Local delivery of parathyroid hormone-related protein-derived peptides coated onto a hydroxyapatite-based implant enhances bone regeneration in old and diabetic rats

Osteostatin, a peptide for the future treatment of musculoskeletal diseases

Nowadays, the treatment of musculoskeletal diseases represents a major challenge in the developed world. Diseases such as osteoporosis, osteoarthritis and arthritis have a high incidence and prevalence as a consequence of population aging, and they are also associated with a socioeconomic burden. Many efforts have been made to find a treatment for these diseases with various levels of success, but new approaches are still needed to deal with these pathologies. In this context, one peptide derived for the C-terminal extreme of the Parathormone related Peptide (PTHrP) called Osteostatin can be useful to treat musculoskeletal diseases. This pentapeptide (TRSAW) has demonstrated both in different in vitro and in vivo models, its role as a molecule with anti-resorptive, anabolic, anti-inflammatory, and anti-antioxidant properties. Our aim with this work is to review the Osteostatin main features, the knowledge of its mechanisms of action as well as its possible use for the treatment of osteoporosis, bone regeneration and fractures and against arthritis given its anti-inflammatory properties.

The treatment efficacy of bone tissue engineering strategy for repairing segmental bone defects under diabetic condition

Background

Diabetes mellitus is a systematic disease which exert detrimental effect on bone tissue. The repair and reconstruction of bone defects in diabetic patients still remain a major clinical challenge. This study aims to investigate the potential of bone tissue engineering approach to improve bone regeneration under diabetic condition.

Methods

In the present study, decalcified bone matrix (DBM) scaffolds were seeded with allogenic fetal bone marrow-derived mesenchymal stem cells (BMSCs) and cultured in osteogenic induction medium to fabricate BMSC/DBM constructs. Then the BMSC/DBM constructs were implanted in both subcutaneous pouches and large femoral bone defects in diabetic (BMSC/DBM in DM group) and non-diabetic rats (BMSC/DBM in non-DM group), cell-free DBM scaffolds were implanted in diabetic rats to serve as the control group (DBM in DM group). X-ray, micro-CT and histological analyses were carried out to evaluate the bone regenerative potential of BMSC/DBM constructs under diabetic condition.

Results

In the rat subcutaneous implantation model, quantitative micro-CT analysis demonstrated that BMSC/DBM in DM group showed impaired bone regeneration activity compared with the BMSC/DBM in non-DM group (bone volume: 46 ± 4.4 mm3 vs 58.9 ± 7.15 mm3, *p < 0.05). In the rat femoral defect model, X-ray examination demonstrated that bone union was delayed in BMSC/DBM in DM group compared with BMSC/DBM in non-DM group. However, quantitative micro-CT analysis showed that after 6 months of implantation, there was no significant difference in bone volume and bone density between the BMSC/DBM in DM group (199 ± 63 mm3 and 593 ± 65 mg HA/ccm) and the BMSC/DBM in non-DM group (211 ± 39 mm3 and 608 ± 53 mg HA/ccm). Our data suggested that BMSC/DBM constructs could repair large bone defects in diabetic rats, but with delayed healing process compared with non-diabetic rats.

Conclusion

Our study suggest that biomaterial sacffolds seeded with allogenic fetal BMSCs represent a promising strategy to induce and improve bone regeneration under diabetic condition.

Recombinant Human Parathyroid Hormone Biocomposite Promotes Bone-to-Tendon Interface Healing by Enhancing Tenogenesis, Chondrogenesis, and Osteogenesis in a Rabbit Model of Chronic Rotator Cuff Tears

PURPOSE

To investigate the effect of recombinant human parathyroid hormone (rhPTH) biocomposite on bone-to-tendon interface (BTI) healing for surgical repair of a chronic rotator cuff tear (RCT) model of rabbit, focusing on genetic, histologic, biomechanical and micro-computed tomography (CT) evaluations.

