Pharmacokinetics and bone formation by BMP-2 entrapped in polyethylenimine-coated albumin nanoparticles

Recent Advancements and Strategies for Overcoming the Blood-Brain Barrier Using Albumin-Based Drug Delivery Systems to Treat Brain Cancer, with a Focus on Glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive malignant tumor, and the most prevalent primary malignant tumor affecting the brain and central nervous system. Recent research indicates that the genetic profile of GBM makes it resistant to drugs and radiation. However, the main obstacle in treating GBM is transporting drugs through the blood-brain barrier (BBB). Albumin is a versatile biomaterial for the synthesis of nanoparticles. The efficiency of albumin-based delivery systems is determined by their ability to improve tumor targeting and accumulation. In this review, we will discuss the prevalence of human glioblastoma and the currently adopted treatment, as well as the structure and some essential functions of the BBB, to transport drugs through this barrier. We will also mention some aspects related to the blood-tumor brain barrier (BTBB) that lead to poor treatment efficacy. The properties and structure of serum albumin were highlighted, such as its role in targeting brain tumors, as well as the progress made until now regarding the techniques for obtaining albumin nanoparticles and their functionalization, in order to overcome the BBB and treat cancer, especially human glioblastoma. The albumin drug delivery nanosystems mentioned in this paper have improved properties and can overcome the BBB to target brain tumors.

Comparison of rhBMP-2 in Combination with Different Biomaterials for Regeneration in Rat Calvaria Critical-Size Defects

Regeneration of critical bone defects requires the use of biomaterials. The incorporation of osteoinductive agents, such as bone morphogenetic proteins (BMPs), improves bone formation. This study aimed to compare the efficacy of rhBMP-2 in combination with different materials for bone regeneration in critical-sized rat calvarial defects. This was an experimental animal study using 30 rats. In each rat, two 5-mm critical-size defects were made in the calvaria (60 bone defects in total) using a trephine. All rats were randomized to one of the six groups: control (C), autograft + rhBMP-2 (A), absorbable collagen sponge + rhBMP-2 (ACS), β-tricalcium phosphate + rhBMP-2 (B-TCP), bovine xenograft + rhBMP-2 (B), and hydroxyapatite + rhBMP-2 (HA). The outcome was assessed after 4 and 8 weeks using histological description and the histological bone healing scale. Statistical analysis was performed using the Kruskal-Wallis and Mann–Whitney U tests, with a p-value set at 0.05. The average bone healing scores per group were as follows: C group, 12.5; A group, 26.5; ACS group, 18.8; B-TCP group, 26.2; HA group, 20.9; and B group, 20.9. The C group showed a significant difference between weeks 4 and 8 (p = 0.032). Among the 4-week groups, the C group showed a significant difference compared to A (p = 0.001), ACS (p = 0.017), and B-TCP (p = 0.005) groups. The 8-week experimental group did not show any significant differences between the groups. The 5-mm critical size defect in rat calvaria requires the use of bone biomaterials to heal at 4 and 8 weeks. rhBMP-2, as applied in this study, showed no difference in new bone formation when combined with bovine, B-TCP, or HA biomaterials.

Precision-engineered niche for directed differentiation of MSCs to lineage-restricted mineralized tissues

The major difference between tissue healing and regeneration is the extent of instructional cues available to precisely direct the biological response. A classic example is reparative or osteodentin that is seen in response to physicochemical injury to the pulp-dentin complex. Dentin regeneration can direct the differentiation of dental stem cells using concerted actions of both soluble (biomolecules, agonists, and antagonists) and insoluble (matrix topology) cues. The major purpose of this study was to examine the synergistic combination of two discrete biomaterial approaches by utilizing nanofiber scaffolds in discrete configurations (aligned or random) with incorporated polymeric microspheres capable of controlled release of growth factors. Further, to ensure appropriate disinfection for clinical use, Radio-Frequency Glow Discharge (RFGD) treatments were utilized, followed by seeding with a mesenchymal stem cell (MSC) line. SEM analysis revealed electrospinning generated controlled architectural features that significantly improved MSC adhesion and proliferation on the aligned nanofiber scaffolds compared to randomly oriented scaffolds. These responses were further enhanced by RFGD pre-treatments. These enhanced cell adhesion and proliferative responses could be attributed to matrix-induced Wnt signaling that was abrogated by pre-treatments with anti-Wnt3a neutralizing antibodies. Next, we incorporated controlled-release microspheres within these electrospun scaffolds with either TGF-β1 or BMP4. We observed that these scaffolds could selectively induce dentinogenic or osteogenic markers (DSPP, Runx2, and BSP) and mineralization. This work demonstrates the utility of a novel, modular combinatorial scaffold system capable of lineage-restricted differentiation into bone or dentin. Future validation of this scaffold system in vivo as a pulp capping agent represents an innovative dentin regenerative approach capable of preserving tooth pulp vitality.

