High doses of bone morphogenetic protein 2 induce structurally abnormal bone and inflammation in vivo

Strategies to Control or Mimic Growth Factor Activity for Bone, Cartilage, and Osteochondral Tissue Engineering

Growth factors play a critical role in tissue repair and regeneration. However, their clinical success is limited by their low stability, short half-life, and rapid diffusion from the delivery site. Supraphysiological growth factor concentrations are often required to demonstrate efficacy but can lead to adverse reactions, such as inflammatory complications and increased cancer risk. These issues have motivated the development of delivery systems that enable sustained release and controlled presentation of growth factors. This review specifically focuses on bioconjugation strategies to enhance growth factor activity for bone, cartilage, and osteochondral applications. We describe approaches to localize growth factors using noncovalent and covalent methods, bind growth factors via peptides, and mimic growth factor function with mimetic peptide sequences. We also discuss emerging and future directions to control spatiotemporal growth factor delivery to improve functional tissue repair and regeneration.

Multilayered Porous Titanium-Based 3rd Generation Biomaterial Designed for Endosseous Implants

This work proposes a novel complex multi-layered material consisting of porous titanium as a substrate and a complex coating consisting of a chitosan film engulfing microsphere loaded with growth factors such as BMP2 (bone morphogenic protein 2) and IGF1 (insulin-like growth factor-1). The microspheres were obtained through deposition of dual layers of calcium cross linked pectin–chitosan/pectin polyelectrolyte onto a BSA (bovine serum albumin) gel core. The multilayer was conceived to behave like a 3rd generation biomaterial, by slow delivery of viable growth factors around implants, and to assist the healing of implantation wound and the development of new vital bone. The biologic effect of the delivery of growth factors was studied in vitro, on MSC-CD1 mesenchymal stem cells, and in vivo, on CD1 mice. Proliferation and differentiation of cells were accelerated by growth factors, especially IGF1 for proliferation and BMP2 for differentiation. In vivo tests analyzed histologically and by MicroCT show a more structured tissue around BMP2 samples. The present concept will give the best clinical results if both growth factors are delivered together by a coating film that contains a double population of microcarriers.

Osteoinductive 3D printed scaffold healed 5 cm segmental bone defects in the ovine metatarsus

Autologous bone grafts are considered the gold standard grafting material for the treatment of nonunion, but in very large bone defects, traditional autograft alone is insufficient to induce repair. Recombinant human bone morphogenetic protein 2 (rhBMP-2) can stimulate bone regeneration and enhance the healing efficacy of bone grafts. The delivery of rhBMP-2 may even enable engineered synthetic scaffolds to be used in place of autologous bone grafts for the treatment of critical size defects, eliminating risks associated with autologous tissue harvest. We here demonstrate that an osteoinductive scaffold, fabricated by combining a 3D printed rigid polymer/ceramic composite scaffold with an rhBMP-2-eluting collagen sponge can treat extremely large-scale segmental defects in a pilot feasibility study using a new sheep metatarsus fracture model stabilized with an intramedullary nail. Bone regeneration after 24 weeks was evaluated by micro-computed tomography, mechanical testing, and histological characterization. Load-bearing cortical bridging was achieved in all animals, with increased bone volume observed in sheep that received osteoinductive scaffolds compared to sheep that received an rhBMP-2-eluting collagen sponge alone.

Enhanced bone formation of calvarial bone defects by low-intensity pulsed ultrasound and recombinant human bone morphogenetic protein-9: a preliminary experimental study in rats

OBJECTIVES

The aim of this study was to evaluate the combined effects of recombinant human bone morphogenetic protein - 9 (rhBMP-9) loaded onto absorbable collagen sponges (ACS) and low-intensity pulsed ultrasound (LIPUS) on bone formation in rat calvarial defects.

MATERIALS AND METHODS

Circular calvarial defects were surgically created in 18 Wistar rats, which were divided into LIPUS-applied (+) and LIPUS-non-applied (-) groups. The 36 defects in each group received ACS implantation (ACS group), ACS with rhBMP-9 (rhBMP-9/ACS group), or surgical control (control group), yielding the following six groups: ACS (+/-), rhBMP-9/ACS (+/-), and control (+/-). The LIPUS-applied groups received daily LIPUS exposure starting immediately after surgery. At 4 weeks, animals were sacrificed and their defects were investigated histologically and by microcomputed tomography.

RESULTS

Postoperative clinical healing was uneventful at all sites. More new bone was observed in the LIPUS-applied groups compared with the LIPUS-non-applied groups. Newly formed bone area (NBA)/total defect area (TA) in the ACS (+) group (46.49 ± 7.56%) was significantly greater than that observed in the ACS (-) (34.31 ± 5.68%) and control (-) (31.13 ± 6.74%) groups (p < 0.05). The rhBMP-9/ACS (+) group exhibited significantly greater bone volume, NBA, and NBA/TA than the rhBMP-9/ACS (-) group (2.46 ± 0.65 mm³ vs. 1.76 ± 0.44 mm³, 1.25 ± 0.31 mm² vs. 0.88 ± 0.22 mm², and 62.80 ± 11.87% vs. 42.66 ± 7.03%, respectively) (p < 0.05). Furthermore, the rhBMP-9/ ACS (+) group showed the highest level of bone formation among all groups.

CONCLUSION

Within their limits, it can be concluded that LIPUS had osteopromotive potential and enhanced rhBMP-9-induced bone formation in calvarial defects of rats.

CLINICAL RELEVANCE

The use of rhBMP-9 with LIPUS stimulation can be a potential bone regenerative therapy for craniofacial/peri-implant bone defects.

Hesperidin Promotes Osteogenesis and Modulates Collagen Matrix Organization and Mineralization In Vitro and In Vivo

This study evaluated the direct effect of a phytochemical, hesperidin, on pre-osteoblast cell function as well as osteogenesis and collagen matrix quality, as there is little known about hesperidin's influence in mineralized tissue formation and regeneration. Hesperidin was added to a culture of MC3T3-E1 cells at various concentrations. Cell proliferation, viability, osteogenic gene expression and deposited collagen matrix analyses were performed. Treatment with hesperidin showed significant upregulation of osteogenic markers, particularly with lower doses. Mature and compact collagen fibrils in hesperidin-treated cultures were observed by picrosirius red staining (PSR), although a thinner matrix layer was present for the higher dose of hesperidin compared to osteogenic media alone. Fourier-transform infrared spectroscopy indicated a better mineral-to-matrix ratio and matrix distribution in cultures exposed to hesperidin and confirmed less collagen deposited with the 100-µM dose of hesperidin. In vivo, hesperidin combined with a suboptimal dose of bone morphogenetic protein 2 (BMP2) (dose unable to promote healing of a rat mandible critical-sized bone defect) in a collagenous scaffold promoted a well-controlled (not ectopic) pattern of bone formation as compared to a large dose of BMP2 (previously defined as optimal in healing the critical-sized defect, although of ectopic nature). PSR staining of newly formed bone demonstrated that hesperidin can promote maturation of bone organic matrix. Our findings show, for the first time, that hesperidin has a modulatory role in mineralized tissue formation via not only osteoblast cell differentiation but also matrix organization and matrix-to-mineral ratio and could be a potential adjunct in regenerative bone therapies.

BMP-2 delivery strategy modulates local bone regeneration and systemic immune responses to complex extremity trauma

Bone nonunions arising from large bone defects and composite injuries remain compelling challenges for orthopedic surgeons. Biological changes associated with nonunions, such as systemic immune dysregulation, can contribute to an adverse healing environment. Bone morphogenetic protein 2 (BMP-2), an osteoinductive and potentially immunomodulatory growth factor, is a promising strategy; however, burst release from the clinical standard collagen sponge delivery vehicle can result in adverse side effects such as heterotopic ossification (HO) and irregular bone structure, especially when using supraphysiological BMP-2 doses for complex injuries at high risk for nonunion. To address this challenge, biomaterials that strongly bind BMP-2, such as heparin methacrylamide microparticles (HMPs), may be used to limit exposure and spatially constrain proteins within the injury site. Here, we investigate moderately high dose BMP-2 delivered in HMPs within an injectable hydrogel system in two challenging nonunion models exhibiting characteristics of systemic immune dysregulation. The HMP delivery system increased total bone volume and decreased peak HO compared to collagen sponge delivery of the same BMP-2 dose. Multivariate analyses of systemic immune markers showed the collagen sponge group correlated with markers that are hallmarks of systemic immune dysregulation, including immunosuppressive myeloid-derived suppressor cells, whereas the HMP groups were associated with immune effector cells, including T cells, and cytokines linked to robust bone regeneration. Overall, our results demonstrate that HMP delivery of moderately high doses of BMP-2 promotes repair of complex bone nonunion injuries and that local delivery strategies for potent growth factors like BMP-2 may positively affect the systemic immune response to traumatic injury.

