Effects of combinations of BMP-2 with FGF-2 and/or VEGF on HUVECs angiogenesis in vitro and CAM angiogenesis in vivo

Functionalized biomimetic mineralized collagen promotes osseointegration of 3D-printed titanium alloy microporous interface

Mineralized collagen (MC) is the fundamental unit of natural bone tissue and can induce bone regeneration. Unmodified MC has poor mechanical properties and a single component, making it unable to cope with complex physiological environment. In this study, we introduced sodium alginate (SA) and vascular endothelial growth factor (VEGF) into the MC material to construct functionalized mineralized collagen (FMC) with good mechanical strength and the ability to continuously release growth factors. The FMC is filled into the pores of 3D printed titanium alloy scaffold to form a new organic-inorganic bioactive interface. With the continuous degradation of FMC, bone marrow mesenchymal stem cells (BMSCs) and vascular endothelial cells (VECs) in the surrounding environment are recruited to the surface of the scaffold to promote bone and vascular regeneration. After implanting the scaffold into the distal femoral defect of rabbits, Micro CT, histological, push-out, as well as immunohistochemical analysis showed that the composite interface can significantly promote osseointegration. These findings provide a new strategy for the development and application of mineralized collagen materials.

Agaricus bisporus-Derived Glucosamine Hydrochloride Regulates VEGF through BMP Signaling to Promote Zebrafish Vascular Development and Impairment Repair

Glucosamine hydrochloride (GAH) is a natural component of glycoproteins present in almost all human tissues and participates in the construction of human tissues and cell membranes. GAH has a wide range of biological activities, particularly in anti-inflammatory and osteogenic damage repair. At present, little is known about how GAH functions in angiogenesis. To determine the role of GAH on vascular development and impairment repair, we used the inhibitors VRI, DMH1, and dorsomorphin (DM) to construct vascular-impaired models in Tg(kdrl: mCherry) transgenic zebrafish. We then treated with GAH and measured its repair effects on vascular impairment through fluorescence intensity, mRNA, and protein expression levels of vascular-specific markers. Our results indicate that GAH promotes vascular development and repairs impairment by regulating the vascular endothelial growth factor (VEGF) signaling pathway through modulation of bone morphogenetic protein (BMP) signaling. This study provides an experimental basis for the development of GAH as a drug to repair vascular diseases.

Silencing of topical proline hydroxylase domain 2 promotes the healing of rat diabetic wounds by phosphorylating AMPK

BACKGROUND

For diabetic ulcers, the impaired response to hypoxia is a key feature associated with delayed healing. In the early phase of hypoxia, hypoxic signaling activates the AMPK system through direct phosphorylation of the PHD2 pathway, producing a significant endogenous hypoxic protective effect.

METHODS

Twenty Sprague-Dawley (SD) rats were randomly divided into two groups: treatment (sh-PHD2) and control (sh-Control). Using lentiviral encapsulation of PHD2-shRNA and transfection, the silencing efficiency of PHD2 expression was verified in rat dermal fibroblasts (RDF) and in rat aortic endothelial cells (RAECs). Changes in the ability of RDF and RAECs to proliferate, migrate, and in the rate of ATP production were observed and then tested after inhibition of AMPK phosphorylation using dorsomorphin. The lentiviral preparation was injected directly into the wounds of rats and wound healing was recorded periodically to calculate the healing rate. Wounded tissues were excised after 14 days and the efficiency of PHD2 silencing, as well as the expression of growth factors, was examined using molecular biology methods. Histological examination was performed to assess CD31 expression and therefore determine effects on angiogenesis.

RESULTS

Lentiviral-encapsulated PHD2-sh-RNA effectively suppressed PHD2 expression and improved the proliferation, migration, and ATP production rate of RDF and RAEC, which were restored to their previous levels after inhibition of AMPK. The rate of wound healing, vascular growth, and expression of growth factors were significantly improved in diabetic-model rats after local silencing of PHD2 expression.

CONCLUSION

Silencing of PHD2 promoted wound healing in diabetic-model SD rats by activating AMPK phosphorylation.

Feasibility of adipose-derived therapies for hair regeneration: Insights based on signaling interplay and clinical overview

Dermal white adipose tissue (dWAT) is a dynamic component of the skin and closely interacts with the hair follicle. Interestingly, dWAT envelops the hair follicle during anagen and undergoes fluctuations in volume throughout the hair cycle. dWAT-derived extracellular vesicles can significantly regulate the hair cycle, and this provides a theoretical basis for utilizing adipose tissue as a feasible clinical strategy to treat hair loss. However, the amount and depth of the available literature are far from enough to fully elucidate the prominent role of dWAT in modulating the hair growth cycle. This review starts by investigating the hair cycle-coupled dWAT remodeling and the reciprocal signaling interplay underneath. Then, it summarizes the current literature and assesses the advantages and limitations of clinical research utilizing adipose-derived therapies for hair regeneration.

Advances and prospects of platelet-rich plasma therapy in veterinary ophthalmology

In the recent decades, there has been a significant uptick on the use of platelet-rich plasma (PRP) as a better alternative for ophthalmologic therapies in pathologies, primarily of the ocular surface. PRP is a class of liquid platelet concentrate containing a supra-physiological concentration of platelets in a relatively small amount of plasma. Its potential to heal various tissues has piqued interest in its therapeutic application as a biomaterial in regenerative medicine. It is currently a popular therapeutic agent in plastic surgery, cardiothoracic surgery, reconstructive surgery, and even oral and maxillofacial surgery. Based on the data from in vitro and in vivo studies, it can be concluded that PRP possesses adequate therapeutic potential in ocular pathologies, especially those involving cornea. In addition, the high concentrations of growth factors (TGF-β, VEGF, EGF) present in the PRP accelerate the healing of the corneal epithelium. PRP has great therapeutic prospects in veterinary ophthalmology as a regenerative therapeutic modality. However, several variables are yet to be defined and standardized that can directly affect the efficacy of PRP application in different ophthalmic conditions. There is a shortage of research on the use of PRP in ocular surface defects compared to the number of studies and reports on the use of autologous and allogeneic serum eye drops. Therefore, a data-driven approach is required to generate consensus/guidelines for the preparation, characterization, and therapeutic use of PRP in veterinary ophthalmology. This review aims to inform readers of the latest research on PRP, including its preparation methods, physiological and biochemical properties, clinical applications in veterinary ophthalmology, and their safety and efficacy.

Tanshinone I alleviates steroid-induced osteonecrosis of femoral heads and promotes angiogenesis: in vivo and in vitro studies

BACKGROUND

The impaired blood supply to the bones is an important pathological feature of steroid-induced osteonecrosis of the femoral head (SIONFH). Danshen is a Chinese herb that shows therapeutic effects on SIONFH, but the effects of one of its major bioactive constituents, Tanshinone I (TsI), on SIONFH remain unknown. Here, we evaluated the effects of TsI on SIONFH, particularly focusing on its effects on angiogenesis, in in vivo and in vitro research.

METHODS

SIONFH was induced in Sprague-Dawley rats by an intramuscular injection of methylprednisolone (40 mg/kg) in combination with an intraperitoneal injection of lipopolysaccharide (20 μg/kg). Morphological alterations of the femoral head were observed by dual-energy X-ray absorptiometry and HE staining. Western blot, qRT-PCR, and immunohistochemical/immunofluorescence staining were used to determine gene expression.

