Strategies for delivering bone morphogenetic protein for bone healing

An injectable cationic hydrogel electrostatically interacted with BMP2 to enhance in vivo osteogenic differentiation of human turbinate mesenchymal stem cells

We have designed and characterized an injectable, electrostatically bonded, in situ-forming hydrogel system consisting of a cationic polyelectrolyte [(methoxy)polyethylene glycol-b-(poly(ε-caprolactone)-ran-poly(L-lactic acid)] (MP) copolymer derivatized with an amine group (MP-NH₂) and anionic BMP2. To the best of our knowledge, there have been hardly any studies that have investigated electrostatically bonded, in situ-forming hydrogel systems consisting of MP-NH₂ and BMP2, with respect to how they promote in vivo osteogenic differentiation of human turbinate mesenchymal stem cells (hTMSCs). Injectable formulations almost immediately formed an electrostatically loaded hydrogel depot containing BMP2, upon injection into mice. The hydrogel features and stability of BMP2 inside the hydrogel were significantly affected by the electrostatic attraction between BMP2 and MP-NH₂. Additionally, the time BMP2 spent inside the hydrogel depot was prolonged in vivo, as evidenced by in vivo near-infrared fluorescence imaging. Biocompatibility was demonstrated by the fact that hTMSCs survived in vivo, even after 8 weeks and even though relatively few macrophages were in the hydrogel depot. The osteogenic capacity of the electrostatically loaded hydrogel implants containing BMP2 was higher than that of a hydrogel that was simply loaded with BMP2, as evidenced by Alizarin Red S, von Kossa, and hematoxylin and eosin staining as well as osteonectin, osteopontin, osteocalcin, and type 1α collagen mRNA expression. The results confirmed that our injectable, in situ-forming hydrogel system, electrostatically loaded with BMP2, can enhance in vivo osteogenic differentiation of hTMSCs.

Association study of copy number variation in BMP8A gene with the risk of ankylosing spondylitis in Iranian population

BACKGROUND

Copy number variation (CNV) of DNA segments has been considered as an important component of genetic variation, affecting the quality and quantity of gene expression. Bone morphogenic protein 8A (BMP8A) has been reported to function in bone formation. With respect to the bone and joint complications in ankylosing spondylitis (AS), this investigation aimed to study the role of BMP8A gene CNV in impressing the gene expression as well as the disease risk.

METHODS

A total of 900 individuals, including 450 patients with AS and 450 healthy controls were enrolled. The copy numbers of BMP8A gene were detected by TaqMan real-time polymerase chain reaction (PCR) method. BMP8A messenger RNA (mRNA) transcript level in peripheral blood mononuclear cells (PBMCs) was also measured by SYBR Green real-time gene expression PCR method.

RESULTS

No significant association of BMP8A copy number was detected with the risk of AS. BMP8A mRNA expression level was significantly downregulated in patients compared with controls. mRNA expression level of BMP8A in both AS patients with and without syndesmophyte was significantly lower than the healthy control group. There was no correlation between the mRNA expression level of BMP8A and both demographic and clinical data of the patients.

CONCLUSIONS

Although BMP8A gene expression was downregulated in patients with AS, its copy number could not affect the transcript level of BMP8A gene in PBMCs and was not associated with susceptibility to AS in Iranian population. BMP8a may take into account as an indicator of bone formation process in AS, but it seems that mechanisms other than CNV may regulate this protein.

Simple and facile preparation of recombinant human bone morphogenetic protein-2 immobilized titanium implant via initiated chemical vapor deposition technique to promote osteogenesis for bone tissue engineering application

