Osteogenic growth peptide and its use as a bio-conjugate in regenerative medicine applications

Antibacterial sequential growth factor delivery from alginate/gelatin methacryloyl microspheres for bone regeneration

Autologous or allogeneic bone tissue grafts remain the mainstay of treatment for clinical bone defects. However, the risk of infection and donor scarcity in bone grafting pose challenges to the process. Therefore, the development of excellent biomaterial grafts is of great clinical importance for the repair of bone defects. In this study, we used gas-assisted microfluidics to construct double-cross-linked hydrogel microspheres with good biological function based on the ionic cross-linking of Cu2+ with alginate and photo-cross-linking of gelatin methacryloylamide (GelMA) by loading vascular endothelial growth factor (VEGF) and His-tagged bone morphogenetic protein-2 (BMP2) (AGMP@VEGF&BMP2). The Cu2+ component in the microspheres showed good antibacterial and drug-release behavior, whereas VEGF and BMP2 effectively promoted angiogenesis and bone tissue repair. In in vitro and in vivo experiments, the dual cross-linked hydrogel microspheres showed good biological function and biocompatibility. These results demonstrate that AGMP@VEGF&BMP2 microspheres could be used as a bone defect graft substitute to promote effective healing of bone defects and may be applied to other tissue engineering studies.

Advancements in drug-loaded hydrogel systems for bone defect repair

Bone defects are primarily the result of high-energy trauma, pathological fractures, bone tumor resection, or infection debridement. The treatment of bone defects remains a huge clinical challenge. The current treatment options for bone defects include bone traction, autologous/allogeneic bone transplantation, gene therapy, and bone tissue engineering amongst others. With recent developments in the field, composite scaffolds prepared using tissue engineering techniques to repair bone defects are used more often. Among the various composite scaffolds, hydrogel exhibits the advantages of good biocompatibility, high water content, and degradability. Its three-dimensional structure is similar to that of the extracellular matrix, and as such it is possible to load stem cells, growth factors, metal ions, and small molecule drugs upon these scaffolds. Therefore, the hydrogel-loaded drug system has great potential in bone defect repair. This review summarizes the various natural and synthetic materials used in the preparation of hydrogels, in addition to the latest research status of hydrogel-loaded drug systems.

Using dynamic biomaterials to study the temporal role of bioactive peptides during osteogenesis

The extracellular matrix is a highly dynamic environment, and the precise temporal presentation of biochemical signals is critical for regulating cell behavior during development, healing, and disease progression. To mimic this behavior, we developed a modular DNA-based hydrogel platform to enable independent and reversible control over the immobilization of multiple biomolecules during in vitro cell culture. We combined reversible DNA handles with a norbornene-modified hyaluronic acid hydrogel to orthogonally add and remove multiple biomolecule-DNA conjugates at user-defined timepoints. We demonstrated that the persistent presentation of the cell adhesion peptide RGD was required to maintain cell spreading on hyaluronic acid hydrogels. Further, we discovered the delayed presentation of osteogenic growth peptide (OGP) increased alkaline phosphatase activity compared to other temporal variations. This finding is critically important when considering the design of OGP delivery approaches for bone repair. More broadly, this platform provides a unique approach to tease apart the temporal role of multiple biomolecules during development, regeneration, and disease progression.

A Bone Targeting Nanoparticle Loaded OGP to Restore Bone Homeostasis for Osteoporosis Therapy

Restoring bone homeostasis is the key to the treatment of osteoporosis. How to increase osteogenic ability or inhibit osteoclast activity has always been a topic of great concern. In recent years, short peptides with biological activity have received great attention in bone repair. However, the application of short peptides is still limited due to the lack of a stable and targeted delivery system. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles modified by alendronate (AL) to transport osteogenic peptides (OGP) (AL-PLGA@P NPs) are designed. Benefiting from the high affinity of AL for hydroxyapatite, AL-PLGA@P NPs have the ability to target bone. In this delivery system, OGP that promotes osteogenesis synergizes with AL, which inhibits osteoclasts, to regulate bone homeostasis, which gives them more advantages in the treatment of osteoporosis. The data shows that nanoparticles can selectively deliver peptides to the bone surface without systemic toxicity. Moreover, nanoparticles can upregulate osteogenesis-related factors (ALP, Runx-2, and BMP2) and downregulate osteoclast-related factors (TRAP and CTSK) in vitro. With AL-PLGA@P NPs, bone microarchitecture and bone mass are improved in ovariectomized osteoporosis rats. Therefore, this study proposes a novel osteoporosis-based drug system that effectively improves bone density.