Synergism between recombinant human bone morphogenetic protein 2/absorbable collagen sponge and bone substitutes favors vertical bone augmentation and the resorption rate of the biomaterials: Histomorphometric and 3D microcomputed tomography analysis

BACKGROUND

Recombinant human bone morphogenetic protein 2 (rhBMP-2) is an osteoinductor frequently used for bone regeneration in oral and maxillofacial surgery. There is no consensus about the ideal carrier for this growth factor. The aim of this study was to compare the bone augmentation, bone microarchitecture, and biodegradation rate of additional carriers to rhBMP-2/absorbable collagen sponge (ACS) in a vertical guided bone regeneration model.

METHODS

Four titanium cylinders were fixed onto the calvaria of rabbits (n = 20) that received (n = 10) or not (n = 10) rhBMP-2/ACS in conjunction with one of the carriers: beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), bovine bone mineral (BBM) or blood clot. The samples were analyzed by means of microcomputed tomography and histomorphology after 14 weeks.

RESULTS

All the materials with rhBMP-2/ACS exhibited improvement on bone augmentation, mainly BCP (P = 0.033) and β-TCP (P = 0.038), in the upper portion of the cylinder. Although trabecular anisotropy was improved in all the materials groups, trabecular connectivity was diminished when the biomaterials received rhBMP-2/ACS. Resorption rate of the remaining biomaterial was improved by rhBMP-2/ACS, mainly in BBM (P <0.01) and β-TCP (P <0.01). BBM exhibited the highest osteoclast density compared with the other materials groups.

CONCLUSIONS

BCP and β-TCP biomaterials exhibited a synergic effect with rhBMP-2/ACS, acting as suitable and viable carriers for vertical bone augmentation. The addition of rhBMP-2 significantly affected the biodegradation of β-TCP and BBM, accelerating the resorption of these materials.

Dendrimer grafted albumin nanoparticles for the treatment of post cerebral stroke damages: A proof of concept study

Stroke is the second largest disease of mortality. The biggest hurdle in designing effective brain drug delivery systems is offered by the blood-brain barrier (BBB), which is highly impermeable to many drugs. Albumin nanoparticles (NP) have gained attention due to their multiple ligand binding sites and long circulatory half-life. Citicoline (CIT) is reported to enhance the acetylcholine secretion in the brain and also helps in membrane repair and regeneration. However, the poor BBB permeation of CIT results in lower levels of CIT in the brain. This demands the development of a suitable delivery platform to completely realize the therapeutic benefit of CIT in stroke therapy. This investigation reports the synthesis and characterization of second generation (2.0 G) dendrimer Amplified Albumin (dAA) biopolymer by FTIR, MALDI-TOF, and surface charge (mV). Further, the synthesized biopolymer has been utilized to develop a CIT nanoformulation using a commercially translatable one-pot process. Release of CIT from biopolymer was performed within an acetate buffer at pH 5 and Phosphate buffer at pH 7.4. Further, we investigated the ability of biopolymer to permeate BBB by in vitro permeability assay in bEnd.3 cells. MTT assay of CIT-dAA-NP, CIT-ANP, and 2.0 G PAMAM dendrimers was performed in bEnd.3 cells. Therapeutic efficacy of the synthesized biopolymer was determined by VEGF gene expression within an in vitro hypoxia model in PC12 cells. Thus, this investigation resulted in biopolymers that can be used to deliver any therapeutic agent by altering the permeability of the BBB. Also, cationization by dendrimer grafting is one such strategy that may be used to cationize any other negatively charged polymer, such as albumin. The synthesized biopolymer is not limited to deliver molecules to the brain, but can also be used to increase the loading of negatively-charged drug molecules, siRNA, or any other oligonucleotide.

Review of the Pathways Involved in the Osteogenic Differentiation of Adipose-Derived Stem Cells

Grafts and prosthetic materials used for the repair of bone defects are often accompanied by comorbidity and rejection. Therefore, there is an immense need for novel approaches to combating the issues surrounding such defects. Because of their accessibility, substantial proportion, and osteogenic differentiation potential, adipose-derived stem cells (ASCs) make for an ideal source of bone tissue in regenerative medicine. However, efficient induction of ASCs toward an osteoblastic lineage in vivo is met with challenges, and many signaling pathways must come together to secure osteoblastogenesis. Among them are bone morphogenic protein, wingless-related integration site protein, Notch, Hedgehog, fibroblast growth factor, vascular endothelial growth factor, and extracellular regulated-signal kinase. The goal of this literature review is to conglomerate the present research on these pathways to formulate a better understanding of how ASCs are most effectively transformed into bone in the context of tissue engineering.

