Co-immobilization of CD133 antibodies, vascular endothelial growth factors, and REDV peptide promotes capture, proliferation, and differentiation of endothelial progenitor cells

Capture of endothelial progenitor cells (EPCs) in situ has been considered as a promising strategy for the rapid endothelialization and long-term patency of artificial blood vessels and implant devices. In this study, a CD133⁺ EPC capture surface was fabricated by grafting CD133 antibody (a more specific EPC surface marker than CD34) and Arg-Glu-Asp-Val (REDV) peptideon the methacrylate-grafted hyaluronic acid (MA-HA) and heparin-hybridized (MA-HA&Heparin) resisting layer. Vascular endothelial growth factor (VEGF) was further conjugated to the immobilized heparin. This engineered surface showed good hemocompatibility and significantly higher ability of capturing CD133⁺ EPCs from human peripheral blood mononuclear cells (PBMCs) and obviously upregulated the expression of endothelial cell (EC) marker genes of EPCs such as VEGF receptor 2 (VEGFR2), CD31, VE-cadherin, and von Willebrand factor (vWF), facilitating the differentiation of EPCs into ECs. The dramatically enhanced EPC proliferation on this surface was dependent on the integrin-VEGFR synergistic signaling, as ERK1/2 phosphorylation was only significantly enhanced on the REDV and VEGF co-immobilized surface. This study highlights a new surface coating strategy for blood-contact materials based on the specific EPC capturing and rapid endothelialization. STATEMENT OF SIGNIFICANCE: Capture of endothelial progenitor cells (EPCs) in situ is a promising strategy for the rapid endothelialization and long-term patency of artificial blood vessels and scaffolds. More specific capture of EPCs by targeting CD133 rather than CD34 can better reduce the risk of inflammation and restenosis. On the other hand, an appropriate microenvironment for EPC proliferation is equally important for endothelialization, which is rarely considered by the existing EPC capture strategies. In this study, the capture ratio of EPCs was significantly increased by simultaneously grafting CD133 antibody and VEGF on a MA-HA and heparin-hybridized antifouling layer. Further, proliferation of EPCs after capture was significantly promoted by grafting VEGF and REDV peptide through the integrin-VEGFR synergistic signaling. This study highlights a new strategy for the surface coating of blood-contact materials based on specific EPC capture and rapid endothelialization.

Toward Regeneration of the Heart: Bioengineering Strategies for Immunomodulation

Myocardial Infarction (MI) is the most common cardiovascular disease. An average-sized MI causes the loss of up to 1 billion cardiomyocytes and the adult heart lacks the capacity to replace them. Although post-MI treatment has dramatically improved survival rates over the last few decades, more than 20% of patients affected by MI will subsequently develop heart failure (HF), an incurable condition where the contracting myocardium is transformed into an akinetic, fibrotic scar, unable to meet the body's need for blood supply. Excessive inflammation and persistent immune auto-reactivity have been suggested to contribute to post-MI tissue damage and exacerbate HF development. Two newly emerging fields of biomedical research, immunomodulatory therapies and cardiac bioengineering, provide potential options to target the causative mechanisms underlying HF development. Combining these two fields to develop biomaterials for delivery of immunomodulatory bioactive molecules holds great promise for HF therapy. Specifically, minimally invasive delivery of injectable hydrogels, loaded with bioactive factors with angiogenic, proliferative, anti-apoptotic and immunomodulatory functions, is a promising route for influencing the cascade of immune events post-MI, preventing adverse left ventricular remodeling, and offering protection from early inflammation to fibrosis. Here we provide an updated overview on the main injectable hydrogel systems and bioactive factors that have been tested in animal models with promising results and discuss the challenges to be addressed for accelerating the development of these novel therapeutic strategies.