Effects of low-dose rhBMP-2 on peri-implant ridge augmentation in a canine model

AIMS

The aim of this study was to investigate the potential of low-dose rhBMP-2 combined with Hydroxyapatite (HAp)/β-tricalcium phosphate (TCP)/ Collagen (Col) composite in repairing the peri-implant critical size defect and to determine the optimal rhBMP-2 concentration.

MATERIALS AND METHODS

Fifty saddle-type alveolar defects (10 mm mesiodistally and 4 mm apicocoronally) were surgically prepared on edentulous ridges in ten beagle dogs. Following implant placement, the defects with vertically exposed implant fixtures either received (a) no graft, (b) HAp/TCP/Col composite, (c) HAp/TCP/Col +0.02 mg/ml rhBMP-2, (d) HAp/TCP/Col +0.08 mg/ml rhBMP-2 or (e) HAp/TCP/Col +0.2 mg/ml rhBMP-2. After healing for 4 or 8 weeks, bone regeneration and mineralization were assessed through radiography, micro-CT, fluorescence labelling and histologic analyses. Implant stability was measured through resonance frequency analysis.

RESULTS

It was evident HAp/TCP/Col with 0.2 mg/ml rhBMP-2 manifested strong osteogenic potential in this large animal model, as significantly more and faster new bone formation with better implant stability was identified compared to the HAp/TCP/Col-alone control group (adjusted p < .05).

CONCLUSIONS

Our results highlight the constructs of HAp/TCP/Col +0.2 mg/ml rhBMP-2 without barrier membranes as a promising tool for peri-implant ridge augmentation.

Correlation between intestinal BMP2, IFNγ, and neural death in experimental infection with Trypanosoma cruzi

Megacolon is one of the main late complications of Chagas disease, affecting approximately 10% of symptomatic patients. However, studies are needed to understand the mechanisms involved in the progression of this condition. During infection by Trypanosoma cruzi (T. cruzi), an inflammatory profile sets in that is involved in neural death, and this destruction is known to be essential for megacolon progression. One of the proteins related to the maintenance of intestinal neurons is the type 2 bone morphogenetic protein (BMP2). Intestinal BMP2 homeostasis is directly involved in the maintenance of organ function. Thus, the aim of this study was to correlate the production of intestinal BMP2 with immunopathological changes in C57Bl/6 mice infected with the T. cruzi Y strain in the acute and chronic phases. The mice were infected with 1000 blood trypomastigote forms. After euthanasia, the colon was collected, divided into two fragments, and a half was used for histological analysis and the other half for BMP2, IFNγ, TNF-α, and IL-10 quantification. The infection induced increased intestinal IFNγ and BMP2 production during the acute phase as well as an increase in the inflammatory infiltrate. In contrast, a decreased number of neurons in the myenteric plexus were observed during this phase. Collagen deposition increased gradually throughout the infection, as demonstrated in the chronic phase. Additionally, a BMP2 increase during the acute phase was positively correlated with intestinal IFNγ. In the same analyzed period, BMP2 and IFNγ showed negative correlations with the number of neurons in the myenteric plexus. As the first report of BMP2 alteration after infection by T. cruzi, we suggest that this imbalance is not only related to neuronal damage but may also represent a new route for maintaining the intestinal proinflammatory profile during the acute phase.

Cyclodextrin-Based Supramolecular Complexes of Osteoinductive Agents for Dental Tissue Regeneration

Oral tissue regeneration has received growing attention for improving the quality of life of patients. Regeneration of oral tissues such as alveolar bone and widely defected bone has been extensively investigated, including regenerative treatment of oral tissues using therapeutic cells and growth factors. Additionally, small-molecule drugs that promote bone formation have been identified and tested as new regenerative treatment. However, treatments need to progress to realize successful regeneration of oral functions. In this review, we describe recent progress in development of regenerative treatment of oral tissues. In particular, we focus on cyclodextrin (CD)-based pharmaceutics and polyelectrolyte complexation of growth factors to enhance their solubility, stability, and bioactivity. CDs can encapsulate hydrophobic small-molecule drugs into their cavities, resulting in inclusion complexes. The inclusion complexation of osteoinductive small-molecule drugs improves solubility of the drugs in aqueous solutions and increases in vitro osteogenic differentiation efficiency. Additionally, various anionic polymers such as heparin and its mimetic polymers have been developed to improve stability and bioactivity of growth factors. These polymers protect growth factors from deactivation and degradation by complex formation through electrostatic interaction, leading to potentiation of bone formation ability. These approaches using an inclusion complex and polyelectrolyte complexes have great potential in the regeneration of oral tissues.

BMP4 micro-immunotherapy increases collagen deposition and reduces PGE2 release in human gingival fibroblasts and increases tissue viability of engineered 3D gingiva under inflammatory conditions

Background

We aimed to evaluate the effect of low doses (LD) bone morphogenetic protein‐2 (BMP2) and BMP4 micro‐immunotherapy (MI) in two in vitro models of periodontal wound healing/regeneration.

Methods

We first evaluated the effect of LD of BMP2 and BMP4 MI on a 2D cell culture using human gingival fibroblasts (hGF) under inflammatory conditions induced by IL1β. Biocompatibility, inflammatory response (Prostaglandin E2 (PGE2) release), collagen deposition and release of extracellular matrix (ECM) organization‐related enzymes (matrix metalloproteinase‐1 (MMP1) and metalloproteinase inhibitor 1 (TIMP1)) were evaluated after short (3 days) and long‐term (24 days) treatment with BMP2 or BMP4 MI. Then, given the results obtained in the 2D cell culture, LD BMP4 MI treatment was evaluated in a 3D cell culture model of human tissue equivalent of gingiva (GTE) under the same inflammatory stimulus, evaluating the biocompatibility, inflammatory response and effect on MMP1 and TIMP1 release.

Results

LD BMP4 was able to decrease the release of the inflammatory mediator PGE2 and completely re‐establish the impaired collagen metabolism induced by IL1β treatment. In the 3D model, LD BMP4 treatment improved tissue viability compared with the vehicle, with similar levels to 3D tissues without inflammation. No significant effects were observed on PGE2 levels nor MMP1/TIMP1 ratio after LD BMP4 treatment, although a tendency to decrease PGE2 levels was observed after 3 days.

Conclusions

LD BMP4 MI treatment shows anti‐inflammatory and regenerative properties on hGF, and improved viability of 3D gingiva under inflammatory conditions. LD BMP4 MI treatment could be used on primary prevention or maintenance care of periodontitis.

Large three-dimensional cell constructs for tissue engineering

Much research has been conducted on fabricating biomimetic biomaterials in vitro. Tissue engineering approaches are often conducted by combining cells, scaffolds, and growth factors. However, the degradation rate of scaffolds is difficult to control and the degradation byproducts occasionally limit tissue regeneration. To overcome these issues, we have developed a novel system using a thermo-responsive hydrogel that forms scaffold-free, three-dimensional (3D) cell constructs with arbitrary size and morphology. 3D cell constructs prepared using bone marrow-derived stromal stem cells (BMSCs) exhibited self-organizing ability and formed bone-like tissue with endochondral ossification. Endothelial cells were then introduced into the BMSC construct and a vessel-like structure was formed within the constructs. Additionally, the bone formation ability was promoted by endothelial cells and cell constructs could be freeze-dried to improve their clinical application. A pre-treatment with specific protein protectant allowed for the fabrication of novel bone substitutes composed only of cells. This 3D cell construct technology using thermo-responsive hydrogels was then applied to other cell species. Cell constructs composed of dental pulp stem cells were fabricated, and the resulting construct regenerated pulp-like tissue within a human pulpless tooth. In this review, we demonstrate the approaches for the in vitro fabrication of bone and dental pulp-like tissue using thermo-responsive hydrogels and their potential applications.

