latent complex was achieved by acidic or thermal treatments. These results demonstrate that the cis presence of the prodomain is essential for the proper refolding of fish myostatin and that the cleaved mature dimer exists as a latent form.

Homogeneous osteogenesis and bone regeneration by demineralized bone matrix loading with collagen-targeting bone morphogenetic protein-2

Considerable research has been focused on the development of bone morphogenetic protein-2 (BMP-2) delivery system for homologous and efficient bone regeneration. The aim of the present study was to develop a collagen-based targeting bone repair system. A collagen-binding domain (CBD) was added to the N-terminal of native BMP-2 to allow it bind to collagen specifically. We showed that the collagen-binding bone morphogenetic protein-2 (named bone morphogenetic protein2-h, BMP2-h) had maintained the full biological activity as compared to rhBMP2 lacking the CBD. In vitro functional study also demonstrated that collagen matrix could maintain higher bioactivity of BMP2-h than native BMP-2. When demineralized bone matrix (DBM) impregnated with BMP2-h was implanted subcutaneously in rats, homogeneous bone formation was observed. Moreover, in a rabbit mandible defect model, surgical implantation of collagen matrix loaded with BMP2-h exhibited remarkable osteoinductive properties and excellent homogeneous bone formation. Our studies suggested that this novel collagen-based BMP-2 targeting bone repair system induced better bone formation not only in quantity but also in quality. Similar approaches may also be used for the repair of other tissue injuries.

In vivo pro- and anti-inflammatory cytokines in normal and patients with rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic, deforming arthritis that can lead to disabilities and poor quality of life. Cytokines are protein mediators of inflammation and are produced as a result of the activation of various cellular reactions. They are the final mediators and/or regulators of the inflammatory process.

MATERIALS AND METHODS

The sera from 64 RA patients were assayed for both Th-1 and Th-2 related cytokines and soluble TNF-alpha receptors (IFN-gamma, TGF-beta, TNF-alpha, IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18, sTNF-R1 and sTNFR2) using ELISA.

RESULTS

The pro-inflammatory cytokines (IL-1, IL-6, IL-8, IL-18 and TNF- alpha) were significantly elevated in RA patients, while TGF-beta, an immunomodulatory cytokine, was elevated in control individuals. When the RA patients were categorised as active or inactive based on DAS scores, similar cytokines profiles were observed in both RA sub-groups. However, assays of sTNF-R1 and sTNFR-2 were noted to be significantly elevated in inactive RA patients when compared to active patients.

CONCLUSION

Our findings indicate that local production of cytokine inhibitors is capable of diminishing disease activity and cytokine activity.

Heat treatment of BMP-2 depots on implant materials generates an immobilized layer of BMP-2 with pronounced bioactivity

Bone cells seeded directly on depots of bone morphogenetic protein-2 (BMP-2) increase alkaline phosphatase (ALP) expression. Heating of such BMP-2 depots to 100 degrees C augmented the intensity of this local ALP induction. To understand this unexpected finding, we investigated the effect of heat treatment on BMP-2 depots more closely. Using a novel bioassay based on ALP-induction of remote cells, we found that the amount of released bioactive BMP-2 from heat-treated depots decays within days and could be described by an exponential function. From this function, we expected that pre-incubation of BMP-2 depots in culture medium for 4 weeks renders them insufficient to induce ALP. However, preincubated, heat-treated depots still induced maximal ALP, unless treated with the selective BMP-2 inhibitor noggin. Furthermore, heat treatment of BMP-2 depots generated a layer of immunoreactive BMP-2 at the surface of the carrier. In contrast, BMP-2 was washed off completely if heat treatment of adsorbed protein was omitted. Results show that heat treatment generates both a soluble pool of BMP-2 and a material-bound layer of BMP-2 in which the protein is protected against degradation. Therefore, heat treatment appears useful to locally immobilize BMP-2 on various implant surfaces.

Modified keratin sponge: binding of bone morphogenetic protein-2 and osteoblast differentiation

A keratin sponge was chemically modified to obtain carboxyl and amino sponges by the alkylation of a large amount of active SH group on keratin proteins with iodoacetic acid and 2-bromoethylamine, respectively. The carboxyl sponge having a large amount of carboxyl group was a scaffold that could bind significant amounts of basic bioactive proteins, such as lysozyme and bone morphogenetic protein (BMP)-2, and drugs. Lysozyme (maximum 3.7 mg), a model of basic cytokines such as BMP-2, was absorbed by the carboxyl sponge (4.8 mg), but not by the amino sponge. The lysozyme was rapidly released from the carboxyl sponge in a buffer containing at a concentration higher than 0.5 M, but at 0.15 M, near the physiological ionic strength, after initial burst (only 11%), no significant release was observed (15%, 48 h). BMP-2 also bound the carboxyl sponge. The preosteoblast cells grown inside the BMP-2-loaded sponge differentiated, whereas those grown outside the sponge did not, suggesting that no significant amount of BMP-2 leaked into the surrounding media. The effects of BMP-2 were confined inside modified keratin sponge. Therefore, using in vivo, we expect that only internal osteogenesis will be induced and that no external heterotopis ossification will be induced.

NSAID activated gene (NAG-1), a modulator of tumorigenesis

The NSAID activated gene (NAG-1), a member of the TGF-beta superfamily, is involved in tumor progression and development. The over-expression of NAG-1 in cancer cells results in growth arrest and increase in apoptosis, suggesting that NAG-1 has anti-tumorigenic activity. This conclusion is further supported by results of experiments with transgenic mice that ubiquitously express human NAG-1. These transgenic mice are resistant to the development of intestinal tumors following treatment with azoxymethane or by introduction of a mutant APC gene. In contrast, other data suggest a pro-tumorigenic role for NAG-1, for example, high expression of NAG-1 is frequently observed in tumors. NAG-1 may be like other members of the TGF-beta superfamily, acting as a tumor suppressor in the early stages, but acting pro-tumorigenic at the later stages of tumor progression. The expression of NAG-1 can be increased by treatment with drugs and chemicals documented to prevent tumor formation and development. Most notable is the increase in NAG-1 expression by the inhibitors of cyclooxygenases that prevent human colorectal cancer development. The regulation of NAG-1 is complex, but these agents act through either p53 or EGR-1 related pathways. In addition, an increase in NAG-1 is observed in inhibition of the AKT/GSK-3beta pathway, suggesting NAG-1 alters cell survival. Thus, NAG-1 expression is regulated by tumor suppressor pathways and appears to modulate tumor progression.

Three-dimensional fibrous PLGA/HAp composite scaffold for BMP-2 delivery

A protein loaded three-dimensional scaffold can be used for protein delivery and bone tissue regeneration. The main objective of this project was to develop recombinant human bone morphogenetic protein-2 (rhBMP-2) loaded poly(D,L-lactide-co-glycolide)/hydroxylapatite (PLGA/HAp) composite fibrous scaffolds through a promising fabrication technique, electrospinning. In vitro release of BMP-2 from these scaffolds, and the attachment ability and viability of marrow derived messenchymal stem cells (MSCs) in the presence of the scaffolds were investigated. The PLGA/HAp composite scaffolds developed in this study exhibit good morphology and it was observed that HAp nanoparticles were homogeneously dispersed inside PLGA matrix within the scaffold. The composite scaffolds allowed sustained (2-8 weeks) release of BMP-2 whose release rate was accelerated with increasing HAp content. It was also shown that BMP-2 protein successfully maintained its integrity and natural conformations after undergoing the process of electrospinning. Cell culture experiments showed that the encapsulation of HAp could enhance cell attachment to scaffolds and lower cytotoxicity.