Sequential Delivery of Dual Growth Factors from Injectable Chitosan-Based Composite Hydrogels

Local administration of platelet-derived growth factor-BB (PGDF-BB) and bone morphogenetic protein-2 (BMP-2) in a sequential release manner could substantially promote bone healing. To achieve this goal, a delivery system that could sustain the release of PGDF-BB and BMP-2 by way of temporal separation was developed. One type of PGDF-BB-encapsulated alginate microsphere and another type of BMP-2-encapsulated microsphere with a core-shell structure were respectively produced using emulsification methods. These two types of microspheres were then embedded into chitosan/glycerophosphate hydrogel for constructing composite gels. Some of them were found to be injectable at ambient temperature and had thermo-sensitive features near physiological temperature and pH. The optimally formulated composite gels showed the ability to control the release of PGDF-BB and BMP-2 in a sequential fashion in which PDGF-BB was released earlier than BMP-2. In vitro release patterns indicated that the release rates could be significantly regulated by varying the embedded amount of the factor-encapsulated microspheres, which can in turn mediate the temporal separation release interval between PGDF-BB and BMP-2. The released PDGF-BB and BMP-2 were detected to be bioactive based on their respective effects on Balb/c 3T3 and C2C12 cells. These results suggest that the presently developed composite gels have the potential for bone repair by synergistically utilizing the early chemotactic effect of PDGF-BB and the subsequent osteogenic and angiogenic functions of PDGF-BB and BMP-2.

At the Intersection of Biomaterials and Gene Therapy: Progress in Non-viral Delivery of Nucleic Acids

Biomaterials play a critical role in technologies intended to deliver therapeutic agents in clinical settings. Recent explosion of our understanding of how cells utilize nucleic acids has garnered excitement to develop a range of older (e.g., antisense oligonucleotides, plasmid DNA and transposons) and emerging (e.g., short interfering RNA, messenger RNA and non-coding RNAs) nucleic acid agents for therapy of a wide range of diseases. This review will summarize biomaterials-centered advances to undertake effective utilization of nucleic acids for therapeutic purposes. We first review various types of nucleic acids and their unique abilities to deliver a range of clinical outcomes. Using recent advances in T-cell based therapy as a case in point, we summarize various possibilities for utilizing biomaterials to make an impact in this exciting therapeutic intervention technology, with the belief that this modality will serve as a therapeutic paradigm for other types of cellular therapies in the near future. We subsequently focus on contributions of biomaterials in emerging nucleic acid technologies, specifically focusing on the design of intelligent nanoparticles, deployment of mRNA as an alternative to plasmid DNA, long-acting (integrating) expression systems, and in vitro/in vivo expansion of engineered T-cells. We articulate the role of biomaterials in these emerging nucleic acid technologies in order to enhance the clinical impact of nucleic acids in the near future.

Chitosan-Based Hydrogels Embedded with Hyaluronic Acid Complex Nanoparticles for Controlled Delivery of Bone Morphogenetic Protein-2

Chitosan(CH)-poly(dioxanone) (CH-PDO) copolymers containing varied amounts of PDO and having free amino groups at their CH backbone were synthesized using a group protection method. The selected CH-PDO with soluble characteristics in aqueous media was used together with hyaluronic acid (HA) to prepare HA/CH-PDO polyelectrolyte complex nanoparticles (NPs) via an ionotropic gelation technique, and such a type of HA/CH-PDO NPs was employed as a carrier for delivering bone morphogenetic protein-2 (BMP-2). The optimal BMP-2-encapsulated HA/CH-PDO NPs with high encapsulation efficiency were embedded into CH/glycerophosphate composite solutions to form different hydrogels in order to achieve long-term BMP-2 release. The formulated gels were found to be injectable at room temperature and had its thermosensitive phase transition near physiological temperature and pH. They also showed abilities to administer the release of BMP-2 in approximately linear manners for a few weeks while effectively preserving the bioactivity of the encapsulated BMP-2. In view of their fully biocompatible and biodegradable components, the presently developed gel systems have promising potential for translation to the clinic use in bone repair and regeneration where the sustained and controlled stimuli from active signaling molecules and the stable biomechanical framework for housing the recruited cells are often concurrently needed.