METHODS

Sixty-four rabbits were equally assigned to the 4 groups: saline injection (group A), nanofiber sheet alone (group B), rhPTH-soaked nanofiber sheet (nanofiber sheet was soaked with rhPTH, group C), and rhPTH biocomposite (rhPTH permeated the nanofiber sheet by coaxial electrospinning, group D). The release kinetics of rhPTH (groups C and D) was examined for 6 weeks in vitro. Nanofiber scaffolds were implanted on the surface of the repair site 6 weeks after the induction of chronic RCT. Genetic and histologic analyses were conducted 4 weeks after surgery. Furthermore, genetic, histologic, biomechanical, micro-CT, and serologic analyses were performed 12 weeks after surgery.

RESULTS

In vivo, group D showed the highest collagen type I alpha 1 (COL1A1), collagen type III alpha 1 (COL3A1), and bone morphogenetic protein 2 (BMP-2) messenger RNA (mRNA) expression levels (all P < .001) 4 weeks after surgery; however, there were no differences between groups at 12 weeks postsurgery. After 12 weeks postsurgery, group D showed better collagen fiber continuity and orientation, denser collagen fibers, more mature bone-to-tendon junction, and greater fibrocartilage layer formation compared with the other groups (all P < .05). Furthermore, group D showed the highest load-to-failure rate (28.9 ± 2.0 N/kg for group A, 30.1 ± 3.3 N/kg for group B, 39.7 ± 2.7 N/kg for group C, and 48.2 ± 4.5 N/kg for group D, P < .001) and micro-CT outcomes, including bone and tissue mineral density, and bone volume/total volume rate (all P < .001) at 12 weeks postsurgery.

CONCLUSIONS

In comparison to rhPTH-soaked nanofiber sheet and the other control groups, rhPTH biocomposite effectively accelerated BTI healing by enhancing the mRNA expression levels of COL1A1, COL3A1, and BMP-2 at an early stage and achieving tenogenesis, chondrogenesis, and osteogenesis at 12 weeks after surgical repair of a chronic RCT model of rabbit.

CLINICAL RELEVANCE

The present study might be a transitional study to demonstrate the efficacy of rhPTH biocomposites on BTI healing for surgical repair of chronic RCTs as an adaptable polymer biomaterial in humans.

A parathyroid hormone related supramolecular peptide for multi-functionalized osteoregeneration

Supramolecular peptide nanofiber hydrogels are emerging biomaterials for tissue engineering, but it is difficult to fabricate multi-functional systems by simply mixing several short-motif-modified supramolecular peptides because relatively abundant motifs generally hinder nanofiber cross-linking or the formation of long nanofiber. Coupling bioactive factors to the assembling backbone is an ideal strategy to design multi-functional supramolecular peptides in spite of challenging synthesis and purification. Herein, a multi-functional supramolecular peptide, P1R16, is developed by coupling a bioactive factor, parathyroid hormone related peptide 1 (PTHrP-1), to the basic supramolecular peptide RADA16-Ⅰ via solid-phase synthesis. It is found that P1R16 self-assembles into long nanofibers and co-assembles with RADA16-Ⅰ to form nanofiber hydrogels, thus coupling PTHrP-1 to hydrogel matrix. P1R16 nanofiber retains osteoinductive activity in a dose-dependent manner, and P1R16/RADA16-Ⅰ nanofiber hydrogels promote osteogenesis, angiogenesis and osteoclastogenesis in vitro and induce multi-functionalized osteoregeneration by intramembranous ossification and bone remodeling in vivo when loaded to collagen (Col) scaffolds. Abundant red blood marrow formation, ideal osteointegration and adapted degradation are observed in the 50% P1R16/Col scaffold group. Therefore, this study provides a promising strategy to develop multi-functional supramolecular peptides and a new method to topically administrate parathyroid hormone or parathyroid hormone related peptides for non-healing bone defects.

Recent progress in bone-repair strategies in diabetic conditions

Bone regeneration following trauma, tumor resection, infection, or congenital disease is challenging. Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia. It can result in complications affecting multiple systems including the musculoskeletal system. The increased number of diabetes-related fractures poses a great challenge to clinical specialties, particularly orthopedics and dentistry. Various pathological factors underlying DM may directly impair the process of bone regeneration, leading to delayed or even non-union of fractures. This review summarizes the mechanisms by which DM hampers bone regeneration, including immune abnormalities, inflammation, reactive oxygen species (ROS) accumulation, vascular system damage, insulin/insulin-like growth factor (IGF) deficiency, hyperglycemia, and the production of advanced glycation end products (AGEs). Based on published data, it also summarizes bone repair strategies in diabetic conditions, which include immune regulation, inhibition of inflammation, reduction of oxidative stress, promotion of angiogenesis, restoration of stem cell mobilization, and promotion of osteogenic differentiation, in addition to the challenges and future prospects of such approaches.

