Lipid-coated Membrane Research Articles

Lipid-coated membranes as skin surrogates for permeability assessment

There is a growing interest in developing in vitro skin models, particularly in the fields of skin care and drug delivery regarding optimization of topical drug formulations. The ban of animal experiments for cosmetic products testing has led to the development of alternative in vitro methods. The aim of this study was to develop and characterize simplified, cell-free, lipid-coated membrane models, exploring the usefulness and the potential application of these membranes in comparison to commercial synthetic membrane and to porcine skin. In these model membranes, lipids are deposited onto a polycarbonate membrane to create lipid-rich coated membranes. Two types of lipid-coated membranes were explored depending on the type of lipids used. In one type (phospholipidic), membranes were prepared depositing soybean phosphatidylcholine liposomes and in the other type (non-phospholipidic), major components of the stratum corneum lipid matrix were used to coat the polycarbonate membrane. Coating process was performed using drying and centrifugation steps. Under infinite dose conditions, and caffeine as permeant, high permeation correlation between developed membranes and pig skin was obtained, and similar permeation pro-files were obtained through phospholipidic and non-phospholipidic membranes. This study demonstrated the potential of the developed membranes to conduct permeation studies using Franz-type diffusion cells, and the simplication process to produce lipid-coated membranes.

Solid lipid microparticles for hair follicle targeting of adapalene and benzoyl peroxide - Release through targeted erosion

Sebum-dependent targeting of the upper hair follicle by solid lipid microparticles has been demonstrated for retinoids using adapalene as an example. An extension of this formulation principle to the combination of adapalene/benzoyl peroxide was achieved on the basis of congealed solid-in-oil dispersions of nanoparticulate benzoyl peroxide, which were incorporated into the solid lipid microparticles. To investigate the dermal distribution and release behaviour of the solid lipid microparticles after application, fluorescence microscopic ex vivo studies on porcine ear skin samples treated with the experimental vehicle were supplemented by calorimetric skin lipid interaction studies and release experiments on lipid-coated membranes, investigating the influence of sebum and stratum corneum lipids on the solid lipid microparticle matrix. Fluorescent microscopic images of the treated skin confirm the observation of preferential deposition in the upper hair follicle. In addition, the release experiments show a sebum-dependent release of the active ingredients, with no detectable release in the presence of stratum corneum lipids. The observed discrepancy is probably a result of the rapid disintegration of the particles on contact with sebum, as calorimetric investigations suggest. This behaviour, which is based on the similarity between the sebum components and the lipid matrix, allows a targeted release into sebum and thus increased follicular penetration.

Controlled translocation of DNA through nanopores in carbon nano-, silicon-nitride- and lipid-coated membranes.

We investigated experimentally and theoretically the translocation forces when a charged polymer is threaded through a solid-state nanopore and found distinct dependencies on the nanopore diameter as well as on the nano membrane material chemistry. For this purpose we utilized dedicated optical tweezers force mechanics capable of probing the insertion of negatively charged double-stranded DNA inside a helium-ion drilled nanopore. We found that both the diameter of the nanopore and the membrane material itself have significant influences on the electroosmotic flow through the nanopore and thus on the threading force. Compared to a bare silicon-nitride membrane, the threading of DNA through only 3 nm thin carbon nano membranes as well as lipid bilayer-coated nanopores increased the threading force by 15% or 85%, respectively. This finding was quantitatively described by our recently developed theoretical model that also incorporates hydrodynamic slip effects on the translocating DNA molecule and the force dependence on the membrane thickness. The additional measurements presented in this paper further support our model.

Prolonging the Ultrasound Signal Enhancement From Thrombi Using Targeted Microbubbles Based on Sulfur-Hexafluoride–Filled Gas

The objective of this study is to develop and characterize new microbubbles based on lipids and sulfur hexafluoride (SF6) for targeting thrombi as an improved ultrasound contrast agent. Bioconjugate ligands were inserted into the lipid-coated membranes of SF6 gas microbubbles, and their physicochemical properties were determined. Diagnostic efficacies of SF6-filled microbubbles and the contrast agent SonoVue (Bracco Imaging, Geneve, Switzerland) were compared in dogs. Suspensions of lyophilized powder were reconstituted by injecting saline containing 3.1 x 10(8) SF6 microbubbles/mL with a mean diameter of 4.4 microm. More than 90% of microbubbles had diameters between 1 and 10 microm. After reconstitution, echogenicity and microbubble characteristics were unchanged for 8 hours. Targeted microbubbles increased the echogenicity of thrombi significantly and provided a longer period of optimal signal enhancement compared with nontargeted microbubbles. Our thrombus-targeting microbubble contrast agent shows high echogenicity and stability and thereby enhances the visualization of intravascular thrombi and prolongs the duration of the diagnostic window.