Hollow calcium phosphate microcarriers for bone regeneration: in vitro osteoproduction and ex vivo mechanical assessment

Synthetic grafting materials, such as calcium phosphates (hydroxyapatite, HA; tricalcium phosphate, TCP), polymers, or composites thereof, can be used as osteoconductive scaffolds and delivery vehicles for osteoinductive growth factors. Carrier materials must be engineered to deliver these factors in a controlled fashion at a rate and dose consistent with the biological need and responsiveness of the system to optimize bone formation and ingrowth. They should also simultaneously provide mechanical support and slowly resorb as new bone is formed. This investigation assessed the elution characteristics of BMP-7 (OP-1) from hollow calcium phosphate spheres of varying chemical composition (HA/beta-TCP) and porosity (dense/porous). The pharmacokinetics indicated a bimodal trend of protein release with protein elution peaking between fifteen and thirty minutes in solution (bolus release) and continuing through the eight-week time point (sustained release). Eluted OP-1 bioactivity was characterized over a three-week period using mesenchymal stem cell (MSC) cultures and included assessment of the protein's differential, proliferative, and calcified nodule forming abilities. Alkaline phosphatase enzyme (ALP) activity in MSCs peaked between 12 and 16 days post-OP-1 exposure. Elutant from the HA dense treatment group induced the highest degree of ALP expression while elutant from the beta-TCP treatment groups induced the formation of significantly higher numbers of calcified nodules in culture. The aggregate modulus of a clinically relevant 2 cc dose of carriers was quantified using custom designed testing fixtures to investigate the effects of carrier size, porosity, chemical composition, and the presence of a central hole on mechanical integrity. Significant increases in moduli were noted for carrier size and chemical composition (HA>beta-TCP). These preliminary in vitro and ex vivo results indicate the clinical potential of the hollow calcium phosphate carriers as successful load-bearing delivery vehicles for OP-1.

Identification of an amyloidogenic region on keratoepithelin via synthetic peptides

Mutations of keratoepithelin (KE) gene in human chromosome 5q31 have been linked with corneal epithelial or stromal dystrophies characterized by the abnormal deposits of amyloid fibrils and/or non-amyloid aggregations in corneal tissue. We report herein that synthetic peptide containing amino acid (a.a.) residues of 515-532 of native KE protein can readily form beta-sheet-containing amyloid fibrils in vitro. Amyloid fibrils formed in various conditions from short synthetic peptides (containing a.a. 515-532 and 515-525, respectively) were characterized by thioflavin T (ThT) fluorescence assay, Congo red staining, electron microscopy (EM) and circular dichroism (CD). Triple-N-methylation of the synthetic peptides prevented the beta-sheet polymerization and related amyloid fibril formation. Comparison study with ThT fluorescence further demonstrated that synthetic peptides containing corneal dystrophy-related mutations within this region formed amyloid fibrils to various extents. Our results suggest that each individual dystrophy-related mutation by itself does not necessarily potentiate amyloid fibril formation of KE. Roles of these intrinsically amyloidogenic foci in abnormal KE aggregations and amyloid deposits of stromal corneal dystrophies await further investigation.

E6 and E7 oncoproteins from human papillomavirus type 16 induce activation of human transforming growth factor beta1 promoter throughout Sp1 recognition sequence

Human Papillomavirus (HPV) infection is the main etiologic agent of cervical cancer and HPV E6 and E7 oncogenes trans-regulate many cellular genes. An association between TGF-beta1 gene expression and cervical cancer development has been suggested; however, the mechanisms by which HPV influences TGF-beta1 expression remain unclear. In the present study we analyzed the mechanism through which HPV-16 E6 and E7 oncoproteins regulate the TGF-beta1 promoter in cervical tumor cells. Our results showed that E6 and E7 increased TGF-beta1 promoter activity. Furthermore, we identified a specific DNA sequence motif in the TGF-beta1 core promoter that is responsible for trans-activation and that corresponds to the Sp1e-binding site associated with HPV-16 E6 and E7 oncoproteins. Mutational analysis showed that the Sp1e recognition site abolished the trans-activation caused by E6 and E7. These results suggest a physical interaction and functional cooperation between viral oncoproteins and cellular regulatory elements of the TGF-beta1 promoter, and may explain the contribution of HPV-16 to TGF-beta1 gene expression in cervical cancer.

Monomeric mature protein of Nodal-related 3 activates Xbra expression

Nodal and related proteins play central roles in axes formation, mesendoderm induction, neural patterning, and left-right development. However, Xenopus nodal-related 3 (Xnr3) has unique activities in regulating neural induction and convergent extension movements. Xnr3 is distinguished from other transforming growth factor-beta superfamily members by the absence of the seventh conserved cysteine at the C terminus of the protein, and little is known about the molecular mechanism of Xnr3 action. In this study, we report a novel and unique mechanism of action that the mature region of Xenopus tropicalis nodal-related 3 (Xtnr3) functions as a monomer. Comparative analyses between Xtnr3 and Xnr5 revealed regions required for dimerization: (1) a conserved glycine, (2) the seventh cysteine, and (3) a putative alpha-helix located between the third and the fourth cysteines. These results indicate that the mature region of Nodal-related 3 entirely differs from other Nodal-related proteins in its mechanism of action.

Transforming growth factor-beta1 release from a porous electrostatic spray deposition-derived calcium phosphate coating

This study evaluated the utilization of a porous coating, derived with electrostatic spray deposition (ESD), as a carrier material for transforming growth factor-beta1 (TGF-beta1). A porous beta-tricalcium phosphate coating was deposited with ESD, and 10 ng of (125) I-labeled TGF-beta1 was loaded on the substrates. A burst release during the first hour of incubation of >90% was observed, in either culture medium or phosphate-buffered saline (PBS). Ninety-nine percent of the growth factor was released after 10 days of incubation. All samples were able to inhibit epithelial cell growth, indicating that the growth factor had remained bioactive after release. Thereafter, osteoblast-like cells were seeded upon substrates with or without 10 ng of TGF-beta1. While proliferation of osteoblast-like cells was increased on TGF-beta1-loaded substrates, differentiation was inhibited or delayed. In conclusion, a porous ESD-derived calcium phosphate coating can be used as a carrier material for TGF-beta1, when a burst release is desired.

Targeted delivery system for juxtacrine signaling growth factor based on rhBMP-2-mediated carrier-protein conjugation

We propose a model of artificial juxtacrine signaling for the controlled release of recombinant human bone morphogenetic protein-2 (rhBMP-2) suitable for guided bone regeneration. A porous three-dimensional scaffold of poly-(lactide-co-glycolide) was fabricated by means of gel molding and particulate leaching. Collagen immobilization onto the scaffold surface was produced by performing photo-induced graft polymerization of acrylic acid, and rhBMP-2 was tethered to the collagenous surface by covalent conjugation. On pharmacokinetic analysis, in vitro enzyme-linked immunosorbent and alkaline phosphatase assays revealed sustained, slow release of rhBMP-2 over 28 days, with a cumulative release of one third of the initial load diffusing out of the scaffold. Conjugation of rhBMP-2 inhibited the free lateral diffusion and internalization of the activated complex of rhBMP-2 and the bone morphogenetic protein receptor. Osteoprogenitor cells were used as bone precursors to determine the expression of biosignaling growth factor in regulating cell proliferation and differentiation. To identify the phenotype of cells seeded on the rhBMP-2-conjugated scaffold, cellular activity was evaluated with scanning electron microscopy and with viability, histological, and immunohistochemical testing. The rhBMP-2-conjugated scaffold prolonged stimulation of intracellular signal proteins in cells. Enhancement of cell growth and differentiation was considered a consequence of juxtacrine signaling transduction. Animal studies of rhBMP-2-containing filling implants showed evidence of resorption and de novo bone formation. The present study revealed the potential of biomimetic constructs with co-immobilized adhesion and growth factors to induce osteoinduction and osteogenesis. Such constructs may be useful as synthetic bone-graft materials in orthopaedic tissue engineering.

