Evaluation of the biocompatibility of novel peptide hydrogel in rabbit eye

Characteristics of Mitomycin C-Loaded Peptide Hydrogel In Vitro and Antiscarring Effects in Rat Ocular Injury Model

Purpose: To investigate the characteristics of sustained drug release systems established by an arginine-glycine-aspartic acid (RGD) peptide hydrogel and mitomycin C (MMC) in vitro, and verify their antiscar effects in rat ocular injury model. Methods: Low, medium, and high loading doses of MMC were added to 5 mL 0.25%, 0.5%, and 1% wt RGD peptide hydrogel, respectively, to prepare 9 ratios of MMC-RGD systems. Drug release characteristics of the systems in phosphate-buffered saline solution were investigated by plotting the drug release curves and fitting them with mathematical models in OriginPro8.0 software. Appropriate ratios of MMC-RGD systems were selected as treatment in rat ocular injury model. Scar formation was observed by Masson staining and immunohistochemical staining with alpha-smooth muscle actin (α-SMA) and fibronectin (FN). Results: Nine ratios of MMC-RGD systems could release drug slowly. The maximum drug release proportions of all systems were >80%, and the time to maximum release proportions statistically prolonged with the increase of drug loading. Fitting with mathematical models indicated that the mechanisms of drug release were mainly Fick diffusion at early stage and Anomalous Transport at later stage. Systems of 1% wt RGD hydrogel were evaluated in animal experiments, which could inhibit hyperplasia of collagen and expression of α-SMA and FN. Conclusions: The RGD peptide hydrogel could be used as the carrier of MMC to establish sustained drug release system, which could inhibit scar formation after rat's ocular injury.

Protein and polypeptide mediated delivery to the eye

Hybrid or recombinant protein-polymers, peptide-based biomaterials, and antibody-targeted therapeutics are widely explored for various ocular conditions and vision correction. They have been noted for their potential biocompatibility, potency, adaptability, and opportunities for sustained drug delivery. Unique to peptide and protein therapeutics, their production by cellular translation allows their precise modification through genetic engineering. To a greater extent than drug delivery to other systems, delivery to the eye can benefit from the combination of locally-targeted administration and protein-based specificity. Consequently, a range of delivery platforms and administration methods have been exploited to address the ocular delivery of peptide and protein biomaterials. This review discusses a sample of preclinical and clinical opportunities for peptide-based drug delivery to the eye.

Oral delivery of self-assembling bioactive peptides to target gastrointestinal tract disease

Peptides are known for their diverse bioactivities including antioxidant, antimicrobial, and anticancer activity, all three of which are potentially useful in treating colon-associated diseases. Beside their capability to stimulate positive health effects once released in the body, peptides are able to form useful nanostructures such as hydrogels. Combining peptide bioactivity and peptide gel-forming potentials can create interesting systems that can be used for oral delivery. This combination, acting as a two-in-one system, has the potential to avoid the need for delicate entrapment of a drug or natural bioactive compound. We here review the context and research progress, to date, in this area.

Self-assembling peptide-based hydrogels: Fabrication, properties, and applications

The hierarchical formation of self-assembling peptide-based hydrogels (SAPHs) starts from peptide to nanofibers, following with the entanglement into hydrogels with nanofibrous network. Such characteristic structure and extraordinary biocompatibility, and the peptide components endow the SAPHs with diverse applications in biotechnological field. Therefore, the thorough comprehension of SAPHs is significant to broadening their application. In this review, fabrication, properties, and biological applications of the SAPHs are introduced, and the factors influencing the synthesis process as well as the properties of the SAPHs products are also systematically explained. Meanwhile, we conclude the problems to be solved and provide our perspective to the future development of SAPHs in the biotechnology.

Evaluation of a photocrosslinkable hydroxyethyl chitosan hydrogel as a potential drug release system for glaucoma surgery

Hydroxyethyl chitosan (HECTS) is a critical derivative of chitosan that has been widely used as biomedical materials due to great water-solubility and excellent biocompatibility. Here, photosensitive hydroxyethyl chitosan was synthesized by introducing azide group on NH2 of HECTS (HECTS-AZ), afterwards FTIR and ¹H NMR spectra were detected to confirm the formation of HECTS-AZ. The solution of HECTS-AZ can achieve a sol-gel transition through UV irradiation for 30 s. The evaluation of biocompability and biodegradability in vivo was conducted in rats, visual and pathological examinations exhibited the HECTS-AZ has excellent biocompability and degradation time of the hydrogel is more than 14 weeks. Furthermore, HECTS-AZ hydrogel as an ocular drug delivery system loading heparin was prepared to implant under sclera of rabbit after glaucoma filtration surgery (GFS). The experimental results demonstrated the heparin loaded hydrogel can effectively maintain filtration bleb and lowing intraocular pressure (IOP) after GFS for prolonged time. Besides, obvious inflammatory reactions and side effects have not been observed in ocular during the experimental period. In conclusion, the HECTS-AZ hydrogel is a potential drug delivery device for the treatment of glaucoma and other ocular diseases.

