Branched Amphipathic Peptide Capsules: Different Ratios of the Two Constituent Peptides Direct Distinct Bilayer Structures, Sizes, and DNA Transfection Efficiency.

Branched amphipathic peptide capsules (BAPCs) are biologically derived, bilayer delimited, nanovesicles capable of being coated by or encapsulating a wide variety of solutes. The vesicles and their cargos are readily taken up by cells and become localized in the perinuclear region of cells. When BAPCs are mixed with DNA, the BAPCs act as cationic nucleation centers around which DNA winds. The BAPCs-DNA nanoparticles are capable of delivering plasmid DNA in vivo and in vitro yielding high transfection rates and minimal cytotoxicity. BAPCs share several biophysical properties with lipid vesicles. They are however considerably more stable-resisting disruption in the presence of chaotropes such as urea and guanidinium chloride, anionic detergents, proteases, and elevated temperature (∼95 °C). To date, all of our published results have utilized BAPCs that are composed of equimolar concentrations of the two branched sequences (Ac-FLIVI)2-K-K4-CO-NH2 and (Ac-FLIVIGSII)2-K-K4-CO-NH2. The mixture of sizes was utilized to relieve potential curvature strain in the spherical capsule. In this article, different molar ratios of the two peptides were studied to test whether alternate ratios produced BAPCs with different biological and biophysical properties. Additionally, preparation (annealing) temperature was included as a second variable.

A review of solute encapsulating nanoparticles used as delivery systems with emphasis on branched amphipathic peptide capsules.

Various strategies are being developed to improve delivery and increase the biological half-lives of pharmacological agents. To address these issues, drug delivery technologies rely on different nano-sized molecules including: lipid vesicles, viral capsids and nano-particles. Peptides are a constituent of many of these nanomaterials and overcome some limitations associated with lipid-based or viral delivery systems, such as tune-ability, stability, specificity, inflammation, and antigenicity. This review focuses on the evolution of bio-based drug delivery nanomaterials that self-assemble forming vesicles/capsules. While lipid vesicles are preeminent among the structures; peptide-based constructs are emerging, in particular peptide bilayer delimited capsules. The novel biomaterial-Branched Amphiphilic Peptide Capsules (BAPCs) display many desirable properties. These nano-spheres are comprised of two branched peptides-bis(FLIVI)-K-KKKK and bis(FLIVIGSII)-K-KKKK, designed to mimic diacyl-phosphoglycerides in molecular architecture. They undergo supramolecular self-assembly and form solvent-filled, bilayer delineated capsules with sizes ranging from 20 nm to 2 µm depending on annealing temperatures and time. They are able to encapsulate different fluorescent dyes, therapeutic drugs, radionuclides and even small proteins. While sharing many properties with lipid vesicles, the BAPCs are much more robust. They have been analyzed for stability, size, cellular uptake and localization, intra-cellular retention and, bio-distribution both in culture and in vivo.

Branched amphiphilic peptide capsules: cellular uptake and retention of encapsulated solutes.

Branched amphiphilic peptide capsules (BAPCs) are peptide nano-spheres comprised of equimolar proportions of two branched peptide sequences bis(FLIVI)-K-KKKK and bis(FLIVIGSII)-K-KKKK that self-assemble to form bilayer delimited capsules. In two recent publications we described the lipid analogous characteristics of our BAPCs, examined their initial assembly, mode of fusion, solute encapsulation, and resizing and delineated their capability to be maintained at a specific size by storing them at 4°C. In this report we describe the stability, size limitations of encapsulation, cellular localization, retention and, bio-distribution of the BAPCs in vivo. The ability of our constructs to retain alpha particle emitting radionuclides without any apparent leakage and their persistence in the peri-nuclear region of the cell for extended periods of time, coupled with their ease of preparation and potential tune-ability, makes them attractive as biocompatible carriers for targeted cancer therapy using particle emitting radioisotopes. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Branched amphiphilic cationic oligopeptides form peptiplexes with DNA: a study of their biophysical properties and transfection efficiency.

Over the past decade, peptides have emerged as a new family of potential carriers in gene therapy. Peptides are easy to synthesize and quite stable. Additionally, sequences shared by the host proteome are not expected to be immunogenic or trigger inflammatory responses, which are commonly observed with viral approaches. We recently reported on a new class of branched amphiphilic peptide capsules (BAPCs) that self-assemble into extremely stable nanospheres. These capsules are capable of retaining and delivering alpha-emitting radionuclides to cells. Here we report that, in the presence of double stranded plasmid DNA, BAPCs are unable to form. Instead, depending of the peptide/DNA ratios, the peptides either coat the plasmid surface forming nanofibers (high peptide to DNA ratio) or condense the plasmid into nanometer-sized compacted structures (at low peptide to DNA ratios). Different gene delivery efficiencies are observed for the two types of assemblies. The compacted nanometer-sized structures display much higher transfection efficiencies in HeLa cells. This level of transfection is greater than that observed for a lipid-based reagent when the total number of viable transfected cells is taken into account.

