pH-Sensitive Liposomes with Embedded 3-(isobutylamino)cholan-24-oic Acid: What Is the Possible Mechanism of Fast Cargo Release?

pH-sensitive liposomes have great potential for biomedical applications, in particular as nanocontainers for the delivery of biologically active compounds to specific areas of the human body. In this article, we discuss the possible mechanism of fast cargo release from a new type of pH-sensitive liposomes with embedded ampholytic molecular switch (AMS, 3-(isobutylamino)cholan-24-oic acid) with carboxylic anionic groups and isobutylamino cationic ones attached to the opposite ends of the steroid core. AMS-containing liposomes demonstrated the rapid release of the encapsulated substance when altering the pH of an outer solution, but the exact mechanism of the switch action has not yet been accurately determined. Here, we report on the details of fast cargo release based on the data obtained using ATR-FTIR spectroscopy as well as atomistic molecular modeling. The findings of this study are relevant to the potential application of AMS-containing pH-sensitive liposomes for drug delivery.

Complexes of Cationic Pyridylphenylene Dendrimers with Anionic Liposomes: The Role of Dendrimer Composition in Membrane Structural Changes.

In the last decades, dendrimers have received attention in biomedicine that requires detailed study on the mechanism of their interaction with cell membranes. In this article, we report on the role of dendrimer structure in their interaction with liposomes. Here, the interactions between cationic pyridylphenylene dendrimers of the first, second, and third generations with mixed or completely charged pyridyl periphery (D16+, D215+, D229+, and D350+) with cholesterol-containing (CL/Chol/DOPC) anionic liposomes were investigated by microelectrophoresis, dynamic light scattering, fluorescence spectroscopy, and conductometry. It was found that the architecture of the dendrimer, namely the generation, the amount of charged pyridynium groups, the hydrophobic phenylene units, and the rigidity of the spatial structure, determined the special features of the dendrimer-liposome interactions. The binding of D350+ and D229+ with almost fully charged peripheries to liposomes was due to electrostatic forces: the dendrimer molecules could be removed from the liposomal surfaces by NaCl addition. D350+ and D229+ did not display a disruptive effect toward membranes, did not penetrate into the hydrophobic lipid bilayer, and were able to migrate between liposomes. For D215+, a dendrimer with a mixed periphery, hydrophobic interactions of phenylene units with the hydrocarbon tails of lipids were observed, along with electrostatic complexation with liposomes. As a result, defects were formed in the bilayer, which led to irreversible interactions with lipid membranes wherein there was no migration of D215+ between liposomes. A first-generation dendrimer, D16+, which was characterized by small size, a high degree of hydrophobicity, and a rigid structure, when interacting with liposomes caused significant destruction of liposomal membranes. Evidently, this interaction was irreversible: the addition of salt did not lead to the dissociation of the complex.

Interaction of Ionenes with Lipid Membrane: Unusual Impact of Charge Density.

Synthetic water-soluble polymers are increasingly used for gene delivery, stabilization, and delivery of proteins, and as prospective antimicrobial and antiviral agents. Therefore, study of their interaction with lipid membranes is of special importance. Herein, we studied interaction of aliphatic cationic ionenes (recently tested for gene delivery efficiency) differed in the length of spacer between charged groups (and therefore in charge density) with anionic lipid membrane. A range of approaches such as measurement of particle size and electrophoretic mobility, liposome integrity, ATR-FTIR spectroscopy, isothermal titration calorimetry as well as atomistic molecular modeling was used. Ionene with a spacer of 10 methylene groups has been shown to be incorporated into membrane and interact with its inner hydrophobic part in contrast to ionenes with shorter spacer, which interacted only with outer polar head groups of lipids staying at the water-membrane interface. It affects membrane integrity and results in a different behavior of the polymer-liposome complexes. These findings are relevant for potential biomedical application of ionenes, including creation of composite polymer-liposome systems for drug delivery.

Plasticity control of poly(vinyl alcohol)-graphene oxide nanocomposites.

Composite films containing poly(vinyl alcohol) filled with different amounts of graphene oxide (2 and 4 wt%) were prepared by the solution casting technique, and the mechanical properties of the resulting materials were modified with different amounts of glycerol as a plasticizer. Two series of pure poly(vinyl alcohol) and graphene oxide-loaded films with fixed amounts of water were used for modification with glycerol, since water can also serve as a plasticizer for poly(vinyl alcohol). The morphology and physical properties of the plasticized and non-plasticized composites were studied; tensile tests were performed to investigate and compare their mechanical properties. Glycerol addition does not affect the excellent compatibility of the filler with the polymer matrix and uniform distribution of graphene oxide in poly(vinyl alcohol). For poly(vinyl alcohol)/graphene oxide films an increase of the Young's modulus and yield stress was found with an increase of the filler content; the Young's modulus for poly(vinyl alcohol) filled with 4 wt% of graphene oxide is almost two times higher than that of the pure polymer. Simultaneously, a sharp decrease of the elongation at break from 80% for pure PVA to about 5% for the PVA/GO composite with 4 wt% of GO is observed, and the film's brittleness dramatically increases. It was shown that the addition of glycerol to the composite films leads both to the Young's modulus decrease and tensile energy at break increase; here the Young's modulus decreases by 18 times after addition of 20 wt% of glycerol to the poly(vinyl alcohol) film filled with 4 wt% of graphene oxide. Thus, the use of plasticizer results in a significant increase of the ductile properties of graphene oxide filled poly(vinyl alcohol) composite films, and the higher the water content in the composite film, the more drastic the increase of the ductile properties observed.