Metal-Enzyme Nanoaggregates Eradicate Both Gram-Positive and Gram-Negative Bacteria and Their Biofilms

To palliate the appearance of antimicrobial resistance (AMR), the use of bactericidal agents acting differently than conventional antibiotics and the elimination of bacterial biofilm, are the two most promising strategies. Here, we integrated these two complementary strategies into new antimicrobial metal-enzyme nanoaggregates (NAs) of α-amylase and silver (αAgNAs) that are able to eliminate bacteria and their biofilm. The nanoparticle (NP) synthesis approach applied protein desolvation and laccase-mediated NP stabilization to innovatively produce catalytically active α-amylase nanoparticles (αNPs) for the elimination of the bacterial biofilm. At the same time, αNPs efficiently reduced silver for the incorporation of bactericidal Ag⁰ and formation of the αAgNAs. The bactericidal and antibiofilm efficacies of αAgNAs were demonstrated by 5.4 and 6.1 log reduction of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, respectively, and more than 80% removal of their biofilms, coupled with high biocompatibility. The biofilm-αAgNA interaction was assessed by quartz crystal microbalance and atomic force microscopy revealing how the degradation of a settled biofilm by αAgNAs caused an increase of the biofilm water content, thus weakening the biofilm surface attachment and facilitating its removal. With the present work, we not only provide a new efficient antimicrobial material to face the AMR threat, but we also envisage that the newly established method for the synthesis of metal-enzyme NAs is potentially transferable to other biocatalysts to expand the enzyme NP toolbox.

Bone-seeking agents for the treatment of bone disorders

The targeting and delivery of therapeutic and diagnostic agents to bone tissue presents both a challenge and opportunity. Osteoporosis, Paget's disease, cancer, and bone metastases are all skeletal diseases whose treatment would benefit from new targeted therapeutic strategies. Osteoporosis, in particular, is a very prevalent disease, affecting over one in three women and one in five men in Canada alone with the cost to the healthcare system estimated at over $2.3 billion in 2010. Bone tissue is often considered a rigid structure when in reality there is a process of continuous remodeling that takes place via complex endocrine-regulated cell signaling pathways in addition to the signaling pathways unique to bone tissue. It is these specific boneremodeling processes that provide unique targeting opportunities but also present a number of challenges.

Strategies for Preparing Albumin-based Nanoparticles for Multifunctional Bioimaging and Drug Delivery

Biosafety is the primary concern in clinical translation of nanomedicine. As an intrinsic ingredient of human blood without immunogenicity and encouraged by its successful clinical application in Abraxane, albumin has been regarded as a promising material to produce nanoparticles for bioimaging and drug delivery. The strategies for synthesizing albumin-based nanoparticles could be generally categorized into five classes: template, nanocarrier, scaffold, stabilizer and albumin-polymer conjugate. This review introduces approaches utilizing albumin in the preparation of nanoparticles and thereby provides scientists with knowledge of goal-driven design on albumin-based nanomedicine.

Polyethylenimine-based micro/nanoparticles as vaccine adjuvants

Vaccines have shown great success in treating and preventing tumors and infections, while adjuvants are always demanded to ensure potent immune responses. Polyethylenimine (PEI), as one of the well-studied cationic polymers, has been used as a transfection reagent for decades. However, increasing evidence has shown that PEI-based particles are also capable of acting as adjuvants. In this paper, we briefly review the physicochemical properties and the broad applications of PEI in different fields, and elaborate on the intracellular processes of PEI-based vaccines. In addition, we sum up the proof of their in vivo and clinical applications. We also highlight some mechanisms proposed for the intrinsic immunoactivation function of PEI, followed by the challenges and future perspectives of the applications of PEI in the vaccines, as well as some strategies to elicit the desirable immune responses.

Graphene oxide nanolayers as nanoparticle anchors on biomaterial surfaces with nanostructures and charge balance for bone regeneration

Graphene oxide (GO) is a carbon-based nanomaterial with high surface area and abundant functional groups, providing various sites for binding and immobilization of growth factor vehicles. This study used GO nanolayer as an anchor for the immobilization of bone morphogenetic protein-2 (BMP-2)-encapsulated bovine serum albumin nanoparticles (NPs) on the hydroxyapatite (HA) and tricalcium phosphate (TCP) scaffolds by electrostatic interaction between the positive charges of the NPs and negative charges of GO. GO nanolayers prevented the rapid degradation of TCP scaffolds. Moreover, GO nanolayers promoted NP adsorption on these scaffolds, and realized BMP-2 sustained release. NPs endowed the scaffold surfaces with a nanostructure similar to that of the extracellular matrix (ECM), improving bone marrow stromal cell (BMSC) attachment. Furthermore, the positive charged NPs and negative charged GO nanolayers constructed a charge-balanced surface on the scaffolds, enhancing BMSC proliferation. The nanostructure, charge balance and BMP-2 sustained release capability synergistically improved BMSC differentiation and bone regeneration. In summary, GO is a potential candidate to modify biomaterial surfaces as an anchor for efficient immobilization of growth factor vehicles. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1311-1323, 2017.

Photoluminescent polyphosphazene nanoparticles for in situ simvastatin delivery for improving the osteocompatibility of BMSCs

Photoluminescent prodrug nanoparticles for BMSCs’ endocytosis to improve osteogenesis via in situ simvastatin delivery resulting from polyphosphazene hydrolysis.