RESULTS

TsI (10 mg/kg) alleviated bone loss and rescued the expression of angiogenesis-related molecules (CD31, VWF, VEGF, and VEGFR2) in the femoral heads of SIONFH rats. Notably, TsI rescued the down-regulated expression of SRY-box transcription factor 11 (SOX11) in CD31⁺ endothelial cells in the femoral heads of SIONFH rats. In vitro studies showed that TsI preserved the dexamethasone-harmed angiogenic property (migration and tube formation) of human umbilical vein cells (EA.hy926), suppressed dexamethasone-induced cell apoptosis, reduced pro-apoptotic proteins (cytosolic cytochrome C, Bax, and caspase 3/9) and increased anti-apoptotic protein Bcl-2, whereas silencing of SOX11 reversed these beneficial effects.

CONCLUSIONS

This study demonstrates that TsI alleviates SIONFH and promotes angiogenesis by regulating SOX11 expression. Our work would provide new evidence for the application of TsI to treat SIONFH.

Advances in the Clinical Application of Platelet-Rich Plasma in the Foot and Ankle: A Review

Autologous and recombinant biologic substances have been generated as a result of the research into the cellular features of the healing process. Orthobiologics are increasingly being used in sports medicine and musculoskeletal surgery. Nevertheless, clinical data are limited; consequently, further studies are required, particularly in foot and ankle pathologies. This review aims to provide evidence of the most recent literature results and ignite the interest of orthopedic specialists eager for an update about the most current discussion on platelet-rich plasma (PRP) clinical applications in the foot and ankle fields. Previous studies have shown that platelet-rich plasma can be beneficial in treating various conditions, such as chronic foot ulcers, osteoarthritis, Achilles tendinopathy, etc. Despite the positive effects of PRP on various musculoskeletal conditions, more prospective studies are needed to confirm its effectiveness at treating ankle and foot pathologies. In addition to clinical trials, other factors, such as the quality of the research and the procedures involved, must be considered before they can be used in patients. More long-term evaluations are needed to support or oppose its application in treating foot and ankle disorders. We present the most extensive review of PRP's clinical applications in the foot and ankle field.

Emerging roles of growth factors in osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a potentially disabling orthopedic condition that requires total hip arthroplasty in most late-stage cases. However, mechanisms underlying the development of ONFH remain unknown, and the therapeutic strategies remain limited. Growth factors play a crucial role in different physiological processes, including cell proliferation, invasion, metabolism, apoptosis, and stem cell differentiation. Recent studies have reported that polymorphisms of growth factor-related genes are involved in the pathogenesis of ONFH. Tissue and genetic engineering are attractive strategies for treating early-stage ONFH. In this review, we summarized dysregulated growth factor-related genes and their role in the occurrence and development of ONFH. In addition, we discussed their potential clinical applications in tissue and genetic engineering for the treatment of ONFH.

Engineering Spatiotemporal Control in Vascularized Tissues

A major challenge in engineering scalable three-dimensional tissues is the generation of a functional and developed microvascular network for adequate perfusion of oxygen and growth factors. Current biological approaches to creating vascularized tissues include the use of vascular cells, soluble factors, and instructive biomaterials. Angiogenesis and the subsequent generation of a functional vascular bed within engineered tissues has gained attention and is actively being studied through combinations of physical and chemical signals, specifically through the presentation of topographical growth factor signals. The spatiotemporal control of angiogenic signals can generate vascular networks in large and dense engineered tissues. This review highlights the developments and studies in the spatiotemporal control of these biological approaches through the coordinated orchestration of angiogenic factors, differentiation of vascular cells, and microfabrication of complex vascular networks. Fabrication strategies to achieve spatiotemporal control of vascularization involves the incorporation or encapsulation of growth factors, topographical engineering approaches, and 3D bioprinting techniques. In this article, we highlight the vascularization of engineered tissues, with a focus on vascularized cardiac patches that are clinically scalable for myocardial repair. Finally, we discuss the present challenges for successful clinical translation of engineered tissues and biomaterials.

Sesamin Promotes Osteoporotic Fracture Healing by Activating Chondrogenesis and Angiogenesis Pathways

Osteoporotic fracture has been regarded as one of the most common bone disorders in the aging society. The natural herb-derived small molecules were revealed as potential treatment approaches for osteoporotic fracture healing. Sesamin is a member of lignan family, which possesses estrogenic activity and plays a significant role in modulating bone homeostasis. Our previous study reported the promoting effect of sesamin on postmenopausal osteoporosis treatment. However, the role of sesamin in osteoporotic fracture healing has not been well studied yet. In this study, we further investigated the putative treatment effect of sesamin on osteoporotic fracture healing. Our study indicated that sesamin could activate bone morphogenetic protein 2 (BMP2) signaling pathway and further promotes in vitro chondrogenesis and angiogenesis activities. This promoting effect was abolished by the treatment of ERα inhibitor. In the osteoporotic bone fracture model, we demonstrated that sesamin markedly improves the callus formation and increases the cartilaginous area at the early-stage, as well as narrowing the fracture gap, and expands callus volume at the late-stage fracture healing site of the OVX mice femur. Furthermore, the angiogenesis at the osteoporotic fracture site was also significantly improved by sesamin treatment. In conclusion, our research illustrated the therapeutic potential and underlying regulation mechanisms of sesamin on osteoporotic fracture healing. Our studies shed light on developing herb-derived bioactive compounds as novel drugs for the treatment of osteoporotic fracture healing, especially for postmenopausal women with low estrogen level.

Advanced PLGA hybrid scaffold with a bioactive PDRN/BMP2 nanocomplex for angiogenesis and bone regeneration using human fetal MSCs

Biodegradable polymers have been used with various systems for tissue engineering. Among them, poly(lactic-co-glycolic) acid (PLGA) has been widely used as a biomaterial for bone regeneration because of its great biocompatibility and biodegradability properties. However, there remain substantial cruxes that the by-products of PLGA result in an acidic environment at the implanting site, and the polymer has a weak mechanical property. In our previous study, magnesium hydroxide (MH) and bone extracellular matrix are combined with a PLGA scaffold (PME) to improve anti-inflammation and mechanical properties and osteoconductivity. In the present study, the development of a bioactive nanocomplex (NC) formed along with polydeoxyribonucleotide and bone morphogenetic protein 2 (BMP2) provides synergistic abilities in angiogenesis and bone regeneration. This PME hybrid scaffold immobilized with NC (PME/NC) achieves outstanding performance in anti-inflammation, angiogenesis, and osteogenesis. Such an advanced PME/NC scaffold suggests an integrated bone graft substitute for bone regeneration.

Mechanistic characterization of endothelial sprouting mediated by pro-angiogenic signaling

Objective

We aim to quantitatively characterize the crosstalk between VEGF‐ and FGF‐mediated angiogenic signaling and endothelial sprouting, to gain mechanistic insights and identify novel therapeutic strategies.

Methods

We constructed an experimentally validated hybrid agent‐based mathematical model that characterizes endothelial sprouting driven by FGF‐ and VEGF‐mediated signaling. We predicted the total sprout length, number of sprouts, and average length by the mono‐ and co‐stimulation of FGF and VEGF.

