William Abraham

Interaction between corneocytes and stratum corneum lipid liposomes in vitro

Small unilamellar vesicles were made from a mixture of epidermal ceramides (45%), cholesterol (35%), free fatty acids (15%) and cholesteryl sulfate (5%). Isolated corneocytes prepared from pig epidermis were added to the liposomes and the interaction between corneocytes and liposomes was studied by (1) thin-section electron microscopy and (2) monitoring the release of aqueous contents of the vesicles by following the fluorescence intensity of carboxyfluorescein entrapped in the vesicles. The vesicles adsorbed readily onto the corneocytes and slowly transformed into lamellar sheets. Enhanced fluorescence intensity indicated a corneocyte-induced membrane fusion process that resulted in the release of aqueous contents of the vesicles. The results suggest a cohesive role for the corneocyte cell envelope, which consists of a monomolecular layer of lipids covalently bound to the outside of a cross-linked protein envelope. This may be one of the major factors in the reassembly of extruded membranous disks into lamellar sheets which occurs during the final stages of epidermal differentiation.

Deuterium NMR investigation of polymorphism in stratum corneum lipids

The intercellular lipid lamellae of stratum corneum constitute the major barrier to percutaneous penetration. Deuterium magnetic resonance and freeze-fracture electron microscopic investigation of hydrated lipid mixtures consisting of ceramides, cholesterol, palmitic acid and cholesteryl sulfate and approximating the stratum corneum intercellular lipid composition, revealed thermally induced polymorphism. The transition temperature of bilayer to hexagonal transition decreased as the ratio of cholesterol to ceramides in these mixtures was lowered. Lipid mixtures in which the stratum corneum ceramides were replaced by synthetic dipalmitoylphosphatidylcholine did not show any polymorphism throughout the temperature range used in the present study. The ability of the ceramide-containing samples to form hexagonal structures establishes a plausible mechanism for the assembly of the stratum corneum intercellular lamellae during the final stages of epidermal differentiation. Also, the bilayer to hexagonal phase transition of these nonpolar lipid mixtures could be used to enhance the penetration of drugs through skin.

Lamellar Structures Formed by Stratum Corneum Lipids in Vitro: A Deuterium Nuclear Magnetic Resonance (NMR) Study

Hydrated lipid mixtures consisting of stratum corneum ceramides, cholesterol, specifically deuterated palmitic acid, and cholesteryl sulfate were investigated by solid-state 2H NMR spectroscopy at different temperatures. The mole ratio of cholesterol to ceramides was varied from 1 to 0. 2H NMR spectra from these mixtures showed powder patterns with quadrupolar splittings smaller than those obtained from control mixtures containing dipalmitoylphosphatidylcholine (DPPC) instead of the ceramides. This result is attributed to the rigid amide group of the ceramides, with a planar configuration, which could prevent close packing of the α-methylenes of the acyl chains. There was a gradual loss of symmetry in the powder pattern as the amount of cholesterol was decreased and the amount of ceramides (or DPPC) was increased concomitantly. The loss was more pronounced in the ceramide-containing samples. This phenomenon is interpreted as a decrease in the axial reorientation rate of the α-deuterated palmitic acid in the bilayers, presumably caused by the increased hydrogen bonding resulting from the high amount of hydroxyl-bearing ceramides. Spectra obtained at temperatures above 60°C indicated the formation of a hexagonal phase (HII) by the ceramide-containing mixtures. Spectra of the ω-deuterated palmitic acid in the mixture containing 76 mol% ceramides and no cholesterol indicated phase separation into a more rigid phase and a more mobile phase in the temperature range of 25 to 60°C. The bilayer configuration of lipids at 25°C was confirmed by thin-section electron microscopy.