Supramolecular Peptide Nanofiber Hydrogels for Bone Tissue Engineering: From Multihierarchical Fabrications to Comprehensive Applications

Bone tissue engineering is becoming an ideal strategy to replace autologous bone grafts for surgical bone repair, but the multihierarchical complexity of natural bone is still difficult to emulate due to the lack of suitable biomaterials. Supramolecular peptide nanofiber hydrogels (SPNHs) are emerging biomaterials because of their inherent biocompatibility, satisfied biodegradability, high purity, facile functionalization, and tunable mechanical properties. This review initially focuses on the multihierarchical fabrications by SPNHs to emulate natural bony extracellular matrix. Structurally, supramolecular peptides based on distinctive building blocks can assemble into nanofiber hydrogels, which can be used as nanomorphology-mimetic scaffolds for tissue engineering. Biochemically, bioactive motifs and bioactive factors can be covalently tethered or physically absorbed to SPNHs to endow various functions depending on physiological and pharmacological requirements. Mechanically, four strategies are summarized to optimize the biophysical microenvironment of SPNHs for bone regeneration. Furthermore, comprehensive applications about SPNHs for bone tissue engineering are reviewed. The biomaterials can be directly used in the form of injectable hydrogels or composite nanoscaffolds, or they can be used to construct engineered bone grafts by bioprinting or bioreactors. Finally, continuing challenges and outlook are discussed.

Design of 3D Scaffolds for Hard Tissue Engineering: From Apatites to Silicon Mesoporous Materials

Advanced bioceramics for bone regeneration constitutes one of the pivotal interests in the multidisciplinary and far-sighted scientific trajectory of Prof. Vallet Regí. The different pathologies that affect osseous tissue substitution are considered to be one of the most important challenges from the health, social and economic point of view. 3D scaffolds based on bioceramics that mimic the composition, environment, microstructure and pore architecture of hard tissues is a consolidated response to such concerns. This review describes not only the different types of materials utilized: from apatite-type to silicon mesoporous materials, but also the fabrication techniques employed to design and adequate microstructure, a hierarchical porosity (from nano to macro scale), a cell-friendly surface; the inclusion of different type of biomolecules, drugs or cells within these scaffolds and the influence on their successful performance is thoughtfully reviewed.

Systemically impaired fracture healing in small animal research: A review of fracture repair models

Fracture healing is a complex process requiring mechanical stability, an osteoconductive matrix, and osteoinductive and osteogenic biology. This intricate process is easily disrupted by various patient factors such as chronic disease and lifestyle. As the medical complexity and age of patients with fractures continue to increase, the importance of developing relevant experimental models is becoming paramount in preclinical research. The objective of this review is to describe the most common small animal models of systemically impaired fracture healing used in the orthopedic literature including osteoporosis, diabetes mellitus, smoking, alcohol use, obesity, and ageing. This review will provide orthopedic researchers with a summary of current models of systemically impaired fracture healing used in small animals and present an overview of the methods of induction for each condition.

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO₂-10.3CaO-3.3P₂O₅-4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice.

Customized Therapeutic Surface Coatings for Dental Implants

Dental implants are frequently used to support fixed or removable dental prostheses to replace missing teeth. The clinical success of titanium dental implants is owed to the exceptional biocompatibility and osseointegration with the bone. Therefore, the enhanced therapeutic effectiveness of dental implants had always been preferred. Several concepts for implant coating and local drug delivery had been developed during the last decades. A drug is generally released by diffusion-controlled, solvent-controlled, and chemical controlled methods. Although a range of surface modifications and coatings (antimicrobial, bioactive, therapeutic drugs) have been explored for dental implants, it is still a long way from designing sophisticated therapeutic implant surfaces to achieve the specific needs of dental patients. The present article reviews various interdisciplinary aspects of surface coatings on dental implants from the perspectives of biomaterials, coatings, drug release, and related therapeutic effects. Additionally, the various types of implant coatings, localized drug release from coatings, and how released agents influence the bone–implant surface interface characteristics are discussed. This paper also highlights several strategies for local drug delivery and their limitations in dental implant coatings as some of these concepts are yet to be applied in clinical settings due to the specific requirements of individual patients.