Results

The experimentally fitted and validated model predicts that FGF induces stronger angiogenic responses in the long‐term compared with VEGF stimulation. Also, FGF plays a dominant role in the combination effects in endothelial sprouting. Moreover, the model suggests that ERK and Akt pathways and cellular responses contribute differently to the sprouting process. Last, the model predicts that the strategies to modulate endothelial sprouting are context‐dependent, and our model can identify potential effective pro‐ and anti‐angiogenic targets under different conditions and study their efficacy.

Conclusions

The model provides detailed mechanistic insight into VEGF and FGF interactions in sprouting angiogenesis. More broadly, this model can be utilized to identify targets that influence angiogenic signaling leading to endothelial sprouting and to study the effects of pro‐ and anti‐angiogenic therapies.

Sustained Release of VEGF to Promote Angiogenesis and Osteointegration of Three-Dimensional Printed Biomimetic Titanium Alloy Implants

Tumor resection and treatment of trauma-related regional large bone defects have major challenges in the field of orthopedics. Scaffolds that treat bone defects are the focus of bone tissue engineering. 3D printing porous titanium alloy scaffolds, prepared via electron beam melting technology, possess customized structure and strength. The addition of a growth factor coating to the scaffold introduces a specific form of biological activation. Vascular endothelial growth factor (VEGF) is key to angiogenesis and osteogenesis in vivo. We designed a porous titanium alloy scaffold/thermosensitive collagen hydrogel system, equipped with VEGF, to promote local osseointegration and angiogenesis. We also verified the VEGF release via thermosensitive collagen and proliferation and induction of the human umbilical vein endothelial cells (HUVECs) via the composite system in vitro. In vivo, using microscopic computed tomography (Micro-CT), histology, and immunohistochemistry analysis, we confirmed that the composite scaffold aids in angiogenesis-mediated bone regeneration, and promotes significantly more bone integration. We also discovered that the composite scaffold has excellent biocompatibility, provides bioactive VEGF for angiogenesis and osteointegration, and provides an important theoretical basis for the restoration of local blood supply and strengthening of bone integration.

Polymer Scaffolds-Enhanced Bone Regeneration in Osteonecrosis Therapy

Osteonecrosis without effective early treatment eventually leads to the collapse of the articular surface and causes arthritis. For the early stages of osteonecrosis, core decompression combined with bone grafting, is a procedure worthy of attention and clinical trial. And the study of bone graft substitutes has become a hot topic in the area of osteonecrosis research. In recent years, polymers have received more attention than other materials due to their excellent performance. However, because of the harsh microenvironment in osteonecrosis, pure polymers may not meet the stringent requirements of osteonecrosis research. The combined application of polymers and various other substances makes up for the shortcomings of polymers, and to meet a broad range of requirements for application in osteonecrosis therapy. This review focuses on various applying polymers in osteonecrosis therapy, then discusses the development of biofunctionalized composite polymers based on the polymers combined with different bioactive substances. At the end, we discuss their prospects for translation to clinical practice.

Therapeutic Study of Thermosensitive Hydrogel Loaded with Super-Activated Platelet Lysate Combined with Core Decompression Technology for the Treatment of Femoral Head Necrosis

Super activated platelet lysate (sPL) is a derivative of platelet-rich plasma (PRP) that contains high levels of several growth factors. In this study, we synthesized a temperature-sensitive hydrogel that contained temperature-sensitive Poly(DL-lactide-glycolide-glycolide acid) (PLGA), SrCl2, and HA, and loaded it with different concentrations of sPL. The hydrogel showed satisfactory encapsulation efficiency and release of the growth factors in a sustained manner, indicating its suitability as a drug carrier. The sPL-loaded hydrogel was inserted into the necrotic femoral head of a rat model and core decompression was applied and resulted in significantly accelerated bone repair and regeneration. Therefore, encapsulation of sPL in a hydrogel scaffolding may be an effective strategy for treating femoral head necrosis.

Clinical Application of Novel Therapies for Coronary Angiogenesis: Overview, Challenges, and Prospects

Cardiovascular diseases continue to be the leading cause of death worldwide, with ischemic heart disease as the most significant contributor. Pharmacological and surgical interventions have improved clinical outcomes, but are unable to ameliorate advanced stages of end-heart failure. Successful preclinical studies of new therapeutic modalities aimed at revascularization have shown short lasting to no effects in the clinical practice. This lack of success may be attributed to current challenges in patient selection, endpoint measurements, comorbidities, and delivery systems. Although challenges remain, the field of therapeutic angiogenesis is evolving, as novel strategies and bioengineering approaches emerge to optimize delivery and efficacy. Here, we describe the structure, vascularization, and regulation of the vascular system with particular attention to the endothelium. We proceed to discuss preclinical and clinical findings and present challenges and future prospects in the field.

Endothelialization of an ePTFE vessel prosthesis modified with an antithrombogenic fibrin/heparin coating enriched with bound growth factors

Early and late thrombosis remain the most frequent reasons for the failure of synthetic cardiovascular grafts. Long-term hemocompatibility of implanted synthetic grafts can be achieved if a natural living endothelium is formed over its blood-contacting surface. Here we present a modification of a standard expanded polytetrafluorethylene (ePTFE) vessel prosthesis by a controlled preparation of a fibrin mesh enriched with covalently bound heparin and noncovalently bound vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). Compared to a bare prosthesis, the coated prosthesis showed excellent antithrombogenic properties after contact with heparinized fresh human blood. Human umbilical vein endothelial cells seeded on the inner surface of the coated prosthesis formed a confluent layer in 5 days, whereas only small colonies of cells were scattered on the bare prosthesis. Viability of the cells was promoted mainly by FGF immobilized on the coating. These findings suggest that the coating may prevent acute thrombus formation and support the self-endothelialization of an implanted ePTFE vascular graft in vivo.

Understanding angiogenesis and the role of angiogenic growth factors in the vascularisation of engineered tissues

Tissue engineering is a rapidly developing field with many potential clinical applications in tissue and organ regeneration. The development of a mature and stable vasculature within these engineered tissues (ET) remains a significant obstacle. Currently, several growth factors (GFs) have been identified to play key roles within in vivo angiogenesis, including vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), FGF and angiopoietins. In this article we attempt to build on in vivo principles to review the single, dual and multiple GF release systems and their effects on promoting angiogenesis. We conclude that multiple GF release systems offer superior results compared to single and dual systems with more stable, mature and larger vessels produced. However, with more complex release systems this raises other problems such as increased cost and significant GF-GF interactions. Upstream regulators and pericyte-coated scaffolds could provide viable alternative to circumnavigate these issues.

ERK and Akt exhibit distinct signaling responses following stimulation by pro-angiogenic factors

Background

Angiogenesis plays an important role in the survival of tissues, as blood vessels provide oxygen and nutrients required by the resident cells. Thus, targeting angiogenesis is a prominent strategy in many different settings, including both tissue engineering and cancer treatment. However, not all of the approaches that modulate angiogenesis lead to successful outcomes. Angiogenesis-based therapies primarily target pro-angiogenic factors such as vascular endothelial growth factor-A (VEGF) or fibroblast growth factor (FGF) in isolation, and there is a limited understanding of how these promoters combine together to stimulate angiogenesis. Targeting one pathway could be insufficient, as alternative pathways may compensate, diminishing the overall effect of the treatment strategy.