Phosphonic acid monolayers for binding of bioactive molecules to titanium surfaces

Two different phosphonic acid monolayer films for immobilization of bioactive molecules such as the protein BMP-2 on titanium surfaces have been prepared. Monolayers of (11-hydroxyundecyl)phosphonic acid and (12-carboxydodecyl)phosphonic acid molecules were produced by a simple dipping process (the T-BAG method). The terminal functional groups on these monolayers were activated (carbonyldiimidazole for hydroxyl groups and N-hydroxysuccinimide for carboxyl groups) to bind amine-containing molecules. The reactivity of the surfaces was investigated using trifluoroethylamine hydrochloride and BMP-2. Each step of the surface modification procedure was characterized by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry.

Novel solvent-free fabrication of biodegradable poly-lactic-glycolic acid (PLGA) capsules for antibiotics and rhBMP-2 delivery

Osteomyelitis has been one of the most common causes of post-operative problems and complications despite the advances in surgical techniques and the availability of newly developed antibiotics. Local antibiotic and growth factor delivery devices for treatment of various surgical infections have been studied recently, especially in the case of orthopedic infections. The report was to develop novel solvent-free biodegradable capsules for antibiotics and growth factors delivery. To fabricate a biodegradable capsule, polylactide-polyglycolide copolymers were pre-mixed with vancomycin. The mixture was then compression molded and sintered to form a cylinder with a cover of 8 mm in diameter. After the addition of 1 and 10 microg recombinant bone morphogenetic protein (rhBMP-2) into the core, an ultrasonic welder was used to seal the capsules. An elution method was employed to characterize the in vitro release characteristics of the antibiotics and the rhBMP-2 over a 30-day period. The HPLC analysis and the bacterial inhibition test showed that biodegradable capsules released high concentrations and activity of vancomycin (well above the minimum inhibition concentration) in vitro for the period of time needed to treat bone infection; i.e. 4-6 weeks. In addition, the results of ELISA and ALP tests also suggested that the capsules released active rhBMP-2 for up to 30 days. By adopting this novel technique, we will be able to fabricate biodegradable capsules of various medicines for long-term drug deliveries.

The structural basis of TGF-β, bone morphogenetic protein, and activin ligand binding

The transforming growth factor-β (TGF-β) superfamily is a large group of structurally related growth factors that play prominent roles in a variety of cellular processes. The importance and prevalence of TGF-β signaling are also reflected by the complex network of check points that exist along the signaling pathway, including a number of extracellular antagonists and membrane-level signaling modulators. Recently, a number of important TGF-β crystal structures have emerged and given us an unprecedented clarity on several aspects of the signal transduction process. This review will highlight these latest advances and present our current understanding on the mechanisms of specificity and regulation on TGF-β signaling outside the cell.

Myostatin regulation of muscle development: Molecular basis, natural mutations, physiopathological aspects

Since its identification in 1997, myostatin has been considered as a novel and unique negative regulator of muscle growth, as mstn-/- mice display a dramatic and widespread increase in skeletal muscle mass. Myostatin also appears to be involved in muscle homeostasis in adults as its expression is regulated during muscle atrophy. Moreover, deletion of the myostatin gene seems to affect adipose tissue mass in addition to skeletal muscle mass. Natural myostatin gene mutations occur in cattle breeds such as Belgian Blue, exhibiting an obviously increased muscle mass, but also in humans, as has recently been demonstrated. Here we review these natural mutations and their associated phenotypes as well as the physiological influence of the alterations in myostatin expression and the physiopathological consequences of changes in myostatin expression, especially with regard to satellite cells. Interestingly, studies have demonstrated some rescue effects of myostatin in muscular pathologies such as myopathies, providing a novel pharmacological strategy for treatment. Furthermore, the myostatin pathway is now better understood thanks to in vitro studies and it consists of inhibition of myoblast progression in the cell cycle, inhibition of myoblast terminal differentiation, in both cases associated to protection from apoptosis. The molecular pathway driving the myogenic myostatin influence is currently under extensive study and many molecular partners of myostatin have been identified, suggesting novel potent muscle growth enhancers for both human and agricultural applications.

Frequency of polymorphisms of signal peptide of TGF-beta1 and -1082G/A SNP at the promoter region of Il-10 gene in patients with carotid stenosis

The role of inflammation in atherosclerosis is well recognized. We have evaluated the allele frequencies of the +869T/C and +915G/C polymorphisms (SNPs) at the TGF-beta1 gene and -1082G/A SNP at IL-10 promoter sequence, two well-known immunosuppressive and anti-inflammatory cytokines, in patients with carotid stenosis. Our data suggest a lack of association between these SNPs and the susceptibility to atherosclerosis although other reports have demonstrated this association. These results may be due to the pleiotropic effects of the cytokines and/or differences in haplotype combination that should be investigated to elucidate the role of TGF-beta1 and IL-10 polymorphisms in atherosclerosis.

Ectopic bone formation in mice associated with a lactic acid/dioxanone/ethylene glycol copolymer–tricalcium phosphate composite with added recombinant human bone morphogenetic protein-2

A new putty-like material with bone-inducing capacity was made by combining a block copolymer of poly d,l-lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG) and beta-tricalcium phosphate (beta-TCP) powder with added recombinant human bone morphogenetic protein-2 (rhBMP-2). To optimize the material's efficacy for bone formation, we formulated the optimal composition ratio of the respective constituent that gives the greatest osteoinductive efficacy in a mouse model of ectopic bone formation. In this series of studies, we investigated the size of ectopic bone mass induced 3 and 6 weeks after implantation of the materials composed of 30 mg of PLA-DX-PEG with 2 microg of rhBMP-2 and 0, 15, 30, or 60 mg of beta-TCP powder. An additional experiment was designed to investigate how content ratios of beta-TCP powder in 30 mg-putty implants (0%, 16.7%, 33.3%, 50%, 66.7%, 83.3%, or 100%) for a fixed dose (5 microg) of the rhBMP-2 altered the size of the induced ossicle. The results from the first experiment indicated that the bone yields were linearly dependent on the amount of additional beta-TCP powder. In the second experiment, the largest ossicles induced by 5 microg of rhBMP-2 were obtained when the polymer/beta-TCP ratio was 1/2 in mice. The data provide important insights into the fabrication of implants that provide efficacious delivery of rhBMP-2. The new putty-like material may be valuable for repairing or regenerating bone in a clinical setting.

Fabrication and release behavior of a novel freeze-gelled chitosan/γ-PGA scaffold as a carrier for rhBMP-2

OBJECTIVE

The aim of this study was to fabricate a novel composite porous scaffold by blending chitosan and gamma-poly(glutamic acid) (gamma-PGA) for the sustained delivery of rhBMP-2.