Enhancement of local bone formation on titanium implants in osteoporotic rats by biomimetic multilayered structures containing parathyroid hormone (PTH)-related protein

Osteoporosis is a severe health problem causing bone fragility and consequent fracture. Titanium (Ti) implants, used in patients with osteoporotic fractures, are prone to failure because of the decreased bone mass and strength. Therefore, it is of utmost importance to fabricate implants possessing osteogenic properties to improve implant osseointegration. To improve the long-term survival rate of Ti implants in osteoporotic patients, hyaluronic acid/ϵ-polylysine multilayers containing the parathyroid hormone (PTH)-related protein (PTHrP) were deposited on Ti implants by a layer-by-layer (LBL) electro assembly technique. The murine pre-osteoblast cell line MC3T3-E1, possessing a high potential of osteoblast differentiation, was used to evaluate the osteo-inductive effects of Ti-LBL-PTHrP in vitro. In addition, the performance of the Ti (Ti-LBL-PTHrP) implant was evaluated in vivo in a femoral intramedullary implantation in Sprague Dawley rats. The Ti-LBL-PTHrP implant regulated the release of the loaded PTHrP to increase bone formation in the early stage of implantation. The in vitro results revealed that cells on Ti-LBL-PTHrP did not show any evident proliferation, but a high level of alkaline phosphatase activity and osteoblast-related protein expression was found, compared to the uncoated Ti group (p < 0.05). In addition, in vivo micro-CT and histological analysis demonstrated that the Ti-LBL-PTHrP implants could significantly promote the formation and remodeling of new bone in osteoporotic rats at 14 d after implantation. Overall, this study established a profound and straightforward methodology for the manufacture of biofunctional Ti implants for the treatment of osteoporosis.

Metal-Based Nanostructures/PLGA Nanocomposites: Antimicrobial Activity, Cytotoxicity, and Their Biomedical Applications

Among the different synthetic polymers developed for biomedical applications, poly(lactic-co-glycolic acid) (PLGA) has attracted considerable attention because of its excellent biocompatibility and biodegradability. Nanocomposites based on PLGA and metal-based nanostructures (MNSs) have been employed extensively as an efficient strategy to improve the structural and functional properties of PLGA polymer. The MNSs have been used to impart new properties to PLGA, such as antimicrobial properties and labeling. In the present review, the different strategies available for the fabrication of MNS/PLGA nanocomposites and their applications in the biomedical field will be discussed, beginning with a description of the preparation routes, antimicrobial activity, and cytotoxicity concerns of MNS/PLGA nanocomposites. The biomedical applications of these nanocomposites, such as carriers and scaffolds in tissue regeneration and other therapies are subsequently reviewed. In addition, the potential advantages of using MNS/PLGA nanocomposites in treatment illnesses are analyzed based on in vitro and in vivo studies, to support the potential of these nanocomposites in future research in the biomedical field.

Is a Local Administration of Parathyroid Hormone Effective to Tendon-to-Bone Healing in a Rat Rotator Cuff Repair Model?