Methods

To gain mechanistic insight and identify novel therapeutic strategies, we have developed a detailed mathematical model to quantitatively characterize the crosstalk of FGF and VEGF intracellular signaling. The model focuses on FGF- and VEGF-induced mitogen-activated protein kinase (MAPK) signaling to promote cell proliferation and the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway, which promotes cell survival and migration. We fit the model to published experimental datasets that measure phosphorylated extracellular regulated kinase (pERK) and Akt (pAkt) upon FGF or VEGF stimulation. We validate the model with separate sets of data.

Results

We apply the trained and validated mathematical model to characterize the dynamics of pERK and pAkt in response to the mono- and co-stimulation by FGF and VEGF. The model predicts that for certain ranges of ligand concentrations, the maximum pERK level is more responsive to changes in ligand concentration compared to the maximum pAkt level. Also, the combination of FGF and VEGF indicates a greater effect in increasing the maximum pERK compared to the summation of individual effects, which is not seen for maximum pAkt levels. In addition, our model identifies the influential species and kinetic parameters that specifically modulate the pERK and pAkt responses, which represent potential targets for angiogenesis-based therapies.

Conclusions

Overall, the model predicts the combination effects of FGF and VEGF stimulation on ERK and Akt quantitatively and provides a framework to mechanistically explain experimental results and guide experimental design. Thus, this model can be utilized to study the effects of pro- and anti-angiogenic therapies that particularly target ERK and/or Akt activation upon stimulation with FGF and VEGF.

Osteogenesis and bone remodeling: A focus on growth factors and bioactive peptides

Bone is one of the most frequently transplanted tissues. The bone structure and its physiological function and stem cells biology were known to be closely related to each other for many years. Bone is considered a home to the well-known systems of postnatal mesenchymal stem cells (MSCs). These bone resident MSCs provide a range of growth factors (GF) and cytokines to support cell growth following injury. These GFs include a group of proteins and peptides produced by different cells which are regulators of important cell functions such as division, migration, and differentiation. GF signaling controls the formation and development of the MSCs condensation and plays a critical role in regulating osteogenesis, chondrogenesis, and bone/mineral homeostasis. Thus, a combination of both MSCs and GFs receives high expectations in regenerative medicine, particularly in bone repair applications. It is known that the delivery of exogenous GFs to the non-union bone fracture site remarkably improves healing results. Here we present updated information on bone tissue engineering with a specific focus on GF characteristics and their application in cellular functions and tissue healing. Moreover, the interrelation of GFs with the damaged bone microenvironment and their mechanistic functions are discussed.

Engineered three-dimensional scaffolds for enhanced bone regeneration in osteonecrosis

Osteonecrosis, which is typically induced by trauma, glucocorticoid abuse, or alcoholism, is one of the most severe diseases in clinical orthopedics. Osteonecrosis often leads to joint destruction, and arthroplasty is eventually required. Enhancement of bone regeneration is a critical management strategy employed in osteonecrosis therapy. Bone tissue engineering based on engineered three-dimensional (3D) scaffolds with appropriate architecture and osteoconductive activity, alone or functionalized with bioactive factors, have been developed to enhance bone regeneration in osteonecrosis. In this review, we elaborate on the ideal properties of 3D scaffolds for enhanced bone regeneration in osteonecrosis, including biocompatibility, degradability, porosity, and mechanical performance. In addition, we summarize the development of 3D scaffolds alone or functionalized with bioactive factors for accelerating bone regeneration in osteonecrosis and discuss their prospects for translation to clinical practice.

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Engineered three-dimensional scaffolds boost bone regeneration in osteonecrosis.

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The ideal properties of three-dimensional scaffolds for osteonecrosis treatment are discussed.

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Bioactive factors-functionalized three-dimensional scaffolds are promising bone regeneration devices for osteonecrosis management.

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The challenges and opportunities of engineered three-dimensional scaffolds for osteonecrosis therapy are predicted.

Engineered human myocardium with local release of angiogenic proteins improves vascularization and cardiac function in injured rat hearts

Heart regeneration after myocardial infarction requires new cardiomyocytes and a supportive vascular network. Here, we evaluate the efficacy of localized delivery of angiogenic factors from biomaterials within the implanted muscle tissue to guide growth of a more dense, organized, and perfused vascular supply into implanted engineered human cardiac tissue on an ischemia/reperfusion injured rat heart. We use large, aligned 3-dimensional engineered tissue with cardiomyocytes derived from human induced pluripotent stem cells in a collagen matrix that contains dispersed alginate microspheres as local protein depots. Release of angiogenic growth factors VEGF and bFGF in combination with morphogen sonic hedgehog from the microspheres into the local microenvironment occurs from the epicardial implant site. Analysis of the 3D vascular network in the engineered tissue via Microfil® perfusion and microCT imaging at 30 days shows increased volumetric network density with a wider distribution of vessel diameters, proportionally increased branching and length, and reduced tortuosity. Global heart function is increased in the angiogenic factor-loaded cardiac implants versus sham. These findings demonstrate for the first time the efficacy of a combined remuscularization and revascularization therapy for heart regeneration after myocardial infarction.

Evaluation of BMP-2 and VEGF loaded 3D printed hydroxyapatite composite scaffolds with enhanced osteogenic capacity in vitro and in vivo

Large-sized bone defect repair is a challenging task in orthopedic surgery. Porous scaffolds with controlled release of growth factors have been investigated for many years. In this study, a hydroxyapatite composite scaffold was prepared by 3D printing at low temperature and coating with layer-by-layer (LBL) assembly. Bone morphogenic protein-2 (BMP-2) and vascular endothelial growth factors (VEGF) were loaded into the composite scaffolds. The release of dual growth factors was analyzed in vitro. The cell growth and osteogenic differentiation were assessed by culturing MC3T3-E1 cells onto the scaffolds. In an established rabbit model of critical-sized calvarial defect (15 mm in diameter), the osteogenic and angiogenic properties after implantation of scaffolds were evaluated by micro-computed tomography (micro-CT) and stained sections. Our results showed that the scaffolds possessed well-designed porous structure and could release two growth factors in a sustained way. The micro-CT analysis showed that the scaffolds with BMP-2/VEGF could accelerate new bone formation. Findings of immunochemical staining of collagen type I and lectin indicated that better osteogenic and angiogenic properties induced by BMP-2 and VEGF. These results suggested that the novel composite scaffolds combined with BMP-2/VEGF had both osteogenic and angiogenic abilities which could enhance new bone formation with good quality. Thus, the combination of 3D printed scaffolds loaded with BMP-2/VEGF might provide a potential solution for bone repair and regeneration in clinical applications.

