Angiogenesis induced by novel peptides selected from a phage display library by screening human vascular endothelial cells under different physiological conditions

Peptide-Based Biomaterials for Bone and Cartilage Regeneration

The healing of osteochondral defects (OCDs) that result from injury, osteochondritis, or osteoarthritis and bear lesions in the cartilage and bone, pain, and loss of joint function in middle- and old-age individuals presents challenges to clinical practitioners because of non-regenerative cartilage and the limitations of current therapies. Bioactive peptide-based osteochondral (OC) tissue regeneration is becoming more popular because it does not have the immunogenicity, misfolding, or denaturation problems associated with original proteins. Periodically, reviews are published on the regeneration of bone and cartilage separately; however, none of them addressed the simultaneous healing of these tissues in the complicated heterogeneous environment of the osteochondral (OC) interface. As regulators of cell adhesion, proliferation, differentiation, angiogenesis, immunomodulation, and antibacterial activity, potential therapeutic strategies for OCDs utilizing bone and cartilage-specific peptides should be examined and investigated. The main goal of this review was to study how they contribute to the healing of OCDs, either alone or in conjunction with other peptides and biomaterials.

Biological aspects in controlling angiogenesis: current progress

All living beings continue their life by receiving energy and by excreting waste products. In animals, the arteries are the pathways of these transfers to the cells. Angiogenesis, the formation of the arteries by the development of pre-existed parental blood vessels, is a phenomenon that occurs naturally during puberty due to certain physiological processes such as menstruation, wound healing, or the adaptation of athletes' bodies during exercise. Nonetheless, the same life-giving process also occurs frequently in some patients and, conversely, occurs slowly in some physiological problems, such as cancer and diabetes, so inhibiting angiogenesis has been considered to be one of the important strategies to fight these diseases. Accordingly, in tissue engineering and regenerative medicine, the highly controlled process of angiogenesis is very important in tissue repairing. Excessive angiogenesis can promote tumor progression and lack of enough angiogensis can hinder tissue repair. Thereby, both excessive and deficient angiogenesis can be problematic, this review article introduces and describes the types of factors involved in controlling angiogenesis. Considering all of the existing strategies, we will try to lay out the latest knowledge that deals with stimulating/inhibiting the angiogenesis. At the end of the article, owing to the early-reviewed mechanical aspects that overshadow angiogenesis, the strategies of angiogenesis in tissue engineering will be discussed.

Detection of cancer stem cells by EMT-specific biomarker-based peptide ligands

The occurrence of epithelial-mesenchymal transition (EMT) within tumors, which enables invasion and metastasis, is linked to cancer stem cells (CSCs) with drug and radiation resistance. We used two specific peptides, F7 and SP peptides, to detect EMT derived cells or CSCs. Human tongue squamous carcinoma cell line-SAS transfected with reporter genes was generated and followed by spheroid culture. A small molecule inhibitor-Unc0642 and low-dose ionizing radiation (IR) were used for induction of EMT. Confocal microscopic imaging and fluorescence-activated cell sorting analysis were performed to evaluate the binding ability and specificity of peptides. A SAS xenograft mouse model with EMT induction was established for assessing the binding affinity of peptides. The results showed that F7 and SP peptides not only specifically penetrated into cytoplasm of SAS cells but also bound to EMT derived cells and CSCs with high nucleolin and vimentin expression. In addition, the expression of CSC marker and the binding of peptides were increased in tumors isolated from Unc0642/IR-treated groups. Our study demonstrates the potential of these peptides for detecting EMT derived cells or CSCs and might provide an alternative isolation method for these subpopulations within the tumor in the future.

The unfolded protein response in ischemic heart disease

Ischemic heart disease is a severe stress condition that causes extensive pathological alterations and triggers cardiac cell death. Accumulating evidence suggests that the unfolded protein response (UPR) is strongly induced by myocardial ischemia. The UPR is an evolutionarily conserved cellular response to cope with protein-folding stress, from yeast to mammals. Endoplasmic reticulum (ER) transmembrane sensors detect the accumulation of unfolded proteins and stimulate a signaling network to accommodate unfolded and misfolded proteins. Distinct mechanisms participate in the activation of three major signal pathways, viz. protein kinase RNA-like ER kinase, inositol-requiring protein 1, and activating transcription factor 6, to transiently suppress protein translation, enhance protein folding capacity of the ER, and augment ER-associated degradation to refold denatured proteins and restore cellular homeostasis. However, if the stress is severe and persistent, the UPR elicits inflammatory and apoptotic pathways to eliminate terminally affected cells. The ER is therefore recognized as a vitally important organelle that determines cell survival or death. Recent studies indicate the UPR plays critical roles in the pathophysiology of ischemic heart disease. The three signaling branches may elicit distinct but overlapping effects in cardiac response to ischemia. Here, we outline the findings and discuss the mechanisms of action and therapeutic potentials of the UPR in the treatment of ischemic heart disease.