Over the past few decades, titanium (Ti) implants have been widely used to repair fractured bones. To promote osteogenesis, immobilization of osteoinductive agents, such as recombinant human bone morphogenic protein-2 (rhBMP2), onto the Ti surface is required. In this study, we prepared rhBMP2 immobilized on glycidyl methacrylate (GMA) deposited Ti surface through initiated chemical vapor deposition (iCVD) technique. After preparation, the bio-functionalized Ti surface was characterized by physicochemical analysis. For in vitro analysis, the developed Ti was evaluated by cell proliferation, alkaline phosphatase activity, calcium deposition, and real-time polymerase chain reaction to verify their osteogenic activity against human adipose-derived stem cells (hASCs). The GMA deposited Ti surface was found to effectively immobilize a large dose of rhBMP2 as compared to untreated Ti. Additionally, rhBMP2 immobilized on Ti showed significantly enhanced osteogenic differentiation and increased calcium deposition with nontoxic cell viability. These results clearly confirm that our strategy may provide a simple, solvent-free strategy to prepare an osteoinductive Ti surface for bone tissue engineering applications.

Orientation effects on the nanoscale adsorption behavior of bone morphogenetic protein-2 on hydrophilic silicon dioxide

Bone Morphogenetic Protein-2 (BMP-2) is a growth factor associated with different developmental functions in regenerative medicine and tissue engineering. Because of its favorable properties for the development of bone and cartilage tissue, BMP-2 promotes the biocompatibility of medical implants. In this research, molecular dynamics simulations were implemented to simulate the interaction of BMP-2 with a flat hydrophilic silicon dioxide substrate, an important biomaterial for medical applications. We considered the influence of four orthogonal protein orientations on the adsorption behavior. Results showed that arginine and lysine were the main residues to interact with the silicon dioxide substrate, directly adsorbing onto the surface and overcoming water layers. However, between these charged residues, we observed a preference for arginine to adsorb. Orientations with the α-helix loop closer to the surface at the beginning of the simulations had greater loss of secondary structure as compared to the other configurations. Among all the orientations, the end-on B configuration had favorable adsorption characteristics with a binding energy of 14 000 kJ mol-1 and retention of 21.7% β-sheets as confirmed by the Ramachandran plots. This research provides new insights into the nanoscale interaction of BMP-2 and silicon dioxide substrate with applications in orthopedic implants and regenerative medicine.

Bone Morphogenetic Proteins (BMPs) and Bone Regeneration

Many research methods exist to elucidate the role of BMP-2 during bone regeneration. This chapter briefly reviews important animal models used in these studies and provides details on the rat femur defect model. This animal model is frequently utilized to measure the efficacy of osteogenic factors like BMP-2. Detailed information about delivery methods, dose range, and dose duration used in BMP-2-related studies are provided.

Polyethylenimine-alginate nanocomposites based bone morphogenetic protein 2 gene-activated matrix for alveolar bone regeneration

The repair and treatment of lost or damaged alveolar bone is of great significance in dentistry. Gene-activated matrix (GAM) technology provides a new way for bone regeneration. It is a local gene delivery system, which can not only recruit cells, but also influence their fate. For this purpose, we fabricated a bone morphogenetic protein 2 (BMP-2) gene-loaded absorbable gelatin sponge (AGS) and studied its effect on promoting alveolar bone formation and preventing resorption following tooth extraction in rats. In order to obtain better transfection efficiency, polyethylenimine-alginate (PEI-al) nanocomposites were synthesized and used as gene vectors to deliver BMP-2 cDNA plasmids (PEI-al/pBMP-2). The transfection efficiency, BMP-2 protein expression and osteogenic differentiation of the cells were investigated in vitro. In vivo, we established an alveolar bone regeneration model by extracting the rats' left mandibular incisors. The rats were randomly assigned into 3 groups: control group, unfilled sockets; AGS group, sockets filled with PEI-al solution-loaded gelatin sponges; AGS/BMP group, sockets filled with PEI-al/pBMP-2 solution-loaded gelatin sponge. Radiological and histological assays were performed at 4 and 8 weeks later. In vitro transfection assays indicated that PEI-al/pBMP-2 complexes could effectively transfect MC3T3-E1 cells, promoting the secretion of BMP-2 protein for at least 14 days, as well as increasing the expression of osteogenesis-related gene, ALP activity and calcium deposition. In vivo, western blot analysis showed BMP-2 protein was expressed in bone tissues of AGS/BMP group. The relative height of the residual alveolar ridge and bone mineral density (BMD) of the AGS/BMP group were significantly greater than those in the AGS and control groups at 4 and 8 weeks, respectively. Histological examination showed that, at 4 weeks, osteoblasts had grown in a cubic shape around the new bone in the AGS/BMP group, suggesting new bone formation. In conclusion, the combination of PEI-al/pBMP-2 complexes and gelatin sponge could promote alveolar bone regeneration, which may provide an easy and valuable method for alveolar ridge preservation and augmentation.