Evolving applications of the egg: chorioallantoic membrane assay and ex vivo organotypic culture of materials for bone tissue engineering

The chick chorioallantoic membrane model has been around for over a century, applied in angiogenic, oncology, dental and xenograft research. Despite its often perceived archaic, redolent history, the chorioallantoic membrane assay offers new and exciting opportunities for material and growth factor evaluation in bone tissue engineering. Currently, superior/improved experimental methodology for the chorioallantoic membrane assay are difficult to identify, given an absence of scientific consensus in defining experimental approaches, including timing of inoculation with materials and the analysis of results. In addition, critically, regulatory and welfare issues impact upon experimental designs. Given such disparate points, this review details recent research using the ex vivo chorioallantoic membrane assay and the ex vivo organotypic culture to advance the field of bone tissue engineering, and highlights potential areas of improvement for their application based on recent developments within our group and the tissue engineering field.

Spatial immobilization of endogenous growth factors to control vascularization in bone tissue engineering

An engineered biofunctional system comprises endogenous BMP-2 and VEGF bound in a parallel pattern. It successfully enabled obtaining the spatial osteogenic and angiogenic differentiation of human hBM-MSCs under basal culture conditions.

Dual Roles of the AMP-Activated Protein Kinase Pathway in Angiogenesis

Angiogenesis plays important roles in development, stress response, wound healing, tumorigenesis and cancer progression, diabetic retinopathy, and age-related macular degeneration. It is a complex event engaging many signaling pathways including vascular endothelial growth factor (VEGF), Notch, transforming growth factor-beta/bone morphogenetic proteins (TGF-β/BMPs), and other cytokines and growth factors. Almost all of them eventually funnel to two crucial molecules, VEGF and hypoxia-inducing factor-1 alpha (HIF-1α) whose expressions could change under both physiological and pathological conditions. Hypoxic conditions stabilize HIF-1α, while it is upregulated by many oncogenic factors under normaxia. HIF-1α is a critical transcription activator for VEGF. Recent studies have shown that intracellular metabolic state participates in regulation of sprouting angiogenesis, which may involve AMP-activated protein kinase (AMPK). Indeed, AMPK has been shown to exert both positive and negative effects on angiogenesis. On the one hand, activation of AMPK mediates stress responses to facilitate autophagy which stabilizes HIF-1α, leading to increased expression of VEGF. On the other hand, AMPK could attenuate angiogenesis induced by tumor-promoting and pro-metastatic factors, such as the phosphoinositide 3-kinase /protein kinase B (Akt)/mammalian target of rapamycin (PI3K/Akt/mTOR), hepatic growth factor (HGF), and TGF-β/BMP signaling pathways. Thus, this review will summarize research progresses on these two opposite effects and discuss the mechanisms behind the discrepant findings.

Mechanistic insight into activation of MAPK signaling by pro-angiogenic factors

Background

Angiogenesis is important in physiological and pathological conditions, as blood vessels provide nutrients and oxygen needed for tissue growth and survival. Therefore, targeting angiogenesis is a prominent strategy in both tissue engineering and cancer treatment. However, not all of the approaches to promote or inhibit angiogenesis lead to successful outcomes. Angiogenesis-based therapies primarily target pro-angiogenic factors such as vascular endothelial growth factor-A (VEGF) or fibroblast growth factor (FGF) in isolation. However, pre-clinical and clinical evidence shows these therapies often have limited effects. To improve therapeutic strategies, including targeting FGF and VEGF in combination, we need a quantitative understanding of the how the promoters combine to stimulate angiogenesis.

Results

In this study, we trained and validated a detailed mathematical model to quantitatively characterize the crosstalk of FGF and VEGF intracellular signaling. This signaling is initiated by FGF binding to the FGF receptor 1 (FGFR1) and heparan sulfate glycosaminoglycans (HSGAGs) or VEGF binding to VEGF receptor 2 (VEGFR2) to promote downstream signaling. The model focuses on FGF- and VEGF-induced mitogen-activated protein kinase (MAPK) signaling and phosphorylation of extracellular regulated kinase (ERK), which promotes cell proliferation. We apply the model to predict the dynamics of phosphorylated ERK (pERK) in response to the stimulation by FGF and VEGF individually and in combination. The model predicts that FGF and VEGF have differential effects on pERK. Additionally, since VEGFR2 upregulation has been observed in pathological conditions, we apply the model to investigate the effects of VEGFR2 density and trafficking parameters. The model predictions show that these parameters significantly influence the response to VEGF stimulation.

Conclusions

The model agrees with experimental data and is a framework to synthesize and quantitatively explain experimental studies. Ultimately, the model provides mechanistic insight into FGF and VEGF interactions needed to identify potential targets for pro- or anti-angiogenic therapies.

Electronic supplementary material

The online version of this article (10.1186/s12918-018-0668-5) contains supplementary material, which is available to authorized users.

Approaches to therapeutic angiogenesis for ischemic heart disease

Ischemic heart disease (IHD) is caused by the narrowing of arteries that work to provide blood, nutrients, and oxygen to the myocardial tissue. The worldwide epidemic of IHD urgently requires innovative treatments despite the significant advances in medical, interventional, and surgical therapies for this disease. Angiogenesis is a physiological and pathophysiological process that initiates vascular growth from pre-existing blood vessels in response to a lack of oxygen. This process occurs naturally over time and has encouraged researchers and clinicians to investigate the outcomes of accelerating or enhancing this angiogenic response as an alternative IHD therapy. Therapeutic angiogenesis has been shown to revascularize ischemic heart tissue, reduce the progression of tissue infarction, and evade the need for invasive surgical procedures or tissue/organ transplants. Several approaches, including the use of proteins, genes, stem/progenitor cells, and various combinations, have been employed to promote angiogenesis. While clinical trials for these approaches are ongoing, microvesicles and exosomes have recently been investigated as a cell-free approach to stimulate angiogenesis and may circumvent limitations of using viable cells. This review summarizes the approaches to accomplish therapeutic angiogenesis for IHD by highlighting the advances and challenges that addresses the applicability of a potential pro-angiogenic medicine.

Detection of Pro- and Antiangiogenic Factors in the Human Sclera

PURPOSE

Avascular tissues can be used to identify antilymph- or antihemangiogenic factors. The human sclera-the outer covering layer of the eye, lacks lymphatic vessels and contains only a superficial network of blood vessels and was used here to identify endogenous antiangiogenic factors.

METHODS

Expression levels of a panel of 96 known pro- and antiangiogenic factors were analyzed in 12 scleral or conjunctival control samples from normal human donors using real-time PCR. In vitro, scleral homogenate was cocultured with blood- and lymphatic endothelial cells (BECs and LECs) and immunohistochemistry was performed of scleral fibroblasts and BECs.

RESULTS

Three antiangiogenic factors were significantly upregulated in the human sclera compared to the conjunctiva, including FBLN5 (fibulin 5), SERPINF1 (serpin peptidase inhibitor, clade F, member 1 = pigment epithelium derived factor) and TIMP2 (Tissue inhibitor of metalloproteinases 2). Six proangiogenic factors were significantly downregulated in the sclera, including FLT4 (Fms-related tyrosine kinase 4=VEGF-R3), HGF (hepatocyte growth factor), KIT (CD117 / c-kit), PROX1 (prospero homeobox 1), SEMA3F (semaphorin-3F) and TGFA (transforming growth factor alpha). In vitro, scleral homogenate inhibited the growth of both BECs and LECs. Immunohistochemistry labeling of three major antiangiogenic factors from scleral tissue confirmed TIMP3 and PEDF expression both in scleral fibroblasts and in blood endothelial cells, whereas TIMP2 was not detectable.