In Vivo Imaging of the Stability and Sustained Cargo Release of an Injectable Amphipathic Peptide-Based Hydrogel

Hydrogels are promising materials for biomedical applications such as tissue engineering and controlled drug release. In the past two decades, the peptide hydrogel subclass has attracted an increasing level of interest from the scientific community because of its numerous advantages, such as biocompatibility, biodegradability, and, most importantly, injectability. Here, we report on a hydrogel consisting of the amphipathic hexapeptide H-FEFQFK-NH₂, which has previously shown promising in vivo properties in terms of releasing morphine. In this study, the release of a small molecule, a peptide, and a protein cargo as representatives of the three major drug classes is directly visualized by in vivo fluorescence and nuclear imaging. In addition, the in vivo stability of the peptide hydrogel system is investigated through the use of a radiolabeled hydrogelator sequence. Although it is shown that the hydrogel remains present for several days, the largest decrease in volume takes place within the first 12 h of subcutaneous injection, which is also the time frame wherein the cargos are released. Compared to the situation in which the cargos are injected in solution, a prolonged release profile is observed up to 12 h, showing the potential of our hydrogel system as a scaffold for controlled drug delivery. Importantly, this study elucidates the release mechanism of the peptide hydrogel system that seems to be based on erosion of the hydrogel providing a generally applicable controlled release platform for small molecule, peptide, and protein drugs.

Recent advances in self-assembled peptides: Implications for targeted drug delivery and vaccine engineering

Self-assembled peptides have shown outstanding characteristics for vaccine delivery and drug targeting. Peptide molecules can be rationally designed to self-assemble into specific nanoarchitectures in response to changes in their assembly environment including: pH, temperature, ionic strength, and interactions between host (drug) and guest molecules. The resulting supramolecular nanostructures include nanovesicles, nanofibers, nanotubes, nanoribbons, and hydrogels and have a diverse range of mechanical and physicochemical properties. These molecules can be designed for cell-specific targeting by including adhesion ligands, receptor recognition ligands, or peptide-based antigens in their design, often in a multivalent display. Depending on their design, self-assembled peptide nanostructures have advantages in biocompatibility, stability against enzymatic degradation, encapsulation of hydrophobic drugs, sustained drug release, shear-thinning viscoelastic properties, and/or adjuvanting properties. These molecules can also act as intracellular transporters and respond to changes in the physiological environment. Furthermore, this class of materials has shown sequence- and structure-dependent impacts on the immune system that can be tailored to non-immunogenic for drug targeting, and immunogenic for vaccine delivery. This review explores self-assembled peptide nanostructures (beta sheets, alpha helices, peptide amphiphiles, amino acid pairing, elastin like polypeptides, cyclic peptides, short peptides, Fmoc peptides, and peptide hydrogels) and their application in vaccine delivery and drug targeting.

D-amino acid-containing supramolecular nanofibers for potential cancer therapeutics

Nanostructures formed by peptides that self-assemble in water through non-covalent interactions have attracted considerable attention because peptides possess several unique advantages, such as modular design and easiness of synthesis, convenient modification with known functional motifs, good biocompatibility, low immunogenicity and toxicity, inherent biodegradability, and fast responses to a wide range of external stimuli. After about two decades of development, peptide-based supramolecular nanostructures have already shown great potentials in the fields of biomedicine. Among a range of biomedical applications, using such nanostructures for cancer therapy has attracted increased interests since cancer remains the major threat for human health. Comparing with L-peptides, nanostructures containing peptides made of D-amino acid (i.e., D-peptides) bear a unique advantage, biostability (i.e., resistance towards most of endogenous enzymes). The exploration of nanostructures containing D-amino acids, especially their biomedical applications, is still in its infancy. Herein we review the recent progress of D-amino acid-containing supramolecular nanofibers as an emerging class of biomaterials that exhibit unique features for the development of cancer therapeutics. In addition, we give a brief perspective about the challenges and promises in this research direction.

Self-assembly of a 5-fluorouracil-dipeptide hydrogel

The self-assembly of 5-fluorouracil dilysine conjugates into self-supporting hydrogels, comprised of entangled nanofibers or rigid nanotubes with diameters of 10 and 16 nm, respectively, is reported. The rate of release of 5-Fu from the conjugates was highly dependent on concentration in solution, whereas, release from the fully formed hydrogels was significantly slower. The 5-Fu conjugate also exhibited promising in vitro cytotoxicity against human tumor cell lines A549, H460 and H23.