Engineering a favourable osteogenic microenvironment by heparin mediated hybrid coating assembly and rhBMP-2 loading

(1) HApNPs are conferred with negative charges by surface modification with heparin. (2) Heparinized HApNPs and polycation CS are assembled to form a hybrid coating. (3) RhBMP-2 is introduced into the coating via the intermolecular binding with heparin.

Strategies for delivering bone morphogenetic protein for bone healing

Bone morphogenetic proteins (BMPs) are the most significant growth factors that belong to the Transforming Growth Factor Beta (TGF-β) super-family. Though more than twenty members of this family have been identified so far in humans, Food and Drug Administration (FDA) approved two growth factors: BMP-2 and BMP-7 for treatments of spinal fusion and long-bone fractures with collagen carriers. Currently BMPs are clinically used in spinal fusion, oral and maxillofacial surgery and also in the repair of long bone defects. The efficiency of BMPs depends a lot on the selection of suitable carriers. At present, different types of carrier materials are used: natural and synthetic polymers, calcium phosphate and ceramic-polymer composite materials. Number of research articles has been published on the minute intricacies of the loading process and release kinetics of BMPs. Despite the significant evidence of its potential for bone healing demonstrated in animal models, future clinical investigations are needed to define dose, scaffold and route of administration. The efficacy and application of BMPs in various levels with a proper carrier and dose is yet to be established. The present article collates various aspects of success and limitation and identifies the prospects and challenges associated with the use of BMPs in orthopaedic surgery.

Biomimetic Mineralized Hierarchical Graphene Oxide/Chitosan Scaffolds with Adsorbability for Immobilization of Nanoparticles for Biomedical Applications

Biomimetic calcium phosphate mineralized graphene oxide/chitosan (GO/CS) scaffolds with hierarchical structures were developed. First, GO/CS scaffolds with large micropores (∼300 μm) showed high mechanical strength due to the electrostatic interaction between the oxygen-containing functional groups of GO and the amine groups of CS. Second, octacalcuim phosphate (OCP) with porous structures (∼1 μm) was biomimetically mineralized on the surfaces of the GO/CS scaffolds (OCP-GO/CS). The hierarchical microporous structures of OCP-GO/CS scaffolds provide a suitable environment for cell adhesion and growth. The scaffolds have exceptional adsorbability of nanoparticles. Bone morphogenetic protein-2 (BMP-2)-encapsulated bovine serum albumin (BSA) nanoparticles and Ag nanoparticles (Ag-NPs) were adsorbed in the scaffolds for enhancement of osteoinductivity and antibacterial properties, respectively. Antibacterial tests showed that the scaffolds exhibited high antibacterial properties against both Escherichia coli and Staphylococcus epidermidis. In vitro and in vivo experiments revealed that the scaffolds have good biocompatibility, enhanced bone marrow stromal cells proliferation and differentiation, and induced bone tissue regeneration. Thus, the biomimetic OCP-GO/CS scaffolds with immobilized growth factors and antibacterial agents might be excellent candidates for bone tissue engineering.

Nanoparticles combined with growth factors: recent progress and applications

Increasing attention has been focused on the applications of nanoparticles combined with growth factors (NPs/GFs) due to the substantial functions of GFs in regenerative medicine and disease treatments.

Nanoparticle-based bioactive agent release systems for bone and cartilage tissue engineering

The inability to deliver bioactive agents locally in a transient but sustained manner is one of the challenges on the development of bio-functionalized scaffolds for tissue engineering (TE) and regenerative medicine. The mode of release is especially relevant when the bioactive agent is a growth factor (GF), because the dose and the spatiotemporal release of such agents at the site of injury are crucial to achieve a successful outcome. Strategies that combine scaffolds and drug delivery systems have the potential to provide more effective tissue regeneration relative to current therapies. Nanoparticles (NPs) can protect the bioactive agents, control its profile, decrease the occurrence and severity of side effects and deliver the bioactive agent to the target cells maximizing its effect. Scaffolds containing NPs loaded with bioactive agents can be used for their local delivery, enabling site-specific pharmacological effects such as the induction of cell proliferation and differentiation, and, consequently, neo-tissue formation. This review aims to describe the concept of combining NPs with scaffolds, and the current efforts aiming to develop highly multi-functional bioactive agent release systems, with the emphasis on their application in TE of connective tissues.

Accelerated Bone Formation in Distracted Alveolar Bone After Injection of Recombinant Human Bone Morphogenetic Protein-2

BACKGROUND

This study evaluates the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the quality and quantity of regenerated bone when injected into distracted alveolar bone.