CONCLUSION

Balancing anti- and proangiogenic factors actively regulates human scleral avascularity, inhibits endothelial cell growth in vitro, and thus may help maintaining the vascular privilege of the inner eye.

Dual release of growth factor from nanocomposite fibrous scaffold promotes vascularisation and bone regeneration in rat critical sized calvarial defect

A promising strategy for augmenting bone formation involves the local delivery of multiple osteoinductive and vasculogenic growth factors. However, success depends on sustained growth factor release and its appropriate combination to induce stem cells and osteogenic cells at the bony site. Herein, we have developed a nanocomposite fibrous scaffold loaded with fibroblast growth factor 2 (FGF2), vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP2) and its ability to promote vascularisation and bone regeneration in critical sized calvarial defect was compared to the scaffold with VEGF + BMP2 and FGF2 + BMP2. Simple loading of growth factors on the scaffold could provide a differential release pattern, both in vitro and in vivo (VEGF release for 1 week where as BMP2 and FGF2 release for 3 weeks). Among all the groups, dual growth factor loaded scaffold (VEGF + BMP2 & FGF2 + BMP2) enhanced vascularisation and new bone formation, but there was no difference between FGF2 and VEGF loaded scaffolds although its release pattern was different. FGF2 mainly promoted stem cell migration, whereas VEGF augmented new blood vessel formation at the defect site. This study suggests that biomimetic nanocomposite scaffold is a promising growth factor delivery vehicle to improve bone regeneration in critical sized bone defects.

STATEMENT OF SIGNIFICANCE

Many studies have shown the effect of growth factors like VEGF-BMP2 or FGF2-BMP2 in enhancing bone formation in critical sized defects, but there are no reports that demonstrate the direct comparison of VEGF-BMP2 and FGF2-BMP2. In this study, we have developed a nanocomposite fibrous scaffold that could differentially release growth factors like VEGF, BMP2 and FGF2 (VEGF release for 1 week where as BMP2 and FGF2 release for 3 weeks), which in turn promoted neovascularisation and new bone formation in critical sized defects. There was no difference in vascularisation and bone formation induced by VEGF + BMP2 or FGF2 + BMP2. The growth factor was loaded in a simple manner, which would ensure ease of use for the end-user, especially for the surgeons treating a patient in an operating room.

Current advances for bone regeneration based on tissue engineering strategies

Bone tissue engineering (BTE) is a rapidly developing strategy for repairing critical-sized bone defects to address the unmet need for bone augmentation and skeletal repair. Effective therapies for bone regeneration primarily require the coordinated combination of innovative scaffolds, seed cells, and biological factors. However, current techniques in bone tissue engineering have not yet reached valid translation into clinical applications because of several limitations, such as weaker osteogenic differentiation, inadequate vascularization of scaffolds, and inefficient growth factor delivery. Therefore, further standardized protocols and innovative measures are required to overcome these shortcomings and facilitate the clinical application of these techniques to enhance bone regeneration. Given the deficiency of comprehensive studies in the development in BTE, our review systematically introduces the new types of biomimetic and bifunctional scaffolds. We describe the cell sources, biology of seed cells, growth factors, vascular development, and the interactions of relevant molecules. Furthermore, we discuss the challenges and perspectives that may propel the direction of future clinical delivery in bone regeneration.

VEGF/BMP-2 loaded three-dimensional model for enhanced angiogenic and odontogenic potential of dental pulp stem cells

AIM

To investigate the proliferation and differentiation potential of human dental pulp stem cells (DPSCs) in a three-dimensional culture model (TDM) by incorporation of VEGF and BMP-2.

METHODOLOGY

TDM was established using fibrin gel (fg) as a soft tissue matrix and demineralized dentine disc (dd) as a hard tissue matrix. DPSCs and vascular endothelial growth factor (VEGF) were encapsulated in fibrin gel (fg-VEGF) and then inserted into bone morphogenetic protein (BMP-2)-coated demineralized dentine discs (dd-BMP-2). DPSCs were incubated for 28 days in various fg/dd combinations in the absence or presence of VEGF and BMP-2. Proliferation and morphology of DPSCs in fibrin gel were analysed using MTT and Live&Dead assays. Release profiles of VEGF and BMP-2 from fibrin gel and dentine discs were quantified using ELISA, and the expressions of angiogenic and odontogenic differentiation markers were determined with RT-qPCR analysis. Data were analysed statistically using Wilcoxon signed rank tests, Kruskal-Wallis tests with Mann-Whitney U tests and Bonferroni adjustment. The level of significance was set at P < 0.05.

RESULTS

DPSCs were able to proliferate and showed interconnected cellular elongations in fibrin gel depending on fibrinogen concentration whilst monolayer control group showed typical fibroblast-like cell morphology. Encapsulating of VEGF in fibrin gel and BMP-2 in gelatin that was used to coat dentine discs allowed the controlled releases of growth factors, which induced angiogenic and odontogenic gene expressions by DPSCs. Higher expressions of PECAM as an angiogenic factor, and BSP, DMP-1, OCN and CBFA as odontogenic factors, were observed in TDM as compared to the other fg/dd combinations and the monolayer control group (P < 0.05).

CONCLUSIONS

TDM consisting of fibrin gel and dentine matrix allowed cell-cell interactions. TDM was highly effective in delivering both VEGF and BMP-2 that enhanced the angiogenic and odontogenic potential of DPSCs.

Platelet-Rich Plasma Derived Growth Factors Contribute to Stem Cell Differentiation in Musculoskeletal Regeneration

Stem cell treatment and platelet-rich plasma (PRP) therapy are two significant issues in regenerative medicine. Stem cells such as bone marrow mesenchymal stem cells, adipose-derived stem cells and periodontal ligament stem cells can be successfully applied in the field of tissue regeneration. PRP, a natural product isolated from whole blood, can secrete multiple growth factors (GFs) for regulating physiological activities. These GFs can stimulate proliferation and differentiation of different stem cells in injury models. Therefore, combination of both agents receives wide expectations in regenerative medicine, especially in bone, cartilage and tendon repair. In this review, we thoroughly discussed the interaction and underlying mechanisms of PRP derived GFs with stem cells, and assessed their functions in cell differentiation for musculoskeletal regeneration.

Sequential delivery of VEGF, FGF-2 and PDGF from the polymeric system enhance HUVECs angiogenesis in vitro and CAM angiogenesis

Angiogenesis is an organized series of events, beginning with vessel destabilization, followed by endothelial cell re-organization, and ending with vessel maturation. The formation of a mature vascular network requires precise spatial and temporal regulation of a large number of angiogenic factors, including vascular endothelial growth factor (VEGF), basic fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor (PDGF). VEGF aids in vascular permeability and endothelial cell recruitment, FGF-2 activates endothelial cell proliferation and migration while PDGF stimulates vascular stability. Accordingly, VEGF may inhibit vessel stabilization while PDGF may inhibit endothelial cell recruitment. Therefore, a new polymeric system was prepared by the supercritical carbon dioxide foaming technology, which realized sequential delivery of two or more growth factors with the controlled dose and rate. Increased release of VEGF (71.10%) and FGF-2 (69.76%) compared to PDGF (43.17%) was observed for the first 7 days. Thereafter, up till 21 days, an increased rate of release of BMP-2 compared to VEGF 165 was observed. The effects of PDGF-PLAms/VEGF-FGF-2-PLGA scaffolds on angiogenesis were investigated by human umbilical vein endothelial cells (HUVECs) angiogenic differentiation in vitro and chorioallantoic membrane (CAM) angiogenesis in vivo. Sequential delivery of VEGF, FGF-2 and PDGF from structural polymer scaffolds with distinct kinetics resulted in significant angiogenic differentiation of HUVECs and rapid formation of mature vascular networks in chorioallantoic membrane. This study reported a composite scaffold with distinct release kinetics, and these results clearly indicated the importance of sequential delivery of multiple growth factors in tissue regeneration and engineering.

Fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGFA) synergistically promote steroidogenesis and survival of cultured buffalo granulosa cells

The present study investigated the combined effect of fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGF-A) on estradiol (E₂) secretion and relative abundance of mRNA for aromatase enzyme (CYP19A1), proliferating cell nuclear antigen (PCNA) and BCL-2 associated X protein (BAX) in cultured buffalo granulosa cells (GCs). Follicles were isolated and classified into four groups based on size and E₂ concentration in follicular fluid (FF): Small, 4-6mm diameter, E₂<0.5ng/ml; Medium, 7-9mm, E₂=0.5-5ng/ml; Large, 10-13mm, E₂=5-40ng/ml; Preovulatory (PFs), >14mm, E₂>180ng/ml. The GCs of PF were cultured in 24 well cell culture plates and allowed to become 75-80% confluent. Then cultured GCs were treated with FGF2 (200ng/ml) and VEGF-A (100ng/ml) separately and in combination for three incubation periods (24, 48 and 72h). Estradiol secretion was greater in GCs treated with FGF2+VEGF-A compared to FGF2 or VEGF-A at all incubation periods and was greatest (P<0.05) at 72h of incubation. The relative abundance of CYP19A1 and PCNA mRNA were relatively consistent with the amount E₂ secretion. In contrast, the relative abundance of Bax mRNA was less in GCs treated with the combination of FGF2 and VEGF-A as compared to either FGF2 or VEGF-A alone and the least concentration (P<0.05) was at 72h of incubation. Findings with use of immunocytochemistry of cells treated with these factors were consistent to the relative abundance of mRNA transcript for the factor. The present findings indicate that FGF2 and VEGF-A may function in a synergistic manner to promote steroidogenesis and survival of cultured buffalo GCs.

The role of endoglin in post-ischemic revascularization

Following arterial occlusion, blood vessels respond by forming a new network of functional capillaries (angiogenesis), by reorganizing preexisting capillaries through the recruitment of smooth muscle cells to generate new arteries (arteriogenesis) and by growing and remodeling preexisting collateral arterioles into physiologically relevant arteries (collateral development). All these processes result in the recovery of organ perfusion. The importance of endoglin in post-occlusion reperfusion is sustained by several observations: (1) endoglin expression is increased in vessels showing active angiogenesis/remodeling; (2) genetic endoglin haploinsufficiency in humans causes deficient angiogenesis; and (3) the reduction of endoglin expression by gene disruption or the administration of endoglin-neutralizing antibodies reduces angiogenesis and revascularization. However, the precise role of endoglin in the several processes associated with revascularization has not been completely elucidated and, in some cases, the function ascribed to endoglin by different authors is controversial. The purpose of this review is to organize in a critical way the information available for the role of endoglin in several phenomena (angiogenesis, arteriogenesis and collateral development) associated with post-ischemic revascularization.

Dose Dependent Dual Effect of Baicalin and Herb Huang Qin Extract on Angiogenesis

Huang Qin (root of Scutellaria baicalensis) is a widely used herb in different countries for adjuvant therapy of inflammation, diabetes, hypertension, different kinds of cancer and virus related diseases. Baicalin is the main flavonoid in this herb and has been extensively studied for 30 years. The angiogenic effect of herb Huang Qin extract and baicalin was found 13 years ago, however, the results were controversial with pro-angiogenic effect in some studies and anti-angiogenic effect in others. In this paper, the angiogenic effect of baicalin, its aglycone form baicalein and aqueous extract of Huang Qin was studied in chick embryo chorioallantoic membrane (CAM) model. Dose dependent dual effect was found in both aqueous extract and baicalin, but not in baicalein, in which only inhibitory effect was observed. In order to reveal the cellular and molecular mechanism of how baicalin and baicalein affect angiogenesis, cell proliferation and programmed cell death assays were performed in treated CAM. In addition, quantitative PCR array including 84 angiogenesis related genes was used to detect high and low dosage of baicalin and baicalein responsive genes. Low dose baicalin increased cell proliferation in developing blood vessels through upregulation of multiple angiogenic genes expression, but high dose baicalin induced cell death, performing inhibitory effect on angiogenesis. Both high and low dose of baicalein down regulated the expression of multiple angiogenic genes, decreased cell proliferation, and leads to inhibitory effects on angiogenesis.

Promotive effects of bone morphogenetic protein 2 on angiogenesis in hepatocarcinoma via multiple signal pathways

The effects of Bone morphogenetic protein 2 (BMP-2) on the angiogenesis of hepatocellular carcinoma have not yet been observed and its molecular mechanisms is not clear. We first constructed the recombinant lentivirus vectors expressing small hairpin RNA against BMP-2 gene (LV-SH-BMP2) and the recombinant lentivirus vectors over-expressing BMP-2 (overexpression-LV-BMP2), and then the two recombinant lentivirus vectors were respectively transfected into Hep G2 cells. The Hep G2 cells transfected with LV-SH-BMP2 or overexpression-LV-BMP2 were respectively co-cultured with human umbilical vein endothelial cells (HUVECs) to observe the effects of BMP-2 on HUVECs. The effect of BMP-2 on tumor microvessel density (MVD) was examined. The abilities of proliferation, migration and angiogenesis were significantly inhibited in the HUVECs co-cultured with BMP-2 knockdown Hep G2 (all P < 0.05), but significantly enhanced in the HUVECs co-cultured with BMP-2 overexpression Hep G2 (all P < 0.05). MVD was significantly increased in overexpression-LV-BMP2-transfected Hep G2 tumor, but decreased in LV-SH-BMP2-transfected Hep G2 tumors. The protein expressions of VEGF, p-P38, p-ERK, p-AKT, p-m-TOR were significantly increased after BMP-2 over-expression, or significantly decreased after BMP-2 knockdown (all P < 0.05). These results reveal that BMP-2 can enhance HUVEC proliferation, migration and angiogenesis through P38, ERK and Akt/m-TOR pathway.

Four-week histologic evaluation of grafted calvarial defects with adjunctive hyperbaric oxygen therapy in rats

Purpose

The aim of this study was to characterize the healing in the grafted calvarial defects of rats after adjunctive hyperbaric oxygen therapy.