To evaluate the effect of local parathyroid hormone (PTH) administration on rotator cuff tendon-to-bone healing in a rat model compared with systemic PTH injection and untreated controls. PTH-alginate scaffold was prepared and sustained release of PTH was confirmed. Bilateral supraspinatus tendon repairs were performed in 39 rats (group 1, supraspinatus repair only; group 2, supraspinatus repair with systemic PTH injection; group 3, supraspinatus repair with local PTH administration via an absorbable scaffold; n = 13 each). Biomechanical (cross-sectional area, mode of failure, load to failure, and ultimate stress: right side) and histological analyses (hematoxylin and eosin stain, Masson's Trichrome stain Picrosirius red stain, Immunohistochemistry for BMP2, PTH1R, ColI, and ColIII: Left side) were performed to evaluate tendon-to-bone healing quality at 8 weeks after repair, and blood test (osteocalcin and procollagen type I N-terminal pro-peptide [PINP] levels) was performed in all rats. There was no intergroup difference in the healing failure rate (p = 0.910) or failure mode (p = 0.585). Biomechanically, subjects in groups 2 and 3 exhibited significantly larger cross-sectional areas and higher ultimate failure loads and ultimate stress than those in group 1 (all p < 0.05); however, no differences were noted between groups 2 and 3 (all p > 0.05). Histologically, groups 2 and 3 exhibited more organized tendon-to-bone interface structures with higher density, parallel orientation, and collagen fiber continuity than group 1 (all p < 0.05 except collagen fiber continuity in group 1 vs. 2); however, no differences in histological parameters between groups 2 and 3 (all p > 0.05). The protein levels of bone morphogenic protein 2, PTH 1 receptor, and collagen I and III and the serum level of PINP were increased in groups 2 and 3 versus group 1 (all p < 0.05) without showing differences between groups 2 and 3 (all p > 0.05). Local PTH administration using an absorbable scaffold improved the biomechanical and histological outcomes of rotator cuff tendon-to-bone healing comparable with systemic PTH injection at 8 weeks after repair in a rat model. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:82-91, 2020.

Handling Parathormone Receptor Type 1 in Skeletal Diseases: Realities and Expectations of Abaloparatide

Musculoskeletal disorders represent an elevated socioeconomic burden for developed aging societies. Osteoporosis (OP) has been treated with antiresorptive therapies or with teriparatide that was until recently the only anabolic therapy. However, approval of osteoporosis treatment in postmenopausal women with abaloparatide, which is an analog of parathyroid hormone-related peptide (PTHrP), has created a new alternative for OP management. The success of this new treatment is related to differential mechanisms of activation of PTH receptor type 1 (PTH1R) by abaloparatide and PTH. Here, we address the distinguishing mechanisms of PTH1R activation; the effects of PTH1R stimulation in osteoblast, osteocytes, and chondrocytes; the differences between PTH and abaloparatide actions on PTH1R; potential safety concerns; and future perspectives about abaloparatide use in other musculoskeletal disorders.

Hydrogels For Peptide Hormones Delivery: Therapeutic And Tissue Engineering Applications

Peptides are the most abundant biological compounds in the cells that act as enzymes, hormones, structural element, and antibodies. Mostly, peptides have problems to move across the cells because of their size and poor cellular penetration. Therefore, a carrier that could transfer peptides into cells is ideal and would be effective for disease treatment. Until now, plenty of polymers, e.g., polysaccharides, polypeptides, and lipids were used in drug delivery. Hydrogels made from polysaccharides showed significant development in targeted delivery of peptide hormones because of their natural characteristics such as networks, pore sizes, sustainability, and response to external stimuli. The main aim of the present review was therefore, to gather the important usages of the hydrogels as a carrier in peptide hormone delivery and their application in tissue engineering and regenerative medicine.

Osteostatin potentiates the bioactivity of mesoporous glass scaffolds containing Zn2+ ions in human mesenchymal stem cells