The Influence of the Chain Length of Polycations on their Complexation with Anionic Liposomes.

A series of strong polycations is synthesized through the anionic polymerization of 2-vinylpyridine, followed by subsequent quaternization of the resulting polymer. Polycations based on quaternized 2-vinylpyridine (PVPQs) with degrees of polymerization (DP) from 20 to 440 are adsorbed on the surface of small anionic liposomes. Liposome/PVPQ complexes are characterized by using a number of physicochemical methods. All PVPQs are totally adsorbed onto the liposome surface up to a certain concentration at which saturation is reached (which is specific for each PVPQ). The integrity of the adsorbed liposomes remains intact. Short PVPQs interact with anionic lipids localized on the outer membrane leaflet, whereas long PVPQs extract anionic lipids from the inner to outer leaflet. Complexes tend to aggregate, and the largest aggregates are formed when the initial charge of the liposomes is fully neutralized by the charge of the PVPQ. PVPQs with intermediate DPs demonstrate behavioral features of both short and long PVPQs. These results are important for the interpretation of the biological effects of cationic polymers and the selection of cationic polymers for biomedical applications.

Polymer migration among phospholipid liposomes.

Complexation of phospholipid lipsomes with a cationic polymer, poly(N-ethyl-4-vinylpyridinium bromide) (PEVP), and subsequent interliposomal migration of the adsorbed macromolecules, have been investigated. Liposomes of two different charge types were examined: (a) a liposomal system, with an overall charge near zero, consisting of zwitterionic phosphatidylcholine (egg lecithin, EL) with added doubly anionic phospholipid, cardiolipin (CL(2-)), and cationic dihexadecyldimethylammonium bromide (HMAB(+)), in a CL(2-)/HMAB(+) charge-to-charge ratio of 1:1; (b) an anionic liposomal system composed of an EL/CL(2-) mixture plus polyoxyethylene monocetyl ether (Brij 58). Both three-component systems were designed specifically to preclude liposomal aggregation upon electrostatic association with the PEVP, a phenomenon that had complicated analysis of data from several two-component liposomes. PEVP macromolecules were found from fluorescence experiments to migrate among the charge-neutral EL/CL(2-)/HMAB(+) liposomes. In the case of anionic EL/CL(2-)/Brij liposomes, a combination of fluorescence and laser microelectrophoresis methods showed that PEVP macromolecules travel from liposome to liposome while being electrostatically associated with anionic lipids.

Polyelectrolyte-coated liposomes: stabilization of the interfacial complexes.

Anionic liposomes, composed of egg lecithin (EL) or dipalmitoylphosphatidylcholine (DPPC) with 20 mol% of cardiolipin (CL(2-)), were mixed with cationic polymers, poly(4-vinylpyridine) fully quaternized with ethyl bromide (P2) or poly-L-lysine (PL). Polymer/liposome binding studies were carried out using electrophoretic mobility (EPM), fluorescence, and conductometry as the main analytical tools. Binding was also examined in the presence of added salt and polyacrylic acid (PAA). The following generalizations arose from the experiments: (a) Binding of P2 and PL to small EL/CL(2-) liposomes (60-80 nm in diameter) is electrostatic in nature and completely reversed by addition of salt or PAA. (b) Binding can be enhanced by hydrophobization of the polymer with cetyl groups. (c) Binding can also be enhanced by changing the phase state of the lipid bilayer from liquid to solid (i.e. going from EL to DPPC) or by increasing the size of the liposomes (i.e. going from 60-80 to 300 nm). By far the most promising systems, from the point of view of constructing polyelectrolyte multilayers on liposome cores without disruption of liposome integrity, involve small, liquid, anionic liposomes coated initially with polycations carrying pendant alkyl groups.

What is the effective charge of TGA-stabilized CdTe nanocolloids?

The surface charge of semiconductor nanoparticles, Q, is an important parameter which determines their electrokinetic behavior, stability in water and polar solvents, functions of optical and electronic devices, self-assembly properties, and interactions with cell membranes. We have developed a simple method for quantitative determination of Q in their native aqueous environment. The method does not require the knowledge of exact atomic structure or make assumptions about effects of drying on charge distribution. The method is based on titration of nanoparticle dispersion with a solution of oppositely charged polyelectrolyte. The point of complete neutralization is recognized as an inflection point on the dependence of fluorescence intensity on the amount of polyelectrolyte added. Thioglycolic acid-stabilized CdTe nanoparticles 2 nm in diameter were found to carry an average Q from -2.6 to -5.5 for pH 7.5 to 10, respectively. This charge is found to be smaller than that calculated theoretically for an analogous structure (i.e., Q = -8), presumably due to adsorption of Cd(2+) ions on the stabilizer shell and on Te atoms with unsaturated valence located on the side planes of CdTe tetrahedrons.