Methods

Twenty-eight male Sprague-Dawley rats (body weight, 250–300 g) were randomly divided into two treatment groups: with hyperbaric oxygen therapy (HBO; n=14) and without HBO (NHBO; n=14). Each group was further subdivided according to the bone substitute applied: biphasic calcium phosphate (BCP; n=7) and surface-modified BCP (mBCP; n=7). The mBCP comprised BCP coated with Escherichia-coli-derived recombinant human bone morphogenetic protein-2 (ErhBMP-2) and epigallocatechin-3-gallate (EGCG). Two symmetrical circular defects (6-mm diameter) were created in the right and left parietal bones of each animal. One defect was assigned as a control defect and received no bone substitute, while the other defect was filled with either BCP or mBCP. The animals were allowed to heal for 4 weeks, during which those in the HBO group underwent 5 sessions of HBO. At 4 weeks, the animals were sacrificed, and the defects were harvested for histologic and histomorphometric analysis.

Results

Well-maintained space was found in the grafted groups. Woven bone connected to and away from the defect margin was formed. More angiogenesis was found with HBO and EGCG/BMP-2 (P<0.05). None of the defects achieved complete defect closure. Increased new bone formation with HBO or EGCG/BMP-2 was evident in histologic evaluation, but it did not reach statistical significance in histometric analysis. A synergic effect between HBO and EGCG/BMP-2 was not found.

Conclusions

Within the limitations of this study, the present findings indicate that adjunctive HBO and EGCG/BMP-2 could be beneficial for new bone formation in rat calvarial defects.

IGF-1-containing multi-layered collagen-fibrin hybrid scaffolds for bladder tissue engineering

Clinical success of bladder reconstructive procedures could be promoted by the availability of functional biomaterials. In this study, we have developed a multi-layered scaffold consisting of a bioactive fibrin layer laminated between two collagen sheets all having undergone plastic compression. With this construct we performed bladder augmentation in a nude rat model after partial bladder excision and evaluated the morphological and functional behavior of the implant. The fibrin was functionalized with a recombinant human insulin-like growth factor-1 (IGF-1) variant that covalently binds fibrin during polymerization and has a matrix metalloproteinase-cleavage insert to enable cell-mediated release. The purified IGF-1 variant showed similar bioactivity in vitro compared to commercially available wild type (wt) IGF-1, inducing receptor phosphorylation and induction of human smooth muscle cell proliferation. In vivo, the multi-layered bioactive collagen-fibrin scaffolds loaded with the IGF-1 variant triggered dose-dependent functional host smooth muscle cell invasion and bundle formation with re-urothelialization 4weeks after surgery in a rat model.

STATEMENT OF SIGNIFICANCE

The design of new bio-functional scaffolds that can be employed for bladder reconstructive procedures is a growing focus in the field of tissue engineering. In this study, a fibrin binding form of human insulin-like growth factor-1 (IGF-1) was produced and used to functionalize a multi-layered collagen-fibrin scaffold consisting of bioactive fibrin layer, sandwiched between two collagen gels. An effective dosage of our IGF-1 variant was successfully determined via a nude rat bladder model, which may play a critical role in estimating its therapeutic dosage in clinical trials. Thus, this new bioactive scaffold may offer an advanced approach to accelerate bladder regeneration.

Sustained dual release of placental growth factor-2 and bone morphogenic protein-2 from heparin-based nanocomplexes for direct osteogenesis

OBJECTIVE

To compare the direct osteogenic effect between placental growth factor-2 (PlGF-2) and bone morphogenic protein-2 (BMP-2).

METHODS

Three groups of PlGF-2/BMP-2-loaded heparin-N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) nanocomplexes were prepared: those with 0.5 μg PlGF-2; with 1.0 μg BMP-2; and with 0.5 μg PlGF-2 combined with 1.0 μg BMP-2. The loading efficiencies and release profiles of these growth factors (GFs) in this nanocomplex system were quantified using enzyme-linked immunosorbent assay, their biological activities were evaluated using cell counting kit-8, cell morphology, and cell number counting assays, and their osteogenic activities were quantified using alkaline phosphatase and Alizarin Red S staining assays.

RESULTS

The loading efficiencies were more than 99% for the nanocomplexes loaded with just PlGF-2 and for those loaded with both PlGF-2 and BMP-2. For the nanocomplex loaded with just BMP-2, the loading efficiency was more than 97%. About 83%-84% of PlGF-2 and 89%-91% of BMP-2 were stably retained on the nanocomplexes for at least 21 days. In in vitro biological assays, PlGF-2 exhibited osteogenic effects comparable to those of BMP-2 despite its dose in the experiments being lower than that of BMP-2. Moreover, the results implied that heparin-based nanocomplexes encapsulating two GFs have enhanced potential in the enhancement of osteoblast function.

CONCLUSION

PlGF-2-loaded heparin-HTCC nanocomplexes may constitute a promising system for bone regeneration. Moreover, the dual delivery of PlGF-2 and BMP-2 appears to have greater potential in bone tissue regeneration than the delivery of either GFs alone.

Dual Role of Mesenchymal Stem Cells Allows for Microvascularized Bone Tissue-Like Environments in PEG Hydrogels

In vitro engineered tissues which recapitulate functional and morphological properties of bone marrow and bone tissue will be desirable to study bone regeneration under fully controlled conditions. Among the key players in the initial phase of bone regeneration are mesenchymal stem cells (MSCs) and endothelial cells (ECs) that are in close contact in many tissues. Additionally, the generation of tissue constructs for in vivo transplantations has included the use of ECs since insufficient vascularization is one of the bottlenecks in (bone) tissue engineering. Here, 3D cocultures of human bone marrow derived MSCs (hBM-MSCs) and human umbilical vein endothelial cells (HUVECs) in synthetic biomimetic poly(ethylene glycol) (PEG)-based matrices are directed toward vascularized bone mimicking tissue constructs. In this environment, bone morphogenetic protein-2 (BMP-2) or fibroblast growth factor-2 (FGF-2) promotes the formation of vascular networks. However, while osteogenic differentiation is achieved with BMP-2, the treatment with FGF-2 suppressed osteogenic differentiation. Thus, this study shows that cocultures of hBM-MSCs and HUVECs in biological inert PEG matrices can be directed toward bone and bone marrow-like 3D tissue constructs.

A review on carrier systems for bone morphogenetic protein-2

Bone morphogenetic protein-2 (BMP-2) has unique bone regeneration property. The powerful osteoinductive nature makes it considered as second line of therapy in nonunion bone defect. A large number of carriers and delivery systems made up of different materials have been investigated for controlled and sustained release of BMP-2. The delivery systems are in the form of hydrogel, microsphere, nanoparticles, and fibers. The carriers used for the delivery are made up of metals, ceramics, polymers, and composites. Implantation of these protein-loaded carrier leads to cell adhesion, degradation which eventually releases the drug/protein at site specific. But, problems like ectopic growth, lesser protein delivery, inactivation of the protein are reported in the available carrier systems. Therefore, it is need of an hour to modify the available carrier systems as well as explore other biomaterials with desired properties. In this review, all the reported carrier systems made of metals, ceramics, polymers, composites are evaluated in terms of their processing conditions, loading capacity and release pattern of BMP-2. Along with these biomaterials, the attempts of protein modification by adding some functional group to BMP-2 or extracting functional peptides from the protein to achieve the desired effect, is also evaluated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 904-925, 2017.