Multidomain synthetic peptide B2A2 synergistically enhances BMP-2 in vitro

Peptides for Targeting Chondrogenic Induction and Cartilage Regeneration in Osteoarthritis

OBJECTS

Osteoarthritis (OA) is a widespread degenerative joint condition commonly occurring in older adults. Currently, no disease-modifying drugs are available, and safety concerns associated with commonly used traditional medications have been identified. In this review, a significant portion of research in this field is concentrated on cartilage, aiming to discover methods to halt cartilage breakdown or facilitate cartilage repair.

METHODS

Researchers have mainly investigated the cartilage, seeking methods to promote its repair. This review focuses on peptide-based molecules known for their ability to selectively bind to growth factor cytokines and components of the cartilage extracellular matrix.

RESULTS

Chondroinductive peptides, synthetically producible, boast superior reproducibility, stability, modifiability, and yield efficiency over natural biomaterials. This review outlines a chondroinductive peptide design, molecular mechanisms, and their application in cartilage tissue engineering and also compares their efficacy in chondrogenesis in vitro and in vivo.

CONCLUSIONS

In this paper, we will summarize the application of peptides engineered to regenerate cartilage by acting as scaffolds, functional molecules, or both and discuss additional possibilities for peptides. This review article provides an overview of our current understanding of chondroinductive peptides for treating OA-affected cartilage and explores the delivery systems used for regeneration. These advancements may hold promise for enhancing or even replacing current treatment methodologies.

Advancing drug delivery to articular cartilage: From single to multiple strategies

Articular cartilage (AC) injuries often lead to cartilage degeneration and may ultimately result in osteoarthritis (OA) due to the limited self-repair ability. To date, numerous intra-articular delivery systems carrying various therapeutic agents have been developed to improve therapeutic localization and retention, optimize controlled drug release profiles and target different pathological processes. Due to the complex and multifactorial characteristics of cartilage injury pathology and heterogeneity of the cartilage structure deposited within a dense matrix, delivery systems loaded with a single therapeutic agent are hindered from reaching multiple targets in a spatiotemporal matched manner and thus fail to mimic the natural processes of biosynthesis, compromising the goal of full cartilage regeneration. Emerging evidence highlights the importance of sequential delivery strategies targeting multiple pathological processes. In this review, we first summarize the current status and progress achieved in single-drug delivery strategies for the treatment of AC diseases. Subsequently, we focus mainly on advances in multiple drug delivery applications, including sequential release formulations targeting various pathological processes, synergistic targeting of the same pathological process, the spatial distribution in multiple tissues, and heterogeneous regeneration. We hope that this review will inspire the rational design of intra-articular drug delivery systems (DDSs) in the future.

3D-printed composite scaffold with gradient structure and programmed biomolecule delivery to guide stem cell behavior for osteochondral regeneration

The fabrication of osteochondral scaffolds with both structural and biochemical cues to regulate endogenous bone marrow-derived mesenchymal stem cells (BMSCs) behavior for cartilage and subchondral bone regeneration is still a challenge. To this end, a composite scaffold (BE-PSA) with gradient structure and programmed biomolecule delivery was prepared by fused deposition modeling (FDM) 3D printing and multi-material-based modification. The 3D-printed polycaprolactone (PCL) scaffold included upper pores of 200 μm for cartilage regeneration and lower pores of 400 μm for bone regeneration. For a sequential modulation of BMSCs behavior, fast-degrading sodium alginate (SA) hydrogel was used to deliver a burst release of E7 peptide to enhance BMSCs migration within 72 h, while a slowly-degrading silk fibroin (SF) porous matrix was used to provide a sustained release of B2A peptide to improve BMSCs dual-lineage differentiation lasting for >300 h, depending on the different degradation rates of SA hydrogel and SF matrix. The BE-PSA scaffold had good biocompatibility and could improve the migration and osteogenic/chondrogenic differentiation of BMSCs. Benefiting from the synergistic effects of spatial structures and programmed biomolecule delivery, the BE-PSA scaffold showed enhanced cartilage and subchondral bone regeneration in rabbit osteochondral defect model. This work not only provides a promising scaffold to guide BMSCs behavior for osteochondral regeneration but also offers a method for the fabrication of tissue engineering biomaterials based on the structural and biochemical modification.

Multipotential Role of Growth Factor Mimetic Peptides for Osteochondral Tissue Engineering

Articular cartilage is characterized by a poor self-healing capacity due to its aneural and avascular nature. Once injured, it undergoes a series of catabolic processes which lead to its progressive degeneration and the onset of a severe chronic disease called osteoarthritis (OA). In OA, important alterations of the morpho-functional organization occur in the cartilage extracellular matrix, involving all the nearby tissues, including the subchondral bone. Osteochondral engineering, based on a perfect combination of cells, biomaterials and biomolecules, is becoming increasingly successful for the regeneration of injured cartilage and underlying subchondral bone tissue. To this end, recently, several peptides have been explored as active molecules and enrichment motifs for the functionalization of biomaterials due to their ability to be easily chemically synthesized, as well as their tunable physico-chemical features, low immunogenicity issues and functional group modeling properties. In addition, they have shown a good aptitude to penetrate into the tissue due to their small size and stability at room temperature. In particular, growth-factor-derived peptides can play multiple functions in bone and cartilage repair, exhibiting chondrogenic/osteogenic differentiation properties. Among the most studied peptides, great attention has been paid to transforming growth factor-β and bone morphogenetic protein mimetic peptides, cell-penetrating peptides, cell-binding peptides, self-assembling peptides and extracellular matrix-derived peptides. Moreover, recently, phage display technology is emerging as a powerful selection technique for obtaining functional peptides on a large scale and at a low cost. In particular, these peptides have demonstrated advantages such as high biocompatibility; the ability to be immobilized directly on chondro- and osteoinductive nanomaterials; and improving the cell attachment, differentiation, development and regeneration of osteochondral tissue. In this context, the aim of the present review was to go through the recent literature underlining the importance of studying novel functional motifs related to growth factor mimetic peptides that could be a useful tool in osteochondral repair strategies. Moreover, the review summarizes the current knowledge of the use of phage display peptides in osteochondral tissue regeneration.