METHODS

Chitosan and gamma-PGA were blended to fabricate a novel porous scaffold by the freeze-gelation method. For comparison, scaffolds made of freeze-dried chitosan, freeze-dried PLLA, and freeze-gelled chitosan were also prepared. The scaffolds were loaded with rhBMP-2, and then the controlled release of rhBMP-2 from the scaffolds was assessed by ELISA.

RESULTS

The freeze-gelled chitosan/gamma-PGA scaffold (M0=318.29 ng, k=0.32 d(-1)) gave the most satisfactory release curve, followed by the freeze-gelled chitosan (M0=392.76 ng, k=0.59 d(-1)), freeze-dried chitosan (M0=229.21 ng, k=2.28 d(-1)), and freeze-dried PLLA (M0=8.4 ng, k=482.54 d(-1)) scaffolds. In the stability test, p-dioxane (the solvent for PLLA) seriously deteriorated rhBMP-2, whereas acetic acid (the solvent for chitosan) did not.

SIGNIFICANCE

A novel chitosan/gamma-PGA composite scaffold for the controlled release of rhBMP-2 was established, with an enhanced release amount and sustained release behavior. This scaffold has many potential applications in bone regenerative therapies.

Electrospun silk-BMP-2 scaffolds for bone tissue engineering

Silk fibroin fiber scaffolds containing bone morphogenetic protein 2 (BMP-2) and/or nanoparticles of hydroxyapatite (nHAP) prepared via electrospinning were used for in vitro bone formation from human bone marrow-derived mesenchymal stem cells (hMSCs). BMP-2 survived the aqueous-based electrospinnig process in bioactive form. hMSCs were cultured for up to 31 days under static conditions in osteogenic media on the scaffolds (silk/PEO/BMP-2, silk/PEO/nHAP, silk/PEO/nHAP/BMP-2) and controls (silk/PEO, silk/PEO extracted). Electrospun silk fibroin-based scaffolds supported hMSC growth and differentiation toward osteogenic outcomes. The scaffolds with the co-processed BMP-2 supported higher calcium deposition and enhanced transcript levels of bone-specific markers than in the controls, indicating that these nanofibrous electrospun silk scaffolds were an efficient delivery system for BMP-2. X-ray diffraction (XRD) analysis revealed that the apatite formed on the silk fibroin/BMP-2 scaffolds had higher crystallinity than on the silk fibroin scaffold controls. In addition, nHAP particles were incorporated into the electrospun fibrous scaffolds during processing and improved bone formation. The coexistence of BMP-2 and nHAP in the electrospun silk fibroin fibers resulted in the highest calcium deposition and upregulation of BMP-2 transcript levels when compared with the other systems. The results suggest that electrospun silk-fibroin-based scaffolds are potential candidates for bone tissue engineering. Furthermore, the mild aqueous process required to spin the fibers offers an important option for delivery of labile cytokines and other components into the system.

Limited Mutations in Full-length Tetrameric Human α2-Macroglobulin Abrogate Binding of Platelet-derived Growth Factor-BB and Transforming Growth Factor-β1

alpha2-Macroglobulin (alpha2M) inhibits diverse extracellular proteases, binds growth factors such as platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-beta1 (TGF-beta1), and carries beta-amyloid peptide. alpha2M may also trigger cell signaling by binding to the low density lipoprotein receptor-related protein (LRP-1) and/or other cell surface receptors. Based on studies with recombinant alpha2M fragments expressed in bacteria and synthetic peptides, we previously localized a growth factor-binding site near the center of the alpha2M subunit. However, because intact alpha2M forms a hollow cylinder structure, an alternative model for growth factor binding involves nonspecific entrapment within the alpha2M core. To distinguish between these two models, we engineered mutations in the putative growth factor binding sequence of full-length alpha2M. These mutations did not perturb the tetrameric structure of alpha2M, reaction with proteases, the thiol ester bonds, or binding to LRP-1. A single mutation (E730R) completely blocked binding of platelet-derived growth factor-BB to intact alpha2M. E730R did not alter TGF-beta1 binding; however, this mutation in combination with mutations at Glu714 and Asp719 eliminated the increase in TGF-beta1 binding associated with alpha2M conformational change. These studies demonstrate that growth factor binding to intact alpha2M is specific, involving a defined region of the alpha2M subunit. The exact sequences required for binding different growth factors may be non-identical, mimicking the model of the bait region in which different proteases target adjacent and sometimes overlapping sequences.

Lefty at the crossroads of "stemness" and differentiative events

Stem cells are functionally defined by their ability to self-renew and generate a progeny capable of creation or reconstitution of various tissues. Microarray analysis has shown a member of the transforming growth factor (TGF)-beta superfamily, Lefty, to be the single most abundant inhibitor in stem cells and in maternal decidua that supports embryo implantation. Lefty is regulated by pathways such as Smad (Sma and Mad [mothers against decapentaplegic]) and WNT (wingless-type) and by the transcriptional factor Oct3/4 (octamer-binding transcription factor 3/4), which support "stemness." Lefty is also induced upon exit from the state of stemness, including forced in vitro differentiation, and leukemia inhibitory factor withdrawal. Lefty is a candidate in cell-fate decisions because of its unique ability to modulate the expression of TGF-beta family proteins such as Nodal and by blanket inhibition of the activity of members of this family which require EGF-CFC (epidermal growth factor-Cripto, Frl-1, and Cryptic) as a coreceptor.

Strong binding of bioactive BMP-2 to nanocrystalline diamond by physisorption

Nano-crystalline diamond (NCD)-coated surfaces were efficiently functionalized with bone morphogenetic protein-2 (BMP-2) by means of physisorption. Due to their randomly oriented texture, NCD-coated surfaces appear to bind complex molecules firmly. Applying various highly sensitive analytical methods, the interaction was found extremely stable. The strength of the experimentally measured adherence between BMP-2 and NCD was further corroborated by theoretical calculations. Oxygen treatment rendered NCD hydrophilic by the appearance of surface oxygen containing groups. This particular NCD surface exhibited even higher binding energies towards BMP-2 than the hydrophobic surface, and this surface was also favoured by cultured cells. Most importantly in this context, bound BMP-2 was found fully active. When cultured on BMP-2-treated NCD, osteosarcoma cells strongly up-regulated alkaline phosphatase, a specific marker for osteogenic differentiation. Hence, this simple method will allow generating highly versatile surfaces with complex biomimetic coatings, essentials for novel medical devices and implants as well as for innovative scaffolds in tissue engineering.

Capillary electrophoresis immunoassay chemiluminescence detection of zeptomoles of bone morphogenic protein-2 in rat vascular smooth muscle cells

A capillary electrophoresis immunoassay (CEIA) method based on enhanced chemiluminescence (CL) detection was developed and applied to arteriosclerosis pathology research in the medical field. The system of enzyme-horseradish peroxidase (HRP) catalyzing the luminol/H2O2/p-iodophenol reaction was adopted in this paper. HRP was detected with the detection limit (S/N = 3) of 4.4 pM (53 zmol), which represents one of the highest sensitivities of HRP reported yet. HRP was first linked to bone morphogenic protein-2 (BMP-2) in rat vascular smooth muscle (VSM) cells with noncompetitive format and analyzed by CE-CL. HRP-Ab(2)-mAb-BMP-2 complexes can be baseline separated from free HRP in 3 min. The detection limit (S/N = 3) of BMP-2 is 6.2 pM (75 zmol). This technique has been successfully applied to arteriosclerosis development mechanistic study by investigating the change of BMP-2 content in VSM cells, which were stimulated by angiotensin II for different times. The change trends of BMP-2 contents are well in accord with that of the commonly used pathology image analysis system. It proves that the CEIA-CL technique proposed could be developed into a sensitive and new method for clinical assay and pathology research.