Sustained delivery of osteogenic growth peptide through injectable photoinitiated composite hydrogel for osteogenesis

One of the most challenging clinical issues continues to be the effective bone regeneration and rebuilding following bone abnormalities. Although osteogenic growth peptide (OGP) has been proven to be effective in promoting osteoblast activity, its clinical application is constrained by abrupt release and easily degradation. We developed a GelMA/HAMA dual network hydrogel loaded with OGP based on a combination of physical chain entanglement and chemical cross-linking effects to produce an efficient long-term sustained release of OGP. The hydrogel polymers were quickly molded under ultraviolet (UV) light and had the suitable physical characteristics, porosity structure and biocompatibility. Significantly, the GelMA/HAMA-OGP hydrogel could promote cell proliferation, adhesion, increase osteogenic-related gene and protein expression in vitro. In conclusion, the OGP sustained-release system based on GelMA/HAMA dual network hydrogel offers a fresh perspective on bone regeneration therapy.

Combining Mg–Zn–Ca Bulk Metallic Glass with a Mesoporous Silica Nanocomposite for Bone Tissue Engineering

Mg–Zn–Ca bulk metallic glass (BMG) is a promising orthopedic fixation implant because of its biodegradable and biocompatible properties. Structural supporting bone implants with osteoinduction properties for effective bone regeneration have been highly desired in recent years. Osteogenic growth peptide (OGP) can increase the proliferation and differentiation of mesenchymal stem cells and enhance the mineralization of osteoblast cells. However, the short half-life and non-specificity to target areas limit applications of OGP. Mesoporous silica nanoparticles (MSNs) as nanocarriers possess excellent properties, such as easy surface modification, superior targeting efficiency, and high loading capacity of drugs or proteins. Accordingly, we propose a system of combining the OGP-containing MSNs with Mg–Zn–Ca BMG materials to promote bone regeneration. In this work, we conjugated cysteine-containing OGP (cgOGP, 16 a.a.) to interior walls of channels in MSNs and maintained the dispersity of MSNs via PEGylation. An in vitro study showed that metal ions released from Mg–Zn–Ca BMG promoted cell proliferation and migration and elevated alkaline phosphatase (ALP) activity and mineralization. On treating cells with both BMG ion-containing Minimum Essential Medium Eagle-alpha modification (α-MEM) and OGP-conjugated MSNs, enhanced focal adhesion turnover and promoted differentiation were observed. Hematological analyses showed the biocompatible nature of this BMG/nanocomposite system. In addition, in vivo micro-computed tomographic and histological observations revealed that our system stimulated osteogenesis and new bone formation around the implant site.

A CD10-OGP Membrane Peptolytic Signaling Axis in Fibroblasts Regulates Lipid Metabolism of Cancer Stem Cells via SCD1

Carcinoma-associated fibroblasts (CAFs) consist of heterogeneous subpopulations that play a critical role in the dynamics of the tumor microenvironment. The extracellular signals of CAFs have been attributed to the extracellular matrix, cytokines, cell surface checkpoints, and exosomes. In the present study, it is demonstrated that the CD10 transmembrane hydrolase expressed on a subset of CAFs supports tumor stemness and induces chemoresistance. Mechanistically, CD10 degenerates an antitumoral peptide termed osteogenic growth peptide (OGP). OGP restrains the expression of rate-limiting desaturase SCD1 and inhibits lipid desaturation, which is required for cancer stem cells (CSCs). Targeting CD10 significantly improves the efficacy of chemotherapy in vivo. Clinically, CD10-OGP signals are associated with the response to neoadjuvant chemotherapy in patients with breast cancer. The collective data suggest that a nexus between the niche and lipid metabolism in CSCs is a promising therapeutic target for breast cancer.

[Electrospun PLGA scaffold loaded with osteogenic growth peptide accelerates cranial bone repair in rats]

OBJECTIVE

To study the feasibility of electrospun poly(D, L-lactide-co-glycolide) (PLGA) scaffold loaded with osteogenic growth peptide (OGP) for bone tissue engineering.

