Angiopoietin-1 Mimetic Peptide Promotes Neuroprotection after Stroke in Type 1 Diabetic Rats

Angiopoietin-1 (Ang1) mediates vascular maturation and immune response. Diabetes decreases Ang1 expression and disrupts Ang1/Tie2 signaling activity. Vasculotide is an Ang1 mimetic peptide, and has anti-inflammatory effects. In this study, we test the hypothesis that vasculotide treatment induces neuroprotection and decreases inflammation after stroke in type 1 diabetic (T1DM) rats. T1DM rats were subjected to embolic middle cerebral artery occlusion (MCAo) and treated with: 1) phosphate buffered saline (PBS); 2) vasculotide (3µg/kg, i.p. injection) administered half an hour prior to MCAo and at 8 and 24 hours after MCAo. Rats were sacrificed at 48 h after MCAo. Neurological function, infarct volume, hemorrhage, blood brain barrier (BBB) permeability and neuroinflammation were measured. Vasculotide treatment of T1DM-MCAo rats significantly improves functional outcome, decreases infarct volume and BBB permeability, but does not decrease brain hemorrhagic transformation compared with PBS-treated T1DM-MCAo rats. In the ischemic brain, Vasculotide treatment significantly decreases apoptosis, number of cleaved-caspase-3 positive cells, the expression of monocyte chemotactic protein-1 (MCP-1) and tumor necrosis factor (TNF-α). Western blot analysis shows that vasculotide significantly decreases expression of receptor for advanced glycation end products (RAGE), MCP-1 and TNF-α in the ischemic brain compared with T1DM-MCAo rats. Vasculotide treatment in cultured primary cortical neurons (PCN) significantly decreases TLR4 expression compared with control. Decreased neuroinflammation and reduced BBB leakage may contribute, at least in part, to vasculotide-induced neuroprotective effects after stroke in T1DM rats.

Validation of a human angiopoietin-2 ELISA for measurement of angiopoietin-2 concentrations in canine plasma samples and supernatant of primary canine aortic endothelial cell cultures

OBJECTIVE To assess 2 human ELISA kits for measurement of angiopoietin-1 and -2 concentrations in canine plasma samples, determine whether plasma angiopoeitin-2 concentration differed between septic and healthy dogs, and determine the effect of tumor necrosis factor-α (TNF-α) stimulation on angiopoeitin-2 release from primary canine aortic endothelial cells (pCAECs) in vitro. ANIMALS 10 healthy dogs and 10 septic dogs. PROCEDURES Human angiopoietin-1 and -2 ELISAs were used to detect recombinant canine angiopoietins-1 and -2 in canine plasma samples. The angiopoietin-2 ELISA was further validated by use of plasma samples from healthy and septic dogs and supernatants of pCAEC cultures. Associations between plasma angiopoeitin-2 and C-reactive protein (CRP) concentrations were examined. RESULTS Angiopoeitin-2 but not angiopoeitin-1 was detected in canine plasma samples by the respective ELISAs. The angiopoeitin-2 ELISA had excellent dilutional linearity, parallelism, accuracy, precision, and reproducibility for measurements in canine plasma samples and pCAEC supernatants. Plasma angiopoeitin-2 concentration was significantly higher in septic dogs (median, 25.5 ng/mL) than in healthy dogs (median, 6.7 ng/mL) and was positively correlated with plasma CRP concentration (R² = 0.60). Stimulation of pCAECs with TNF-α resulted in a significant increase in supernatant angiopoietin-2 concentration. CONCLUSIONS AND CLINICAL RELEVANCE The tested human angiopoietin-2 ELISA kit was useful for measuring angiopoietin-2 concentrations in canine plasma samples and pCAEC supernatants. Sepsis appeared to increase angiopoietin-2 concentration in dogs in vivo, whereas TNF-α stimulation caused release of angiopoietin-2 from pCAECs in vitro. These findings support the use of angiopoietin-2 as a marker of endothelial cell activation and inflammation in dogs.