Trb3 controls mesenchymal stem cell lineage fate and enhances bone regeneration by scaffold-mediated local gene delivery

Aberrant lineage commitment of mesenchymal stem cells (MSCs) in marrow contributes to abnormal bone formation due to reduced osteogenic and increased adipogenic potency. While several major transcriptional factors associated with lineage differentiation have been found during the last few decades, the molecular switch for MSC fate determination and its role in skeletal regeneration remains largely unknown, limiting creation of effective therapeutic approaches. Tribbles homolog 3 (Trb3), a member of tribbles family pseudokinases, is known to exert diverse roles in cellular differentiation. Here, we investigated the reciprocal role of Trb3 in the regulation of osteogenic and adipogenic differentiation of MSCs in the context of bone formation, and examined the mechanisms by which Trb3 controls the adipo-osteogenic balance. Trb3 promoted osteoblastic commitment of MSCs at the expense of adipocyte differentiation. Mechanistically, Trb3 regulated cell-fate choice of MSCs through BMP/Smad and Wnt/β-catenin signals. Importantly, in vivo local delivery of Trb3 using a novel gelatin-conjugated caffeic acid-coated apatite/PLGA (GelCA-PLGA) scaffold stimulated robust bone regeneration and inhibited fat-filled cyst formation in rodent non-healing mandibular defect models. These findings demonstrate Trb3-based therapeutic strategies that favor osteoblastogenesis over adipogenesis for improved skeletal regeneration and future treatment of bone-loss disease. The distinctive approach implementing a scaffold-mediated local gene transfer may further broaden the translational use of targeting specific therapeutic gene related to lineage commitment for clinical bone treatment.

Current and future trends in periodontal tissue engineering and bone regeneration

Periodontal tissue engineering involves a multi-disciplinary approach towards the regeneration of periodontal ligament, cementum and alveolar bone surrounding teeth, whereas bone regeneration specifically applies to ridge reconstruction in preparation for future implant placement, sinus floor augmentation and regeneration of peri-implant osseous defects. Successful periodontal regeneration is based on verifiable cementogenesis on the root surface, oblique insertion of periodontal ligament fibers and formation of new and vital supporting bone. Ultimately, regenerated periodontal and peri-implant support must be able to interface with surrounding host tissues in an integrated manner, withstand biomechanical forces resulting from mastication, and restore normal function and structure. Current regenerative approaches utilized in everyday clinical practice are mainly guided tissue/bone regeneration-based. Although these approaches have shown positive outcomes for small and medium-sized defects, predictability of clinical outcomes is heavily dependent on the defect morphology and clinical case selection. In many cases, it is still challenging to achieve predictable regenerative outcomes utilizing current approaches. Periodontal tissue engineering and bone regeneration (PTEBR) aims to improve the state of patient care by promoting reconstitution of damaged and lost tissues through the use of growth factors and signaling molecules, scaffolds, cells and gene therapy. The present narrative review discusses key advancements in PTEBR including current and future trends in preclinical and clinical research, as well as the potential for clinical translatability.

Learning from BMPs and their biophysical extracellular matrix microenvironment for biomaterial design

It is nowadays well-accepted that the extracellular matrix (ECM) is not a simple reservoir for growth factors but is an organization center of their biological activity. In this review, we focus on the ability of the ECM to regulate the biological activity of BMPs. In particular, we survey the role of the ECM components, notably the glycosaminoglycans and fibrillary ECM proteins, which can be promoters or repressors of the biological activities mediated by the BMPs. We examine how a process called mechano-transduction induced by the ECM can affect BMP signaling, including BMP internalization by the cells. We also focus on the spatio-temporal regulation of the BMPs, including their release from the ECM, which enables to modulate their spatial localization as well as their local concentration. We highlight how biomaterials can recapitulate some aspects of the BMPs/ECM interactions and help to answer fundamental questions to reveal previously unknown molecular mechanisms. Finally, the design of new biomaterials inspired by the ECM to better present BMPs is discussed, and their use for a more efficient bone regeneration in vivo is also highlighted.

Progress and Prospects of Polymer-Based Drug Delivery Systems for Bone Tissue Regeneration

Despite the high regenerative capacity of bone tissue, there are some cases where bone repair is insufficient for a complete functional and structural recovery after damage. Current surgical techniques utilize natural and synthetic bone grafts for bone healing, as well as collagen sponges loaded with drugs. However, there are certain disadvantages associated with these techniques in clinical usage. To improve the therapeutic efficacy of bone tissue regeneration, a number of drug delivery systems based on biodegradable natural and synthetic polymers were developed and examined in in vitro and in vivo studies. Recent studies have demonstrated that biodegradable polymers play a key role in the development of innovative drug delivery systems and tissue engineered constructs, which improve the treatment and regeneration of damaged bone tissue. In this review, we discuss the most recent advances in the field of polymer-based drug delivery systems for the promotion of bone tissue regeneration and the physical-chemical modifications of polymers for controlled and sustained release of one or more drugs. In addition, special attention is given to recent developments on polymer nano- and microparticle-based drug delivery systems for bone regeneration.

Degradable Poly(Methyl Methacrylate)-co-Methacrylic Acid Nanoparticles for Controlled Delivery of Growth Factors for Bone Regeneration

Bone tissue engineering strategies have been developed to address the limitations of the current gold standard treatment options for bone-related disorders. These systems consist of an engineered scaffold that mimics the extracellular matrix and provides an architecture to guide the natural bone regeneration process, and incorporated growth factors that enhance cell recruitment and ingress into the scaffold and promote the osteogenic differentiation of stem cells and angiogenesis. In particular, the osteogenic growth factor bone morphogenetic protein 2 (BMP-2) has been widely studied as a potent agent to improve bone regeneration. A key challenge in growth factor delivery is that the growth factors must reach their target sites without losing bioactivity and remain in the location for an extended period to effectively aid in the formation of new bone. Protein incorporation into nanoparticles can both protect protein bioactivity and enable its sustained release. In this study, a poly(methyl methacrylate-co-methacrylic acid) nanoparticle-based system was synthesized incorporating a custom poly(ethylene glycol) dimethacrylate crosslinker. It was demonstrated that the nanoparticle degradation rate can be controlled by tuning the number of hydrolytically degradable ester units along the crosslinker. We also showed that the nanoparticles had high affinity for a model protein for BMP-2, and optimal conditions for maximum protein loading efficiency were elucidated. Ultimately, the proposed system and its high degree of tunability can be applied to a wide range of growth factors and tissue engineering applications. Impact Statement In this study, we developed a novel method of synthesizing nanoparticles with tunable degradation rates through the incorporation of a custom synthesized, hydrolytically degradable crosslinker. In addition, we demonstrated the affinity of the synthesized nanoparticles for a model protein for bone morphogenetic protein 2 (BMP-2). The tunability of these nanoparticles can be used to develop complex tissue engineering systems, for example, for the delivery of multiple growth factors involved at different stages of the bone regeneration process.

A facile one-stage treatment of critical bone defects using a calcium sulfate/hydroxyapatite biomaterial providing spatiotemporal delivery of bone morphogenic protein-2 and zoledronic acid

Bone morphogenic proteins (BMPs) are the only true osteoinductive molecules. Despite being tremendously potent, their clinical use has been limited for reasons including supraphysiological doses, suboptimal delivery systems, and the pro-osteoclast effect of BMPs. Efforts to achieve spatially controlled bone formation using BMPs are being made. We demonstrate that a carrier consisting of a powder of calcium sulfate/hydroxyapatite (CaS/HA) mixed with bone active molecules provides an efficient drug delivery platform for critical femoral defect healing in rats. The bone-active molecules were composed of osteoinductive rhBMP-2 and the bisphosphonate, and zoledronic acid (ZA) was chosen to overcome BMP-2-induced bone resorption. It was demonstrated that delivery of rhBMP-2 was necessary for critical defect healing and restoration of mechanical properties, but codelivery of BMP-2 and ZA led to denser and stronger fracture calluses. Together, the CaS/HA biomaterial with rhBMP-2 and/or ZA can potentially be used as an off-the-shelf alternative to autograft bone.