Chondroinductive/chondroconductive peptides and their-functionalized biomaterials for cartilage tissue engineering

The repair of articular cartilage defects is still challenging in the fields of orthopedics and maxillofacial surgery due to the avascular structure of articular cartilage and the limited regenerative capacity of mature chondrocytes. To provide viable treatment options, tremendous efforts have been made to develop various chondrogenically-functionalized biomaterials for cartilage tissue engineering. Peptides that are derived from and mimic the functions of chondroconductive cartilage extracellular matrix and chondroinductive growth factors, represent a unique group of bioactive agents for chondrogenic functionalization. Since they can be chemically synthesized, peptides bear better reproducibility, more stable efficacy, higher modifiability and yielding efficiency in comparison with naturally derived biomaterials and recombinant growth factors. In this review, we summarize the current knowledge in the designs of the chondroinductive/chondroconductive peptides, the underlying molecular mechanisms and their-functionalized biomaterials for cartilage tissue engineering. We also systematically compare their in-vitro and in-vivo efficacies in inducing chondrogenesis. Our vision is to stimulate the development of novel peptides and their-functionalized biomaterials for cartilage tissue engineering.

Chondroinductive Peptides for Cartilage Regeneration

Inducing and maintaining a hyaline cartilage phenotype is the greatest challenge for cartilage regeneration. Synthetic chondroinductive biomaterials might be the answer to the unmet clinical need for a safe, stable, and cost-effective material capable of inducing true hyaline cartilage formation. The past decade witnessed an emergence of peptides to achieve chondrogenesis, as peptides have the advantages of versatility, high target specificity, minimized toxicity and immunogenicity, and ease of synthesis. Here, we review peptides as the basis for creating promising synthetic chondroinductive biomaterials for in situ scaffold-based cartilage regeneration. We provide a thorough review of peptides evaluated for cartilage regeneration while distinguishing between peptides reported to induce chondrogenesis independently, and peptides reported to act in synergy with other growth factors to induce cartilage regeneration. Additionally, we highlight that most peptide studies have been in vitro, and appropriate controls are not always present. A few rigorously-performed in vitro studies have proceeded to in vivo studies, but the peptides in those in vivo studies were mainly introduced via systemic, subcutaneous, or intraarticular injections, with a paucity of studies employing in situ defects with appropriate controls. Clinical translation of peptides will require the evaluation of these peptides in well-controlled in vivo cartilage defect studies. In the decade ahead, we may be poised to leverage peptides to design devices that are safe, reproducible, cost-efficient, and scalable biomaterials, which are themselves chondroinductive to achieve true hyaline cartilage regeneration without the need for growth factors and other small molecules.

Investigational growth factors utilized in animal models of spinal fusion: Systematic review

BACKGROUND

Over 400000 Americans annually undergo spinal fusion surgeries, yet up to 40% of these procedures result in pseudoarthrosis even with iliac crest autograft, the current “gold standard” treatment. Tissue engineering has the potential to solve this problem via the creation of bone grafts involving bone-promoting growth factors (e.g., bone morphogenetic protein 2). A broad assessment of experimental growth factors is important to inform future work and clinical potential in this area. To date, however, no study has systematically reviewed the investigational growth factors utilized in preclinical animal models of spinal fusion.

AIM

To review all published studies assessing investigational growth factors for spinal fusion in animal models and identify promising agents for translation.

METHODS

We conducted a systematic review of the literature using PubMed, Embase, Cochrane Library, and Web of Science databases with searches run on May 29^th, 2018. The search query was designed to include all non-human, preclinical animal models of spinal fusion reported in the literature without a timespan limit. Extracted data for each model included surgical approach, level of fusion, animal species and breed, animal age and sex, and any other relevant characteristics. The dosages/sizes of all implant materials, spinal fusion rates, and follow-up time points were recorded. The data were analyzed and the results reported in tables and text. PRISMA guidelines were followed for this systematic review.

RESULTS

Twenty-six articles were included in this study, comprising 14 experimental growth factors: AB204 (n = 1); angiopoietin 1 (n = 1); calcitonin (n = 3); erythropoietin (n = 1); basic fibroblast growth factor (n = 1); growth differentiation factor 5 (n = 4), combined insulin-like growth factor 1 + transforming growth factor beta (n = 4); insulin (n = 1); NELL-1 (n = 5); noggin (n = 1); P-15 (n = 1); peptide B2A (n = 2); and secreted phosphoprotein 24 (n = 1). The fusion rates of the current gold standard treatment (autologous iliac crest bone graft, ICBG) and the leading clinically used growth factor (BMP-2) ranged widely in the included studies, from 0-100% for ICBG and from 13%-100% for BMP-2. Among the identified growth factors, calcitonin, GDF-5, NELL-1, and P-15 resulted in fusion rates of 100% in some cases. In addition, six growth factors - AB204, angiopoietin 1, GDF-5, insulin, NELL-1, and peptide B2A - resulted in significantly enhanced fusion rates compared to ICBG, BMP-2, or other internal control in some studies. Large heterogeneity in animal species, fusion method, and experimental groups and time points was observed across the included studies, limiting the direct comparison of the growth factors identified herein.