Synergistic effects of hyaluronate - epidermal growth factor conjugate patch on chronic wound healing

The proteolytic microenvironment in the wound area reduces the stability and the half-life of growth factors in vivo, making difficult the topical delivery of growth factors. Here, epidermal growth factor (EGF) was conjugated to hyaluronate (HA) to improve the long-term stability against enzymatic degradation and the therapeutic effect by enhancing the biological interaction with HA receptors on skin cells. After the synthesis of HA-EGF conjugates, they were incorporated into a patch-type formulation for the facile topical application and sustained release of EGF. According to ELISA, the HA-EGF conjugates showed a long-term stability compared with native EGF. Furthermore, HA-EGF conjugates appeared to interact with skin cells through two types of HA and EGF receptors, resulting in a synergistically improved healing effect. Taken together, we could confirm the feasibility of HA-EGF conjugates for the transdermal treatment of chronic wounds.

Local delivery of antitumor necrosis factor-α through conjugation to hyaluronic acid: dosing strategies and early healing effects in a rat burn model

The objective of this study was to measure dose-response effects of topical delivery of inhibitors of tumor necrosis factor-α (TNF-α) through conjugation to hyaluronic acid in a rat burn model to determine effects on inflammatory responses, burn progression, and early stages of healing. Monoclonal antibodies against TNF-α were conjugated to hyaluronic acid and applied topically in a rat partial-thickness burn model. Metrics of inflammatory responses and tissue necrosis were measured as well as the quantitative analysis of collagen composition and organization. The minimum effective conjugated antibody dose was found to be 100 μg with three applications 48 hours apart. Nonviable tissue thicknesses decreased with increasing dose and dose frequency. Free antibody retarded macrophage infiltration in the periphery but not at the surface, while the conjugated antibody was able to hinder macrophage infiltration at both the periphery and the surface. Quantification of collagen I and III staining ratios at days 4, 7, and 14 and quantitative image analysis of collagen organization at day 14 demonstrated differences between saline and conjugate treatment. This correlated with increases in re-epithelialization observed in conjugate-treated sites. Reductions in inflammatory markers and secondary tissue necrosis under treatment with the conjugates were understood in terms of differences in antibody transport compared to nonconjugated antibody. Differences in collagen composition and organization at Day 14 suggested that the reductions in inflammatory responses altered early healing responses. These results indicate anti-TNF-α conjugated to hyaluronic acid can be an effective treatment for reducing secondary necrosis and improving healing outcomes in burns.

Therapeutic intradermal delivery of tumor necrosis factor-alpha antibodies using tip-loaded dissolvable microneedle arrays

Tumor necrosis factor-alpha (TNF-α) specific antibodies (anti-TNF-α Ab) have been shown to be potent TNF inhibitors and effective therapeutics for a range of inflammatory diseases. Typically, these drugs are administered systemically, but systemic dosing sufficient to achieve locally effective concentrations in peripheral tissues has been associated with systemic immunosuppression and related adverse events. Here, we evaluated the use of tip-loaded dissolvable microneedle arrays (MNAs) for localized intradermal delivery of anti-TNF-α Ab. MNAs with obelisk shape microneedles that incorporate the antibody cargo in the needle tips were created from carboxymethylcellulose (CMC) using a micromilling/spin-casting fabrication method. We found that anti-TNF-α Ab integrated into MNAs using this room temperature fabrication process maintained conformationally dependent TNF-α binding activity. Further, these MNAs efficiently delivered anti-TNF-α antibodies to the dermis of human skin with clinically applicable release profiles. To evaluate MNA delivered anti-TNF-α Ab function, we applied anti-TNF-α Ab containing MNAs to established psoriasiform lesions on the skin of mice. MNA anti-TNF-α Ab treatment reduced key biomarkers of psoriasiform inflammation including epidermal thickness and IL-1β expression. Taken together, these results demonstrate efficient and biologically effective MNA delivery of anti-TNF-α Ab to the intradermal microenvironment of the skin in mice and humans, and support the development of MNA mediated antibody delivery for clinical applications.