Biocompatible fluorescent supramolecular nanofibrous hydrogel for long-term cell tracking and tumor imaging applications

Biocompatible peptide-based supramolecular hydrogel has recently emerged as a new and promising system for biomedical applications. In this work, Rhodamine B is employed as a new capping group of self-assembling peptide, which not only provides the driving force for supramolecular nanofibrous hydrogel formation, but also endows the hydrogel with intrinsic fluroescence signal, allowing for various bioimaging applications. The fluorescent peptide nanofibrous hydrogel can be formed via disulfide bond reduction. After dilution of the hydrogel with aqueous solution, the fluorescent nanofiber suspension can be obtained. The resultant nanofibers are able to be internalized by the cancer cells and effectively track the HeLa cells for as long as 7 passages. Using a tumor-bearing mouse model, it is also demonstrated that the fluorescent supramolecular nanofibers can serve as an efficient probe for tumor imaging in a high-contrast manner.

Enzyme-responsive Drug-delivery Systems

This chapter offers an overview of recent advances in enzyme-responsive materials potentially useful for drug delivery. The systems already developed provide new insights into the chemical design rules and response dynamics achievable by exploiting enzymatic catalysis as selective triggers in controlled release. The first section provides a general introduction about the role of enzymes in diseased states and examples where molecular therapeutics have been developed specifically to interfere with biochemical processes. The parameters to consider in order to develop enzyme-responsive drug-delivery systems are then discussed. Different approaches to design hydrogels, micelles and silica nanocontainers with moieties that can be substrates of enzymes are described with the help of relevant examples that highlight their performance. The research in this area is gaining momentum at a significant pace and it is likely that the first therapeutic enzyme responsive materials will reach the clinic in the next decade.

Evaluation of RGD peptide hydrogel in the posterior segment of the rabbit eye

The aim of this study was to evaluate the biocompatibility and biodegradability of RGD peptide hydrogel in the posterior segment of the eye as a biomaterial potentially useful for sustained drug delivery systems. RGD peptide hydrogel was injected into the vitreous cavity and suprachoroidal space of rabbit eyes. Clinical follow-up and histological observation were performed up to four weeks. The biodegradability was also evaluated by the lifetime of the hydrogel which was defined by ophthalmoscopic observation or ultrasonography. The results showed that RGD peptide hydrogel was well tolerated in the vitreous cavity and suprachoroidal space, and disappeared from the injection sites progressively. As for suprachoroidal injection, the hydrogel was clearly identified by ultrasound echography and was confirmed innoxious to the retinal vessels by fluorescein angiography. Histological observations showed that the structures of retina, choroid and other tissues around the injection site remained normal after the injection. The lifetime of the hydrogel was 25.7 ± 2.65 days and 14.3 ± 3.3 days in the vitreous cavity and suprachoroidal space, respectively. The results obtained demonstrated that RGD peptide hydrogel, which showed excellent biocompatibility and favorable biodegradability in the posterior segment of rabbit eyes, appears to be a promising biomaterial to deliver drugs focally to the choroid and the retina.

Slow-release RGD-peptide hydrogel monoliths

We report on the formation of hydrogel monoliths formed by functionalized peptide Fmoc-RGD (Fmoc: fluorenylmethoxycarbonyl) containing the RGD cell adhesion tripeptide motif. The monolith is stable in water for nearly 40 days. The gel monoliths present a rigid porous structure consisting of a network of peptide fibers. The RGD-decorated peptide fibers have a β-sheet secondary structure. We prove that Fmoc-RGD monoliths can be used to release and encapsulate material, including model hydrophilic dyes and drug compounds. We provide the first insight into the correlation between the absorption and release kinetics of this new material and show that both processes take place over similar time scales.

Hydrogels as drug-delivery platforms: physicochemical barriers and solutions

The properties of hydrogels, in particular their high biocompatibility and water sorption uptake, make hydrogels very attractive in drug delivery and biomedical devices. These favorable features of hydrogels are compromised by certain structural limitations such as those associated with their low mechanical strength in the swollen state. This review highlights the most important challenges that may seriously affect the practical implementation of hydrogels in clinical practice and the solutions that may be applied to overcome these limitations.

BSA-stabilized molecular hydrogels of a hydrophobic compound

We report a protein-stabilized mechanism to understand the formation of molecular hydrogels from hydrophobic compounds.