Polyethylenimine-alginate nanocomposites based bone morphogenetic protein 2 gene-activated matrix may provide an easy and valuable method for alveolar ridge regeneration.

Recombinant Human Bone Morphogenetic Protein 6 Delivered Within Autologous Blood Coagulum Restores Critical Size Segmental Defects of Ulna in Rabbits

BMP2 and BMP7, which use bovine Achilles tendon-derived absorbable collagen sponge and bovine bone collagen as scaffold, respectively, have been approved as bone graft substitutes for orthopedic and dental indications. Here, we describe an osteoinductive autologous bone graft substitute (ABGS) that contains recombinant human BMP6 (rhBMP6) dispersed within autologous blood coagulum (ABC) scaffold. The ABGS is created as an injectable or implantable coagulum gel with rhBMP6 binding tightly to plasma proteins within fibrin meshwork, as examined by dot-blot assays, and is released slowly as an intact protein over 6 to 8 days, as assessed by ELISA. The biological activity of ABGS was examined in vivo in rats (Rattus norvegicus) and rabbits (Oryctolagus cuniculus). In a rat subcutaneous implant assay, ABGS induced endochondral bone formation, as observed by histology and micro-CT analyses. In the rabbit ulna segmental defect model, a reproducible and robust bone formation with complete bridging and restoration of the defect was observed, which is dose dependent, as determined by radiographs, micro-CT, and histological analyses. In ABGS, ABC scaffold provides a permissive environment for bone induction and contributes to the use of lower doses of rhBMP6 compared with BMP7 in bovine bone collagen as scaffold. The newly formed bone undergoes remodeling and establishes cortices uniformly that is restricted to implant site by bridging with host bone. In summary, ABC carrier containing rhBMP6 may serve as an osteoinductive autologous bone graft substitute for several orthopedic applications that include delayed and nonunion fractures, anterior and posterior lumbar interbody fusion, trauma, and nonunions associated with neurofibromatosis type I.

Cell Type Influences Local Delivery of Biomolecules from a Bioinspired Apatite Drug Delivery System

Recently, the benefit of step-wise sequential delivery of fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 from a bioinspired apatite drug delivery system on mouse calvarial bone repair was demonstrated. The thicknesses of the nanostructured poly-l-Lysine/poly-l-Glutamic acid polyelectrolyte multilayer (PEM) and the bone-like apatite barrier layer that make up the delivery system, were varied. The effects of the structural variations of the coating on the kinetics of cell access to a cytotoxic factor delivered by the layered structure were evaluated. FGF-2 was adsorbed into the outer PEM, and cytotoxic antimycin-A (AntiA) was adsorbed to the substrate below the barrier layer to detect the timing of the cell access. While MC3T3-E1 osteoprogenitor cells accessed AntiA after three days, the RAW 264.7 macrophage access occurred within 4 h, unless the PEM layer was removed, in which case the results were reversed. Pits were created in the coating by the RAW 264.7 macrophages and initiated delivery, while the osteoprogenitor cell access to drugs occurred through a solution-mediated coating dissolution, at junctions between the islands of crystals. Macrophage-mediated degradation is therefore a mechanism that controls drug release from coatings containing bioinspired apatite.