Ternary Complexes of Gentamicin with Iron and Lipid Catalyze Formation of Reactive Oxygen Species

This study was designed to elucidate the mechanisms underlying the formation of reactive oxygen species (ROS) by aminoglycoside antibiotics which may be causally related to the toxic side effects of these drugs to the kidney and the inner ear. ROS formation by aminoglycosides in vitro requires iron and the presence of polyunsaturated lipids as electron donors. Electron spray ionization mass spectrometry (ESI-MS) confirmed earlier observations that gentamicin strongly binds to L-alpha-phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), a membrane lipid rich in arachidonic acid. Studies using lipid-coated membranes (PIP strips) further indicated that iron ions and gentamicin can simultaneously bind to phosphoinositides with at least one phosphate group on the inositol ring, suggesting the existence of ternary complexes among gentamicin, iron, and phospholipids. Peroxidation of PtdIns(4,5)P2 by ferrous ions significantly increased in the presence of gentamicin, and EI-MS measurements indicated that oxidative damage to PtdIns(4,5)P2 was accompanied by the release of arachidonic acid. Arachidonic acid also forms a ternary complex with Fe(2+/3+)-gentamicin, confirmed by ESI-MS, that reacts with lipid peroxides and molecular oxygen, leading to the propagation of arachidonic acid peroxidation.

Targeted-microbubble binding selectively to GPIIb IIIa receptors of platelet thrombi.

New targeted microbubbles directed to the GPIIb IIIa receptor have been developed. The objective was to determine whether targeting microbubbles to clots would enhance ultrasound imaging. Systematic studies were designed to determine whether in vitro methodology is an acceptable predictor of in vivo efficacy. Bioconjugate ligands were inserted into lipid-coated membranes of perfluorocarbon gas microbubbles and binding studies performed on activated platelets immobilized on cell culture plates. Targeted microbubble binding to clots in a flow through chamber was also assessed. Finally, microbubble binding studies on arteriolar and venular clots in a mouse cremasteric muscle model were conducted. Binding studies on platelet-immobilized plates demonstrated an affinity for targeted microbubbles versus untargeted microbubbles. Semiquantitative light obscuration techniques helped to measure extent of targeted microbubble binding. Targeted microbubbles similarly bound to platelet clots in the flow model. Finally, studies in the mouse model confirmed binding of targeted microbubbles in both venules and arterioles. The use of receptor selective targeted microbubbles improved binding to vascular thrombi in both in vitro and in vivo settings.

A METHOD FOR ASSESSING PERCUTANEOUS PERMEABILITY BY USING MODEL LIPIDS OF STRATUM CORNEUM

The maximum fluxes (Jmax) of six β-blockers across keratinized membranes were determined in vitro and compared with their melting points (mp). Rat abdominal skin and hamster cheek pouch mucosa were used as the model membranes. Linear relations of Jmax with mp were observed in both membrane. Permeation studies using the delipidized membranes and the isolated stratum corneum (SC) sheet of hamster cheek pouch clarified that the primary rate-limiting barrier function exists in the SC especially in the intercellular lipid. A lipid mixture system (ceramide : cholesterol : palmitic acid : cholesterol-3-sulfate = 40 : 25 : 25 : 10 by weight, a mimic of intercellular lipids of SC) was used as a lipid-coated membrane and liposomes to evaluate drug permeation through the SC. The Jmax values obtained in the lipid-coated membrane, which showed linear relations with those determined in rat skin and in hamster cheek pouch, correlated with the degree of drug partition to the liposomes prepared with the same model lipid mixture, suggesting the validity of this model lipid mixture system as an in vitro system substituted for animal skin in percutaneous drug permeation studies. The usefulness of the system in assessing the penetration enhancers which act on the lipids in the SC, such as oleic acid (OA), was also clarified.

Keratinized epithelial transport of beta-blocking agents. II. Evaluation of barrier property of stratum corneum by using model lipid systems.

Model lipid mixtures composed of ceramide (40%), cholesterol (25%), palmitic acid (25%) and cholesterol 3-sulfate (10%) were used as the model for intercellular lipids of stratum corneum (SC) to evaluate a barrier function of SC for drug permeation. Six beta-blockers, propranolol, metoprolol, timolol, pindolol, nadolol and atenolol, were used as the model permeants. The maximum flux values (observed flux/thermodynamic activity, Jmax) of drugs through the membrane coated with the model lipid mixtures and two keratinized membranes, rat skin and hamster cheek pouch, were determined in vitro using a Franz-type diffusion cell. Further, drug partition coefficients to the multilamellar liposomes prepared by the model lipid mixtures were determined. The Jmax values obtained in the model lipid-coated membrane, in the intact rat skin and in the intact hamster cheek pouch mucosa, bore a linear relationship to each other. These results suggest that the model lipid-coated membrane is a useful tool for the prediction of the drug permeability through the keratinized membrane in the in vitro system. The Jmax values also correlated with drug partition to the model lipid liposomes, suggesting the validity of the use of the model lipid mixtures as the substitutes for the intercellular lipids of the stratum corneum.

Nonequilibrium thermodynamic studies of electrokinetic effects across an artificial lipid-coated membrane

Hydraulic permeability, electroosmosis, streaming potential, and current of pure water across a membrane having Pyrex sintered G 4 glass incorporated with lecithin, cephalin, and phosphatidyl serine separately, have been studied and the data analyzed in terms of nonequilibrium thermodynamics. Linear phenomenological equations were found valid and L′ coefficients calculated. Near equality of cross coefficients L 12 and L 21 indicates the validity of Onsagar reciprocal relation. Maximum efficiency of electrokinetic energy conversion for streaming potential and electroosmosis for membrane-permeant system has also been examined.