There is an urgent need of biosynthetic bone grafts with enhanced osteogenic capacity. In this study, we describe the design of hierarchical meso-macroporous 3D-scaffolds based on mesoporous bioactive glasses (MBGs), enriched with the peptide osteostatin and Zn2+ ions, and their osteogenic effect on human mesenchymal stem cells (hMSCs) as a preclinical strategy in bone regeneration. The MBG compositions investigated were 80%SiO2-15%CaO-5%P2O5 (in mol-%) Blank (BL), and two analogous glasses containing 4% ZnO (4ZN) and 5% ZnO (5ZN). By using additive fabrication techniques, scaffolds exhibiting hierarchical porosity: mesopores (around 4 nm), macropores (1-600 μm) and big channels (∼1000 μm), were prepared. These MBG scaffolds with or without osteostatin were evaluated in hMCSs cultures. Zinc promoted hMSCs colonization (both the surface and inside) of MBG scaffolds. Moreover, Zn2+ ions and osteostatin together, but not independently, in the scaffolds were found to induce the osteoblast differentiation genes runt related transcription factor-2 (RUNX2) and alkaline phosphatase (ALP) in hMSCs after 7 d of culture in the absence of an osteogenic differentiation-promoting medium. These results add credence to the combined use of zinc and osteostatin as an effective strategy for bone regeneration applications. STATEMENT OF SIGNIFICANCE: Mesoporous bioactive glasses (MBGs) are bioceramics whose unique properties make them excellent materials for bone tissue engineering. Physico-chemical characterization of MBGs as scaffolds made by rapid prototyping, doped with zinc (potential osteogenic, angiogenic and bactericidal ion) and loaded with osteostatin (osteogenic peptide) are described. These Zn-MBGs scaffolds showed 3D hierarchical meso-macroporous structure that enables to host and release osteostatin. When decorated with human mesenchymal stem cells (hMSCs), MBGs scaffoldsenriched with both zinc and osteostatin exhibited a synergistic effect to enhance hMSCs growth, and also hMSCs osteogenic differentiationwithout addition of other osteoblastic differentiation factors to the culture medium. This novel strategy has a great potential for use in bone tissue engineering.

Chitosan/biphasic calcium phosphate scaffolds functionalized with BMP-2-encapsulated nanoparticles and RGD for bone regeneration

Advancements in bone tissue engineering require the improvement of tissue scaffolds, which should not only exhibit suitable mechanical properties and highly porous structures, but also effectively carry signaling molecules that can mediate bone formation and tissue regeneration. In the present study, we established chitosan/biphasic calcium phosphate (CS/BCP) scaffolds functionalized with Arg-Gly-Asp (RGD) and BMP-2-loaded nanoparticles. The resulting scaffolds were highly similar to natural bone extracellular matrix (ECM) in terms of composition and structural properties. First, we synthesized CS/BCP composite bionic scaffolds via the freeze-drying method. Then, RGD peptides were covalently conjugated onto the scaffolds via the EDC/NHS method. The BMP-2-encapsulated BSA nanoparticles were prepared via a desolvation method and then coated with CS and oxidized alginate to achieve sustained release of BMP-2. In vitro cell culture and in vivo implantation tests confirmed that RGD and BMP-2 synergistically enhanced cell attachment and spreading by providing integrin binding surface and facilitating osteogenic differentiation. In summary, the bioceramic/biopolymer scaffolds functionalized with signaling biomolecules successfully provided a favorable microenvironment for bone formation and thus serve as potential candidates for use in bone tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2613-2624, 2018.

PLGA film/Titanium nanotubues as a sustained growth factor releasing system for dental implants

Ti-based implants sometimes fail to integrate with surrounding bone tissue due to insufficiency of new bone formation and surface bonding. To overcome this problem, this research focused on establishing a sustained bone growth factor delivery system by applying anodized TiO2 nanotube arrays and PLGA film on the titanium implant surface. TiO2 nanotube arrays were made by anodic oxidation method, and were then filled with rhBMP2 by vacuum freeze-drying. Next, PLGA was deposition on the surface of this material. The designed system was characterized, pharmacokinetic release rate of rhBMP2 was determined. Adhesion, proliferation, and differentiation activity of osteoblasts cultured on the new surfaces and traditional titanium surfaced were compared. SEM showed that a surface of TiO2 nanotube arrays were successfully generated. PLGA membranes of 50 nm, 250 nm, 800 nm thickness were successfully deposited on the surfaces of TiO2 nanotube layers by using 1%, 3%, 10% PLGA solutions. PLGA film of 250 nm thickness showed ideally controlled release of rhBMP2, lasting for 4 weeks. Furthermore, 250 nm thickness PLGA film improved osteoblast adhesion, proliferation, and levels of alkaline phosphatase. In conclusion, the PLGA film / TiO2 nanotube growth factor delivery system can effectively sustain the release of rhBMP-2, and promote proliferation and differentiation of MC3T3-E1 osteoblasts.