The Use of Pulsed Electromagnetic Fields to Promote Bone Responses to Biomaterials In Vitro and In Vivo

Implantable biomaterials are extensively used to promote bone regeneration or support endosseous prosthesis in orthopedics and dentistry. Their use, however, would benefit from additional strategies to improve bone responses. Pulsed Electromagnetic Fields (PEMFs) have long been known to act on osteoblasts and bone, affecting their metabolism, in spite of our poor understanding of the underlying mechanisms. Hence, we have the hypothesis that PEMFs may also ameliorate cell responses to biomaterials, improving their growth, differentiation, and the expression of a mature phenotype and therefore increasing the tissue integration of the implanted devices and their clinical success. A broad range of settings used for PEMFs stimulation still represents a hurdle to better define treatment protocols and extensive research is needed to overcome this issue. The present review includes studies that investigated the effects of PEMFs on the response of bone cells to different classes of biomaterials and the reports that focused on in vivo investigations of biomaterials implanted in bone.

Outcomes of Alveolar Ridge Preservation With Recombinant Human Bone Morphogenetic Protein-2: A Systematic Review

PURPOSE

The main focused question of this systematic review was as follows: Does the application of recombinant human bone morphogenetic protein-2 (rhBMP-2) placed in extraction sockets reduce the alveolar ridge changes?

METHODS

A systematic literature search was performed up to February 2017. Clinical studies published in English were included. Outcome variables of interest were as follows: changes in alveolar ridge width and height, the quality of new bone, patient's safety, adverse events, and postoperative complications.

RESULTS

Seven articles were included. Because of the vast heterogeneity and high risk of bias among the studies, performing a meta-analysis deemed not feasible. Application of rhBMP-2 in the extraction socket was more effective in the reduction of ridge width compared with that of ridge height. The superiority of 1.5 mg/mL rhBMP-2/absorbable collagen sponge over the carrier alone on alveolar ridge width/height remodeling was more significant when it was applied in the sockets with ≥50% buccal bone dehiscence. The limited available data showed that rhBMP-2 did not improve the quality of new bone. Antibodies against rhBMP-2 were detected in the serum in 1 trial.

CONCLUSIONS

Within the limits of this review, 1.5 mg/mL rhBMP-2 might be beneficial for preserving the alveolar ridge width within extraction sockets given as to whether the cost-effectiveness is justifiable. Studies with lower risk of bias should be performed to confirm the above findings.

Influence of Mussel-Derived Bioactive BMP-2-Decorated PLA on MSC Behavior in Vitro and Verification with Osteogenicity at Ectopic Sites in Vivo

Osteoinductive activity of the implant in bone healing and regeneration is still a challenging research topic. Therapeutic application of recombinant human bone morphogenetic protein-2 (BMP-2) is a promising approach to enhance osteogenesis. However, high dose and uncontrolled burst release of BMP-2 may introduce edema, bone overgrowth, cystlike bone formation, and inflammation. In this study, low-dose BMP-2 of 1 μg was used to design PLA-PD-BMP for functionalization of polylactic acid (PLA) implants via mussel-inspired polydopamine (PD) assist. For the first time, the binding property and efficiency of the PD coating with BMP-2 were directly demonstrated and analyzed using an antigen-antibody reaction. The obtained PLA-PD-BMP surface immobilized with this low BMP-2 dose can endow the implants with abilities of introducing strong stem cell adhesion and enhanced osteogenicity. Furthermore, in vivo osteoinduction of the PLA-PD-BMP-2 scaffolds was confirmed by a rat ectopic bone model, which is marked as the "gold standard" for the evidence of osteoinductive activity. The microcomputed tomography, Young's modulus, and histology analyses were also employed to demonstrate that PLA-PD-BMP grafted with 1 μg of BMP-2 can induce bone formation. Therefore, the method in this study can be used as a model system to immobilize other growth factors onto various different types of polymer substrates. The highly biomimetic mussel-derived strategy can therefore improve the clinical outcome of polymer-based medical implants in a facile, safe, and effective way.

Paradoxical side effects of bisphosphonates on the skeleton: What do we know and what can we do?