Core Ossification of Bone Morphogenetic Protein-2-Loaded Collagenated Bone Mineral in the Sinus

The objective of this study was to investigate in vitro release kinetics and ossification patterns of bone morphogenetic protein-2-soaked collagenated porcine bone mineral (BMP-2/CPBM) in rabbit sinuses. Release kinetics of BMP-2/CPBM was determined in vitro up to 56 days. In 16 rabbits, BMP-2/CPBM (BMP group) and CPBM alone (control group) were bilaterally grafted in both sinuses. After 4 (N = 8) and 12 (N = 8) weeks, radiographic and histologic analyses were performed. Approximately 40% of BMP-2 was released from CPBM during 3 days in vitro; release maintained at a reduced level until day 56. In vivo, new bone formation in BMP group was dominant at the center and decreased toward the borders of the sinus, while it mainly possessed close to the sinus membrane and basal bone in control group. At the center, significantly more new bone was found in BMP group compared to control group at 4 weeks (29.14% vs. 16.50%; p < 0.05). The total augmented volume of BMP group was significantly greater than control group at 4 (370.13 mm³ vs. 299.32 mm³) and 12 (400.40 mm³ vs. 290.10 mm³) weeks (p < 0.05). In conclusion, BMP-2/CPBM demonstrated a core ossification with a greater augmented volume and new bone formation in the center of the sinus compared to CPBM alone. Impact statement The center of the augmented maxillary sinus tends to show a slower and inferior new bone formation compared to the sites near the sinus membrane and basal bone. In this study, bone morphogenetic protein-2 (BMP-2) loaded onto collagenated porcine bone mineral (CPBM) resulted in a greater augmented volume and new bone formation at the center of the grafted sinus compared to CPBM alone. Therefore, BMP-2-added CPBM in maxillary sinus augmentation may potentially be beneficial to the clinicians, in terms of accelerating the new bone formation at the center area where the apical half of the implant fixture usually places.

Osteogenic-differentiated mesenchymal stem cell-secreted extracellular matrix as a bone morphogenetic protein-2 delivery system for ectopic bone formation

While human bone morphogenetic protein-2 (BMP-2) is a promising growth factor for bone regeneration, a major challenge in biomedical applications is finding an optimal carrier for its delivery at the site of injury. Because of their natural affinities for growth factors (including BMP-2) as well as their role in instructing cell function, cultured cell-derived extracellular matrices (ECM) are of special interest. We hereby hypothesized that a "bony matrix" containing mineralized, osteogenic ECM is a potential efficacious carrier of BMP-2 for promoting bone formation and, therefore, compared the efficacy of the decellularized ECM derived from osteogenic-differentiated human mesenchymal stem cells (hMSCs) to the one obtained from ECM from undifferentiated hMSCs. Our results provided evidence that both ECMs can bind BMP-2 and promote bone formation when implanted ectopically in mice. The osteoinductive potential of BMP-2, however, was greater when loaded within an osteogenic MSC-derived ECM; this outcome was correlated with higher sequestration capacity of BMP-2 over time in vivo. Interestingly, although the BMP-2 mainly bound onto the mineral crystals contained within the osteogenic MSC derived-ECM, these mineral components were not involved in the observed higher osteoinductivity, suggesting that the organic components were the critical components for the matrix efficacy as BMP-2 carrier.

Effects of FK506 on the healing of diaphyseal, critical size defects in the rat femur

There is much interest in understanding the influence of the immune system on bone healing, including a number of reports suggesting a beneficial effect of FK506 (tacrolimus) in this regard. The influence of FK506 in a rat, femoral, critical size defect was examined using locally implanted, recombinant, human (rh) BMP-2 and adenovirally-transduced, autologous, adipose-derived mesenchymal stromal cells (AD-MSCs) expressing BMP-2. FK506 was delivered systemically using an implanted osmotic pump. Empty defects and those implanted with unmodified AD-MSCs did not heal in the presence or absence of FK506. Defects treated with rhBMP-2 healed with a large callus containing thin cortices and wispy trabeculae; this, too, was unaffected by FK506. A third of defects implanted with adenovirally-transduced AD-MSCs healed, but this improved to 100 % in the presence of FK506. New bone formed in response to BMP-2 synthesised endogenously by the genetically modified cells had a slimmer callus than those healed by rhBMP-2, with improved cortication and advanced reconstitution of marrow. These results suggest that FK506 may have had little effect on the intrinsic biology of bone healing, but improved healing in response to adenovirally-transduced cells by inhibiting immune responses to the first-generation adenovirus used here. Because the genetically modified cells produced bone of higher quality at far lower doses of BMP-2, this approach should be explored in subsequent research.

Osteogenic differentiation and inflammatory response of recombinant human bone morphogenetic protein-2 in human maxillary sinus membrane-derived cells

The aim of the present study was to investigate the osteogenic potential of human maxillary sinus membrane (hMSM)-derived cells, and the role of recombinant human bone morphogenetic protein-2 (rhBMP-2) in the inflammatory response of hMSM-derived cells and gingival fibroblasts following sinus floor elevation procedure (SFE). hMSM-derived cells from the samples were isolated, subcultured, and analyzed using immunohistochemical staining and flow cytometry. The hMSM-derived cells obtained from passage 6 were used for Alizarin Red staining and quantitative reverse transcription-quantitative PCR to observe its osteogenic activity and inflammatory reaction upon supplementation with rhBMP-2. The hMSM-derived cells were shown to be heterogeneous, as indicated by their positive expression of human mesenchymal stem cell markers (STRO-1, high mobility group AT-hook 2, CD44, CD105 and OCT-3/4), fibroblast cell marker (fibroblast-specific protein 1) and epithelial cell marker (epithelial cell adhesion molecule). Calcium nodules were found to be more notably evident in the rhBMP-2 group, following osteogenic differentiation. The gene expression of osteogenic markers was significantly upregulated in the cells supplemented with rhBMP-2. Supplementation with rhBMP-2 also enhanced the expression of inflammatory markers in hMSM-derived cells and gingival fibroblasts; however, NF-κB and TNF-α expression was not significantly increased compared with the control in the hMSM-derived cells. hMSM contains mesenchymal stem cells (MSCs) capable of differentiating into osteogenic cells. The supplementation of rhBMP-2 enhanced osteogenic differentiation and induced an inflammatory response which was greater in gingival fibroblasts compared with hMSM-derived cells. In summary, the hMSM is a potential contributor to the osteogenic process following SFE, and the use of rhBMP-2 may increase the inflammatory response accordingly. The gingival tissue may be responsible for the increased inflammatory response by rhBMP-2 and postoperative complications.

Advances on Bone Substitutes through 3D Bioprinting

Reconstruction of bony defects is challenging when conventional grafting methods are used because of their intrinsic limitations (biological cost and/or biological properties). Bone regeneration techniques are rapidly evolving since the introduction of three-dimensional (3D) bioprinting. Bone tissue engineering is a branch of regenerative medicine that aims to find new solutions to treat bone defects, which can be repaired by 3D printed living tissues. Its aim is to overcome the limitations of conventional treatment options by improving osteoinduction and osteoconduction. Several techniques of bone bioprinting have been developed: inkjet, extrusion, and light-based 3D printers are nowadays available. Bioinks, i.e., the printing materials, also presented an evolution over the years. It seems that these new technologies might be extremely promising for bone regeneration. The purpose of the present review is to give a comprehensive summary of the past, the present, and future developments of bone bioprinting and bioinks, focusing the attention on crucial aspects of bone bioprinting such as selecting cell sources and attaining a viable vascularization within the newly printed bone. The main bioprinters currently available on the market and their characteristics have been taken into consideration, as well.

Effect of bone morphogenetic protein-2/hydroxyapatite on ankle fusion with bone defect in a rabbit model: a pilot study

Background

Revision ankle-fusion surgery after a failure of total ankle arthroplasty has a problem with bone-defect management by implant removal. For the reconstruction of bone defects, autogenous bone often causes minor and major complications. Recombinant human-bone morphogenetic protein-2 (rhBMP-2) plays essential roles in bone regeneration strategies, and hydroxyapatite (HA) is beneficial as the rhBMP-2 carrier. In this study, we evaluate whether rhBMP-2/HA can replace autogenous bone in a rabbit ankle-fusion model with distal tibia bone defect.