Peptides for bone tissue engineering

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

Enzymatically-responsive pro-angiogenic peptide-releasing poly(ethylene glycol) hydrogels promote vascularization in vivo

Therapeutic angiogenesis holds great potential for a myriad of tissue engineering and regenerative medicine approaches. While a number of peptides have been identified with pro-angiogenic behaviors, therapeutic efficacy is limited by poor tissue localization and persistence. Therefore, poly(ethylene glycol) hydrogels providing sustained, enzymatically-responsive peptide release were exploited for peptide delivery. Two pro-angiogenic peptide drugs, SPARC113 and SPARC118, from the Secreted Protein Acidic and Rich in Cysteine, were incorporated into hydrogels as crosslinking peptides flanked by matrix metalloproteinase (MMP) degradable substrates. In vitro testing confirmed peptide drug bioactivity requires sustained delivery. Furthermore, peptides retain bioactivity with residual MMP substrates present after hydrogel release. Incorporation into hydrogels achieved enzymatically-responsive bulk degradation, with peptide release in close agreement with hydrogel mass loss and released peptides retaining bioactivity. Interestingly, SPARC113 and SPARC118-releasing hydrogels had significantly different degradation time constants in vitro (1.16 and 8.77×10(-2) h(-1), respectively), despite identical MMP degradable substrates. However, upon subcutaneous implantation, both SPARC113 and SPARC118 hydrogels exhibited similar degradation constants of ~1.45×10(-2) h(-1), and resulted in significant ~1.65-fold increases in angiogenesis in vivo compared to controls. Thus, these hydrogels represent a promising pro-angiogenic approach for applications such as tissue engineering and ischemic tissue disorders.

Depot-Based Delivery Systems for Pro-Angiogenic Peptides: A Review

Insufficient vascularization currently limits the size and complexity for all tissue engineering approaches. Additionally, increasing or re-initiating blood flow is the first step toward restoration of ischemic tissue homeostasis. However, no FDA-approved pro-angiogenic treatments exist, despite the many pre-clinical approaches that have been developed. The relatively small size of peptides gives advantages over protein-based treatments, specifically with respect to synthesis and stability. While many pro-angiogenic peptides have been identified and shown promising results in vitro and in vivo, the majority of biomaterials developed for pro-angiogenic drug delivery focus on protein delivery. This narrow focus limits pro-angiogenic therapeutics as peptides, similar to proteins, suffer from poor pharmacokinetics in vivo, necessitating the development of controlled release systems. This review discusses pro-angiogenic peptides and the biomaterials delivery systems that have been developed, or that could easily be adapted for peptide delivery, with a particular focus on depot-based delivery systems.

RoY peptide-modified chitosan-based hydrogel to improve angiogenesis and cardiac repair under hypoxia

Myocardial infarction (MI) still represents the "Number One Killer" in the world. The lack of functional vasculature of the infracted myocardium under hypoxia is one of the main problems for cardiac repair. In this study, a thermosensitive chitosan chloride-RoY (CSCl-RoY) hydrogel was developed to improve angiogenesis under hypoxia after MI. First, RoY peptides were conjugated onto the CSCl chain via amide linkages, and our data show that the conjugation of RoY peptide to CSCl does not interfere with the temperature sensitivity. Then, the effect of CSCl-RoY hydrogels on vascularization in vitro under hypoxia was investigated using human umbilical vein endothelial cells (HUVECs). Results show that CSCl-RoY hydrogels can promote the survival, proliferation, migration and tube formation of HUVECs under hypoxia compared with CSCl hydrogel. Further investigations suggest that CSCl-RoY hydrogels can modulate the expression of membrane surface GRP78 receptor of HUVECs under hypoxia and then activate Akt and ERK1/2 signaling pathways related to cell survival/proliferation, thereby enhancing angiogenic activity of HUVECs under hypoxia. To assess its therapeutic properties in vivo, a MI model was induced in rats by the left anterior descending artery ligation. CSCl or CSCl-RoY hydrogels were injected into the border of infracted hearts. The results demonstrate that the introduction of RoY peptide can not only improve angiogenesis at MI region but also improve the cardiac functions. Overall, we conclude that the CSCl-RoY may represent an ideal scaffold material for injectable cardiac tissue engineering.