CONCLUSION

Several promising investigational growth factors for spinal fusion have been identified herein; directly comparing the fusion efficacy and safety of these agents may inform clinical translation.

ONO-1301 Enhances in vitro Osteoblast Differentiation and in vivo Bone Formation Induced by Bone Morphogenetic Protein

STUDY DESIGN

In vitro and in vivo assessment of osteogenic effect by prostacyclin agonist (ONO-1301).

OBJECTIVE

The aim of this study was to investigate the effects of ONO-1301 on in vitro osteoblastic differentiation and in vivo bone formation induced by bone morphogenetic protein (BMP).

SUMMARY OF BACKGROUND DATA

Among prostaglandins (PGs), PGE2 is the most abundant in bone tissue and its effects on bone formation have been well studied. PGI2 (prostacyclin) is the second most abundant PG in bone tissue and plays important roles in hemodynamics. However, the effects of PGI2 on osteoblast differentiation and bone regeneration have not been elucidated.

METHODS

The effects of PGI2 agonist (ONO-1301), with and without recombinant human (rh) BMP-2, on osteoblastic differentiation and cell proliferation were investigated in vitro using alkaline phosphatase (ALP) and WST-1 assays. Murine primary osteoblasts and cell lines (ST2, MC3T3-E1, C2C12, and CH310T1/2) were used for the study. The effects of ONO-1301 on rhBMP-2 induced bone formation were investigated in a mouse model of muscle pouch transplantation (ectopic model) and in a rat model of spinal fusion (orthotopic model).

RESULTS

ONO-1301 significantly increased ALP activity in the primary osteoblasts and ST2 cells. In addition, cotreatment with ONO-1301 and rhBMP-2 significantly increased ALP activity in the primary osteoblasts, as well as in ST2 and MC3T3-E1 cells. Cell proliferation was not affected by both ONO-1301 and ONO-1301 as well as rhBMP-2. In the ectopic model, ONO-1301 significantly increased the volume of ectopic bone whose formation was induced by BMP. In addition, in the orthotopic model, ONO-1301 significantly increased bone volume and fusion rate.

CONCLUSION

This study has demonstrated that the PG IP agonist ONO-1301 improves in vitro BMP-2 induced osteoblast differentiation and in vivo ectopic and orthotopic bone formation. The results suggest that ONO-1301 has a potential clinical application as an enhancer of BMP-induced bone formation.

LEVEL OF EVIDENCE

N/A.

Bone Morphogenetic Protein-Based Therapeutic Approaches

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the transforming growth factor (TGF)-β family of ligands and exert most of their effects through the canonical effectors Smad1, 5, and 8. Appropriate regulation of BMP signaling is critical for the development and homeostasis of numerous human organ systems. Aberrations in BMP pathways or their regulation are increasingly associated with diverse human pathologies, and there is an urgent and growing need to develop effective approaches to modulate BMP signaling in the clinic. In this review, we provide a wide perspective on diseases and/or conditions associated with dysregulated BMP signal transduction, outline the current strategies available to modulate BMP pathways, highlight emerging second-generation technologies, and postulate prospective avenues for future investigation.

Zero-order controlled release of BMP2-derived peptide P24 from the chitosan scaffold by chemical grafting modification technique for promotion of osteogenesis in vitro and enhancement of bone repair in vivo

Combination of tissue-engineered bone scaffolds with cell-adhesive, osteoconductive, or osteoinductive biomolecules is a critical strategy to improve their properties that significantly influence cellular behaviors, such as adhesion, proliferation, and differentiation, which is beneficial for critical-sized bone defects repairing. However, the traditional surface modification techniques, such as physical adsorption, coating, and plasma treatment, et al, have great limitations for immobilization of bioactive molecules due to undesirable controlled delivery performance or overly complex multistep procedures. In this study, we functionalized the chitosan/hydroxyapatite (CS/HA) biomimetic composite scaffold for controlled delivery of BMP2-derived peptide (P24) by the chemical grafting modification technique: firstly, P24 was conjugated with a thiolated chitosan, chitosan-4-thiobutylamidine (CS-TBA); secondly, the resultant CS-P24 was then combined with HA to prepare CS-P24/HA scaffolds. The effect of CS-P24/HA scaffolds on bone regeneration was evaluated, along with the underlying biological mechanisms responsible in vitro and in vivo. In vitro, the controlled and sustained release of bioactive P24 could last up to 90 days, furthermore, the release profiles of CS-5%P24/HA and CS-10%P24/HA were linear and could be fitted according to zero-order kinetic model (R²=0.9929; R²=0.9757); P24 on the scaffold significantly promoted cell adhesion, proliferation, osteodifferentiation, and mineralization with synergistic effects. Bone marrow stromal cells (BMSCs) revealed spindle-shaped surface morphology, indicating the CS-P24/HA scaffolds supported cell adhesion and possessed a high proliferation rate that varied according to the P24 concentration levels. Furthermore, mRNA levels for OCN, Runx2, and collagen I were significantly up-regulated on CS-P24/HA scaffolds compared with cells grown on CS/HA scaffolds in vitro (p < 0.05). Similarly, the BMSCs exhibited a higher ALP expression and calcium deposition level on CS-P24/HA scaffolds compared with CS/HA scaffolds (p < 0.05). In vivo, osteoinductive studies revealed a significantly higher ectopic osteogenesis level of CS-10%P24/HA scaffolds in rat dorsal muscle pockets compared with that of CS/HA scaffolds. Finally, CS-P24/HA scaffolds showed superior performance in the reconstruction of rat calvarial bone defects. This novel CS-P24/HA scaffold is deemed a strong potential candidate for the repair of bone defects in human bone tissue engineering.