STATEMENT OF SIGNIFICANCE

Tumor necrosis factor-alpha (TNF-α) specific antibodies (anti-TNF-α Ab) have been shown to be potent TNF inhibitors and effective therapeutics for a range of inflammatory diseases. Typically, these drugs are administered systemically, but systemic dosing sufficient to achieve locally effective concentrations in peripheral tissues has been associated with systemic immunosuppression and related adverse events. Here we demonstrate efficient and biologically effective MNA delivery of anti-TNF-α Ab to the intradermal microenvironment of the skin in mice and humans. These results support the development of MNA mediated antibody delivery of therapeutic antibodies for clinical applications.

Polymer-conjugated inhibitors of tumor necrosis factor-α for local control of inflammation

Burns, chronic wounds, osteoarthritis, and uveitis are examples of conditions characterized by local, intense inflammatory responses that can impede healing or even further tissue degradation. The most powerful anti-inflammatory drugs available are often administered systemically, but these carry significant side effects and are not compatible for patients that have underlying complications associated with their condition. Conjugation of monoclonal antibodies that neutralize pro-inflammatory cytokines to high molecular weight hydrophilic polymers has been shown to be an effective strategy for local control of inflammation. Lead formulations are based on antibody inhibitors of tumor necrosis factor-α conjugated to hyaluronic acid having molecular weight greater than 1 MDa. This review will discuss fundamental aspects of medical conditions that could be treated with these conjugates and design principles for preparing these cytokine-neutralizing polymer conjugates. Results demonstrating that infliximab, an approved inhibitor of tumor necrosis factor-α, can be incorporated into the conjugates using a broad range of water-soluble polymers are also presented, along with a prospectus for clinical translation.

Effects of hyaluronic acid conjugation on anti-TNF-α inhibition of inflammation in burns

Biomaterials capable of neutralizing specific cytokines could form the basis for treating a broad range of conditions characterized by intense, local inflammation. Severe burns, spanning partial- to full-thickness of the dermis, can result in complications due to acute inflammation that contributes to burn progression, and early mediation may be a key factor in rescuing thermally injured tissue from secondary necrosis to improve healing outcomes. In this work, we examined the effects on burn progression and influence on the inflammatory microenvironment of topical application of anti-tumor necrosis factor-α (anti-TNF-α) alone, mixed with hyaluronic acid (HA) or conjugated to HA. We found that non-conjugated anti-TNF-α decreased macrophage infiltration to a greater extent than that conjugated to HA; however, there was little effect on the degree of progression or IL-1β levels. A simple transport model is proposed to analyze the results, which predicts qualitative and quantitative differences between untreated burn sites and those treated with the conjugates. Our results indicate that conjugation of anti-TNF-α to high molecular weight HA provides sustained, local modulation of the post-injury inflammatory responses compared to direct administration of non-conjugated antibodies.

Single-step grafting of aminooxy-peptides to hyaluronan: a simple approach to multifunctional therapeutics for experimental autoimmune encephalomyelitis

The immune response to antigens is directed in part by the presence or absence of costimulatory signals. The ability to coincidently present both antigen and, for example, a peptide that inhibits or activates the costimulatory pathway, would be a valuable tool for tolerization or immunization, respectively. A simple reaction scheme utilizing oxime chemistry was identified as a means to efficiently conjugate different peptide species to hyaluronan. Peptides synthesized with an aminooxy N-terminus reacted directly to hyaluronan under slightly acidic aqueous conditions without the need for a catalyst. The resulting oxime bond was found to rapidly hydrolyze at pH2 releasing peptide, but was stable at higher pH values (5.5 and 7). Two different peptide species, a multiple sclerosis antigen (PLP) and an ICAM-1 ligand (LABL) known to block immune cell stimulation, were functionalized with the aminooxy end group. These peptides showed similar reactivity to hyaluronan and were conjugated in an equimolar ratio. The resulting hyaluronan with grafted PLP and LABL significantly inhibited disease in mice with experimental autoimmune encephalomyelitis, a model of multiple sclerosis. Aminooxy-peptides facilitate simple synthesis of multifunctional hyaluronan graft polymers, thus enabling novel approaches to antigen-specific immune modulation.