Effect of epidermal acylglucosylceramides and acylceramides on the morphology of liposomes prepared from stratum corneum lipids

Epidermal acylglucosylceramides (AGC) and acylceramides (AC) cause aggregation and stacking of stratum corneum lipid liposomes formed from a lipid mixture containing epidermal ceramides (40%), cholesterol (25%), palmitic acid (25%), and cholesteryl sulfate (10%). This demonstrates the ability of these sphingolipids to hold adjacent bilayers in close apposition and their roles in the assembly of lamellar structures in the epidermis. However, AGC and AC in their hydrogenated form also caused aggregation and stacking of the stratum corneum lipid liposomes. This throws into doubt the proposed structural specificity of linoleate in the function of AGC and AC as molecular rivets in the assembly of the epidermal lamellar granules and the stratum corneum intercellular lamellae, respectively.

Effects of the penetration enhancer glycodeoxycholate on the lipid integrity in porcine buccal epithelium in vitro

Abstract The concentration dependence of the transport enhancing effect of sodium glycodeoxycholate (GDC) on the structural integrity of porcine buccal epithelium was studied in vitro. Lipid analysis of the buccal epithelium indicated that the epithelial lipid content was only changed (a decrease in the amounts of the major polar lipids and cholesterol) well above the GDC concentration necessary for transbuccal transport enhancement. Freeze–fracture replicas of porcine buccal epithelium treated with GDC revealed fine granular structures in the inter and intracellular domain. The fluorescence spectroscopy measurements in buccal mucosa indicated that its environment had become less polar by the GDC addition. Based on the results of this study the mechanism of action of GDC on the buccal epithelium appears to involve an interaction with the epithelial lipids in the intercellular domain, possibly by forming mixed micelles or aggregates. At high GDC concentrations the cell membranes are also affected.

Effect of PGML Excipient Mixture in a Transdermal System on the in Vitro Transport of Estradiol Across Skin

AbstractPurpose. To measure the effect of a combination of excipients from a silicone based pressure sensitive adhesive (PSA) on drug transport across skin. Methods. Partitioning of propylene glycol monolaurate (PG-ML) from silicone PSA and a solution formulation into the stratum corneum (SC) was measured using radiolabeled PG-ML. Transport of a model drug, estradiol, as well as PG-ML across skin were measured in vitro using heat separated epidermis from human cadaver skin. Results. The PG-ML partitioning into SC showed a saturation and was independent of the formulation. The local dielectric of the lipid bilayers of the SC showed an increase as a result of PG-ML uptake, as determined by the decrease in fluorescence lifetime of a lipophilic probe incorporated into the SC. However, there was no alteration of lipid packing in SC. Conclusions. The PG-ML and estradiol transport showed a good correlation over 3 days, suggesting that the two species are co-transported across the epidermis.

Frequency-domain fluorescence spectroscopy of human stratum corneum

The intercellular lipid lamellae of mammalian stratum corneum (SC) constitute the major barrier to percutaneous penetration of drugs and other solute molecules. In order to understand the barrier property of skin on a molecular level, we have initiated fluorescence spectroscopic investigation of the membranous structures of the SC and related model systems using the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Incorporated into distearoylphosphatidylcholine and stratum corneum bilayers, DPH fluorescence reflected the change in lipid structure under thermal and chemical perturbations. Using a multiharmonic frequency approach, we measured the fluorescence lifetime and rotational correlation times for DPH in these systems. Our data indicated that a biexponential decay ((tau) 1 approximately equals 9 ns, (tau) 2 approximately equals 1.5 ns) described the intensity decay, while a hindered rotor model ((phi) approximately equals 5 ns, r(infinity ) approximately equals 0.3) described the anisotropy decay. These parameters reported the known thermotropic phase transition in porcine stratum corneum, and the influence of the penetration enhancer oleic acid in human epidermis. Thus, we have shown frequency- domain fluorescence spectroscopy to be a facile and powerful tool for monitoring the permeability of a solid tissue such as the SC.

Skin surface lipids of the mink

Skin surface lipids from mink (Mustela vison) were collected in acetone and analyzed by thin-layer chromatography and gas chromatography. The principal components were wax monoesters (92%), cholesteryl esters (5%), free fatty acids (1%), fatty alcohols (1%) and cholesterol (1%). The fatty acids and alcohols contained in these lipids were composed principally of homologous series of straight chained omega 7-unsaturated structures (C16-C24), accompanied by lesser proportions of homologous series of saturated (C14-C22) and omega 9-unsaturated (C18-C22) structures.