A Survey of Strategies to Modulate the Bone Morphogenetic Protein Signaling Pathway: Current and Future Perspectives

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the TGF-β family of ligands and are unequivocally involved in regulating stem cell behavior. Appropriate regulation of canonical BMP signaling is critical for the development and homeostasis of numerous human organ systems, as aberrations in the BMP pathway or its regulation are increasingly associated with diverse human pathologies. In this review, we provide a wide-perspective on strategies that increase or decrease BMP signaling. We briefly outline the current FDA-approved approaches, highlight emerging next-generation technologies, and postulate prospective avenues for future investigation. We also detail how activating other pathways may indirectly modulate BMP signaling, with a particular emphasis on the relationship between the BMP and Activin/TGF-β pathways.

Reprogramming of mesenchymal stem cells derived from iPSCs seeded on biofunctionalized calcium phosphate scaffold for bone engineering

Human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) are a promising choice of patient-specific stem cells with superior capability of cell expansion. There has been no report on bone morphogenic protein 2 (BMP2) gene modification of iPSC-MSCs for bone tissue engineering. The objectives of this study were to: (1) genetically modify iPSC-MSCs for BMP2 delivery; and (2) to seed BMP2 gene-modified iPSC-MSCs on calcium phosphate cement (CPC) immobilized with RGD for bone tissue engineering. iPSC-MSCs were infected with green fluorescence protein (GFP-iPSC-MSCs), or BMP2 lentivirus (BMP2-iPSC-MSCs). High levels of GFP expression were detected and more than 68% of GFP-iPSC-MSCs were GFP positive. BMP2-iPSC-MSCs expressed higher BMP2 levels than iPSC-MSCs in quantitative RT-PCR and ELISA assays (p < 0.05). BMP2-iPSC-MSCs did not compromise growth kinetics and cell cycle stages compared to iPSC-MSCs. After 14 d in osteogenic medium, ALP activity of BMP2-iPSC-MSCs was 1.8 times that of iPSC-MSCs (p < 0.05), indicating that BMP2 gene transduction of iPSC-MSCs enhanced osteogenic differentiation. BMP2-iPSC-MSCs were seeded on CPC scaffold biofunctionalized with RGD (RGD-CPC). BMP2-iPSC-MSCs attached well on RGD-CPC. At 14 d, COL1A1 expression of BMP2-iPSC-MSCs was 1.9 times that of iPSC-MSCs. OC expression of BMP2-iPSC-MSCs was 2.3 times that of iPSC-MSCs. Bone matrix mineralization by BMP2-iPSC-MSCs was 1.8 times that of iPSC-MSCs at 21 d. In conclusion, iPSC-MSCs seeded on CPC were suitable for bone tissue engineering. BMP2 gene-modified iPSC-MSCs on RGD-CPC underwent osteogenic differentiation, and the overexpression of BMP2 in iPSC-MSCs enhanced differentiation and bone mineral production on RGD-CPC. BMP2-iPSC-MSC seeding on RGD-CPC scaffold is promising to enhance bone regeneration efficacy.

Bone induction by biomimetic PLGA copolymer loaded with a novel synthetic RADA16-P24 peptide in vivo

Bone morphogenetic protein-2 (BMP-2) is a key bone morphogenetic protein, and poly(lactic-co-glycolic acid) (PLGA) has been widely used as scaffold for clinical use to carry treatment protein. In the previous studies, we have synthesized BMP-2-related peptide (P24) and found its capacity of inducing bone regeneration. In this research, we have synthesized a new amphiphilic peptide Ac-RADA RADA RADA RADA S[PO4]KIPKASSVPTELSAISTLYLDDD-CONH2 (RADA16-P24) with an assembly peptide RADA16-Ion the P24 item of BMP2 to form divalent ion-induced gelatin. Two methods of physisorption and chemical cross-linking were used to bind RADA16-P24 onto the surface of the copolymer PLGA to synthesize RADA16-P24-PLGA, and its capacity of attaching bone marrow stromal cells (BMSCs) was evaluated in vitro and inducing ectopic bone formation was examined in vivo. In vitro our results demonstrated that RADA16-P24-PLGA copolymer prepared by physisorbing or prepared by chemical cross-linking had a peptide binding rate of (2.0180±0.5296)% or (10.0820±0.8405)% respectively (P<0.05). In addition the BMSCs proliferated vigorously in the RADA16-P24-PLGA biomaterials. Significantly the percentage of BMSCs attached to RADA16-P24-PLGA composite prepared by chemical cross-linking and physisorbing were (71.4±7.5) % or (46.7±5.8) % (P<0.05). The in vivo study showed that RADA16-P24-PLGA chemical cross-linking could better induce ectopic bone formation compared with RADA16-P24-PLGA physisorbing and PLGA. It is concluded that the PLGA copolymer is a good RADA16-P24 carrier. This novel RADA16-P24-PLGA composite has strong osteogenic capability.