Methods

The bone defect was created in the distal tibia. The ankle fusion was performed by a cannulated screw from lateral malleolus and various treatments on bone defect. Thirty male white New Zealand rabbits were divided into three groups of 10 animals on each group dependent on treatment methods as control group (no treatment into defect), auto-bone group (autogenous bone treatment), and rhBMP-2/HA group (40 μL of 1 μg/mL rhBMP-2/100 μL HA). Bone formation on defect and the union of the ankle joint were evaluated by X-ray, micro-CT, and histological analysis at 8 weeks and 12 weeks, postoperatively.

Results

Radiographic assessment found the control and auto-bone groups still had the bone defect present, but rhBMP-2/HA group showed complete replacement of the defect with newly formed bone at 12 weeks. Micro-CT showed significantly higher new bone formation within the defect in the rhBMP-2/HA group than in the auto-bone and control groups at 8 weeks (p > 0.05 and p < 0.01, respectively) and 12 weeks (p < 0.05, p < 0.001, respectively). Fusion rate (%) analysis of micro-CT showed a higher percentage of union in the rhBMP-2/HA group than in the auto bone and control groups at 8 weeks (p > 0.05, p < 0.001, respectively) and 12 weeks (p < 0.001 and p < 0.001, respectively). The histological showed the highest osteointegration between distal tibia and talus in the rhBMP-2/HA group at 12 weeks.

Conclusions

This study indicated that rhBMP-2/HA showed much better bone fusion than did the autogenous bone graft and was effective in promoting fusion rate and improving the quality of the ankle joint fusion.

In Vivo Validation of Spray-Dried Mesoporous Bioactive Glass Microspheres Acting as Prolonged Local Release Systems for BMP-2 to Support Bone Regeneration

Bone morphogenetic protein-2 (BMP-2) is a known key mediator of physiological bone regeneration and is clinically approved for selected musculoskeletal interventions. Yet, broad usage of this growth factor is impeded due to side effects that are majorly evoked by high dosages and burst release kinetics. In this study, mesoporous bioactive glass microspheres (MBGs), produced by an aerosol-assisted spray-drying scalable process, were loaded with BMP-2 resulting in prolonged, low-dose BMP-2 release without affecting the material characteristics. In vitro, MBGs were found to be cytocompatible and to induce a pro-osteogenic response in primary human mesenchymal stromal cells (MSCs). In a pre-clinical rodent model, BMP-2 loaded MBGs significantly enhanced bone formation and influenced the microarchitecture of newly formed bone. The MBG carriers alone performed equal to the untreated (empty) control in most parameters tested, while additionally exerting mild pro-angiogenic effects. Using MBGs as a biocompatible, pro-regenerative carrier for local and sustained low dose BMP-2 release could limit side effects, thus enabling a safer usage of BMP-2 as a potent pro-osteogenic growth factor.

Which substances loaded onto collagen scaffolds influence oral tissue regeneration?-an overview of the last 15 years

BACKGROUND

Collagen scaffolds are widely used for guided bone or tissue regeneration. Aiming to enhance their regenerative properties, studies have loaded various substances onto these scaffolds. This review aims to provide an overview of existing literature which conducted in vitro, in vivo, and clinical testing of drug-loaded collagen scaffolds and analyze their outcome of promoting oral regeneration.

MATERIALS AND METHODS

PubMed, Scopus, and Ovid Medline® were systematically searched for publications from 2005 to 2019. Journal articles assessing the effect of substances on oral hard or soft tissue regeneration, while using collagen carriers, were screened and qualitatively analyzed. Studies were grouped according to their used substance type-biological medical products, pharmaceuticals, and tissue-, cell-, and matrix-derived products.

RESULTS

A total of 77 publications, applying 36 different substances, were included. Collagen scaffolds were demonstrating favorable adsorption behavior and release kinetics which could even be modified. BMP-2 was investigated most frequently, showing positive effects on oral tissue regeneration. BMP-9 showed comparable results at lower concentrations. Also, FGF2 enhanced bone and periodontal healing. Antibiotics improved the scaffold's anti-microbial activity and reduced the penetrability for bacteria.

CONCLUSION

Growth factors showed promising results for oral tissue regeneration, while other substances were investigated less frequently. Found effects of investigated substances as well as adsorption and release properties of collagen scaffolds should be considered for further investigation.

CLINICAL RELEVANCE

Collagen scaffolds are reliable carriers for any of the applied substances. BMP-2, BMP-9, and FGF2 showed enhanced bone and periodontal healing. Antibiotics improved anti-microbial properties of the scaffolds.

BMP gene delivery for skeletal tissue regeneration

Musculoskeletal disorders are common and can be associated with significant morbidity and reduced quality of life. Current treatments for major bone loss or cartilage defects are insufficient. Bone morphogenetic proteins (BMPs) are key players in the recruitment and regeneration of damaged musculoskeletal tissues, and attempts have been made to introduce the protein to fracture sites with limited success. In the last 20 years we have seen a substantial progress in the development of various BMP gene delivery platforms for several conditions. In this review we cover the progress made using several techniques for BMP gene delivery for bone as well as cartilage regeneration, with focus on recent advances in the field of skeletal tissue engineering. Some methods have shown success in large animal models, and with the global trend of introducing gene therapies into the clinical setting, it seems that the day in which BMP gene therapy will be viable for clinical use is near.

Teriparatide (recombinant parathyroid hormone 1-34) enhances bone allograft integration in a clinically relevant pig model of segmental mandibulectomy

Massive craniofacial bone loss poses a clinical challenge to maxillofacial surgeons. Structural bone allografts are readily available at tissue banks but are rarely used due to a high failure rate. Previous studies showed that intermittent administration of recombinant parathyroid hormone (rPTH) enhanced integration of allografts in a murine model of calvarial bone defect. To evaluate its translational potential, the hypothesis that rPTH would enhance healing of a mandibular allograft in a clinically relevant large animal model of mandibulectomy was tested. Porcine bone allografts were implanted into a 5-cm-long continuous mandible bone defect in six adult Yucatan minipigs, which were randomized to daily intramuscular injections of rPTH (1.75 μg/kg) and placebo (n = 3). Blood tests were performed on Day 56 preoperation, Day 0 and on Day 56 postoperation. Eight weeks after the surgery, bone healing was analyzed using high-resolution X-ray imaging (Faxitron and micro computed tomography [CT]) and three-point bending biomechanical testing. The results showed a significant 2.6-fold rPTH-induced increase in bone formation (p = 0.02). Biomechanically, the yield failure properties of the healed mandibles were significantly higher in the rPTH group (yield load: p < 0.05; energy to yield: p < 0.01), and the post-yield displacement and energy were higher in the placebo group (p < 0.05), suggesting increased mineralized integration of the allograft in the rPTH group. In contrast to similar rPTH therapy studies in dogs, no signs of hypercalcemia, hyperphosphatemia, or inflammation were detected. Taken together, we provide initial evidence that rPTH treatment enhances mandibular allograft healing in a clinically relevant large animal model.

Osteochondral repair combining therapeutics implant with mesenchymal stem cells spheroids

Functional articular cartilage regeneration remains challenging, and it is essential to restore focal osteochondral defects and prevent secondary osteoarthritis. Combining autologous stem cells with therapeutic medical device, we developed a bi-compartmented implant that could promote both articular cartilage and subchondral bone regeneration. The first compartment based on therapeutic collagen associated with bone morphogenetic protein 2, provides structural support and promotes subchondral bone regeneration. The second compartment contains bone marrow-derived mesenchymal stem cell spheroids to support the regeneration of the articular cartilage. Six-month post-implantation, the regenerated articular cartilage surface was 3 times larger than that of untreated animals, and the regeneration of the osteochondral tissue occurred during the formation of hyaline-like cartilage. Our results demonstrate the positive impact of this combined advanced therapy medicinal product, meeting the needs of promising osteochondral regeneration in critical size articular defects in a large animal model combining not only therapeutic implant but also stem cells.