Intravitreal AAV2.COMP-Ang1 Prevents Neurovascular Degeneration in a Murine Model of Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness in the working-age population in the U.S. The vision-threatening processes of neuroglial and vascular dysfunction in DR occur in concert, driven by hyperglycemia and propelled by a pathway of inflammation, ischemia, vasodegeneration, and breakdown of the blood retinal barrier. Currently, no therapies exist for normalizing the vasculature in DR. Here, we show that a single intravitreal dose of adeno-associated virus serotype 2 encoding a more stable, soluble, and potent form of angiopoietin 1 (AAV2.COMP-Ang1) can ameliorate the structural and functional hallmarks of DR in Ins2Akita mice, with sustained effects observed through six months. In early DR, AAV2.COMP-Ang1 restored leukocyte-endothelial interaction, retinal oxygenation, vascular density, vascular marker expression, vessel permeability, retinal thickness, inner retinal cellularity, and retinal neurophysiological response to levels comparable with nondiabetic controls. In late DR, AAV2.COMP-Ang1 enhanced the therapeutic benefit of intravitreally delivered endothelial colony-forming cells by promoting their integration into the vasculature and thereby stemming further visual decline. AAV2.COMP-Ang1 single-dose gene therapy can prevent neurovascular pathology, support vascular regeneration, and stabilize vision in DR.

van der Waals force-induced loading of proangiogenic nanoparticles on microbubbles for enhanced neovascularization

Nanoparticles emerged as carriers of promising diagnostic and therapeutic molecules due to their unique size, injectability, and potential to sustainably release molecular cargos. However, with local injection of particles into target tissue, the significant particle loss caused by external biomechanical forces is a great challenge yet to be resolved to date. We hypothesized that nanoparticles associated with tissue-adherent microbubbles in the form of core-shell particles due to van der Waals attractive forces would stably remain on an implanted site and significantly increase therapeutic efficacy of drug cargos. To examine this hypothesis, we used 100 nm diameter nanoparticles made of poly(lactide-co-glycolic acid) (PLGA) as a model nanoparticle and 50 μm diameter microbubbles made of poly(2-hydroxyethyl aspartamide) (PHEA) grafted with octadecyl chains, PHEA-g-C18, as a model microbubble. Simple mixing of PLGA nanoparticles and PHEA-g-C18 microbubbles resulted in the core-shell particles. Following implantation, the PHEA-g-C18 microbubbles acted as glue to minimize the displacement of PLGA nanoparticles, because of the association between the octadecyl chains on PHEA-g-C18 and the epithelium of the tissue. As a consequence, the core-shell particles prepared with Angiopoietin-1 (Ang1)-encapsulated PLGA nanoparticles significantly promoted vascularization in the implanted tissue. Overall, the results of this study provide a simple but advanced strategy for improving therapeutic efficacy of drug-carrying nanoparticles without altering their surface chemistry and potential.

Hydrogels with integrin-binding angiopoietin-1-derived peptide, QHREDGS, for treatment of acute myocardial infarction

BACKGROUND

Hydrogels are being actively investigated for direct delivery of cells or bioactive molecules to the heart after myocardial infarction (MI) to prevent cardiac functional loss. We postulate that immobilization of the prosurvival angiopoietin-1-derived peptide, QHREDGS, to a chitosan-collagen hydrogel could produce a clinically translatable thermoresponsive hydrogel to attenuate post-MI cardiac remodeling.

METHODS AND RESULTS

In a rat MI model, QHREDGS-conjugated hydrogel (QHG213H), control gel, or PBS was injected into the peri-infarct/MI zone. By in vivo tracking and chitosan staining, the hydrogel was demonstrated to remain in situ for 2 weeks and was cleared in ≈3 weeks. By echocardiography and pressure-volume analysis, the QHG213H hydrogel significantly improved cardiac function compared with the controls. Scar thickness and scar area fraction were also significantly improved with QHG213H gel injection compared with the controls. There were significantly more cardiomyocytes, determined by cardiac troponin-T staining, in the MI zone of the QHG213H hydrogel group; and hydrogel injection did not induce a significant inflammatory response as assessed by polymerase chain reaction and an inflammatory cytokine assay. The interaction of cardiomyocytes and cardiac fibroblasts with QHREDGS was found to be mediated by β1-integrins.