B2A, a receptor modulator, increases the growth of pluripotent and preosteoblast cells through bone morphogenetic protein receptors

B2A (B2A2-K-NS) is a synthetic, multidomain peptide which is being developed to augment spinal fusion and bone repair locally. Using pluripotent mesenchymal cells of murine and human origin, we show that B2A-induced cell proliferation in a modest but dose-dependent manner. However, essentially all human tumor lines tested were not responsive or were weakly responsive to B2A. B2A treatment activated extracellular signal-regulated kinases 1 and 2 (ERK1/2), and the proliferation was partially blocked by an mitogen-activated protein kinase (MEK) inhibitor. The bone morphogenetic protein (BMP) type I receptor kinase inhibitors depressed B2A-induced proliferation. Upregulation of bone morphogenetic protein 2 was not involved, as noggin, DAN, or chordin did not block B2A-induced proliferation. These data suggest that B2A-induced proliferation results from cell-type-specific activation of bone morphogenetic protein receptor, which, in turn, regulates ERK1/2 activity. B2A-induced proliferation, acting through ERK1/2, is a phenomenon that, while not strictly related to the ability of B2A to augment BMP-induced differentiation via the small mothers against decapentaplegic pathway, may ultimately contribute to bone repair in vivo.

Peptide-based delivery to bone

Peptides are attractive as novel therapeutic reagents, since they are flexible in adopting and mimicking the local structural features of proteins. Versatile capabilities to perform organic synthetic manipulations are another unique feature of peptides compared to protein-based medicines, such as antibodies. On the other hand, a disadvantage of using a peptide for a therapeutic purpose is its low stability and/or high level of aggregation. During the past two decades, numerous peptides were developed for the treatment of bone diseases, and some peptides have already been used for local applications to repair bone defects in the clinic. However, very few peptides have the ability to form bone themselves. We herein summarize the effects of the therapeutic peptides on bone loss and/or local bone defects, including the results from basic studies. We also herein describe some possible methods for overcoming the obstacles associated with using therapeutic peptide candidates.

B2A peptide induces chondrogenic differentiation in vitro and enhances cartilage repair in rats

This study investigated whether the synthetic peptide B2A (B2A2-K-NS) could induce in vitro chondrogenic differentiation and enhance the in vivo repair of damaged cartilage in an osteoarthritis model. In vitro, micromass cultures of murine and human stem cells with and without B2A were used as models of chondrogenic differentiation. Micromasses were evaluated for gene expression using microarray analysis and quantitative PCR; and for extracellular matrix production by Alcian blue staining for sulfated glycosaminoglycan and immunochemical detection of collagen type II. In vivo, osteoarthritis was chemically induced in knees of adult rats by an injection of mono-iodoacetate (MIA) into the synovial space. Treatment was administered at 7- and 14 days after the MIA by injection into the synovial space of B2A or saline and terminated at 21 days, after which knee cartilage damage was determined and scored by histological analysis. In murine C3H10T1/2 micromass culture, B2A induced the expression of more than 11 genes associated with growth factors/receptors, transcription, and the extracellular matrix, including PDGF-AA. B2A also significantly increased the sulfated glycosaminoglycan and collagen of murine- and human micromass cultures. In the knee osteoarthritis model, B2A treatment enhanced cartilage repair compared to untreated knees as determined histologically by a decrease in damage indicators. These findings suggest that B2A induces stem cells chondrogenic differentiation in vitro and enhances cartilage repair in vivo. The results suggest that B2A might be useful to promote cartilage repair.

B2A as a positive BMP receptor modulator

B2A (B2A2-K-NS) is a synthetic multi-domain peptide that in vitro augments bone morphogenetic protein (BMP)-2-induced cell responsiveness and osteodifferentiation. Augmentation of endogenous BMP-2 is thought to ultimately improve bone repair, and has led to clinical evaluation of B2A in orthopedic applications. In this study, we show that B2A binds to BMP receptor (BMPR)-IB, BMPR-II, and BMPR-IA. B2A reduces the EC50 of rh-BMP-2, thus shifting the response curve to the left. B2A enhances the osteogenic activity of BMP-2, but not growth and differentiation factor-5, BMP-7, or BMP-9, indicating its action is highly BMP-2 selective. Additionally, B2A did not augment Wnt-3a- and retinoic acid-induced differentiation. All three functional domains (receptor-binding domain, hydrophobic-linker domain, heparin-binding domain) of B2A are required for optimal bioactivity. Collectively, the results suggest that B2A, via its unique sequence, acts in a manner consistent with a positive receptor modulator to selectively enhance BMP-2 osteodifferentiation, and yet in the absence of BMP-2, B2A is without cooperative effect.

Bone induction by biomimetic PLGA-(PEG-ASP)n copolymer loaded with a novel synthetic BMP-2-related peptide in vitro and in vivo

BMP-2 is one of the most important growth factors of bone regeneration. Polylactide-co-glycolic acid (PLGA), which is used as a biodegradable scaffold for delivering therapeutic agents, has been intensively investigated. In previous studies, we synthesized a novel BMP-2-related peptide (designated P24) and found that it could enhance the osteoblastic differentiation of bone marrow stromal cells (BMSCs). The objective of this study was to construct a biomimetic composite by incorporating P24 into a modified PLGA-(PEG-ASP)n copolymer to promote bone formation. In vitro, our results demonstrated that PLGA-(PEG-ASP)n scaffolds were shown to be an efficient system for sustained release of P24. Significantly more BMSCs attached to the P24/PLGA-(PEG-ASP)n and PLGA-(PEG-ASP)n membranes than to PLGA, and the cells in the two groups subsequently proliferated more vigorously than those in the PLGA group. The expression of osteogenic markers in P24/PLGA-(PEG-ASP)n group was stronger than that in the PLGA-(PEG-ASP)n and PLGA groups. Radiographic and histological examination, Western blotting and RT-PCR showed that P24/PLGA-(PEG-ASP)n scaffold could induce more effective ectopic bone formation in vivo, as compared with PLGA-(PEG-ASP)n or gelatin sponge alone. It is concluded that the PLGA-(PEG-ASP)n copolymer is a good P24 carrier and can serve as a good scaffold for controlled release of P24. This novel P24/PLGA-(PEG-ASP)n composite promises to be an excellent biomaterial for inducing bone regeneration.