Characterization of a pluripotent stem cell-derived matrix with powerful osteoregenerative capabilities

Approximately 10% of fractures will not heal without intervention. Current treatments can be marginally effective, costly, and some have adverse effects. A safe and manufacturable mimic of anabolic bone is the primary goal of bone engineering, but achieving this is challenging. Mesenchymal stem cells (MSCs), are excellent candidates for engineering bone, but lack reproducibility due to donor source and culture methodology. The need for a bioactive attachment substrate also hinders progress. Herein, we describe a highly osteogenic MSC line generated from induced pluripotent stem cells that generates high yields of an osteogenic cell-matrix (ihOCM) in vitro. In mice, the intrinsic osteogenic activity of ihOCM surpasses bone morphogenic protein 2 (BMP2) driving healing of calvarial defects in 4 weeks by a mechanism mediated in part by collagen VI and XII. We propose that ihOCM may represent an effective replacement for autograft and BMP products used commonly in bone tissue engineering.

Production of a safe and manufacturable material to mimic anabolic bone for tissue engineering has been hard to achieve to date. Here the authors use a mesenchymal stem cell line generated from induced pluripotent stem cells to produce osteogenic cell-matrix, displaying significant healing properties in mice.

Concentration-dependent effects of latex F1-protein fraction incorporated into deproteinized bovine bone and biphasic calcium phosphate on the repair of critical-size bone defects

F1-protein fraction (F1) is a natural bioactive compound extracted from the rubber tree, Hevea brasiliensis, and has been recently studied for its therapeutic potential in wound healing. In this study, we investigated the concentration-dependent effects of F1 (0.01%, 0.025%, 0.05%, and 0.1%) incorporated into deproteinized bovine bone (DBB) and porous biphasic calcium phosphate (pBCP), on the repair of rat calvarial critical-size bone defects (CSBD). The defects were analyzed by 3D-microtomography and 2D-histomorphometry at 12 weeks postsurgery. The binding efficiency of F1 to pBCP (96.3 ± 1.4%) was higher than that to DBB (67.7 ± 3.3%). In vivo analysis showed a higher bone volume (BV) gain in all defects treated with DBB (except in 0.1% of F1) and pBCP (except in 0.05% and 0.1% of F1) compared to the CSBD without treatment/control group (9.96 ± 2.8 mm³ ). DBB plus 0.025% F1 promoted the highest BV gain (29.7 ± 2.2 mm³ , p < .0001) compared to DBB without F1 and DBB plus 0.01% and 0.1% of F1. In the pBCP group, incorporation of F1 did not promote bone gain when compared to pBCP without F1 (15.9 ± 4.2 mm³ , p > .05). Additionally, a small BV occurred in defects treated with pBCP plus 0.1% F1 (10.4 ± 1.4 mm^3, p < .05). In conclusion, F1 showed a higher bone formation potential in combination with DBB than with pBCP, in a concentration-dependent manner. Incorporation of 0.25% F1 into DBB showed the best results with respect to bone formation/repair in CSBD. These results suggest that DBB plus 0.25% F1 can be used as a promising bioactive material for application in bone tissue engineering.

Enhanced osteogenic differentiation of human mesenchymal stem cells by direct delivery of Cbfβ protein

Core binding factor β (Cbfβ) is a non-DNA binding cofactor of Runx2 that potentiates DNA binding. Previously, it has been reported that Cbfβ plays an essential role in osteogenic differentiation and skeletal development by inhibition adipogenesis. Here, we delivered the recombinant Cbfβ protein into human mesenchymal stem cells (MSCs) and triggered osteogenic lineage commitment. The efficient delivery of Cbfβ was achieved by fusing 30Kc19 protein, which is a cell-penetrating protein derived from the silkworm. After the production of the recombinant Cbfβ-30Kc19 protein in the Escherichia coli expression system, and confirmation of its intracellular delivery, MSCs were treated with the Cbfβ-30Kc19 once or twice up to 300 µg/ml. By investigating the upregulation of osteoblast-specific genes and phenotypical changes, such as calcium mineralization, we demonstrated that Cbfβ-30Kc19 efficiently induced osteogenic differentiation in MSCs. At the same time, Cbfβ-30Kc19 suppressed adipocyte formation and downregulated the expression of adipocyte-specific genes. Our results demonstrate that the intracellularly delivered Cbfβ-30Kc19 enhances osteogenesis in MSCs, whereas it suppresses adipogenesis by altering the transcriptional regulatory network involved in osteoblast-adipocyte lineage commitment. Cbfβ-30Kc19 holds great potential for the treatment of bone-related diseases, such as osteoporosis, by allowing transcriptional regulation in MSCs, and overcoming the limitations of current therapies.

Functionally engineered extracellular vesicles improve bone regeneration

Lineage specific differentiation of host mesenchymal stem cells (MSCs) is a necessary step for bone repair/regeneration. Clinically, growth factors such as bone morphogenetic protein 2 (BMP2) are used to enhance/hasten this process to heal critical sized defects. However, the clinical application of such growth factors is fraught with dosage challenges as well as immunological and ectopic complications. The identification of extracellular vesicles (EVs) as active components of the MSC secretome suggest alternative approaches to enhancing bone regeneration. Based on our earlier studies on the properties of EVs from lineage specified MSCs, this study sought to engineer EVs to enhance osteogenic differentiation. To generate MSC EVs with enhanced osteoinductive abilities, genetically modified human bone marrow derived MSCs (HMSCs) were generated by constitutively expressing BMP2. We hypothesized that these cells would generate functionally engineered EVs (FEEs) with enhanced osteoinductive properties. Our results show that these FEEs maintained the general physical and biochemical characteristics of naïve HMSC EVs in the form of size distribution, EV marker expression and endocytic properties but show increased bone regenerative potential compared to MSC EVs in a rat calvarial defect model in vivo. Mechanistic studies revealed that although BMP2 was constitutively expressed in the parental cells, the corresponding EVs (FEEs) do not contain BMP2 protein as an EV constituent. Further investigations revealed that the FEEs potentiate the BMP2 signaling cascade possibly due to an altered miRNA composition. Collectively, these studies indicate that EVs' functionality may be engineered by genetic modification of the parental MSCs to induce osteoinduction and bone regeneration. SIGNIFICANCE STATEMENT: With mounting evidence for the potential of MSC EVs in treatment of diseases and regeneration of tissues, it is imperative to evaluate if they can be modified for application specificity. The results presented here indicate the possibility for generating Functionally Engineered EVs (FEEs) from MSC sources. As a proof of concept approach, we have shown that EVs derived from genetically modified MSCs (BMP2 overexpression) can be effective as biomimetic substitutes for growth factors for enhanced tissue-specific regeneration (bone regeneration) in vivo. Mechanistic studies highlight the role of EV miRNAs in inducing pathway-specific changes. We believe that this study will be useful to researchers evaluating EVs for regenerative medicine applications.

Activin A and BMP chimera (AB204) induced bone fusion in osteoporotic spine using an ovariectomized rat model

BACKGROUND CONTEXT

Recombinant human bone morphogenic protein 2 (rhBMP2) has been used to induce bone fusion in patients with spinal fusion surgery. However, the effectiveness of rhBMP2 in the bone fusion process is limited in osteoporosis patients, and a high dose of rhBMP2 for enough bone fusion sometimes provokes side effects. Therefore, substitutes for rhBMP2 with a higher therapeutic potency are needed, and already several studies have published the effectiveness of Activin A/BMP2 chimera (AB204) in new bone formation process in vitro and in vivo.

PURPOSE

In the present study, we provide evidence that bone fusion activity of AB204 is superior to that of rhBMP2 in osteoporotic rat models.

STUDY DESIGN/SETTINGS

An in vivo animal study was carried out.