Bisphosphonates are considered the most effective drugs for controlling adult and pediatric osteolytic diseases. Although they have been used successfully for many years, several side effects, such as osteonecrosis of the jaw, delayed dental eruption, atypical femoral fracture, and alterations to the bone growth system, have been described. After an overview of nitrogenous bisphosphonate, the purpose of this article is to describe their mechanisms of action and current applications, review the preclinical and clinical evidence of their side effects in the skeleton ("what we know"), and describe current recommendations for preventing and managing these effects ("what we can do"). Finally, promising future directions on how to limit the occurrence of these side effects will be presented.

Epigenetics and pathogenesis of systemic sclerosis; the ins and outs

The pathogenesis of many diseases is influenced by environmental factors which can affect human genome and be inherited from generation to generation. Adverse environmental stimuli are recognized through the epigenetic regulatory complex, leading to gene expression alteration, which in turn culminates in disease outcomes. Three epigenetic regulatory mechanisms modulate the manifestation of a gene, namely DNA methylation, histone changes, and microRNAs. Both epigenetics and genetics have been implicated in the pathogenesis of systemic sclerosis (SSc) disease. Genetic inheritance rate of SSc is low and the concordance rate in both monozygotic (MZ) and dizygotic (DZ) twins is little, implying other possible pathways in SSc pathogenesis scenario. Here, we provide an extensive overview of the studies regarding different epigenetic events which may offer insights into the pathology of SSc. Furthermore, epigenetic-based interventions to treat SSc patients were discussed.

A straightforward approach to enhance the textural, mechanical and biological properties of injectable calcium phosphate apatitic cements (CPCs): CPC/blood composites, a comprehensive study

Two commercial formulations of apatitic calcium phosphate cements (CPCs), Graftys® Quickset (QS) and Graftys® HBS (HBS), similar in composition but with different initial setting time (7 and 15min, respectively), were combined to ovine whole blood. Surprisingly, although a very cohesive paste was obtained after a few minutes, the setting time of the HBS/blood composite dramatically delayed when compared to its QS analogue and the two blood-free references. Using solid state NMR, scanning electron microscopy and high frequency impedance measurements, it was shown that, in the particular case of the HBS/blood composite, formation of a reticulated and porous organic network occurred in the intergranular space, prior to the precipitation of apatite crystals driven by the cement setting process. The resulting microstructure conferred unique biological properties to this material upon implantation in bone defects, since its degradation rate after 4 and 12weeks was more than twice that for the three other CPCs, with a significant replacement by newly formed bone.

STATEMENT OF SIGNIFICANCE

A major challenge in the design of bone graft substitutes is the development of injectable, cohesive, resorbable and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with initial mechanical properties as close as bone ones. Thus, we describe specific conditions in CPC-blood composites where the formation of a 3D clot-like network can interact with the precipitated apatite crystals formed during the cement setting process. The resulting microstructure appears more ductile at short-term and more sensitive to biological degradation which finally promotes new bone formation. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology.

Continuous stimulation with differentiation factors is necessary to enhance osteogenic differentiation of human mesenchymal stem cells in-vitro

Bone defect treatment belongs to the most challenging fields in orthopedic surgery and requires the well-coordinated application of mesenchymal stem cells (MSC) and differentiation factors. MSC isolated from reaming material (RMSC) and iliac crest (BMSC) in combination with bone morphogenetic protein-7 (BMP-7) and insulin-like growth factor-1 (IGF-1) have been used. The short half-life of both factors limit their applications: a burst release of the factor can probably not induce sustainable differentiation. We stimulated MSC in osteogenic differentiation medium with three different concentrations of BMP-7 or IGF-1: Group A was stimulated continuously, group B for 24 h and group C remained without any stimulation. Osteogenic differentiation was measured after seven and 14 days by alizarin red staining and alkaline phosphatase (ALP) activity. Continuous stimulation led to higher levels of osteogenic differentiation than short-term stimulation. This could lead to a reconsideration of established application forms for differentiation factors, aiming to provide a more sustained release.