Ceramic granules enhanced with B2A peptide for lumbar interbody spine fusion: an experimental study using an instrumented model in sheep

OBJECT

New generations of devices for spinal interbody fusion are expected to arise from the combined use of bioactive peptides and porous implants. The purpose of this dose-ranging study was to evaluate the fusion characteristics of porous ceramic granules (CGs) coated with the bioactive peptide B2A2-K-NS (B2A) by using a model of instrumented lumbar interbody spinal fusion in sheep.

METHODS

Instrumented spinal arthrodesis was performed in 40 operative sites in 20 adult sheep. In each animal, posterior instrumentation (pedicle screw and rod) and a polyetheretherketone cage were placed in 2 single-level procedures (L2-3 and L4-5). All cages were packed with graft material prior to implantation. The graft materials were prepared by mixing (1:1 vol/vol) CGs with or without a B2A coating and morselized autograft. Ceramic granules were coated with B2A at 50, 100, 300, and 600 microg/ml granules (50-B2A/CG, 100-B2A/CG, 300-B2A/CG, and 600-B2A/CG, respectively), resulting in 4 B2A-coated groups plus a control group (uncoated CGs). Graft material from each of these groups was implanted in 8 operative sites. Four months after arthrodesis, interbody fusion status was assessed with CT, and the interbody site was further evaluated with quantitative histomorphometry.

RESULTS

All B2A/CG groups had higher CT-confirmed interbody fusion rates compared with those in controls (CGs only). Seven of 8 sites were fused in the 50-B2A/CG, 100-B2A/CG, and 300-B2A/CG groups, whereas 5 of 8 sites were fused in the group that had received uncoated CGs. New woven and lamellar bone spanned the fusion sites with excellent osseointegration. There was no heterotopic ossification or other untoward events attributed to the use of B2A/CG in any group. Each B2A/CG treatment produced more new bone than that in the CG group.

CONCLUSIONS

Bioactive treatment with B2A effectively enhanced the fusion capacity of porous CGs. These findings suggest that B2A/CG may well represent a new generation of biomaterials for lumbar interbody fusion and indicate that additional studies are warranted.

Targeted delivery with peptidomimetic conjugated self-assembled nanoparticles

Peptides produce specific nanostructures, making them useful for targeting in biological systems but they have low bioavailability, potential immunogenicity and poor metabolic stability. Peptidomimetic self-assembled NPs can possess biological recognition motifs as well as providing desired engineering properties. Inorganic NPs, coated with self-assembled macromers for stability and anti-fouling, and conjugated with target-specific ligands, are advancing imaging from the anatomy-based level to the molecular level. Ligand conjugated NPs are attractive for cell-selective tumor drug delivery, since this process has high transport capacity as well as ligand dependent cell specificity. Peptidomimetic NPs can provide stronger interaction with surface receptors on tumor cells, resulting in higher uptake and reduced drug resistance. Self-assembled NPs conjugated with peptidomimetic antigens are ideal for sustained presentation of vaccine antigens to dendritic cells and subsequent activation of T cell mediated adaptive immune response. Self-assembled NPs are a viable alternative to encapsulation for sustained delivery of proteins in tissue engineering. Cell penetrating peptides conjugated to NPs are used as intracellular delivery vectors for gene expression and as transfection agents for plasmid delivery. In this work, synthesis, characterization, properties, immunogenicity, and medical applications of peptidomimetic NPs in imaging, tumor delivery, vaccination, tissue engineering, and intracellular delivery are reviewed.

Effect of grafting RGD and BMP-2 protein-derived peptides to a hydrogel substrate on osteogenic differentiation of marrow stromal cells

Osteogenic differentiation and mineralization of bone marrow stromal (BMS) cells depends on the cells' interactions with bioactive peptides associated with the matrix proteins. The RGD peptides of ECM proteins interact with BMS cells through integrin surface receptors to facilitate cell spreading and adhesion. The BMP peptide corresponding to residues 73-92 of bone morphogenetic protein-2 promotes differentiation and mineralization of BMS cells. The objective of this work was to investigate the effects of RGD and BMP peptides, grafted to a hydrogel substrate, on osteogenic differentiation and mineralization of BMS cells. RGD peptide was acrylamide-terminated by reacting acrylic acid with the N-terminal amine group of the peptide to produce the functionalized Ac-GRGD peptide. The PEGylated BMP peptide was reacted with 4-carboxybenzenesulfonazide to produce an azide functionalized Az-mPEG-BMP peptide. Poly (lactide-co-ethylene oxide- co-fumarate) (PLEOF) macromer was cross-linked with Ac-GRGD peptide and propargyl acrylate to produce an RGD conjugated hydrogel. Az-mPEG-BMP peptide was grafted to the hydrogel by "click chemistry". The RGD and BMP peptide density on the hydrogel surface was 1.62+/-0.37 and 5.2+/-0.6 pmol/cm2, respectively. BMS cells were seeded on the hydrogels and the effect of RGD and BMP peptides on osteogenesis was evaluated by measuring ALPase activity and calcium content with incubation time. BMS cells cultured on RGD conjugated, BMP peptide grafted, and RGD+BMP peptide modified hydrogels showed 3, 2.5, and 5-fold increase in ALPase activity after 14 days incubation. BMS cells seeded on RGD+BMP peptides modified hydrogel showed 4.9- and 11.8-fold increase in calcium content after 14 and 21 days, respectively, which was significantly higher than RGD conjugated or BMP grafted hydrogels. These results demonstrate that RGD and BMP peptides, grafted to a hydrogel substrate, act synergistically to enhance osteogenic differentiation and mineralization of BMS cells. These findings are potentially useful in developing engineered scaffolds for bone regeneration.