CONCLUSIONS

We demonstrated for the first time that the QHG213H peptide-modified hydrogel can be injected in the beating heart where it remains localized for a clinically effective period. Moreover, the QHG213H hydrogel induced significant cardiac functional and morphological improvements after MI relative to the controls.

QHREDGS enhances tube formation, metabolism and survival of endothelial cells in collagen-chitosan hydrogels

Cell survival in complex, vascularized tissues, has been implicated as a major bottleneck in advancement of therapies based on cardiac tissue engineering. This limitation motivates the search for small, inexpensive molecules that would simultaneously be cardio-protective and vasculogenic. Here, we present peptide sequence QHREDGS, based upon the fibrinogen-like domain of angiopoietin-1, as a prime candidate molecule. We demonstrated previously that QHREDGS improved cardiomyocyte metabolism and mitigated serum starved apoptosis. In this paper we further demonstrate the potency of QHREDGS in its ability to enhance endothelial cell survival, metabolism and tube formation. When endothelial cells were exposed to the soluble form of QHREDGS, improvements in endothelial cell barrier functionality, nitric oxide production and cell metabolism (ATP levels) in serum starved conditions were found. The functionality of the peptide was then examined when conjugated to collagen-chitosan hydrogel, a potential carrier for in vivo application. The presence of the peptide in the hydrogel mitigated paclitaxel induced apoptosis of endothelial cells in a dose dependent manner. Furthermore, the peptide modified hydrogels stimulated tube-like structure formation of encapsulated endothelial cells. When integrin αvβ3 or α5β1 were antibody blocked during cell encapsulation in peptide modified hydrogels, tube formation was abolished. Therefore, the dual protective nature of the novel peptide QHREDGS may position this peptide as an appealing augmentation for collagen-chitosan hydrogels that could be used for biomaterial delivered cell therapies in the settings of myocardial infarction.

A peptide-modified chitosan-collagen hydrogel for cardiac cell culture and delivery

Myocardial infarction (MI) results in the death of cardiomyocytes (CM) followed by scar formation and pathological remodeling of the heart. We propose that chitosan conjugated with the angiopoietin-1 derived peptide, QHREDGS, and mixed with collagen I forms a thermoresponsive hydrogel better suited for the survival and maturation of transplanted cardiomyocytes in vitro compared to collagen and chitosan-collagen hydrogels alone. Conjugation of QHREDGS peptide to chitosan does not interfere with the gelation, structure or mechanical properties of the hydrogel blends. The storage modulus of 2.5 mg ml(-1) 1:1 mass:mass (m:m) chitosan-collagen was measured to be 54.9 ± 9.1 Pa, and the loss modulus 6.1±0.9 Pa. The dose-response of the QHREDGS peptide was assessed and it was found that CMs encapsulated in High-peptide gel (651 ± 8 nmol peptide ml-gel(-1)) showed improved morphology, viability and metabolic activity in comparison to the Low-peptide (100 ± 30 nmol peptide ml-gel(-1)) and Control (No Peptide) groups. Construct (CMs in hydrogel) functional properties were not significantly different between the groups; however, the success rate of obtaining a beating construct was improved in the hydrogel with the High amount of QHREDGS peptide immobilized compared to the Low and Control groups. Subcutaneous injection of hydrogel (Control, Low and High) with CMs in the back of Lewis rats illustrated its ability to localize at the site of injection and retain cells, with CM contractile apparati identified after seven days. The hydrogel was also able to successfully localize at the site of injection in a mouse MI model.

Bioactive scaffolds for engineering vascularized cardiac tissues

Functional vascularization is a key requirement for the development and function of most tissues, and most critically cardiac muscle. Rapid and irreversible loss of cardiomyocytes during cardiac infarction directly results from the lack of blood supply. Contractile cardiac grafts, engineered using cardiovascular cells in conjunction with biomaterial scaffolds, are an actively studied method for cardiac repair. In this article, we focus on biomaterial scaffolds designed to mediate the development and maturation of vascular networks, by immobilized growth factors. The interactive effects of multiple vasculogenic factors are discussed in the context of cardiac tissue engineering.