Enhanced bone formation by transforming growth factor-beta1-releasing collagen/chitosan microgranules

Collagen/chitosan composite microgranules were fabricated as bone substitutes for the purpose of obtaining high bone-forming efficacy. The microgranules have the flexibility to fill various types of defect sites with closer packing. The interconnected pores formed spaces between the microgranules, which allowed new bone ingrowth and vascularization. In addition, the transforming growth factor-beta 1 (TGF-beta1) was incorporated into the microgranules in order to improve bone-healing efficacy. The collagen/chitosan microgranules were fabricated by dropping a mixed solution into a NaOH/ethanol solution. TGF-beta1 was loaded into the collagen/chitosan microgranules by soaking the microgranules in a TGF-beta1 solution. Scanning electron microscopy (SEM) observations and experiments examining the release of TGF-beta1 from chitosan and the collagen/chitosan microgranules were performed. SEM was used to examine the cell morphologies on the microgranules and cell proliferation was evaluated using a dimethylthiazole tetrazolium bromide assay. The differentiated cell function was assessed by measuring the alkaline phosphatase (ALPase) activity as well as detecting an osteocalcin assay. The in vivo bone-regeneration experiments were performed using a rabbit calvarial defect model. TGF-beta1 was released from the collagen/chitosan microgranules at a therapeutic concentration for 4 weeks. SEM indicated that the seeded osteoblastic cells were firmly attached to the microgranules and proliferated in a multilayer manner. The proliferation of the osteoblasts on the TGF-beta1-loaded microgranules was the highest among the different types of microgranules tested. The ALPase activity and osteocalcin level of all the samples increased during the culture period, and the TGF-beta1-loaded microgranules had a significantly higher ALPase activity and osteocalcin content than the other microgranules. The TGF-beta1-loaded microgranules demonstrated a higher bone-regenerative capacity in the rabbit calvarial defects after 4 weeks than the TGF-beta1-unloaded microgranules.

Structure of the ternary signaling complex of a TGF-beta superfamily member

The crystal structure of the complete signaling complex formed between bone morphogenetic protein 2 (BMP-2) and the extracellular domains (ECDs) of its type I receptor [bone morphogenetic protein receptor type Ia (BMPR-Ia)-ECD] and its type II receptor [activin receptor type II (ActRII)-ECD] shows two fundamental structural constraints for receptor assembly. First, the homodimeric BMP-2 ligand assembles two pairs of each receptor symmetrically, where each of the receptor ECDs does not make physical contact. Therefore, conformational communication between receptor ECDs, if any, should be propagated through the central ligand. Second, the type I and II receptor interfaces of the complex, when compared with those of binary complexes such as BMP-2/BMPR Ia-ECD, BMP-7/ActRII-ECD, and activin/ActRIIb-ECD, respectively, show there are common sets of positions repeatedly used by both ligands and receptors. Therefore, specificity-determining amino acid differences at the receptor interfaces should also account for the disparity in affinity of individual receptors for different ligand subunits. We find that a specific mutation to BMP-2 increases its affinity to ActRII-ECD by 5-fold. These results together establish that the specific signaling output is largely determined by two variables, the ligand-receptor pair identity and the mode of cooperative assembly of relevant receptors governed by the ligand flexibility in a membrane-restricted manner.

Integrity and stability studies of precipitated rhBMP-2 microparticles with a focus on ATR-FTIR measurements

A major obstacle in the development of protein drug formulations is the need to maintain the native, active protein structure both during the formulation process and upon long time storage. Controlled precipitation was evaluated for its potential to supply stable microparticulate formulations of bone-regenerating recombinant human Bone Morphogenetic Protein-2 (rhBMP-2). Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) did provide insight into the protein formulation and stability. Temperature dependent ATR-FTIR measurements and DSC measurements allow for the study of changes in the protein structure during melting. To address the question of isomerization, peptide mapping was performed, and protein aggregation was monitored by size exclusion chromatography (SEC). It could be demonstrated by ATR-FTIR that controlled precipitation did not harm the protein and the process is fully reversible. DSC measurements further confirmed these findings. No changes in the transition temperature and process were observed after precipitation and redissolution. Upon storage, isomerization and aggregation could be detected, but to a lower extent in the precipitated formulation as compared to a solution reference. Thus, controlled precipitation of rhBMP-2 is fully reversible and has the potential as alternative formulation tool for the generation of a microparticulate drug delivery system.

cDNA encoding sequences for myostatin and FGF6 in sea bass (Dicentrarchus labrax, L.) and the effect of fasting and refeeding on their abundance levels

Fish have the ability to compensate for set-backs in growth as a result of fasting. When food levels are restored, growth in these fish can increase over and above normal rates. This phenomenon, known as "compensatory growth", has been studied with respect to enhancing food conversion efficiency. However, the mechanisms by which food intake activates an increase in somatic growth, and especially in muscle growth, are not well understood. In this study, we report first on the isolation of two complete cDNAs sequences encoding sea bass (Dicentrarchus labrax) myostatin and fibroblast growth factor 6 (FGF6), which have been shown to be major genetic determinants of skeletal muscle growth. The open reading frames of myostatin (376 amino acids) and FGF6 (209 amino acids) showed 97-63% and 87-62% sequence identity with other vertebrate myostatins and FGF6s, respectively. We also report on the expression profile of myostatin and FGF6 in sea bass skeletal muscle in response to different feeding regimens, as quantified by real-time RT-PCR. Nutritional status significantly influenced the myostatin expression levels in muscle, inducing an up-regulation during fasting and a down-regulation during the recovery from fasting, whereas the muscular FGF6 mRNA levels were not significantly affected by the feeding status of the animals. These findings suggest that myostatin has an inhibitory role in muscle growth in response to different feeding regimens, whereas FGF6 is not involved in the muscle compensatory growth induced by refeeding.

In Vitro Culture of Chondrocytes in a Novel Thermoreversible Gelation Polymer Scaffold Containing Growth Factors

In this study we examined the potential of a novel thermoreversible gelation polymer (TGP) to act as a 3-D hydrogel scaffold and deliver both chondrocytes and growth factors. Chondrocytes obtained from bovine articular cartilage were studied as a suspension in TGP chilled to 4 degrees C, in the presence or absence of the growth factors IGF-1 and/or TGF beta2. The cold cell/aqueous suspensions were injected into a cylindrical mold and cultured at 37 degrees C for up to 16 weeks. Specimens obtained at 12 and 16 weeks were semitranslucent and elastic. The matrices surrounding the chondrocytes were histologically positive to Safranin-O staining and type II collagen staining. The glycosaminoglycan and hydroxyproline contents in the specimens increased as a function of time and because of the presence of growth factors; those cultured with growth factors produced significantly more of these substances than those cultured without. We have concluded that TGP has potential as a scaffold material in the generation of tissue-engineered cartilage in vitro.