B2A peptide on ceramic granules enhance posterolateral spinal fusion in rabbits compared with autograft

STUDY DESIGN

Six groups of 10 animals underwent single level, uninstrumented posterolateral lumbar fusions. Graft sites were implanted with autologous bone, autologous bone plus B2A coated granules with concentrations of 0-, 50-, 100-, or 300 microg/mL, or no graft material. Explanted motion segments were analyzed by Faxitron radiographs, computerized tomography (CT), manual palpation, and histology.

OBJECTIVE

The synthetic peptide B2A2-K-NS (B2A) was evaluated as a novel agent for augmenting spinal fusion in a posterolateral, noninstrumented rabbit lumbar spine fusion model.

SUMMARY OF BACKGROUND DATA

There have been many efforts to increase the rate of posterolateral spinal fusion while, at the same time minimizing, use of autologous bone with its inherent harvest morbidity.

METHODS

B2A coated ceramic granules (0-, 50-, 100-, and 300 microg/mL) were mixed 1:1 with autogenous iliac crest bone and implanted. Autogenous bone alone was used as a positive control. Fusion was assessed at 6 weeks via radiographs and manual palpation. These results were confirmed with histology and CT.

RESULTS

Fusion results from palpation and radiographic evaluations were similar. CT and histology confirmed bridging bone across the transverse processes for fused spines. The highest fusion rates were observed in the 100 mug B2A/mL group-89% in comparison to 33% for uncoated granules (0 microg B2A/mL) and 63% for autograft alone. These differences were statistically significant.

CONCLUSION

All investigated B2A concentrations demonstrated increased fusion rates. Fusion masses resulting from the implantation of 100 mug B2A/mL granules demonstrated new woven bone: fused to the transverse processes, within granule pores, bridging bone across the transverse processes, and bridging residual bone graft and granules. It was concluded that each investigated concentration of B2A coated granules in a 1:1 mixture with autograft increased fusion rates in comparison to controls in this rabbit model.

Osterix is a key target for mechanical signals in human thoracic ligament flavum cells

Mechanical stress is considered to be an important factor in the progression of thoracic ossification of the ligament flavum (TOLF). To elucidate the mechanism underlying mechanical stress-induced TOLF, we investigated the effect of stretching on cultured flavum ligament cells derived from TOLF and non-TOLF patients. We found that the mRNA expression of alkaline phosphatase (ALP), osteocalcin, Runx2, and osterix, but not that of Dlx5 and Msx2, was significantly increased by stretching in TOLF cells. In addition, the effect seems to be finely tuned by stretching-triggered activation of distinct mitogen-activated protein kinase cascades. Specifically, a p38 specific inhibitor, SB203580, significantly inhibited stretching-induced osterix expression as well as ALP activity, whereas a specific inhibitor of ERK1/2, U0126, prevented stretching-induced Runx2 expression. We showed that overexpression of osterix resulted in a significant increase of ALP activity in TOLF cells, and osterix-specific RNAi completely abrogated the stretching-induced ALP activity, indicating that osterix plays a key role in stretching-stimulated osteogenic effect in TOLF cells. These results suggest that mechanical stress plays important roles in the progression of TOLF through induction of osteogenic differentiation of TOLF cells, and our findings support that osterix functions as a molecular link between mechanostressing and osteogenic differentiation.

A synthetic, bioactive PDGF mimetic with binding to both alpha-PDGF and beta-PDGF receptors

A multi-domain peptide, PAB2-1c, was designed and synthesized as a bioactive mimic of PDGF. PBA2-1c bound to both alpha- and beta-PDGF receptors as determined by surface plasmon resonance (SPR). The equilibrium dissociation constant (Kd) of binding to alpha-PDGF receptors by PAB2-1c (1.7 x 10(-8) M) compared favorably rhPDGF-AA (1.34 x 10(-8) M). Binding to -PDGF receptor by PAB2-1c (2.2 x 10(-8) M) was less favorable than, that of recombinant human PDGFBB (1.59 x 10(-9) M). Interestingly, PBA2-1c bound to these two receptors with similar affinity suggesting that, PBA2-1c was not PDGF receptor selective. In a murine myoblast cell line C2C12, PBA2-1c increased the tyrosine phosphorylation on PDGF receptors and the phosphorylation of AKT and ERK1/2 in a concentration-related manner. PBA2-1c also stimulated an increase in cell proliferation, cell migration, and collagen gel contraction. In these cell-based assays, PAB2-1c was effective at 1 microg/ml or lesser. The results support the hypothesis that PBA2-1c is a mimetic of PDGF, although it has a more promiscuous receptor interaction.

Augmentation of osseous phenotypes in vivo with a synthetic peptide

The synthetic peptide B2A2-K-NS augmented the in vitro expression of osseous phenotypes when cells were stimulated with BMP-2, an osteoinductive growth factor. B2A2-K-NS significantly enhanced the effects of BMP-2-induced alkaline phosphatase activity and mineralization. In the absence of BMP-2, B2A2-K-NS did not have an effect on these endpoints. Based on these observations, in vivo studies were conducted to evaluate if B2A2-K-NS could augment osseous phenotypes in an osteoinductive environment in which BMP-2 should be present. In one study, human demineralized bone matrix (DBM) was used to generate an osteoinductive environment and the effects of B2A2-K-NS on ectopic mineralization of subcutaneous implants evaluated. In the second study, a noncritical sized defect in rabbit ulnas with inherent reparative capacity was used as the osteoinductive environment and was treated with or without B2A2-K-NS. In the DBM studies, B2A2-K-NS augmented mineralization as determined using a combination of radiographic analysis and von Kossa staining at 4 weeks postimplant. In the rabbit ulna model, B2A2-K-NS significantly increased the radiographic bone density in the defects compared to carrier-only or no-treatment controls after 6 weeks. Histological staining confirmed that B2A2-K-NS generated a pronounced bone repair response. The results are consistent with the hypothesis that B2A2-K-NS augments osseous phenotypes in an osteoinductive environment, and suggests that B2A2-K-NS may have clinical utility.