Photocrosslinkable chitosan modified with angiopoietin-1 peptide, QHREDGS, promotes survival of neonatal rat heart cells

Myocardial infarction (MI) results in the death of cardiomyocytes (CM), which causes scar formation and pathological remodeling of the heart. The delivery of healthy myocytes or bone marrow cells reduces pathological remodeling after MI, however, current cell injection methods have low cell survival rates and high cell loss. The main objective of this work was to develop a novel hydrogel that can promote survival of CMs. Photocrosslinkable azidobenzoic acid modified chitosan (Az-chitosan) was conjugated with the angiopoietin-1-derived peptide, QHREDGS. This novel peptide is thought to mediate attachment and survival responses of CM to angiopoietin-1 via integrin binding. Thin layers of Az-chitosan, Az-chitosan-QHREDGS, and Az-chitosan-DGQESHR (scrambled peptide control) were spin coated on glass slides and photocrosslinked with application of UV light (365 nm). Neonatal rat heart cells cultured up to 5 days, demonstrated significantly higher attachment and viability on Az-chitosan-QHREDGS compared to cells on other hydrogel controls. Surfaces were also stained for the CM-specific marker troponin I, demonstrating significantly higher percentage of CMs on Az-chitosan-QHREDGS compared to Az-chitosan. The cells cultivated on Az-chitosan-QHREDGS demonstrated significantly lower levels of caspase 3/7 activation after taxol treatment in comparison to cells cultivated on the control hydrogels, glass substrate, or Az-chitosan linked to RGD, an established integrin binding peptide that did not protect against apoptosis. Thus, Az-chitosan-QHREDGS supports attachment and survival of neonatal rat heart cells.

COMP-Ang1, angiopoietin-1 variant protects radiation-induced bone marrow damage in C57BL/6 mice

Angiopoietin-1 (Ang1) is a vasculogenic factor which is signaled through the endothelial and bone marrow cell-specific, Tie2 receptor tyrosine kinase and has potential therapeutic applications for the induction of angiogenesis, enhancing endothelial cell survival, and preventing vascular leakage. In this study, we examined whether Ang1 directly exhibits bone marrow protection after ionizing radiation (IR) using an adenoviral vector of COMP-Ang1 (Ad-COMP-Ang1). This is a variant of Ang1 by replacement of the N-terminal portion of Ang1 with short coiled-coil domains of cartilage oligomeric matrix protein-Angiopoietin 1 (COMP-Ang1) which are, long enough for oligomerization but short enough to avoid problems of aggregation and insolubility. A spleen colony assay after 4.5 Gy whole body radiation, indicated that COMP-Ang1 significantly increased the mean colony numbers. Both the decrease in bone marrow cellularity and increased TUNEL (Terminal deoxynucleotidyl Transferase Biotin-dUTP Nick End Labeling) positive cells produced by radiation in bone marrow were significantly inhibited by COMP-Ang1 transfer. The expression of the ligands of Ang1 and Tie2 receptors were increased by radiation and, the COMP-Ang1 transfer potentiated this protein expression. Pre-treatment of Ang1 could be beneficial in protecting bone marrow from damage by radiation and COMP-Ang1 may be an effective alternative to native Ang1 for therapeutic purposes.

Oligomerization and multimerization are critical for angiopoietin-1 to bind and phosphorylate Tie2

Angiopoietin-1 (Ang1) is an essential molecule for blood vessel formation; however, little is known about the structure-function relationships of Ang1 with its receptor, Tie2 (tyrosine kinase with immunoglobulin and epidermal growth factor homology domain-2'). In this study, we generated several Ang1 and angiopoietin-2 (Ang2) variants to define the role of the superclustering and oligomerization domains of the Ang1 protein. Then we analyzed the molecular structure of the variants with SDS-PAGE and rotary metal-shadowing transmission electron microscopy (RMSTEM) and determined the effects of these variants on the binding and activation of Tie2. Ang1 exists as heterogeneous multimers with basic trimeric, tetrameric, and pentameric oligomers, whereas Ang2 exists as trimeric, tetrameric, and pentameric oligomers. The variant Ang1C265S, consisting of trimers, tetramers, and pentamers without multimeric forms of Ang1, yielded less Tie2 activation than did Ang1, whereas monomeric Ang1 (Ang1/FD), dimeric Ang1 variants (Ang1D2, and Ang1D3), and dimeric and trimeric Ang1 variant (Ang1D1) dramatically lost their ability to bind and activate Tie2. An Ang1 protein in which two cysteines (amino acids 41 and 54) were replaced with serines (Ang1C41S/C54S) formed mostly dimers and trimers that were not able to bind and activate Tie2. In addition, improper creation of a new cysteine in Ang2 (Ang2S263C) dramatically induced Ang2 aggregation without activating Tie2. In conclusion, proper oligomerization of Ang1 having at least four subunits by the intermolecular disulfide linkage involving cysteines 41 and 54 is critical for Tie2 binding and activation. Thus, our data shed a light on the structure-function relationships of Ang1 with Tie2.