Safety evaluation of intracameral and subconjunctival injection of a novel mucoadhesive polysaccharide isolated from Bletilla striata in rabbit eye

PURPOSE

To evaluate the safety of intracameral and subconjunctival injection of a novel mucoadhesive polysaccharide isolated from Bletilla striata in rabbit eye.

METHODS

One hundred microliters (100 μL) of Bletilla striata polysaccharide (BsP) at concentrations of 10, 40, and 80 mg/mL was intracamerally or subconjunctivally injected into rabbit eyes. Phosphate-buffered saline and 10 mg/mL hyaluronic acid solution were also injected as controls. BsP safety was evaluated via clinical follow-up and histological analysis. The dead corneal endothelial cells were observed by vital staining with alizarin red and trypan blue at 14 days after intracameral injection. Finally, in the intracameral injection study, scanning electron microscopy was performed for evaluation of the structure of the corneal endothelium and anterior lens capsules.

RESULTS

Subconjunctival injection of 10 mg/mL BsP does not cause pathological changes or an inflammatory response. Concentration greater than 10 mg/mL of BsP (40 or 80 mg/mL) leaded to a slight inflammatory response, but the rabbits recovered well in 3 days. The pathological observation further confirmed the safety of subconjunctival injection of BsP, and subconjunctival injection of 80 mg/mL BsP caused no lesion of the ocular tissues. Intracameral injection of 80 mg/mL of BsP did not cause a significant inflammatory reaction, and an even lower inflammatory response was observed in rabbits intracamerally injected with 40 or 10 mg/mL BsP. All rabbits intracamerally injected with BsP recovered within 7-14 days. BsP had little effect on the blood-aqueous barrier's integrity when the concentration was 10 mg/mL; at 40 or 80 mg/mL, a mild effect was observed, and the rabbits recovered in 1-3 days. Intracameral BsP injected at a concentration of 80 mg/mL had a negative impact on the corneal endothelium and lens, but concentrations of 40 or 10 mg/mL could be injected safely.

CONCLUSIONS

BsP injection into the subconjunctival space and anterior chamber in rabbits at low concentrations (such as 10 mg/mL) did not have adverse effects.

Morphology transformation via pH-triggered self-assembly of peptides

Three flexible peptides (P1: (C(17)H(35)CO-NH-GRGDG)(2)KG; P2: (Fmoc-GRGDG)(2)KG; P3: (CH(3)CO-NH-GRGDG)(2)KG) self-assembled to form a variety of morphologically distinct assemblies at different pHs. P1 formed nanofibers at pH 3, then self-assembled into nanospheres with pH up to 6 and further changed to lamellar structures when the pH value was further increased to 10. P2 aggregated into an entwined network structure at pH 3, and then self-assembled into well-defined nanospheres, lamellar structures, and vesicles via adjusting the pH value. However, P3 did not self-assemble into well-ordered nanostructures, presumably due to the absence of a large hydrophobic group. The varying self-assembly behaviors of the peptides at different pHs are attributed to molecular conformational changes. These self-assembled supramolecular materials might contribute to the development of new peptide-based biomaterials.

Efficient and facile formation of two-component nanoparticles via aromatic moiety directed self-assembly

Here we present a two-component self-assembling system employing the interaction of aromatic groups (Fmoc) to construct nanoparticles. Spherical particles of around 70 nm were formed spontaneously by a simple trigonal Fmoc-conjugate, which were then stabilized by Fmoc-dipeptides at physiological pH in aqueous solution. These novel particles, being well-tolerated by cells, capable of encapsulating hydrophobic compounds, and readily decorated by short peptides, are promising carriers for drug delivery.

Peptide hydrogel as an intraocular drug delivery system for inhibition of postoperative scarring formation

A biocompatible hydrogel self-assembled from a peptide comprised of a peptide backbone containing Arg-Gly-Asp (RGD) sequence and a hydrophobic N-fluorenyl-9-methoxycarbonyl (FMOC) tail was designed and prepared to load antiproliferative model drug (5-fluorouracil, 5-Fu). After administering this 5-Fu-loaded peptide hydrogel in the filtering surgery of rabbit eyes, because of the sustained release of 5-Fu from the hydrogel to inhibit the scleral flap fibrosis efficiently, the pathology and immunohistochemistry demonstrate that the filtration fistula is patent without postoperative scarring formation, resulting in the significantly low intraocular pressure (IOP) of the rabbit eyes within postoperative 28 days. In a comparison with the conventional 5-Fu exposure, the strategy demonstrated here presents several advantages including providing convenience and preventing the toxicity of 5-Fu to the surrounding ocular tissues efficiently, suggesting a feasibility of this peptide hydrogel as a potential implanted drug delivery system for the inhibition of postoperative scarring formation.