Dual delivery nanosystem for biomolecules. Formulation, characterization, and in vitro release

Because of the biocompatible and biodegradable properties of poly (lactic-co-glycolic acid) (PLGA), nanoparticles (NPs) based on this polymer have been widely studied for drug/biomolecule delivery and long-term sustained-release. In this work, two different formulation methods for lysozyme-loaded PLGA NPs have been developed and optimized based on the double-emulsion (water/oil/water, W/O/W) solvent evaporation technique. They differ mainly in the phase in which the surfactant (Pluronic^® F68) is added: water (W-F68) and oil (O-F68). The colloidal properties of these systems (morphology by SEM and STEM, hydrodynamic size by DLS and NTA, electrophoretic mobility, temporal stability in different media, protein encapsulation, release, and bioactivity) have been analyzed. The interaction surfactant-protein depending on the formulation procedure has been characterized by surface tension and dilatational rheology. Finally, cellular uptake by human mesenchymal stromal cells and cytotoxicity for both systems have been analyzed. Spherical hard NPs are made by the two methods However, in one case, they are monodisperse with diameters of around 120nm (O-F68), and in the other case, a polydisperse system of NPs with diameters between 100 and 500nm is found (W-F68). Protein encapsulation efficiency, release and bioactivity are maintained better by the W-F68 formulation method. This multimodal system is found to be a promising "dual delivery" system for encapsulating hydrophilic proteins with strong biological activity at the cell-surface and cytoplasmic levels.

Isolation and Characterization of Lactoferrin Peptides with Stimulatory Effect on Osteoblast Proliferation

Lactoferrin is reported to be a potential food protein with osteogenic activity. However, the activity of lactoferrin peptides is questionable. In the present study, we isolated and characterized peptides from lactoferrin with stimulatory effect on osteoblast proliferation. Peptides from the lactoferrin pepsin hydrolysate were purified using cation-exchange and gel-filtration chromatography. Effects of different hydrolysates and peptides on the proliferation of osteoblast MC3T3-E1 cells were compared by MTT assay. Results showed that fraction P5-a from Superdex Peptide 10/300 GL gel chromatography showed better activity. Tricine-sodium dodecyl sulfate polyacrylamide gel electrophoresis and high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry confirmed that two peptides components of P5-a corresponded to fractions of 20-78 and 191-277 amino acids in Bos taurus lactoferrin molecule (GI: 221706349). These results will provide some theoretical and practical data for the preparation and application of osteogenic peptides in functional food industry.

Controlled dual delivery of low doses of BMP-2 and VEGF in a silk fibroin-nanohydroxyapatite scaffold for vascularized bone regeneration

The controlled co-release of osteoinductive and angiogenic factors is an efficient approach to promote vascularized bone regeneration, and a suitable controlled release system can largely reduce the usage of these factors to avoid cost and safety problems. In this study, a cell-free vascularized bone tissue engineering system based on a silk fibroin (SF)/nanohydroxyapatite (nHAp) scaffold was developed, in which very low doses of osteoinductive and angiogenic factors, bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), were embedded and released in a controlled manner to facilitate bone formation and vascularization, respectively. BMP-2 and VEGF were adsorbed onto SF microspheres (diameter of 1.5 ± 0.3 μm) that were prepared using a co-flow capillary device, and these microspheres were subsequently incorporated within the SF/nHAp scaffolds to provide controlled release. BMP-2 and VEGF were incorporated into SF microspheres via chemical covalent bonding and physical adsorption, respectively, leading to their controlled and sustained release from the SF/nHAp scaffolds. The rapid initial release of VEGF mimicked its expression at the early bone healing stage and promoted angiogenesis, and the relatively slow and sustained release of BMP-2 facilitated osteogenic differentiation both in vitro and in vivo, and the bone completely bridged the rat calvarial defects after 12 weeks of implantation. Overall, our findings suggest that the controlled dual release of very low doses of BMP-2 (300 ng per scaffold) and VEGF (20 ng per scaffold) from SF/nHAp scaffolds results in a synergistic effect on vascularized bone regeneration; this controlled release system can largely reduce the usage of BMP-2 as compared to other systems.