Reduction of burn progression with topical delivery of (antitumor necrosis factor-α)-hyaluronic acid conjugates

In this study, we explored whether topical application of antibodies targeting tumor necrosis factor-α (TNF-α) or interleukin-6 (IL-6) conjugated to hyaluronic acid (HA) could reduce the extension of necrosis by modulating inflammation locally in a partial-thickness rat burn model. Partial-thickness to deep partial-thickness burn injuries present significant challenges in healing, as these burns often progress following the initial thermal insult, resulting in necrotic expansion and increased likelihood of secondary complications. Necrotic expansion is driven by a microenvironment with elevated levels of pro-inflammatory mediators, and local neutralization of these using antibody conjugates could reduce burn progression. Trichrome-stained tissue sections indicated the least necrotic tissue in (anti-TNF-α)-HA-treated sites, while (anti-IL-6)-HA-treated sites displayed similar outcomes to saline controls. This was confirmed by vimentin immunostaining, which demonstrated that HA treatment alone reduced burn progression by nearly 30%, but (anti-TNF-α)-HA reduced it by approximately 70%. At all time points, (anti-TNF-α)-HA-treated sites showed reduced tissue levels of IL-1β compared to controls, suggesting inhibition of a downstream mediator of inflammation. Decreased macrophage infiltration in (anti-TNF-α)-HA-treated sites compared to controls was elucidated by immunohistochemical staining of macrophages, suggesting a reduction in overall inflammation in all time points. These results suggest that local targeting of TNF-α may be an effective strategy for preventing progression of partial-thickness burns.

Polymerizable superoxide dismutase mimetic protects cells encapsulated in poly(ethylene glycol) hydrogels from reactive oxygen species-mediated damage

A polymerizable superoxide dismutase mimetic (SODm) was incorporated into poly(ethylene glycol) (PEG) hydrogels to protect encapsulated cells from superoxide-mediated damage. Superoxide and other small reactive oxygen species (ROS) can cause oxidative damage to donor tissue encapsulated within size exclusion barrier materials. To enzymatically breakdown ROS within biomaterial cell encapsulation systems, Mn(III) Tetrakis[1-(3-acryloxy-propyl)-4-pyridyl] porphyrin (MnTTPyP-acryl), a polymerizable manganese metalloporphyrin SOD mimetic, was photopolymerized with PEG diacrylate (PEGDA) to create functional gels. In unmodified PEG hydrogels, a significant reduction in metabolic activity was observed when encapsulated Min6 β-cells were challenged with chemically generated superoxide. Cells encapsulated within MnTPPyP-co-PEG hydrogels, however, demonstrated greatly improved metabolic activity following various superoxide challenges. Further, cells were encapsulated and cultured for 10 days within MnTPPyP-co-PEG hydrogels and challenged with superoxide on days 4, 6, and 8. At the conclusion of this study, cells in blank PEG hydrogels had no observable metabolic activity but when encapsulated in MnTPPyP-functionalized hydrogels, cells retained 60 ± 5% of the metabolic activity compared to untreated controls.