METHODS

Sixteen adult beagle dogs were assigned to either the control or rhBMP-2 group. After distraction was completed, an rhBMP-2 dose of 330 μg in 0.33 mL was injected slowly into the distracted alveolar crest of the mesial, middle, and distal parts of the alveolar bone in the experimental group. Histologic and microcomputed tomography analyses of regenerated bone were done after 2 and 6 weeks of consolidation.

RESULTS

After 6 weeks of consolidation, the vertical defect height in the middle of the regenerated bone was significantly lower in the rhBMP-2 group (2.2 mm) than in the control group (3.4 mm) (P <0.05). Additionally, the width of the regenerated bone was significantly greater in the rhBMP-2 group (4.3 mm) than in the control group (2.8 mm) (P <0.05). The bone density and volume of regenerated bone in the rhBMP-2 group were greater than in the control group after 6 weeks of consolidation (P <0.001).

CONCLUSION

Injection of rhBMP-2 into regenerated bone after a distraction osteogenesis procedure significantly increased bone volume in the dentoalveolar distraction site and improved both the width and height of the alveolar ridge and increased the bone density.

Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers

Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration.

Protein nanoparticles for therapeutic protein delivery

This review describes nanoparticles made from protein by self-assembly or desolvation as carriers for the delivery of therapeutic proteins.

Adipose-derived stem cells: a review of signaling networks governing cell fate and regenerative potential in the context of craniofacial and long bone skeletal repair

Improvements in medical care, nutrition and social care are resulting in a commendable change in world population demographics with an ever increasing skew towards an aging population. As the proportion of the world's population that is considered elderly increases, so does the incidence of osteodegenerative disease and the resultant burden on healthcare. The increasing demand coupled with the limitations of contemporary approaches, have provided the impetus to develop novel tissue regeneration therapies. The use of stem cells, with their potential for self-renewal and differentiation, is one potential solution. Adipose-derived stem cells (ASCs), which are relatively easy to harvest and readily available have emerged as an ideal candidate. In this review, we explore the potential for ASCs to provide tangible therapies for craniofacial and long bone skeletal defects, outline key signaling pathways that direct these cells and describe how the developmental signaling program may provide clues on how to guide these cells in vivo. This review also provides an overview of the importance of establishing an osteogenic microniche using appropriately customized scaffolds and delineates some of the key challenges that still need to be overcome for adult stem cell skeletal regenerative therapy to become a clinical reality.

Realizing the potential of gene-based molecular therapies in bone repair

A better understanding of osteogenesis at genetic and biochemical levels is yielding new molecular entities that can modulate bone regeneration and potentially act as novel therapies in a clinical setting. These new entities are motivating alternative approaches for bone repair by utilizing DNA-derived expression systems, as well as RNA-based regulatory molecules controlling the fate of cells involved in osteogenesis. These sophisticated mediators of osteogenesis, however, pose unique delivery challenges that are not obvious in deployment of conventional therapeutic agents. Viral and nonviral delivery systems are actively pursued in preclinical animal models to realize the potential of the gene-based medicines. This article will summarize promising bone-inducing molecular agents on the horizon as well as provide a critical review of delivery systems employed for their administration. Special attention was paid to synthetic (nonviral) delivery systems because they are more likely to be adopted for clinical testing because of safety considerations. We present a comparative analysis of dose-response relationships, as well as pharmacokinetic and pharmacodynamic features of various approaches, with the purpose of clearly defining the current frontier in the field. We conclude with the authors' perspective on the future of gene-based therapy of bone defects, articulating promising research avenues to advance the field of clinical bone repair.

Multi-protein delivery by nanodiamonds promotes bone formation

Bone morphogenetic proteins (BMPs) are well-studied regulators of cartilage and bone development that have been Food and Drug Administration (FDA)-approved for the promotion of bone formation in certain procedures. BMPs are seeing more use in oral and maxillofacial surgeries because of recent FDA approval of InFUSE(®) for sinus augmentation and localized alveolar ridge augmentation. However, the utility of BMPs in medical and dental applications is limited by the delivery method. Currently, BMPs are delivered to the surgical site by the implantation of bulky collagen sponges. Here we evaluate the potential of detonation nanodiamonds (NDs) as a delivery vehicle for BMP-2 and basic fibroblast growth factor (bFGF). Nanodiamonds are biocompatible, 4- to 5-nm carbon nanoparticles that have previously been used to deliver a wide variety of molecules, including proteins and peptides. We find that both BMP-2 and bFGF are readily loaded onto NDs by physisorption, forming a stable colloidal solution, and are triggered to release in slightly acidic conditions. Simultaneous delivery of BMP-2 and bFGF by ND induces differentiation and proliferation in osteoblast progenitor cells. Overall, we find that NDs provide an effective injectable alternative for the delivery of BMP-2 and bFGF to promote bone formation.