METHODS

A total of 40 Sprague-Dawley rats underwent bilateral ovariectomy. At 6 weeks after ovariectomy, a lumbar spinal bone fusion model of bilateral intertransverse process was performed. All rats were randomly divided into four groups as follows: rats receiving 5 µg of rhBMP2 (Group I), rats receiving 10 µg of rhBMP2 (Group II), rats receiving 5 µg of AB204 (Group III), and rats receiving 10 µg of AB204 (Group IV). Simple radiographs were performed at 6 and 12 weeks after bone fusion, and direct palpation, micro-CT, and immunohistochemistry (hematoxylin-eosin stain and Masson's trichrome stain) were performed at 12 weeks after bone fusion. The qualitative degree of bone fusion was assessed as manual fusion score from direct palpation, and radio-histologic fusion score from simple radiographs, micro-CT, and immunohistochemistry. Also, the quantitative degree of bone fusion was assessed using fusion bone volume by micro-CT and serum osteocalcin level as bone turnover markers.

RESULTS

The change of body weight was not different among the groups during follow-up. The qualitative degree of bone fusion assessed by direct palpation, simple radiographs, micro-CT, and histologic evaluation was significantly different among the four groups. Also, the quantitative degree of bone fusion including fusion bone volume and serum osteocalcin was significantly different among the groups. Especially, in manual fusion score, radio-histologic fusion score, and fusion bone volume, the AB204 group revealed superior results to the rhBMP2 group when using the same dose. Furthermore, even the low-dose AB204 group (Group III) showed superior results to the high-dose rhBMP2 group (Group II) in radio-histologic fusion score and fusion bone volume.

CONCLUSION

The effect of bone fusion in osteoporotic rats was significantly higher in the AB204 group than in the rhBMP2 group.

CLINICAL SIGNIFICANCE

If further organized animal studies and clinical trials are provided, AB204 may be a good substitute for rhBMP2 in osteoporotic spinal fusion surgery, as a superior osteogenesis inducer.

Noggin Inhibits IL-1β and BMP-2 Expression, and Attenuates Cartilage Degeneration and Subchondral Bone Destruction in Experimental Osteoarthritis

Osteoarthritis (OA) is a chronic inflammatory and progressive joint disease that results in cartilage degradation and subchondral bone remodeling. The proinflammatory cytokine interleukin 1 beta (IL-1β) is abundantly expressed in OA and plays a crucial role in cartilage remodeling, although its role in the activity of chondrocytes in cartilage and subchondral remodeling remains unclear. In this study, stimulating chondrogenic ATDC5 cells with IL-1β increased the levels of bone morphogenetic protein 2 (BMP-2), promoted articular cartilage degradation, and enhanced structural remodeling. Immunohistochemistry staining and microcomputed tomography imaging of the subchondral trabecular bone region in the experimental OA rat model revealed that the OA disease promotes levels of IL-1β, BMP-2, and matrix metalloproteinase 13 (MMP-13) expression in the articular cartilage and enhances subchondral bone remodeling. The intra-articular injection of Noggin protein (a BMP-2 inhibitor) attenuated subchondral bone remodeling and disease progression in OA rats. We also found that IL-1β increased BMP-2 expression by activating the mitogen-activated protein kinase (MEK), extracellular signal-regulated kinase (ERK), and specificity protein 1 (Sp1) signaling pathways. We conclude that IL-1β promotes BMP-2 expression in chondrocytes via the MEK/ERK/Sp1 signaling pathways. The administration of Noggin protein reduces the expression of IL-1β and BMP-2, which prevents cartilage degeneration and OA development.

Application of Cytokines of the Bone Morphogenetic Protein (BMP) Family in Spinal Fusion - Effects on the Bone, Intervertebral Disc and Mesenchymal Stromal Cells

Low back pain is a prevalent socio-economic burden and is often associated with damaged or degenerated intervertebral discs (IVDs). When conservative therapy fails, removal of the IVD (discectomy), followed by intersomatic spinal fusion, is currently the standard practice in clinics. The remaining space is filled with an intersomatic device (cage) and with bone substitutes to achieve disc height compensation and bone fusion. As a complication, in up to 30% of cases, spinal non-fusions result in a painful pseudoarthrosis. Bone morphogenetic proteins (BMPs) have been clinically applied with varied outcomes. Several members of the BMP family, such as BMP2, BMP4, BMP6, BMP7, and BMP9, are known to induce osteogenesis. Questions remain on why hyper-physiological doses of BMPs do not show beneficial effects in certain patients. In this respect, BMP antagonists secreted by mesenchymal cells, which might interfere with or block the action of BMPs, have drawn research attention as possible targets for the enhancement of spinal fusion or the prevention of non-unions. Examples of these antagonists are noggin, gremlin1 and 2, chordin, follistatin, BMP3, and twisted gastrulation. In this review, we discuss current evidence of the osteogenic effects of several members of the BMP family on osteoblasts, IVD cells, and mesenchymal stromal cells. We consider in vitro and in vivo studies performed in human, mouse, rat, and rabbit related to BMP and BMP antagonists in the last two decades. We give insights into the effects that BMP have on the ossification of the spine. Furthermore, the benefits, pitfalls, and possible safety concerns using these cytokines for the improvement of spinal fusion are discussed.

Exogenous Stimulation of Human Intervertebral Disc Cells in 3-Dimensional Alginate Bead Culture With BMP2 and L51P: Cytocompatibility and Effects on Cell Phenotype

Objective

Spinal fusion surgery is a common treatment modality for various pathologic conditions of the spine. The bone morphogenetic protein 2 (BMP2) analogue L51P acts as a general inhibitor of BMP antagonists, whereas it shows a weak affinity for BMP type I receptor. It is suggested that L51P applied in bone disorders might prevent side effects of highly concentrated BMP dosage applications in the order of milligrams. The objective of this study was to investigate the effects of L51P and BMP2 on intervertebral disc cells (IVDCs), i.e. on nucleus pulposus cells, on annulus fibrosus cells (AFCs), and on cartilaginous endplate cells (CEPCs), respectively, in 3-dimensional (3D) culture.

Methods

Low-passage primary IVDCs were cultured in 3D alginate bead culture and exposed to 100-ng/mL BMP2 and/or L51P for 21 days. Here, we analyzed glycosaminoglycan (GAG) and DNA content and further performed gene expression analysis for major matrix genes.

Results

AFCs and cartilaginous CEPCs stimulated with each 100-ng/mL L51P and BMP2, showed a significant upregulation in GAG (AFCs: p = 0.00347 and CEPCs: p = 0.0115) and DNA production (AFCs: p = 0.0182 and CEPCs: p = 0.0179) compared to control.

Conclusion

These results allow first insights into the behavior of IVDCs upon L51P stimulation.

Biofabrication of SDF-1 Functionalized 3D-Printed Cell-Free Scaffolds for Bone Tissue Regeneration

Large segmental bone defects occurring after trauma, bone tumors, infections or revision surgeries are a challenge for surgeons. The aim of our study was to develop a new biomaterial utilizing simple and cheap 3D-printing techniques. A porous polylactide (PLA) cylinder was printed and functionalized with stromal-derived factor 1 (SDF-1) or bone morphogenetic protein 7 (BMP-7) immobilized in collagen type I. Biomechanical testing proved biomechanical stability and the scaffolds were implanted into a 6 mm critical size defect in rat femur. Bone growth was observed via x-ray and after 8 weeks, bone regeneration was analyzed with µCT and histological staining methods. Development of non-unions was detected in the control group with no implant. Implantation of PLA cylinder alone resulted in a slight but not significant osteoconductive effect, which was more pronounced in the group where the PLA cylinder was loaded with collagen type I. Addition of SDF-1 resulted in an osteoinductive effect, with stronger new bone formation. BMP-7 treatment showed the most distinct effect on bone regeneration. However, histological analyses revealed that newly formed bone in the BMP-7 group displayed a holey structure. Our results confirm the osteoinductive character of this 3D-biofabricated cell-free new biomaterial and raise new options for its application in bone tissue regeneration.

Icariin controlled release on a silk fibroin/mesoporous bioactive glass nanoparticles scaffold for promoting stem cell osteogenic differentiation

The treatment of bone defects caused by various reasons is still a major problem in orthopedic clinical work. Many studies on osteogenic implant materials have used various biologically active factors such as osteogenic inducers, but these biologically active factors have various side effects. Therefore, in this study, silk fibroin (SF) was used as a scaffold material, mesoporous bioactive glass nanoparticles (MBGNs) as a sustained release carrier, and the traditional Chinese drug icariin (ICA) was loaded to promote bone formation. The experiments in this study have proven that SF/MBGNs-ICA scaffolds can successfully load and release ICA for a long time, and the sustained-release ICA can promote the proliferation and differentiation of BMSCs for a long time. This controlled-release ICA organic/inorganic two-component scaffold material is expected to become a new bone grafting solution.

