Destabilization of Liposomes by Uncharged Hydrophilic and Amphiphilic Polymers

Liposome leakage and increased cellular permeability induced by guanidine-based oligomers: effects of liposome composition on liposome leakage and human lung epithelial barrier permeability

In this study, liposome leakage using different liposome compositions and increased cellular permeability of human lung monolayer models induced by PHMG and PHMB were investigated.

Critical role of the degree of substitution in the interaction of biocompatible cholic acid-modified dextrans with phosphatidylcholine liposomes

The interaction between biocompatible cholic acid-modified dextrans with different pendent cholic acid groups' content and phosphatidylcholine liposomes was studied by a variety of techniques including isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), turbidity measurements, microscopy imaging (transmission electron microscopy (TEM), and cryo-scanning electron microscopy (cryo-SEM)). The variation of the interaction enthalpy with polymer concentration, as obtained by ITC, highlighted the formation of different aggregates. Complete phase modification, from vesicles covered with a few polymer chains to vesicle disintegration, was observed by turbidity measurements. DSC showed the effect of polymer addition to the liposome gel to liquid-crystalline phase transition, and microscopy images gave information about the size and morphology of the aggregates. The composition, structure, and morphology of polymer/liposome aggregates were found to be strongly influenced by the cholic acid content in the polymer (degree of substitution, DS). Along with a rather monotonous change in the polymer/liposome system's properties with increasing DS, a discontinuity in behavior could also be observed at DS = 4 mol %. For DS ≤ 4 mol %, the polymer/liposome interaction takes place mainly between individual components, and liposome disintegration occurs in a narrow concentration range, whereas for DS > 4 mol % extended physical networks are formed, which last over a wide concentration range. A mechanism of interaction, as a function of DS, is proposed and discussed in detail.

Exploring uptake mechanisms of oral nanomedicines using multimodal nonlinear optical microscopy

Advances in pharmaceutical nanotechnology have yielded ever increasingly sophisticated nanoparticles for medicine delivery. When administered via oral, intravenous, ocular and transcutaneous delivery routes, these nanoparticles can elicit enhanced drug performance. In spite of this, little is known about the mechanistic processes underlying interactions between nanoparticles and tissues, or how these correlate with improved pharmaceutical effects. These mechanisms must be fully understood before nanomedicines can be rationally engineered to optimise their performance. Methods to directly visualise these particulates within tissue samples have traditionally involved imaging modalities requiring covalent labelling of fluorescent or radioisotope contrast agents. We present CARS, second harmonic generation and two photon fluorescence microscopy combined as a multi-modal label-free method for pinpointing polymeric nanoparticles within the stomach, intestine, gall bladder and liver. We demonstrate for the first time that orally administered chitosan nanoparticles follow a recirculation pathway from the GI tract via enterocytes, to the liver hepatocytes and intercellular spaces and then to the gall bladder, before being re-released into the gut together with bile.

In-vitro permeability screening of melt extrudate formulations containing poorly water-soluble drug compounds using the phospholipid vesicle-based barrier

Objectives

The phospholipid vesicle-based barrier has recently been introduced as an in-vitro permeation model mimicking gastro-epithelial barriers in terms of passive diffusion of drugs. The aim of this study was to investigate whether the phospholipid vesicle-based barrier was suitable for permeability screening of complex formulations such as solid dispersions.

Methods

Solid dispersions containing the poorly water-soluble drugs HIV-PI 1 (log P = 6.2, molar mass = 628.80 g/mol) and HIV-PI 2 (log P = 5.3, molar mass = 720.95 g/mol), a hydrophilic polymer and different surfactants were tested with respect to their influence on integrity of the barrier in terms of electrical resistance and permeability for calcein. Furthermore, utilisation of a more biologically relevant medium, Hank's balanced salt solution supplemented with Mg2+- and Ca2+-ions (HBSS (Mg2+, Ca2+)), has been tested.

Key findings

Except for the polyoxyl 40 hydrogenated castor oil-containing solid dispersion, no influence on the phospholipid vesicle-based barrier could be observed from the tested samples. Presence of active pharmaceutical ingredients (APIs) in the solid dispersions led to the same results as the corresponding placebo results. First experiments analysing the passive diffusion of both APIs in HBSS (Mg2+, Ca2+), evaluated as suitable transport medium, have shown promising results regarding the suitability of the phospholipid vesicle-based barrier for investigation of solid dispersions.

Conclusions

The study indicated that the phospholipid vesicle-based barrier was compatible with selected melt extrudate formulations. The model seemed capable to reveal different transport routes in comparison with Caco-2 cell permeability tests.

Flexible macromolecules attached to lipid bilayers: impact on fluidity, curvature, permeability and stability of the membranes

This review summarizes recent investigations on the association of macromolecules on lipid bilayers. Hydrophilic and flexible polymers can form soft coronae tenuously adsorbed or anchored on the lipid membrane. Other synthetic macromolecules are embedded in the apolar region of the membrane. Recent experimental and theoretical works focus on the perturbation of lipid properties achieved depending on the nature and strength of binding. Of importance to biomimicry, to tethered model membranes, and drug carriers, the effects achievable include modulation of the lateral diffusivity of lipids, shape distortions, lateral segregations, formation of well-defined nanopores and ultimately the stimuli responsive disruption of the membrane.

Interactions between flavonoids and hemoglobin in lecithin liposomes

In this paper, the binding of flavonoids (quercetin and rutin) to hemoglobin (Hb) have been investigated by fluorescence, absorption spectroscopy and circular dichroism (CD) spectroscopy. The binding parameters and binding mode between flavonoids and Hb are determined and the results of CD and synchronous fluorescence spectra indicate a conformational change of Hb with addition of flavonoids. The effects of lecithin liposomes on the binding parameter of quercetin and rutin to Hb are also studied. When incorporated into liposome, flavonoids can reduce the fluorescence of tryptophanyl residues of Hb to a lesser extent. The difference of the structure characteristics between quercetin and rutin has a significant effect on their binding affinity for Hb.

Synthesis and characterization of poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide]-g-poly(L-lactide) biodegradable copolymers as drug carriers

A series of biodegradable amphiphilic graft polymers were successfully synthesized by grafting poly(L-lactide) (PLLA) sequences onto a water-soluble polymer poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide] (PHEA) backbone. We established the feasibility of preparing these novel graft polymers by the ring-opening polymerization initiated by the macroinitiator PHEA bearing hydroxyl groups without adding any catalyst. The successful grafting of PLLA sequences onto the PHEA backbone was verified by combined size exclusion chromatography (SEC) and multiangle laser light scattering (MALLS) analysis. The chemical structures of graft polymers were characterized by FTIR and (1)H NMR. The critical micelle concentration (CMC) of the graft polymer was determined by fluorescence probe technique using pyrene. By controlling the feed ratio of the macroinitiator to the monomer, graft polymers with different branch lengths can be obtained. Using the 3-(4,5 dimethylthiozol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay, the graft copolymer has been proved to have low cytotoxicity. Based on the amphiphilicity of the graft copolymers, nanoparticular drug delivery systems were prepared by the direct dissolution method and the dialysis method. The anticancer drug Tegafur was encapsulated into polymeric nanoparticles, and in vitro drug release behavior was investigated. Transmission electron microscopy (TEM) images demonstrate that these nanoparticles are regularly spherical in shape. The particle size and distribution of the nanoparticles were measured.