A comparative evaluation of factors influencing osteoinductivity among scaffolds designed for bone regeneration

Due to differing compositions, synthetic scaffolds developed for bone regeneration vary widely in efficacy. To quantify the impact of such differences on osteoinductivity, numerous parameters were examined. Absorbable collagen sponge (ACS), three ceramic-based carriers (#1-3) of varying compositions, mineralized allograft chips, and an experimental phosphoserine-rich nanofiber scaffold [S(P) gel] were compared in their ability to promote cell adhesion, proliferation/survival, growth factor binding/release, and osteogenic gene expression. Human preosteoblasts were found to adhere most efficiently to the S(P) gel, and the growth/survival was greatest on the S(P) and ACS scaffolds, with minimal growth seen on the allograft and Ceramic #3. In bone morphogenetic protein-2 (BMP-2) binding/release assays, ACS demonstrated a burst release pattern, whereas the allograft and the ceramics inefficiently released BMP-2. The S(P) gel showed the most ideal rates of growth factor binding and release. QPCR analyses showed significant differences in the CXCL12, CXCR4, and RANKL transcripts among the cells grown on these various scaffolds. Although some scaffolds showed an advantage over others in individual parameters, the nanofiber gel appears to provide the optimal balance in the factors important to osteoinductivity evaluated here.

From nano- to macro-scale: nanotechnology approaches for spatially controlled delivery of bioactive factors for bone and cartilage engineering

The field of biomaterials has advanced towards the molecular and nanoscale design of bioactive systems for tissue engineering, regenerative medicine and drug delivery. Spatial cues are displayed in the 3D extracellular matrix and can include signaling gradients, such as those observed during chemotaxis. Architectures range from the nanometer to the centimeter length scales as exemplified by extracellular matrix fibers, cells and macroscopic shapes. The main focus of this review is the application of a biomimetic approach by the combination of architectural cues, obtained through the application of micro- and nanofabrication techniques, with the ability to sequester and release growth factors and other bioactive agents in a spatiotemporal controlled manner for bone and cartilage engineering.

Brief review of models of ectopic bone formation

Ectopic bone formation is a unique biologic entity--distinct from other areas of skeletal biology. Animal research models of ectopic bone formation most often employ rodent models and have unique advantages over orthotopic (bone) environments, including a relative lack of bone cytokine stimulation and cell-to-cell interaction with endogenous (host) bone-forming cells. This allows for relatively controlled in vivo experimental bone formation. A wide variety of ectopic locations have been used for experimentation, including subcutaneous, intramuscular, and kidney capsule transplantation. The method, benefits and detractions of each method are summarized in the following review. Briefly, subcutaneous implantation is the simplest method. However, the most pertinent concern is the relative paucity of bone formation in comparison to other models. Intramuscular implantation is also widely used and relatively simple, however intramuscular implants are exposed to skeletal muscle satellite progenitor cells. Thus, distinguishing host from donor osteogenesis becomes challenging without cell-tracking studies. The kidney capsule (perirenal or renal capsule) method is less widely used and more technically challenging. It allows for supraphysiologic blood and nutrient resource, promoting robust bone growth. In summary, ectopic bone models are extremely useful in the evaluation of bone-forming stem cells, new osteoinductive biomaterials, and growth factors; an appropriate choice of model, however, will greatly increase experimental success.

Cationic albumin nanoparticles for enhanced drug delivery to treat breast cancer: preparation and in vitro assessment

Most anticancer drugs are greatly limited by the serious side effects that they cause. Doxorubicin (DOX) is an antineoplastic agent, commonly used against breast cancer. However, it may lead to irreversible cardiotoxicity, which could even result in congestive heart failure. In order to avoid these harmful side effects to the patients and to improve the therapeutic efficacy of doxorubicin, we developed DOX-loaded polyethylenimine- (PEI-) enhanced human serum albumin (HSA) nanoparticles. The formed nanoparticles were ~137 nm in size with a surface zeta potential of ~+15 mV, prepared using 20 μg of PEI added per mg of HSA. Cytotoxicity was not observed with empty PEI-enhanced HSA nanoparticles, formed with low-molecular weight (25 kDa) PEI, indicating biocompatibility and safety of the nanoparticle formulation. Under optimized transfection conditions, approximately 80% of cells were transfected with HSA nanoparticles containing tetramethylrhodamine-conjugated bovine serum albumin. Conclusively, PEI-enhanced HSA nanoparticles show potential for developing into an effective carrier for anticancer drugs.