The Role of Marine Organic Extract in Bone Regeneration: A Pilot Study

Novel biomaterials capable of accelerating the healing process of skeletal tissues are urgently needed in dentistry. The present in vivo study assessed the osteoconductive and osteoinductive properties of experimental biphasic bioceramics (HA-TCP) modified or not by a nacre extract (marine organic extract, MOE) in a sheep model. Fabrication of MOE involved mixing ground nacre (0.05 g, particle sizes < 0.1 mm) with glacial ethanoic acid (5 mL, pH 7) for 72 hours using external magnetic stirring (25°C). Nonreactive carriers (sterile polythene tubes; 3/animal, radius: 2.5 mm, length: 10.0 mm) pertaining to the control (empty) or experimental groups (HA-TCP or MOE-modified HA-TCP) were implanted intramuscularly into the abdominal segment of the torso in sheep (n = 8, age: 2 years, weight: 45 kg). Euthanization of animals was performed at 3 and 6 months after surgery. Tissues harvested were subjected to macroscopic and radiographic assessments. Specimens were then stained for histological analysis. Both control and experimental animals were capable of inducing the neoformation of fibrous connective tissue at both time points where superior amounts of tissue formation and mineralization were detected for experimental groups (unaltered (at 3 and 6 mos) and MOE-modified HA-TCP (at 3 mos)). Histological results, however, revealed that mature bone formation was only observed for specimens fabricated with MOE-modified HA-TCP in a time-dependent manner. The present study has successfully demonstrated the in vivo utility of experimental biphasic bioceramics modified by MOE in an ectopic grafting sheep model. Promising osteoconductive and osteoinductive properties must be further developed and confirmed by subsequent research.

[Biocompatibility and osteoinductive properties of collagen and fibronectin hydrogel impregnated with rhBMP-2]

The study aimed to demonstrate the biocompatibility and osteoinductive properties of a hydrogel based on highly purified collagen and fibronectin impregnated with rhBMP-2. In vitro and in vivo experiments have shown that the minimum effective dosage of rhBMP-2 is 10 μg/ml. The cytocompatibility of the collagen-fibronectin gel was determined using MTT test and staining with PKH-26. There was no inflammation reaction when the material was subcutaneously implanted in rats (n=30) in vivo. The collagen-fibronectin hydrogel containing 10 μg/ml rhBMP-2 showed high osteogenic properties. By the end of 28 days 8±4% of its volume was replaced by newly formed bone tissue in case of subcutaneous implantation, 17±10% in intramuscular implantation and 26±11% in intraosseous implantation in the calvarial critical-size. The optimal combination of biocompatible and osteogenic properties of collagen-fibronectin hydrogel impregnated with BMP-2 allows us to consider it as a promising basis for creating the new generation of osteoplastic materials for dentistry.

The Secretome of Hypoxia Conditioned hMSC Loaded in a Central Depot Induces Chemotaxis and Angiogenesis in a Biomimetic Mineralized Collagen Bone Replacement Material

The development of biomaterials with intrinsic potential to stimulate endogenous tissue regeneration at the site of injury is a main demand on future implants in regenerative medicine. For critical-sized bone defects, an in situ tissue engineering concept is devised based on biomimetic mineralized collagen scaffolds. These scaffolds are functionalized with a central depot loaded with a signaling factor cocktail, obtained from secretome of hypoxia-conditioned human mesenchymal stem cells (MSC). Therefore, hypoxia-conditioned medium (HCM)-production is standardized and adapted to achieve high signaling factor-yields; a concentration protocol based on dialysis and freeze-drying is established to enable the integration of sufficient and defined amounts into the depot. In humid milieu-as after implantation-signaling factors are released by forming a chemotactic gradient, inducing a directed migration of human bone marrow stroma cells (hBMSC) into the scaffold. Angiogenic potential, determined by coculturing human umbilical vein endothelial cells (HUVEC) with osteogenically induced hBMSC shows prevascular structures, which sprout throughout the interconnected pores in a HCM-concentration-dependent manner. Retarded release by alginate-based (1 vol%) depots, significantly improves sprouting-depth and morphology of tubular structures. With the intrinsic potential to supply attracted cells with oxygen and nutrients, this bioactive material system has great potential for clinical translation.

Segmental long bone regeneration guided by degradable synthetic polymeric scaffolds

Recent developments in synthetic bone grafting materials and adjuvant therapeutic agents have opened the door to the regenerative reconstruction of critical-size long bone segmental defects resulting from trauma, osteoporotic fractures or tumour resections. Polymeric scaffolds with controlled macroporosities, degradability, useful surgical handling characteristics, and the ability to deliver biotherapeutics to promote new bone ingrowth have been developed for this challenging orthopaedic application. This review highlights major classes of degradable synthetic polymers and their biomineral composites, including conventional and amphiphilic polyesters, polyanhydrides, polycarbonates, and polyethylene glycol-based hydrogels, that have been explored for the regenerative reconstruction of critical-size long bone segmental defects over the past two decades. The pros and cons of these synthetic scaffold materials are presented in the context of enabling or impeding the functional (mechanical and radiographic) repair of a long bone segmental defect, with the long bone regeneration outcomes compared with healthy long bone controls or results achieved with current grafting standards.

Implantable electrical stimulation bioreactor with liquid crystal polymer-based electrodes for enhanced bone regeneration at mandibular large defects in rabbit

The osseous regeneration of large bone defects is still a major clinical challenge in maxillofacial and orthopedic surgery. Previous studies demonstrated that biphasic electrical stimulation (ES) stimulates bone formation; however, polyimide electrode should be removed after regeneration. This study presents an implantable electrical stimulation bioreactor with electrodes based on liquid crystal polymer (LCP), which can be permanently implanted due to excellent biocompatibility to bone tissue. The bioreactor was implanted into a critical-sized bone defect and subjected to ES for one week, where bone regeneration was evaluated four weeks after surgery using micro-CT. The effect of ES via the bioreactor was compared with a sham control group and a positive control group that received recombinant human bone morphogenetic protein (rhBMP)-2 (20 μg). New bone volume per tissue volume (BV/TV) in the ES and rhBMP-2 groups increased to 132% (p < 0.05) and 174% (p < 0.01), respectively, compared to that in the sham control group. In the histological evaluation, there was no inflammation within the bone defects and adjacent to LCP in all the groups. This study showed that the ES bioreactor with LCP electrodes could enhance bone regeneration at large bone defects, where LCP can act as a mechanically resistant outer box without inflammation. Graphical abstract To enhance bone regeneration, a bioreactor comprising collagen sponge and liquid crystal polymer-based electrode was implanted in the bone defect. Within the defect, electrical current pulses having biphasic waveform were applied from the implanted bioreactor.

Local application of alendronate controls bone formation and β-tricalcium phosphate resorption induced by recombinant human bone morphogenetic protein-2

This study examined the ability of local alendronate (ALN) administration to control β-tricalcium phosphate (β-TCP) resorption as well as the induction of bone formation by recombinant human bone morphogenetic protein-2 (rhBMP-2). A 15-mm critical-sized bone defect was created in the diaphysis of rabbit ulnae. Nine female rabbits (4 to 5 months-old) were divided into 3 groups. Group 1 (n = 6 ulnae) animals received implants consisting of β-TCP granules and 25 μg of rhBMP-2 in 6.5% collagen gel. Group 2 (6 ulnae) and Group 3 (6 ulnae) animals received the same implants, but with 10^-6 M and 10^-3 M ALN-treated TCP granules, respectively. Two weeks postsurgery, tartrate-resistant acid phosphatase-positive cell counts, new bone formation, and residual β-TCP were evaluated. This study showed that a high dose of ALN strongly reduced osteoclastic resorption of β-TCP induced by rhBMP-2, resulting in decreased bone formation. In contrast, a low dose of ALN slightly reduced the bone resorptive effect but increased bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in the β-TCP-implanted area, and that administration of a low dose of ALN may solve clinical bone resorptive problems induced by rhBMP-2.