Collective review: bioactive implants coated with poly(D,L-lactide) and growth factors IGF-I, TGF-beta1, or BMP-2 for stimulation of fracture healing

Demographic data reveal that due to the increasing aging of the population, complications with the musculoskeletal system will increase in the next years. One major problem in orthopedic and trauma surgery are the delayed healing or non-unions of long bone fractures. The exogenous application of growth factors can stimulate the bone healing to reduce these complications. Beside the choice of the optimal growth factor the application system is important. Therefore, we developed a new bioactive coating method for implants, which is based on a biodegradable poly(D,L-lactide) (coating thickness: 10 mum). This coating allows the incorporation of growth factors and the controlled release of these factors during the healing process without the need for further devices. The effect of different growth factors (IGF-I, TGF-beta1, and BMP-2) locally released from coated intramedullary implants on fracture healing was investigated with biomechanical and histological analysis in rats. All investigated growth factors stimulated the fracture healing as assessed with biomechanical tests and histological analysis. The local application of combined IGF-I and TGF-beta1 had the most stimulating effect on fracture healing, followed by the effect of BMP-2, IGF-I, and TGF-beta1 alone. Bioactive coating of biomechanical well-established implants can on the one hand stabilize the fracture and on the other hand stimulate healing processes to increase healing and to reduce the rate of complications.

Identification of distinct inhibin and transforming growth factor beta-binding sites on betaglycan: functional separation of betaglycan co-receptor actions

Betaglycan is a co-receptor that mediates signaling by transforming growth factor beta (TGFbeta) superfamily members, including the distinct and often opposed actions of TGFbetas and inhibins. Loss of betaglycan expression, or abrogation of betaglycan function, is implicated in several human and animal diseases, although both betaglycan actions and the ligands involved in these disease states remain unclear. Here we identify a domain spanning amino acids 591-700 of the betaglycan extracellular domain as the only inhibin-binding region in betaglycan. This binding site is within the betaglycan ZP domain, but inhibin binding is not integral to the ZP motif of other proteins. We show that the inhibin and TGFbeta-binding residues of this domain overlap and identify individual amino acids essential for binding of each ligand. Mutation of Val614 to Tyr abolishes both inhibin and TGFbeta binding to this domain. Full-length betaglycan V614Y, and other mutations, retain TGFbeta binding activity via a distinct site, but are unable to bind inhibin-A. These betaglycan mutants fail to mediate inhibin antagonism of activin signaling but can present TGFbeta to TbetaRII. Separating the co-receptor actions of betaglycan toward inhibin and TGFbeta will allow the clarification of the role of betaglycan in disease states such as renal cell carcinoma and endometrial adenocarcinoma.

Expression, purification, and renaturation of bone morphogenetic protein-2 from Escherichia coli

Homodimeric bone morphogenetic protein-2 (BMP-2) is a member of the transforming growth factor beta superfamily that has been used for bone grafting. We were interested in exploring the functions of BMP-2 in other disease areas and focused on expressing and purifying active BMP-2 proteins. We have developed a new approach which involves using FoldIt refolding buffer to refold BMP-2 followed by a heparin affinity column to separate correctly folded dimer from monomer. A high yield of 29.4 mg BMP-2 dimer per gram cell wet weight was achieved. The purified BMP-2 dimer was shown to possess the same level of activity as BMP-2 from CHO cells as tested by the induction of alkaline phosphatase activity in C2C12 cells. This approach has potential application in refolding and purifying other homodimeric proteins.

The effect of a fibrin-fibronectin/beta-tricalcium phosphate/recombinant human bone morphogenetic protein-2 system on bone formation in rat calvarial defects

In spite of good prospects for bone morphogenetic proteins (BMP) applications, an ideal carrier system for BMPs has not yet been identified. The purpose of this study was to evaluate the osteogenic effect of a fibrin-fibronectin sealing system (FFSS) combined with beta-tricalcium phosphate (beta-TCP) as a carrier system for recombinant human bone morphogenetic proteins (rhBMP-2) in the rat calvarial defect model. Eight-millimeter critical-size calvarial defects were created in 100 male Sprague-Dawley rats. The animals were divided into five groups of 20 animals each. The defects were treated with rhBMP-2/FFSS, rhBMP-2/FFSS/beta-TCP, FFSS and FFSS/beta-TCP carrier control or were left untreated as a sham-surgery control. Defects were evaluated by histologic and histometric parameters following a 2- and 8-week healing interval (10 animals/group/healing intervals). The FFSS/beta-TCP carrier group was significantly greater in new bone area at 2 weeks (p<0.05) and new tissue area at 2 and 8 weeks (p<0.01) relative to the FFSS carrier group. New bone and new tissue area in the rhBMP-2/FFSS/beta-TCP group were significantly greater than in the rhBMP-2/FFSS group at 8 weeks (p<0.01). On histologic observation, FFSS remnants were observed at 2 weeks, but by 8 weeks, the FFSS appeared to be completely resorbed. rhBMP-2 combined with FFSS/beta-TCP produced significantly more new bone and new tissue formation in this calvarial defect model. In conclusion, FFSS/beta-TCP may be considered as an available carrier for rhBMP-2.

Bone induction by recombinant human osteogenic protein-1 (hOP-1, BMP-7) in the primate Papio ursinus with expression of mRNA of gene products of the TGF-beta superfamily

Predictable bone induction in clinical contexts requires information on the expression and cross regulation of gene products of the transforming growth factor-beta (TGF-beta) superfamily elicited by single applications of each recombinant human bone morphogenetic/osteogenic proteins (BMPs/OPs). Using the calvarium and the rectus abdominis muscle of adult baboons Papio ursinus as a model for tissue induction and morphogenesis, this study investigated the induction of bone morphogenesis by gamma-irradiated hOP-1 delivered by gamma-irradiated bovine insoluble collagenous bone matrix, the hOP-1 osteogenic device, for bone induction in heterotopic and orthotopic sites of the primate Papio ursinus and the expression patterns of OP-1, collagen type IV, BMP-3 and TGFbeta1mRNAs elicited by increasing single applications of doses of the hOP-1 osteogenic devices (0.1, 0.5 and 2.5 mg hOP-1/g of matrix) applied heterotopically in the rectus abdominis muscle and orthotopically in 48 calvarial defects of 12 adult baboons. Histology and histomorphometry on serial undecalcified sections prepared from the specimens harvested on day 15, 30 and 90 showed that all the doses of the hOP-1 osteogenic device induced bone formation culminating in complete calvarial regeneration by day 90. Type IV collagen mRNA expression, a marker of angiogenesis, was strongly expressed in both heterotopic and orthotopic tissues. High levels of expression of OP-1 mRNA demonstrated autoinduction of OP-1 mRNAs. Expression levels of BMP-3 mRNA varied from tissues induced in heterotopic vs. orthotopic sites with high expression in rapidly forming heterotopic ossicles together with high expression of type IV collagen mRNA. The temporal and spatial expressions of TGF-beta1 mRNAindicate a specific temporal transcriptional window during which expression of TGF-beta1 is mandatory for successful and optimal osteogenesis. The induction of bone by hOP-1 in Papio ursinus develops as a mosaic structure with distinct spatial and temporal patterns of gene expression of members of the TGF-beta superfamily that singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis.

Bone morphogenetic protein-2 binds as multilayers to a collagen delivery matrix: an equilibrium thermodynamic analysis

Recombinant human bone morphogenetic protein-2 (rhBMP-2) promotes bone growth but must be retained at the delivery site for optimal efficacy in vivo. rhBMP-2 release from a collagen-based matrix has shown favorable pharmacokinetics. The present study assessed binding affinity and binding saturation of rhBMP-2 to a collagen matrix as a function of solution and rhBMP-2 isoform variables. Results indicate that rhBMP-2 binds to the collagen matrix with affinities on the order of 10(3) to 10(4) M(-1). Maximum binding, nu, was primarily a function of pH for heterogeneous rhBMP-2 and the extended (T(266)/T(266)) isoform. However, binding saturation of the <Q(283)/<Q(283) isoform was unaffected by pH. Overall, binding saturation was higher than the calculated saturation of a rhBMP-2 monolayer, suggesting both hydrophobic and ionic interactions in a multilayer formation. The contributions of pH and ionic strength to the linkage free energy of interaction was on the order of 1.3 kcal mol(-1) and approximately 0.3 kcal mol(-1), respectively. This thermodynamic approach can serve to optimize interactions between therapeutic proteins and delivery systems.