Albumin-based nanoparticles as potential controlled release drug delivery systems

Albumin, a versatile protein carrier for drug delivery, has been shown to be nontoxic, non-immunogenic, biocompatible and biodegradable. Therefore, it is ideal material to fabricate nanoparticles for drug delivery. Albumin nanoparticles have gained considerable attention owing to their high binding capacity of various drugs and being well tolerated without any serious side-effects. The current review embodies an in-depth discussion of albumin nanoparticles with respect to types, formulation aspects, major outcomes of in vitro and in vivo investigations as well as site-specific drug targeting using various ligands modifying the surface of albumin nanoparticles with special insights to the field of oncology. Specialized nanotechnological techniques like desolvation, emulsification, thermal gelation and recently nano-spray drying, nab-technology and self-assembly that have been investigated for fabrication of albumin nanoparticles, are also discussed. Nanocomplexes of albumin with other components in the area of drug delivery are also included in this review.

Bisphosphonate-coated BSA nanoparticles lack bone targeting after systemic administration

A polymeric conjugate of polyethyleneimine-graft-poly(ethylene glycol) and 2-(3-mercaptopropylsulfanyl)-ethyl-1,1-bisphosphonic acid (PEI-PEG-thiolBP) was prepared and used for surface coating of bovine serum albumin (BSA) nanoparticles (NPs) designed for bone-specific delivery of bone morphogenetic protein-2 (BMP-2). The NP coating was achieved with a dialysis and an evaporation method, and the obtained NPs were characterized by particle size, zeta-potential, morphology, and cytotoxicity in vitro. The particle size and surface charge of the NPs could be effectively tuned by the PEG and thiolBP substitution ratios of the conjugate, the coating method, and the polymer concentration used for coating. The PEG modification on PEI reduced the toxicity of PEI and the coated NPs, based on in vitro assessment with human C2C12 cells and rat bone marrow stromal cells. On the basis of an alkaline phosphatase (ALP) induction assay, the NP-encapsulated BMP-2 displayed full retention of its bioactivity, except for BMP-2 in PEI-coated NPs. By encapsulating (125)I-labeled BMP-2, the polymer-coated NPs were assessed for hydroxyapatite (HA) affinity; all NP-encapsulated BMP-2 showed significant affinity to HA as compared with free BMP-2 in vitro, and the PEI-PEG-thiolBP coated NPs improved the in vivo retention of BMP-2 compared with uncoated NPs. However, the biodistribution of NPs after intravenous injection in a rat model indicated no beneficial effects of thiolBP-coated NPs for bone targeting. Our results suggested that the BP-conjugated NPs are useful for localized delivery of BMP-2 in bone repair and regeneration, but they are not effective for bone targeting after intravenous administration.

Recent developments in liposomes, microparticles and nanoparticles for protein and peptide drug delivery

Proteins and peptides are increasingly recognized as potential leads for the development of new therapeutics for a variety of human ailments. Due to their relatively specific mode of action, proteins and peptides can be administered at relatively low doses for therapeutic effects. As natural biological products, these low doses reduce the risk otherwise caused by other small molecular drugs or larger charged molecules. Unfortunately, their therapeutic potential and clinical application is frequently hampered by various obstacles to their successful delivery. This review discusses the recent developments in the fields of liposome, microparticle and nanoparticle pertinent to protein and peptide delivery covering those systems tested and/or validated in vivo.

Polyethylenimine-PEG coated albumin nanoparticles for BMP-2 delivery

Bone Morphogenetic Protein-2 (BMP-2) plays an important role in stimulating new bone formation, and has been utilized in clinical bone repair by implantation. In this study, we report a nanoparticulate (NP) system for BMP-2 delivery based on bovine serum albumin (BSA) NPs stabilized with a poly(ethylene glycol) modified polyethylenimine (PEI-PEG) coating. PEI-PEG with different PEG substitutions were synthesized, and the cell viability assay showed PEG substitution greatly reduced the cytotoxicity of the native PEI. Furthermore, PEI-PEG coated BSA NPs demonstrated smaller size and decreased zeta potential compared to PEI-coated NPs. The bioactivity of the encapsulated BMP-2 and the toxicity of PEI-PEG coated NPs were examined by the alkaline phosphatase (ALP) induction assay and the MTT assay, respectively, using human C2C12 cells. The results indicated that BMP-2 remained bioactive in NPs and PEI-PEG coating was advantageous in reducing the NP toxicity as compared to PEI. A 7-day pharmacokinetics study showed the BMP-2 retention in PEI-PEG coated NPs was similar to the uncoated NPs, but lower than that of the PEI-coated NPs. The osteoinductivity of BMP-2 delivered in NPs was determined by subcutaneous implantation in rats, and the results revealed that PEI-PEG coated BSA NPs induced significant de novo bone formation after implantation, while PEI-coated NPs demonstrated much less bone formation. We conclude that BMP-2 delivered by PEGylated PEI-coated BSA NPs displays favorable biocompatibility and promotes new bone formation after implantation.