Osteogenic Effect of ZnO-Mesoporous Glasses Loaded with Osteostatin

Mesoporous Bioactive Glasses (MBGs) are a family of bioceramics widely investigated for their putative clinical use as scaffolds for bone regeneration. Their outstanding textural properties allow for high bioactivity when compared with other bioactive materials. Moreover, their great pore volumes allow these glasses to be loaded with a wide range of biomolecules to stimulate new bone formation. In this study, an MBG with a composition, in mol%, of 80% SiO₂⁻15% CaO⁻5% P₂O₅ (Blank, BL) was compared with two analogous glasses containing 4% and 5% of ZnO (4ZN and 5ZN) before and after impregnation with osteostatin, a C-terminal peptide from a parathyroid hormone-related protein (PTHrP107-111). Zn2+ ions were included in the glass for their bone growth stimulator properties, whereas osteostatin was added for its osteogenic properties. Glasses were characterized, and their cytocompatibility investigated, in pre-osteoblastic MC3T3-E1 cell cultures. The simultaneous additions of osteostatin and Zn2+ ions provoked enhanced MC3T3-E1 cell viability and a higher differentiation capacity, compared with either raw BL or MBGs supplemented only with osteostatin or Zn2+. These in vitro results show that osteostatin enhances the osteogenic effect of Zn2+-enriched glasses, suggesting the potential of this combined approach in bone tissue engineering applications.

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.

Porous Chitosan/Nano-Hydroxyapatite Composite Scaffolds Incorporating Simvastatin-Loaded PLGA Microspheres for Bone Repair

The combination of bone tissue scaffolds with osteogenic induction factors is an effective strategy to facilitate bone healing processes. Here, chitosan (CS)/nano-hydroxyapatite (HA) scaffolds containing simvastatin (SIM)-loaded PLGA microspheres were fabricated by combining a freeze-drying technique with a modified water-oil-water emulsion method. The CS/HA weight ratio of 1:2 was selected by analyzing the effect of HA content on the micro-architecture, mechanical strength, and biocompatibility of the scaffold. Drug release kinetics showed that the SIM encapsulated in the scaffold was released in a sustained manner for up to 30 days. In vitro bioactivity study in rat bone marrow-derived mesenchymal stem cells showed that the SIM-loaded scaffolds had a strong ability in accelerating cell proliferation and inducing osteogenic differentiation. Moreover, an in vivo experiment using a rat calvarial defect model also documented that the SIM-loaded scaffolds had a remarkable effect on bone-promoting regeneration. The results of this study suggest that the SIM-loaded CS/HA scaffold is feasible and effective in bone repair and thus may provide a promising route for the treatment of critical-sized bone defects.

Immunomodulatory ECM-like Microspheres for Accelerated Bone Regeneration in Diabetes Mellitus

Bone repair and regeneration process is markedly impaired in diabetes mellitus (DM) that affects hundreds of millions of people worldwide. As a chronic inflammatory disease, DM creates a proinflammatory microenvironment in defective sites. Most of the studies on DM-associated bone regeneration, however, neglect the importance of immunomodulation under the DM condition and adopt the same approaches to normal bone healing, leading to limited bone healing. In this study, we developed a unique bioinspired injectable microsphere as an osteoimmunomodulatory biomaterial that modulates macrophages to create a prohealing microenvironment under the DM condition. The microsphere was self-assembled with heparin-modified gelatin nanofibers, and interleukin 4 (IL4) was incorporated into the nanofibrous heparin-modified gelatin microsphere (NHG-MS). IL4 has binding domains with heparin, and the binding of IL4 to heparin stabilizes this cytokine, protects it from denaturation and degradation, and subsequently prolongs its sustained release to modulate macrophage polarization. The IL4-loaded NHG-MS switched the proinflammatory M1 macrophage into a prohealing M2 phenotype, recovered the M2/M1 ratio to a normal level, efficiently resolved the inflammation, and ultimately enhanced osteoblastic differentiation and bone regeneration. The development of osteoimmunomodulatory biomaterials that harness the power of macrophages for immunomodulation, therefore, is a novel and promising strategy to enhance bone regeneration under DM condition.

Parathyroid hormone-related protein exhibits antioxidant features in osteoblastic cells through its N-terminal and osteostatin domains

Objectives

Oxidative stress plays a major role in the onset and progression of involutional osteoporosis. However, classical antioxidants fail to restore osteoblast function. Interestingly, the bone anabolism of parathyroid hormone (PTH) has been shown to be associated with its ability to counteract oxidative stress in osteoblasts. The PTH counterpart in bone, which is the PTH-related protein (PTHrP), displays osteogenic actions through both its N-terminal PTH-like region and the C-terminal domain.