Protein PEGylation attenuates adsorption and aggregation on a negatively charged and moderately hydrophobic polymer surface

Covalent grafting of poly(ethylene glycol) chains to proteins ("PEGylation") is emerging as an effective technique to increase the in vivo circulation time and efficacy of protein drugs. PEGylated protein adsorption at a variety of solid/aqueous interfaces is a critical aspect of their manufacture, storage, and delivery. A special category of block copolymer, PEGylated proteins have one or more water-soluble linear polymer (PEG) blocks and a single globular protein block that each exert distinct intermolecular and surface interaction forces. We report the impact of PEGylation on protein adsorption at the interface between aqueous solutions and solid films of poly(lactide-co-glycolide) (PLG), a moderately hydrophobic and negatively charged polymer. Using the model protein lysozyme with controlled degrees of PEGylation, we employ total internal reflection fluorescence techniques to measure adsorption isotherms, adsorption reversibility, and the extent of surface-induced aggregation. Lysozyme PEGylation reduces the extent of protein adsorption and surface-induced aggregation and increases the reversibility of adsorption compared to the unconjugated protein. Results are interpreted in terms of steric forces among grafted PEG chains and their effects on protein-protein interactions and protein orientation on the surface.

Design principles for cytokine-neutralizing gels: Cross-linking effects

Constructs composed of cytokine-neutralizing antibodies conjugated to high-molecular-weight hyaluronic acid have been shown to be effective at controlling inflammatory responses in vivo. A critical question in the development of this new class of biomaterial is whether crosslinked conjugates have similar anti-inflammatory effects, which would open up a broad range of tissue engineering applications in which the material would have intrinsic inflammation-controlling function. To test this, high-molecular-weight hyaluronic acid was conjugated with monoclonal antibodies to the pro-inflammatory cytokines interleukin-1β and tumor necrosis factor-α in two forms of the material: viscous, non-crosslinked polymer-antibody conjugates and crosslinked, elastomeric polymer-antibody conjugates. The cytokine affinities of both constructs were validated using molecular characterization methods, and the biological activities were tested through subcutaneous implantation in Sprague-Dawley rats. In vitro, both forms of these constructs are capable of binding cytokines, but in vivo only the non-crosslinked polymer significantly reduces markers of acute inflammation compared to controls that lack the antibodies. We propose that these materials function by retarding cytokine diffusion, with the non-crosslinked polymers being capable of retarding the diffusion of cytokines in the extracellular matrix and preventing engagement with receptors. In contrast, crosslinked materials have long diffusion lengths into the gel compared with those between cells on the surface of the material, which may make them ineffective at sequestering pro-inflammatory cytokines on biologically relevant timescales. These results suggest an important design principle for preparing cytokine-regulating materials based on consideration of transport phenomena.

Cytokine binding by polysaccharide-antibody conjugates

Cytokine-neutralizing antibodies are used in treating a broad range of inflammatory conditions. We demonstrate that monoclonal antibodies against interleukin-1β and tumor necrosis factor-α were still active when conjugated to high molecular weight polysaccharides. These polysaccharides are hydrophilic, but their size makes them unable to circulate in the bloodstream when delivered to tissues, opening up the possibility of localized treatment of inflammatory conditions. To explore this new class of protein-polysaccharide conjugates, we covalently modified interleukin-1β and tumor necrosis factor-α monoclonal antibodies with high molecular weight hyaluronic acid and carboxymethylcellulose. Rigorous purification using dialysis with a 300 kDa-cutoff membrane removed unconjugated monoclonal antibodies. We characterized the composition of the constructs and demonstrated using molecular binding affinity measurements and cell assays that the conjugates were capable of binding proinflammatory cytokines. The binding affinities of both the unconjugated antibodies for their cytokines were measured to be approximately 120 pM. While all conjugates had pM-level binding constants, they ranged from 40 pM for the hyaluronic acid-(anti-interleukin-1β) conjugate to 412 pM for the carboxymethylcellulose-(anti-interleukin-1β) conjugate. Interestingly, the dissociation time constants varied more than the association time constants, suggesting that conjugation to a high molecular weight polysaccharide did not interfere with the formation of the antibody-cytokine complex but could stabilize or destabilize it once formed. Conjugation of cytokine-neutralizing antibodies to high molecular weight polymers represents a novel method of delivering anticytokine therapeutics that may avoid many of the complications associated with systemic delivery.