Development and in vitro assessment of enzymatically-responsive poly(ethylene glycol) hydrogels for the delivery of therapeutic peptides

Despite the recent expansion of peptide drugs, delivery remains a challenge due to poor localization and rapid clearance. Therefore, a hydrogel-based platform technology was developed to control and sustain peptide drug release via matrix metalloproteinase (MMP) activity. Specifically, hydrogels were composed of poly(ethylene glycol) and peptide drugs flanked by MMP substrates and terminal cysteine residues as crosslinkers. First, peptide drug bioactivity was investigated in expected released forms (e.g., with MMP substrate residues) in vitro prior to incorporation into hydrogels. Three peptides (Qk (from Vascular Endothelial Growth Factor), SPARC113, and SPARC118 (from Secreted Protein Acidic and Rich in Cysteine)) retained bioactivity and were used as hydrogel crosslinkers in full MMP degradable forms. Upon treatment with MMP2, hydrogels containing Qk, SPARC113, and SPARC118 degraded in 6.7, 6, and 1 days, and released 5, 8, and, 19% of peptide, respectively. Further investigation revealed peptide drug size controlled hydrogel swelling and degradation rate, while hydrophobicity impacted peptide release. Additionally, Qk, SPARC113, and SPARC118 releasing hydrogels increased endothelial cell tube formation 3.1, 1.7, and 2.8-fold, respectively. While pro-angiogenic peptides were the focus of this study, the design parameters detailed allow for adaptation of hydrogels to control peptide release for a variety of therapeutic applications.

Endothelial cell surface vimentin binding peptide induces angiogenesis under hypoxic/ischemic conditions

We have previously identified several angiogenic peptides that bind cell surface proteins by screening a phage display peptide library on human umbilical endothelial cells exposed to hypoxic conditions. In this study we describe one of the selected peptides, SP. We found by protein precipitation of endothelial cell lysates that the 12 amino acid SP peptide binds cell surface vimentin. Surprisingly, vimentin was detected on the cell surface of about 30% of intact endothelial cells under both normoxic and hypoxic conditions, as was demonstrated by fluorocytometric analysis on viable cells. The assessment of SP in the induction of angiogenesis was established by a significant increase in endothelial cell proliferation and tube formation under hypoxic conditions and not under normoxic conditions. Cell proliferation and tube length increased two-fold in endothelial cells in the presence of 10 ng/ml SP peptide when compared to controls. The specificity of SP binding to vimentin was demonstrated by SP inhibition of anti-vimentin binding and by the inhibition of tube formation in cells transfected with siRNA against vimentin. Local intramuscular administrations of the peptide SP to ischemic hind limbs using the mouse hind limb ischemia model, demonstrated that SP inoculated at 1 and 10 μg, improved blood perfusion compared to inoculations with an irrelevant peptide or PBS. The recovery of blood perfusion correlated with the increase in the number of detectable capillaries in the ischemic limb. The development of novel peptides for the induction of pro-angiogenic activity may pave the way for new therapeutic strategies in the treatment of cardiovascular ischemic diseases.

Peptide-binding heat shock protein GRP78 protects cardiomyocytes from hypoxia-induced apoptosis

Myocardial ischemia is a severe stress condition that causes extensive biochemical changes triggering cardiac cell death. The 78-kDa glucose-regulated protein (GRP78), a heat shock protein present in all cells and a widely used marker of endoplasmic reticulum stress, functions in controlling the structural maturation of nascent glycoproteins. However, GRP78 was also found to be expressed on the cell surface of several cells such as endothelial cells, macrophages, and tumor cells where it functions as a receptor for a variety of ligands in signaling pathways. Recently, we have identified peptides from two different sources that specifically bind GRP78 protein. We have shown that binding of these peptides to endothelial cell surface GRP78 resulted in angiogenesis. In this study, we first established the presence of cell surface GRP78 on cardiac myocytes. Analysis of cardiomyocytes under hypoxia determined the significant increase in cell surface GRP78 in addition to gene expression and total protein. Apoptosis that was significantly increased in cardiomyocytes under hypoxic conditions was inhibited by the presence of the peptide-binding GRP78 during hypoxia. Inhibition of apoptosis was mediated by the binding of the peptide to cardiomyocytes cell surface GRP78 resulting in blocking caspase-3/7 activation. Silencing GRP78 RNA that reduced GRP78 receptor abrogated the peptide activity. Apoptosis of cardiac cells induced by myocardial infarction in a mouse model was also significantly inhibited by the administration of the peptide to mouse hearts. Our findings may make ADoPep1 a useful therapeutic tool for relieving of ischemia.

Angiogenic peptides improve blood flow and promote capillary growth in a diabetic and ischaemic mouse model

OBJECTIVES

It is a common clinical observation that collateral vessel development is impaired in diabetic patients with ischaemic vascular diseases. Consequently, alternative revascularisation strategies in diabetic patients are needed. This study presents the effect and mechanism of new peptide therapeutic angiogenesis in an ischaemic and diabetic mouse model.

DESIGN

Streptozocin-injected mice that had undergone hind-limb ischaemia were treated with angiogenic peptides. Blood flow restoration was calculated by laser Doppler imager and corroborated by histological section. For the mechanism study, endothelial cells were exposed to hypoxia and high glucose concentrations to study the effect of the peptides on proliferation and anti-apoptosis.