Thermally induced conformational transitions in nascent branched amphiphilic peptide capsules.

Branched amphiphilic peptide capsules (BAPCs) are biocompatible, bilayer delimited polycationic nanospheres that spontaneously form at room temperature through the coassembly of two amphiphilic branched peptides: bis(FLIVI)-K-K4 and bis(FLIVIGSII)-K-K4. BAPCs are readily taken up by cells in culture, where they escape and/or evade the endocytic pathway and accumulate in the perinuclear region, persisting there without apparent degradation or extravasation. Drugs, small proteins, and solutes as well as α particle emitting radionuclides are stably encapsulated for extended periods of time. BAPC formation at room temperature proceeds via a fusogenic process and after 48 h a range of BAPCs sizes are observed, from 50 nm to a few microns in diameter. It was previously reported that cooling BAPCs from 25 to 4 °C and then back to 25 °C eliminated their fusogenic property. In this report, biophysical techniques reveal that BAPCs undergo thermosensitive conformational transitions as a function of both time and temperature and that the properties of BAPCs vary based on the temperature of assembly. The solvent dissociation properties of BAPCs were studied as well as the contributions of specific amino acid residues to the observed conformations. The roles of the potential stabilizing forces present within the bilayer that bestow the unusal stability of the BAPCs are discussed. Ultimately this study presents revised assembly protocols for preparing BAPCs with discrete sizes and solvent-induced extravasation properties.

Branched oligopeptides form nanocapsules with lipid vesicle characteristics.

In a recent article (Gudlur et al. PLOS ONE, 2012, 7 (9) e45374), we described the special properties of a mixed branched peptide assembly in which equimolar bis(FLIVI)-K-KKKK and bis(FLIVIGSII)-K-KKKK self-associate to form bilayer delimited capsules capable of trapping solutes. These polycationic vesicle-like capsules are readily taken up by epithelial cells in culture, escape or evade the endocytic pathway, and accumulate in the perinuclear region where they persist without any apparent degradation. In this report, we examine the lipidlike properties of this system including initial assembly; solute encapsulation and washing; fusion and resizing by membrane extrusion through polycarbonate filters with defined pore sizes. The resized peptide capsules have uniform diameters in nm size ranges. Once resized, the capsules can be maintained at the new size by storing them at 4 °C. Having the ability to prepare stable uniform nanoscale capsules of desired sizes makes them potentially attractive as biocompatible delivery vehicles for various solutes/drugs.

Effect of the synthetic NC-1059 peptide on diffusion of riboflavin across an intact corneal epithelium.

PURPOSE: To investigate the effect of the peptide NC-1059 on riboflavin (RF) diffusion across an intact corneal epithelium into the stroma. METHODS: NC-1059 peptide was synthesized by solid-phase synthesis with 9-fluorenylmethoxycarbonyl chemistry, characterized by reversed-phase HPLC, and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy. The diffusion of RF across embryonic day 18 chick corneal epithelium ex vivo was monitored using confocal microscopy. The depth distributions of RF in the corneal stroma were calculated using a group of linear equations based on the relationship between RF fluorescence intensity and concentration. RESULTS: Data presented in this study demonstrate that the NC-1059 peptide can transiently open the intact epithelial barrier to allow the permeation of RF into the stroma. The effect of NC-1059 peptide on RF diffusion across the corneal epithelium was concentration and time dependent. The amount of RF reaching a 50-µm depth of chick corneal stoma increased dramatically after exposure to NC-1059 for 10 minutes, reaching a plateau by 30 minutes. The concentrations of RF in the presence of NC-1059 at corneal stromal depths of 50, 100, and 150 µm were significantly higher than in the absence of the peptide, and almost as high as in corneas in which the epithelium first had been physically removed. In addition, a cell viability assay indicated that the NC-1059 peptide did not kill corneal epithelial cells. CONCLUSIONS: NC-1059 peptide significantly enhances the diffusion of RF across intact corneal epithelium into the stroma.

Peptide nanovesicles formed by the self-assembly of branched amphiphilic peptides.

Peptide-based packaging systems show great potential as safer drug delivery systems. They overcome problems associated with lipid-based or viral delivery systems, vis-a-vis stability, specificity, inflammation, antigenicity, and tune-ability. Here, we describe a set of 15 & 23-residue branched, amphiphilic peptides that mimic phosphoglycerides in molecular architecture. These peptides undergo supramolecular self-assembly and form solvent-filled, bilayer delimited spheres with 50-200 nm diameters as confirmed by TEM, STEM and DLS. Whereas weak hydrophobic forces drive and sustain lipid bilayer assemblies, these all-peptide structures are stabilized potentially by both hydrophobic interactions and hydrogen bonds and remain intact at low micromolar concentrations and higher temperatures. A linear peptide lacking the branch point showed no self-assembly properties. We have observed that these peptide vesicles can trap fluorescent dye molecules within their interior and are taken up by N/N 1003A rabbit lens epithelial cells grown in culture. These assemblies are thus potential drug delivery systems that can overcome some of the key limitations of the current packaging systems.