Up-regulation of bone morphogenetic protein receptor IB by growth factors enhances BMP-2-induced human bone cell functions

Bone morphogenetic proteins (BMP) stimulate osteoblast differentiation by signal transduction via three BMP receptors (BMPR-IA, -IB, and -II). Several growth factors, including transforming growth factor-beta1 (TGF-beta1), fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor-AB (PDGF-AB), have also been shown to play an important part in osteogenesis. The mechanism underlying these activities is unclear, but these growth factors could modulate the BMP/BMPR pathway by up-regulating BMPR expression, thereby enhancing the osteogenic responses of bone cells to the BMP. In this study we have therefore examined the effects of TGF-beta1, FGF-2, and PDGF-AB on BMPR expression and BMP-2-mediated osteoblast functions in primary human bone cells. The results showed that although the ligand BMP-2 and growth factors had little effect on BMPR-IA and -II transcript expression, they significantly up-regulated BMPR-IB mRNA specifically. However, only the growth factors, but not the ligand BMP-2, increased the surface expression of the BMPR-IB antigen, which was found to be due to a differential effect of BMP-2 and the growth factors on the Smurf1/Smad6-induced breakdown process. Pre-incubation of the cells with the growth factors significantly augmented BMP-2-induced Smad1/5/8 phosphorylation, and Dlx5 expression ALP activity, compared with that of cells treated with BMP-2 alone. When cells were transfected with siRNA targeting BMPR-IB, the growth factors neither up-regulated BMPR-IB transcript expression nor enhanced BMP-2-induced Smad1/5/8 phosphorylation, Dlx5 expression and ALP activity. The results indicate that increased BMPR-IB by TGF-beta1, FGF-2, and PDGF-AB significantly enhances BMP-2-induced osteogenic functions in vitro, suggesting that they might positively modulate bone formation by up-regulating BMPR-IB in vivo.

Enhancement of cell attachment and tissue integration by a IKVAV containing multi-domain peptide

Laminin contains a number of cell binding motifs including IKVAV and some that bind heparin. We developed a multi-domain synthetic peptide, LA2, which combines IKVAV sequences with a heparin-binding domain with the goal of improving cell attachment to otherwise non-adherent substrates. LA2 was used to coat polystyrene, ethyl vinyl acetate (EVA), expanded polytetrafluoroethylene (ePTFE), polycarbonate, titanium and stainless steel. In cell attachment studies, LA2 dramatically increased cell attachment to polystyrene and EVA compared to uncoated counterparts or those coated with SIKVAV. Similar increases were observed on ePTFE and titanium. On polystyrene, LA2 enhanced the attachment of endothelial cells, smooth muscle cells, epithelial cells, myoblasts, and osteoblast progenitor cells. Following adhesion, the cells underwent proliferation to form confluent monolayers with phenotypic morphologies. Using osteoblast progenitor cells (MC3T3 cells) grown on LA2/polystyrene, the cells exhibited an increased production of a differentiation marker, alkaline phosphatase. In vivo, LA2 improved tissue integration into ePTFE when implanted subcutaneously in rats. After 2 weeks, cells had penetrated deep into the LA2 coated ePTFE implant whereas little cell penetration was found in uncoated grafts. The implant sites exhibited little inflammation or other untoward effects. The results indicated that the LA2 peptide improved cell adhesion and tissue integration and might be useful in a number of tissue engineering applications.

Semi-synthetic heparin derivatives: chemical modifications of heparin beyond chain length, sulfate substitution pattern and N-sulfo/N-acetyl groups

The glycosaminoglycan heparin is a polyanionic polysaccharide most recognized for its anticoagulant activity. Heparin binds to cationic regions in hundreds of prokaryotic and eukaryotic proteins, termed heparin-binding proteins. The endogenous ligand for many of these heparin-binding proteins is a structurally similar glycosaminoglycan, heparan sulfate (HS). Chemical and biosynthetic modifications of heparin and HS have been employed to discern specific sequences and charge-substitution patterns required for these polysaccharides to bind specific proteins, with the goal of understanding structural requirements for protein binding well enough to elucidate the function of the saccharide-protein interactions and/or to develop new or improved heparin-based pharmaceuticals. The most common modifications to heparin structure have been alteration of sulfate substitution patterns, carboxyl reduction, replacement N-sulfo groups with N-acetyl groups, and chain fragmentation. However, an accumulation of reports over the past 50 years describe semi-synthetic heparin derivatives obtained by incorporating aliphatic, aryl, and heteroaryl moieties into the heparin structure. A primary goal in many of these reports has been to identify heparin-derived structures as new or improved heparin-based therapeutics. Presented here is a perspective on the introduction of non-anionic structural motifs into heparin structure, with a focus on such modifications as a strategy to generate novel reduced-charge heparin-based bind-and-block antagonists of HS-protein interactions. The chemical methods employed to synthesize such derivatives, as well as other unique heparin conjugates, are reviewed.