Biological characterization of angiopoietin-3 and angiopoietin-4

The angiopoietin (Ang) family of growth factors includes Ang1, Ang2, Ang3, and Ang4, all of which bind to the endothelial receptor tyrosine kinase Tie2. Ang3 (mouse) and Ang4 (human) are interspecies orthologs. In experiments with human endothelial cell lines, Ang3 was identified as an antagonist of Tie2 and Ang4 was identified as an agonist of Tie2. However, the biological roles of Ang3 and Ang4 are unknown. We examined the biological effect of recombinant Ang3 and Ang4 proteins in primary cultured endothelial cells and in vivo in mice. Recombinant Ang3 and Ang4 formed disulfide-linked dimers. Ang4 (400 ng/mL) markedly increased Tie2 and Akt phosphorylation in primary cultured HUVECs whereas Ang3 (400 ng/mL) did not produce significant changes. Accordingly, Ang4, but not Ang3, induced survival and migration in primary cultured HUVECs. Unexpectedly, intravenously administered Ang3 (30 microg) was more potent than Ang4 (30 microg) in phosphorylating the Tie2 receptor in lung tissue from mice in vivo. Accordingly, Ang3 was more potent than Ang4 in phosphorylating Akt in primary cultured mouse lung microvascular endothelial cells. Ang3 and Ang4 both produced potent corneal angiogenesis extending from the limbus across the mouse cornea in vivo. Thus, Ang3 and Ang4 are agonists of Tie2, but mouse Ang3 has strong activity only on endothelial cells of its own species.

COMP-Ang1: a designed angiopoietin-1 variant with nonleaky angiogenic activity

Angiopoietin-1 (Ang1) has potential therapeutic applications in inducing angiogenesis, enhancing endothelial cell survival, and preventing vascular leakage. However, production of Ang1 is hindered by aggregation and insolubility resulting from disulfide-linked higher-order structures. Here, by replacing the N-terminal portion of Ang1 with the short coiled-coil domain of cartilage oligomeric matrix protein (COMP), we have generated a soluble, stable, and potent Ang1 variant, COMP-Ang1. This variant is more potent than native Ang1 in phosphorylating the tyrosine kinase with Ig and epidermal growth factor homology domain 2 (Tie2) receptor and Akt in primary cultured endothelial cells, enhancing angiogenesis in vitro and increasing adult angiogenesis in vivo. Thus, COMP-Ang1 is an effective alternative to native Ang1 for therapeutic angiogenesis in vivo.

Angiopoietins have distinct modular domains essential for receptor binding, dimerization and superclustering

Angiopoietins are a recently discovered family of angiogenic factors that interact with the endothelial receptor tyrosine kinase Tie2, either as agonists (angiopoietin-1) or as context-dependent agonists/antagonists (angiopoietin-2). Here we show that angiopoietin-1 has a modular structure unlike any previously characterized growth factor. This modular structure consists of a receptor-binding domain, a dimerization motif and a superclustering motif that forms variable-sized multimers. Genetic engineering of precise multimers of the receptor-binding domain of angiopoietin-1, using surrogate multimerization motifs, reveals that tetramers are the minimal size required for activating endothelial Tie2 receptors. In contrast, engineered dimers can antagonize endothelial Tie2 receptors. Surprisingly, angiopoietin-2 has a modular structure and multimerization state similar to that of angiopoietin-1, and its antagonist activity seems to be a subtle property encoded in its receptor-binding domain.