METHODS

PLGA scaffolds were prepared by electrospinning PLGA solution without OGP(control group)or with 0.1%, 0.2%and 0.4%OGP(0.1%OGP@PLGA, 0.2%OGP@PLGA, and 0.4%OGP@PLGA scaffolds, respectively).The microstructure of the scaffolds was observed by scanning electron microscopy(SEM).The scaffolds were soaked in PBS to confirm the release pattern of OGP.The biocompatibility of the scaffolds was evaluated using CCK-8 assay and live/dead staining after a 7-day coculture with rat bone marrow-derived mesenchymal stem cells(BMSCs).ALP assay and ARS staining were used to evaluate osteoinduction capacity of the scaffolds co-cultured with rat BMSCs for 14 days.In a male SD rat model of skull defect(5 mm in diameter), bone defect repair was evaluated 8 weeks after implantation of the scaffolds using Micro-CT, HE and Masson staining.

RESULTS

The electrospun scaffolds had a fibrous structure similar to extracellular matrix(ECM)and were capable of sustained release of OGP for at least one month.Co-culture with 0.2%OGP@PLGA and 0.4%OGP@PLGA scaffolds, as compared with pure PLGA scaffold, significantly promoted the growth of rat BMSCs ((P < 0.01).The cells co-cultured with 0.4%OGP@PLGA scaffold showed the highest ALP activity and the greatest number of calcium nodules, indicating its strong osteoinduction ability (P < 0.01).Micro-CT and HE and Masson staining results showed that 0.4%OGP@PLGA scaffold had significantly better ability for promoting bone repair than the other two OGP-loaded scaffolds(P < 0.01).

CONCLUSION

The electrospun PLGA scaffold loaded with OGP effectively mimics the structure of ECM and has a good biocompatibility and osteoinduction ability, suggesting its potential as a new bone tissue engineering scaffold for bone defect repair.

Expression of angiogenesis-related proteins in bone marrow mesenchymal stem cells induced by osteoprotegerin during osteogenic differentiation in rats

This study aimed to discuss the expression of angiogenesis-related proteins in bone marrow mesenchymal stem cells (BMSCs) induced by osteoprotegerin (OGP) during osteogenic differentiation in rats, and to analyze the effect of fracture healing inflammatory factor TNF-ɑ on the osteogenic differentiation of BMSCs of rats. BMSCs isolated and cultured from the third generation rats were taken as the research object. According to the addition amount of OGP, BMSCs were divided into control group, OGP (10^-7 mol/L) group, OGP (10^-8 mol/L) group, and OGP (10^-9 mol/L) group. The cell growth and morphological characteristics of each group were observed by inverted phase contrast microscope, the cell proliferation rate was measured by MTT method, angiogenesis-related markers (platelet growth factor (VEGF), cingulate protein 5 (Fbln5), and angiogenin-like protein 4 (Angptl4)) were quantitatively detected by Western blot, and the effect of TNF-ɑ on osteogenic differentiation was detected by CCK. Compared with the control group, MTT results showed that the value-added rate of cells in the OGP (10^-8 mol/L) group reached the maximum at 9 days (P < 0.05). The ALP activity in osteoblasts in the OGP (10^-8 mol/L) group reached the maximum at 9 days (P < 0.01). The OGP (10^-8 mol/L) group had the highest expression of vascular regeneration proteins (VEGF, Fbln5, and Angptl4) (P < 0.05). CCK analysis showed that the TNF-ɑ (1.0 ng/mL) group showed a significant increase in absorbance compared with the control group on 6 days (P < 0.05), and the OD value of the TNF-ɑ (10 ng/mL) group decreased at all time points (P < 0.05). Overall, 10^-8 mol/L OGP can induce the proliferation and osteogenic differentiation of MSCs, and promote the expression of angiogenesis-related proteins (VEGF, Fbln5, and Angptl4) during osteogenic differentiation. Besides, 1.0 ng/mL of TNF-ɑ can also promote osteogenesis differentiation of BMSCs in the short term.

Drug Delivery Systems Based on Titania Nanotubes and Active Agents for Enhanced Osseointegration of Bone Implants

TiO2 nanotubes (TNTs) are attractive nanostructures for localized drug delivery. Owing to their excellent biocompatibility and physicochemical properties, numerous functionalizations of TNTs have been attempted for their use as therapeutic agent delivery platforms. In this review, we discuss the current advances in the applications of TNT-based delivery systems with an emphasis on the various functionalizations of TNTs for enhancing osteogenesis at the bone-implant interface and for preventing implant-related infection. Innovation of therapies for enhancing osteogenesis still represents a critical challenge in regeneration of bone defects. The overall concept focuses on the use of osteoconductive materials in combination with the use of osteoinductive or osteopromotive factors. In this context, we highlight the strategies for improving the functionality of TNTs, using five classes of bioactive agents: growth factors (GFs), statins, plant derived molecules, inorganic therapeutic ions/nanoparticles (NPs) and antimicrobial compounds.