Optimized use of a biodegradable polymer as a carrier material for the local delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2)

To improve the efficacy of a block copolymer of poly-d, l-lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG) as a drug delivery system for recombinant human bone morphogenetic proteins (rhBMPs), we examined the relationship between the volume of PLA-DX-PEG, the dose of rhBMP-2 and osteoinduction in a mouse model of ectopic bone formation. In a series of studies, we compared the size and bone mineral content (BMC) of ectopically induced bone by PLA-DX-PEG and collagen sponges carrying different quantities of rhBMP (0, 1, 2, 5, 10, 20 microg). An additional experiment was designed to investigate how a range of PLA-DX-PEG polymer volumes (15, 30, 60, 90 mg) with a fixed rhBMP concentration (0.01 wt%), altered the size and BMC of the induced ossicle. The influence of polymer volume was also examined in a further experiment wherein a fixed amount of rhBMP was placed in a range of PLA-DX-PEG copolymer volumes to give different concentrations of the protein per implant (0.02-0.0017 wt%). The results indicate that the bone yields were linearly dependent on the dose of rhBMP and also were proportional to the polymer volume above the minimal concentration of rhBMP-2 (0.0017 wt% in this series). The optimal concentration of rhBMP-2 in PLA-DX-PEG was 0.003 wt% in mice. The data provide important insights into the fabrication of implants that provide efficacious delivery of rhBMP-2 using the lowest possible dose of this expensive osteoinductive protein. This information will be of value for the clinical use of BMPs.

[Improved osseointegration of titanium implants after surface coating with polymers in a rabbit model]

In this study we present the first results of the investigation of polymer-coated titanium implants implanted in the proximal tibia and distal femora of New Zealand white rabbits. The results of DEXA scans, micro-CT, and histological analysis showed an increase of osseointegration. We suggest that controlled release kinetics after coupling of these polymers with BMP-2 can additionally increase osseointegration.

The role of myostatin and bone morphogenetic proteins in muscular disorders

Skeletal muscle is the largest organ in the human body, and plays an important role in body movement and metabolism. Skeletal muscle mass is lost in genetic disorders such as muscular dystrophy, muscle wasting and ageing. Chemicals and proteins that restore muscle mass and function are potential drugs that can improve human health and could be used in the clinic. Myostatin is a muscle-specific member of the transforming growth factor (TGF)-beta superfamily that plays an essential role in the negative regulation of muscle growth. Inhibition of myostatin activity is a promising therapeutic method for restoring muscle mass and strength. Potential inhibitors of myostatin include follistatin domain-containing proteins, myostatin propeptide, myostatin antibodies and chemical compounds. These inhibitors could be beneficial for the development of clinical drugs for the treatment of muscular disorders. Bone morphogenetic protein (BMP) plays a significant role in the development of neuromuscular architecture and its proper functions. Modulation of BMP activity could be beneficial for muscle function in muscular disorders. This review will describe the current progress in therapy for muscular disorders, emphasising the importance of myostatin as a drug target.

Controlled release of rhBMP-2 loaded poly(dl-lactic-co-glycolic acid)/calcium phosphate cement composites in vivo

The release kinetics of recombinant human bone morphogenetic protein-2 (rhBMP-2) loaded poly(dl-lactic-co-glycolic acid)/calcium phosphate cement (PLGA/Ca-P cement) composites were studied in vivo. RhBMP-2 was radiolabeled with (131)I and entrapped within PLGA microparticles or adsorbed onto the microparticle surface. PLGA microparticles were prepared of high molecular weight (HMW) PLGA (weight average molecular weight [M(w)] 49,100+/-1700) or low molecular weight (LMW) PLGA (M(w) 5,900+/-300) and used for preparation of 30:70 wt.% PLGA/Ca-P cement composite discs. Release of 131I-rhBMP-2 loaded composites was assessed by scintigraphic imaging according to a 2(2) two-level full factorial design in the rat ectopic model during four weeks. In vivo release kinetics varied among formulations. All formulations showed slow release without initial burst, and displayed a linear release from 3 to 28 days. Release of LMW entrapped rhBMP-2 composites (1.7+/-0.3%/day) was significantly faster than release from other formulations (p<0.01). After 28 days, retention within the composites was 65+/-5%, 75+/-4%, 50+/-4% and 70+/-6% of the initial rhBMP-2 for HMW entrapped, HMW adsorbed, LMW entrapped and LMW adsorbed rhBMP-2 composites, respectively. Release from the composite was probably slowed down by an interaction of rhBMP-2 and Ca-P cement after rhBMP-2 release from PLGA microparticles. We conclude that PLGA/Ca-P cement composites can be considered as sustained slow release vehicles and that the release and retention of rhBMP-2 can be modified according to the desired profile to a limited extent.

The effect of calcium hydroxide on solubilisation of bio-active dentine matrix components

Calcium hydroxide (Ca(OH)(2)) has been used extensively to induce dentine regeneration through formation of dentine bridges at sites of pulp exposure after dental tissue injury, however, the biological processes underpinning these events are unclear. We hypothesise that growth factors and other bio-active molecules, sequestered within dentine matrix, may be released by the action of Ca(OH)(2) and signal gene expression in pulp cells, which mediates the changes in cell behaviour observed during regeneration. Powdered sound, human dentine samples were extracted with either 0.02 m Ca(OH)(2), pH 11.7 or 10% EDTA, pH 7.2 ( a control known extractant of bio-active and other ECM molecules from dentine) over a 14-day period. Extracts were compared for non-collagenous protein (NCP) and glycosaminoglycan (GAG) content using dye binding assays and protein compositions were analysed by 1D-polyacrylamide gel electrophoresis (1D-PAGE) and TGF-beta1 ELISA. The effects of extracts on TGF-beta1, Collagen-1alpha and Nestin gene expression were analysed using semi-quantitative RT-PCR in the dental MDPC-23, OD-21 and fibroblastic Swiss 3T3 cell lines following 24h of exposure. Ca(OH)(2) solubilised NCPs and GAGs from the dentine ECM, although with a lower yield than the EDTA solution and with different kinetics. 1D-PAGE analysis demonstrated some differences in profiles for proteins solubilised from dentine by Ca(OH)(2) and EDTA. Both solutions released TGF-beta1 from the dentine with higher concentrations present in the EDTA (1.395 +/- 0.036 ng/mg) versus the Ca(OH)(2) (0.364 +/- 0.012 ng/mg) extract. Notably, both extracts induced similar gene expression profiles in all cell lines. These data provide a rational explanation for the action of Ca(OH)(2) during pulp capping in which the cellular activities involved in dentine bridge formation may be mediated through release of growth factors and other bio-active molecules from the dentine by Ca(OH)(2).