RESULTS

The peptides significantly restored blood perfusion 21 days after surgery in the diabetic mice (p < 0.01) by neo-vascularisation, corroborated by an increase in capillary density. In addition, the peptides induced the proliferation of hypoxic endothelial cells (p < 0.01) and protected the cells from apoptosis in high glucose cultures.

CONCLUSIONS

This is the first approach for treatment of ischaemic vascular disease with peptides in a diabetic mouse model.

Phage display peptide probes for imaging early response to bevacizumab treatment

Early evaluation of cancer response to a therapeutic regimen can help increase the effectiveness of treatment schemes and, by enabling early termination of ineffective treatments, minimize toxicity, and reduce expenses. Biomarkers that provide early indication of tumor therapy response are urgently needed. Solid tumors require blood vessels for growth, and new anti-angiogenic agents can act by preventing the development of a suitable blood supply to sustain tumor growth. The purpose of this study is to develop a class of novel molecular imaging probes that will predict tumor early response to an anti-angiogenic regimen with the humanized vascular endothelial growth factor antibody bevacizumab. Using a bevacizumab-sensitive LS174T colorectal cancer model and a 12-mer bacteriophage (phage) display peptide library, a bevacizumab-responsive peptide (BRP) was identified after six rounds of biopanning and tested in vitro and in vivo. This 12-mer peptide was metabolically stable and had low toxicity to both endothelial cells and tumor cells. Near-infrared dye IRDye800-labeled BRP phage showed strong binding to bevacizumab-treated tumors, but not to untreated control LS174T tumors. In addition, both IRDye800- and (18)F-labeled BRP peptide had significantly higher uptake in tumors treated with bevacizumab than in controls treated with phosphate-buffered saline. Ex vivo histopathology confirmed the specificity of the BRP peptide to bevacizumab-treated tumor vasculature. In summary, a novel 12-mer peptide BRP selected using phage display techniques allowed non-invasive visualization of early responses to anti-angiogenic treatment. Suitably labeled BRP peptide may be potentially useful pre-clinically and clinically for monitoring treatment response.

VEGF expression in patellar tendinopathy: a preliminary study

Vascular function and angiogenesis are regulated by vascular endothelial growth factor-A (VEGF). The purpose of this preliminary study was to address the following questions: Is VEGF expression in the patellar tendon more prevalent in patients with patellar tendinopathy than in individuals with normal, pain-free patellar tendons? Which cell populations express VEGF in normal and tendinopathic tendon? Is there a difference in symptom duration between VEGF+ and VEGF- tendons? We collected patellar tendon tissue from 22 patients undergoing open débridement of the patellar tendon and from 10 patients undergoing intramedullary nailing of the tibia. VEGF expression was assessed immunohistochemically. Relevant inflammatory and repair cell types were immunolabeled. VEGF expression was absent from control tendons, but was present in a subset of patients with histopathological evidence of angiofibroblastic tendinosis. VEGF was expressed in the intimal layer of tendon vessels, but was absent in other cell types. Patients demonstrating VEGF expression in the patellar tendon had a shorter symptom duration (12 +/- 7.8 months) than patients with no detectable VEGF (32.8 +/- 23.5 months). VEGF may contribute to the vascular hyperplasia that is a cardinal feature of symptomatic tendinosis, particularly in cases with more recent onset.

Therapeutic angiogenesis of mouse hind limb ischemia by novel peptide activating GRP78 receptor on endothelial cells

Therapeutic angiogenesis emerged as a non-invasive mean of promoting neovascularization in ischemic tissues. We have searched for new molecules that induce angiogenesis by screening a phage display combinatory peptide library on endothelial cells. One of the selected peptides identified by binding to endothelial cells under hypoxic conditions was further studied. The aim of this study was to assess the therapeutic value of this peptide, RoY, in a mouse hind limb ischemia model and to identify it's receptor on endothelial cells. RoY, a 12 amino-acid synthetic peptide, induced in vitro angiogeneic activity under hypoxic conditions by increasing endothelial cell proliferation, migration and tube formation. In order to assess its therapeutic properties in ischemic tissues, a hind limb ischemia model was induced in C57BL mice by a femoral artery excision. A single local intramuscular injection of RoY peptide to the operated limb, significantly restored blood perfusion and alleviated hind limb ischemia as determined by a laser Doppler imager. Increased capillary density in histological sections corroborated these findings. Protein precipitation and mass spectroscopy studies identified GRP78, a heat shock protein, as the peptide-binding membrane receptor that was increased on endothelial cell membranes under hypoxic conditions. This study demonstrates the efficacy of RoY peptide in alleviation of hind limb ischemia. In addition, it provides evidence that GRP78 is an angiogenic receptor on hypoxic endothelial cells.