Methods

We examined and compared the antioxidant capacity of PTHrP (1-37) with the C-terminal PTHrP domain comprising the 107-111 epitope (osteostatin) in both murine osteoblastic MC3T3-E1 cells and primary human osteoblastic cells.

Results

We showed that both N- and C-terminal PTHrP peptides at 100 nM decreased reactive oxygen species production and forkhead box protein O activation following hydrogen peroxide (H₂O₂)-induced oxidation, which was related to decreased lipid oxidative damage and caspase-3 activation in these cells. This was associated with their ability to restore the deleterious effects of H₂O₂ on cell growth and alkaline phosphatase activity, as well as on the expression of various osteoblast differentiation genes. The addition of Rp-cyclic 3′,5′-hydrogen phosphorothioate adenosine triethylammonium salt (a cyclic 3',5'-adenosine monophosphate antagonist) and calphostin C (a protein kinase C inhibitor), or a PTH type 1 receptor antagonist, abrogated the effects of N-terminal PTHrP, whereas protein phosphatase 1 (an Src kinase activity inhibitor), SU1498 (a vascular endothelial growth factor receptor 2 inhibitor), or an anti osteostatin antiserum, inhibited the effects of C-terminal PTHrP.

Conclusion

These findings indicate that the antioxidant properties of PTHrP act through its N- and C-terminal domains and provide novel insights into the osteogenic action of PTHrP.

Cite this article: S. Portal-Núñez, J. A. Ardura, D. Lozano, I. Martínez de Toda, M. De la Fuente, G. Herrero-Beaumont, R. Largo, P. Esbrit. Parathyroid hormone-related protein exhibits antioxidant features in osteoblastic cells through its N-terminal and osteostatin domains. Bone Joint Res 2018;7:58–68. DOI: 10.1302/2046-3758.71.BJR-2016-0242.R2.

Parathyroid Hormone-Related Protein Protects Osteoblastic Cells From Oxidative Stress by Activation of MKP1 Phosphatase

Oxidative damage is an important contributor to the morphological and functional changes in osteoporotic bone. Aging increases the levels of reactive oxygen species (ROS) that cause oxidative stress and induce osteoblast apoptosis. ROS modify several signaling responses, including mitogen-activated protein kinase (MAPK) activation, related to cell survival. Both parathyroid hormone (PTH) and its bone counterpart, PTH-related protein (PTHrP), can regulate MAPK activation by modulating MAPK phosphatase-1 (MKP1). Thus, we hypothesized that PTHrP might protect osteoblasts from ROS-induced apoptosis by targeting MKP1. In osteoblastic MC3T3-E1 and MG-63 cells, H₂ O₂ triggered p38, JNK, ERK and p66^Shc phosphorylation, and cell apoptosis. Meanwhile, PTHrP (1-37) rapidly but transiently increased ERK and Akt phosphorylation without affecting p38, JNK, or p66^Shc activation. H₂ O₂ -induced p38 and ERK phosphorylation and apoptosis were both decreased by pre-treatment with specific kinase inhibitors or PTHrP (1-37) in both osteoblastic cell types. These dephosphorylating and prosurvival actions of PTHrP (1-37) were prevented by a phosphatase inhibitor cocktail, the phosphatase MKP1 inhibitor sanguinarine or a MKP1 siRNA. PTHrP (1-37) promptly enhanced MKP1 protein and gene expression and MKP1-dependent catalase activity in osteoblastic cells. Furthermore, exposure to PTHrP (1-37) adsorbed in an implanted hydroxyapatite-based ceramic into a tibial defect in aging rats increased MKP1 and catalase gene expression in the healing bone area. Our findings demonstrate that PTHrP counteracts the pro-apoptotic actions of ROS by a mechanism dependent on MKP1-induced dephosphorylation of MAPKs in osteoblasts. J. Cell. Physiol. 232: 785-796, 2017. © 2016 Wiley Periodicals, Inc.