Inactivation of active and latent transforming growth factor beta by free thiols: Potential redox regulation of biological action

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine with important roles in inflammation, wound repair, and cancer. Cells secrete TGF-beta as a latent protein complex, consisting of disulfide-bonded homodimers of growth factor and latency-associated propeptide. Latency regulates extracellular TGF-beta action by controlling the levels of active growth factor available. We report here that active and latent TGF-beta were inactivated in vitro by reduction of the growth factor dimer under physiological conditions. We also demonstrate that the latency-associated propeptide has chaperone-like activity and partially protects TGF-beta from inactivation. TGF-beta inactivation occurred upon incubation with the physiological redox agents, cysteine, homocysteine, and reduced glutathione. Inactivation was temperature- and dose-dependent. While inactivation by physiological concentrations of redox agents was partial at 37 degrees C, active and latent TGF-beta were completely inactivated by raising the temperature in the presence of the redox agents. The mechanism of TGF-beta inactivation involved the generation of biologically inactive growth factor monomer and required the presence of free thiol groups, since thiol blockers protected TGF-beta from reduction. We conclude that non-enzymatic redox reactions may be involved in the regulation of extracellular TGF-beta activity. This might be of particular relevance in wound repair (e.g. in burns), as a mechanism protecting from excess TGF-beta activity, as well as in conditions involving redox dysregulation, such as reperfusion injury of the heart, Alzheimer's disease, and cancer.

Immobilization of bone morphogenetic protein-2 on a nanofibrous chitosan membrane for enhanced guided bone regeneration

BMP-2 (bone morphogenetic protein-2) has been used in promoting bone formation and, in combination with various delivery carriers, in bone regeneration or bone tissue-engineering practice. In the present study, BMP-2 was immobilized directly on a GBR (guided bone-regenerative) membrane surface made of chitosan nanofibres, providing a bioactive surface that can enhance bone-regeneration capacity. The BMP-2-conjugated membrane surface retained bioactivity for up to 4 weeks of incubation, as well as holding over 50% of the initial BMP-2 attached. The BMP-2-conjugated surface increased osteoblastic cell attachment in accordance with the amount of BMP-2 conjugated. In addition, the BMP-2-conjugated chitosan membrane significantly promoted cell proliferation, alkaline phosphatase activity, as well as calcium deposition when compared with BMP-2-adsorbed membrane, indicating a stable localization of BMP-2 at the surface of the chitosan membrane. Taking these findings together, the conjugation of BMP-2 on a chitosan nanofibrous membrane would seen to be applicable for inducing significant and localized bone formation in future GBR procedures.

An in vitro evaluation of PCL-TCP composites as delivery systems for platelet-rich plasma

In this study, we first investigated the in vitro degradation properties of biodegradable, bioresorbable polycaprolactone-20% tricalcium phosphate (PCL-TCP) composites immersed in simulated body fluid (SBF) and phosphate buffered saline (PBS). Then, the release profiles of the growth factors present in platelet-rich plasma (PRP) loaded onto the composites incubated in SBF and PBS were compared. Composites immersed in both buffers showed water uptake of 13.7%+/-0.75 at day 1, followed by a constant uptake of 12.1%+/-0.3 until day 12. Henceforth the water uptake declined for SBF- and increased for PBS-soaked composites. The weight loss data did not reveal any trend. SBF- and PBS-soaked samples displayed 1-2% weight loss for 2 and 5 of the ten time points measured respectively. The original protein retention (PR) of the composites was 49.1%+/-1.50. After immersion in SBF and PBS for 4 weeks, the PR was augmented to 88.5%+/-1.40 and 69.1%+/-1.40 correspondingly. PRP after activation contained 164.7+/-24.8, 194+/-43 and 18.3+/-4.75 ng/ml of TGF-beta1, PDGF-BB and IGF-1. Microscopic analysis verified the attachment of PRP to the rods and pores of the composites. Interestingly, the buffers played an important role in determining the release profiles of TGF and PDGF. Firstly, PBS-soaked composites manifested a tri-phasic burst-like profile that was absent in SBF. Secondly, SBF-soaked composites experienced delayed release of the growth factors and total release was not achieved (64.4% for TGF and 60.5% for PDGF), whereas total release was realized for PBS-soaked composites. Lastly, release profiles from SBF-soaked composites were growth factor mediated in terms of their amounts and sizes. This was not observed for PBS-soaked composites. IGF-1, on the other hand, exhibited a progressive reduction in levels over the entire experimental period for both buffers. The mechanisms of release were theorized to be a combination of diffusion, degradation and bioactivity. Since SBF is analogous to our body fluids in terms of its ionic constituents, we expect the elution profiles derived from SBF-soaked samples to more accurately emulate the in vivo situation. In conclusion, this study has deemed PCL-TCP composites as suitable delivery systems for platelet-rich plasma.

Delivery of TGF-β1 and chondrocytes via injectable, biodegradable hydrogels for cartilage tissue engineering applications

In this work, novel hydrogel composites, based on the biodegradable polymer, oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) were utilized as injectable cell and growth factor carriers for cartilage tissue engineering applications. Specifically, bovine chondrocytes were embedded in composite hydrogels co-encapsulating gelatin MPs loaded with transforming growth factor-beta1 (TGF-beta1). Hydrogels with embedded cells co-encapsulating unloaded MPs and those with no MPs served as controls in order to assess the effects of MPs and TGF-beta1 on chondrocyte function. Samples were cultured up to 28 days in vitro. By 14 days, cell attachment to embedded gelatin MPs within the constructs was observed via light microscopy. Bioassay results showed that, over the 21 day period, there was a statistically significant increase in cellular proliferation for samples containing gelatin MPs, but no increase was exhibited in samples without MPs over the culture period. The release of TGF-beta1 further increased cell construct cellularity. Over the same time period, glycosaminoglycan content per cell remained constant for all formulations, suggesting that the dramatic increase in cell number for samples with TGF-beta1-loaded MPs was accompanied by maintenance of the cell phenotype. Overall, these data indicate the potential of OPF hydrogel composites containing embedded chondrocytes and TGF-beta1-loaded gelatin MPs as a novel strategy for cartilage tissue engineering.

Release of bioactive BMP from dextran-derived microspheres: a novel delivery concept

Recent developments of biotechnology have produced a great variety of protein and bioactive drugs. For these drugs to be used therapeutically, suitable drug delivery systems have become increasingly essential. Dextran-derived biomaterials have been considered to be compatible matrices for protein and bioactive drugs because of their hydrophilic properties and ability to control drug dissolution and permeability. A novel class of dextran-glycidylmethacrylate (Dex-GMA)/poly(ethylene glycol) (PEG) microspheres were designed and synthesized by polymerization of Dex-GMA emulsified in an aqueous PEG solution. Dex-GMA was prepared by substituting the hydroxyl groups in Dex by GMA. The drug loading and in vitro drug release was evaluated by routine procedure and the biological activity of BMP-loaded microspheres was studied by experimental cytology methods. Recombinant human bone morphogenetic protein-2 (rhBMP-2) were entrapped in dextran-derived microspheres quantitatively and with full preservation of their biological activity. In vitro release kinetics indicated that dextran-derived microspheres could retain rhBMP-2 in a variable manner depending on the preparation and degradation of the microspheres. The release profiles of rhBMP-2 from microspheres as a function of time showed that rhBMP-2 releasing kinetics in vitro fitted to first-order and Higuchi equations. The release profile in vitro was in accord with two phases kinetics law and more than 60% drug were released during 20 days. Cytology studies showed rhBMP-2 microspheres have good biological effects on cultured periodontal ligament cells, and could achieve a longer action time than concentration of rhBMP-2 solution. These properties make those microspheres interesting osteo-conductive BMP carriers, allowing to decrease the amount of implanted factor required for tissue regeneration.