Programmed Sustained Release of Recombinant Human Bone Morphogenetic Protein-2 and Inorganic Ion Composite Hydrogel as Artificial Periosteum

Recombinant human bone morphogenetic protein-2 (rhBMP-2) and bioceramic are the widely used bioactive factors in treatment of bone defects, but these easily cause side effects because of uncontrollable local concentration. In this study, rhBMP-2 was grafted on the surface of mesoporous bioglass nanoparticles (MBGNs) with an amide bond and then photo-cross-linked together with methacrylate gelatin (GelMA); in this way, a GelMA/MBGNs-rhBMP-2 hydrogel membrane was fabricated to release rhBMP-2 in a controllable program during the early bone regeneration period and then release calcium and silicon ions to keep promoting osteogenesis instead of rhBMP-2 in a long term. In this way, rhBMP-2 can keep releasing for 4 weeks and then the ions keep releasing after 4 weeks; this process is matched to early and late osteogenesis procedures. In vitro study demonstrated that the early release of rhBMP-2 can effectively promote local cell osteogenic differentiation in a short period, and then, the inorganic ions can promote cell adhesion not only in the early stage but also keep promoting osteogenic differentiation for a long period. Finally, the GelMA/MBGNs-rhBMP-2 hydrogel shows a superior capacity in long-term osteogenesis and promoting bone tissue regeneration in rat calvarial critical size defect. This GelMA/MBGNs-rhBMP-2 hydrogel demonstrated a promising strategy for the controllable and safer use of bioactive factors such as rhBMP-2 in artificial periosteum to accelerate bone repairing.

Functionalization of titanium substrate with multifunctional peptide OGP-NAC for the regulation of osteoimmunology

The immune response to an orthopedic implant is closely related to the nearby bone metabolism balance. To modify titanium (Ti) substrates and accordingly regulate the balance between osteoclast activation and osteoblast differentiation, a multifunctional peptide OGP-NAC was synthesized via conjugating an osteogenic growth peptide (OGP) with N-acetylcysteine (NAC). Then, the synthesized peptide was employed to functionalize Ti substrates and the response of both osteoblasts and osteoclasts was investigated in vitro. The results showed that OGP-NAC was successfully prepared and immobilized onto Ti substrate surfaces. Thereafter, studies on introducing RAW 264.7 cells (one kind of monocyte macrophage responsible for immune responses) to osteoclasts demonstrated that the peptide modified Ti surface could inhibit RAW 264.7 cells from secreting important inflammatory cytokines (TNF-α and IL-1β), and suppress the activation of MAPK, NF-κB and NFAT c1, which are important transcription factors for osteoclastogenesis. Meanwhile, the modified surface promoted osteoblast spreading, proliferation and differentiation. The study offers a feasible strategy to mediate the balance between osteoclast activation and osteoblast differentiation, having great potential for improving osseointegration of an orthopedic implant.

Bacteriophage-based biomaterials for tissue regeneration

Bacteriophage, also called phage, is a human-safe bacteria-specific virus. It is a monodisperse biological nanostructure made of proteins (forming the outside surface) and nucleic acids (encased in the protein capsid). Among different types of phages, filamentous phages have received great attention in tissue regeneration research due to their unique nanofiber-like morphology. They can be produced in an error-free format, self-assemble into ordered scaffolds, display multiple signaling peptides site-specifically, and serve as a platform for identifying novel signaling or homing peptides. They can direct stem cell differentiation into specific cell types when they are organized into proper patterns or display suitable peptides. These unusual features have allowed scientists to employ them to regenerate a variety of tissues, including bone, nerves, cartilage, skin, and heart. This review will summarize the progress in the field of phage-based tissue regeneration and the future directions in this field.

Three-Dimensional Printing of Biodegradable Piperazine-Based Polyurethane-Urea Scaffolds with Enhanced Osteogenesis for Bone Regeneration

Synthetic biodegradable polymeric scaffolds with uniformly interconnected pore structure, appropriate mechanical properties, excellent biocompatibility, and even enhanced osteogenesis ability are urgently required for in situ bone regeneration. In this study, for the first time, a series of biodegradable piperazine (PP)-based polyurethane-urea (P-PUU) scaffolds with a gradient of PP contents were developed by air-driven extrusion 3D printing technology. The P-PUU ink of 60 wt % concentration was demonstrated to have appropriate viscosity for scaffold fabrication. The 3D-printed P-PUU scaffolds exhibited an interconnected porous structure of about 450 μm in macropore size and about 75% in porosity. By regulating the contents of PP in P-PUU scaffolds, their mechanical properties could be moderated, and P-PUU1.4 scaffolds with the highest PP contents exhibited the highest compressive modulus (155.9 ± 5.7 MPa) and strength (14.8 ± 1.1 MPa). Moreover, both in vitro and in vivo biological results suggested that the 3D-printed P-PUU scaffolds possessed excellent biocompatibility and osteoconductivity to facilitate new bone formation. The small molecular PP itself was confirmed for the first time to regulate osteogenesis of osteoblasts in a dose-dependent manner and the optimum concentration for osteoconductivity was about ∼0.5 mM, which suggests that PP molecules, together with the mechanical behavior, nitrogen-contents, and hydrophilicity of P-PUUs, play an important role in enhancing the osteoconductive ability of P-PUU scaffolds. Therefore, the 3D-printed P-PUU scaffolds, with suitable interconnected pore structure, appropriate mechanical properties, and intrinsically osteoconductive ability, should provide a promising alternative for bone regeneration.

Nonunion fractures, mesenchymal stem cells and bone tissue engineering

Depending on the duration of healing process, 5-10% of bone fractures may result in either nonunion or delayed union. Because nonunions remain a clinically important problem, there is interest in the utilization of tissue engineering strategies to augment bone fracture repair. Three basic biologic elements that are required for bone regeneration include cells, extracellular matrix scaffolds and biological adjuvants for growth, differentiation and angiogenesis. Mesenchymal stem cells (MSCs) are capable to differentiate into various types of the cells including chondrocytes, myoblasts, osteoblasts, and adipocytes. Due to their potential for multilineage differentiation, MSCs are considered important contributors in bone tissue engineering research. In this review we highlight the progress in the application of biomaterials, stem cells and tissue engineering in promoting nonunion bone fracture healing. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2551-2561, 2018.

Mass Spectrometry and Ion Mobility Characterization of Bioactive Peptide-Synthetic Polymer Conjugates

The bioconjugate BMP2-(PEO-HA)₂, composed of a dendron with two monodisperse poly(ethylene oxide) (PEO) branches terminated by a hydroxyapatite binding peptide (HA), and a focal point substituted with a bone growth stimulating peptide (BMP2), has been comprehensively characterized by mass spectrometry (MS) methods, encompassing matrix-assisted laser desorption ionization (MALDI), electrospray ionization (ESI), tandem mass spectrometry (MS²), and ion mobility mass spectrometry (IM-MS). MS² experiments using different ion activation techniques validated the sequences of the synthetic, bioactive peptides HA and BMP2, which contained highly basic amino acid residues either at the N-terminus (BMP2) or C-terminus (HA). Application of MALDI-MS, ESI-MS, and IM-MS to the polymer-peptide biomaterial confirmed its composition. Collision cross-section measurements and molecular modeling indicated that BMP2-(PEO-HA)₂ exists in several folded and extended conformations, depending on the degree of protonation. Protonation of all basic sites of the hybrid material nearly doubles its conformational space and accessible surface area.

Peptides for bone tissue engineering

Molecular signals in the form of growth factors are the main modulators of cell behavior. However, the use of growth factors in tissue engineering has several drawbacks, including their costs, difficult production, immunogenicity and short half-life. Furthermore, many of them are pleiotropic and, since a single growth factor can have different active domains, their effect is not always fully controllable. A very interesting alternative that has recently emerged is the use of biomimetic peptides. Sequences derived from the active domains of soluble or extracellular matrix proteins can be used to functionalize the biomaterials used as scaffolds for new tissue growth to either direct the attachment of cells or to be released as soluble ligands. Since these short peptides can be easily designed and cost-effectively synthesized in vitro, their use has opened up a world of new opportunities to obtain cheaper and more effective implants for regenerative medicine strategies. In this extensive review we will go through many of the most important peptides with potential interest for bone tissue engineering, not limiting to those that only mediate cell adhesion or induce the osteogenic differentiation of progenitor cells, but also focusing on those that direct angiogenesis because of its close relation with bone formation.