Examination of the Mechanism of Oleic Acid-Induced Percutaneous Penetration Enhancement: An Ultrastructural Study.

Abstract

The outermost layer of mammalian skin, the stratum corneum, by virtue of its unique architecture presents a significant barrier to the transdermal delivery of drugs. Recently, biophysical, morphological, and biochemical results have indicated that the stratum corneum forms a continuous sheath of protein-enriched corneocytes embedded in an intercellular matrix enriched in nonpolar lipids that are organized as lamellar layers.1,2) Although only 10 to 15% of the stratum corneum mass is comprised of lipids, these lipids largely dictate the overall skin permeability property.3) Transdermal drug delivery promises many advantages over oral or intravenous administration, and as a consequence it would be very useful to reduce the skin barrier using physical approaches and chemical enhancers, which would reversibly remove the barrier resistance of the stratum corneun and thus allow the drug to penetrate into the viable tissue and enter the systemic circulation.There is continued interest in the development of strategies to alter the skin barrier to percutaneous absorption of compounds. Oleic acid (OA) has been studied as a skin penetration enhancer for drugs via its action primarily on stratum corneum lipid structures. Studies have shown that the modes of action of OA have generated two mechanistic scenarios, which may account for the action of this enhancer: 1) lipid fluidization; and 2) lipid phase separation. 4) Since the stratum corneum lipids constitute the primary permeability barrier of the skin and these lipids exist in the stratum corneum intercellular spaces as a highly organized lamellar bilayers, 1,5) it is reasonable to expect that OA applied to the skin would emulsify or otherwise disorganize the stratum corneum lipid lamellae and thus increase skin permeability. In the present study, we investigated the use of ruthenium tetroxide postfixation and a lanthanum tracer study to ascertain the effects of OA on the stratum corneum lipids and epidermal permeability barrier function. Experimental Protocols Male Wistar rats weighing 250-300 g were used in this study. Under general anesthesia with 4% chloral hydrate by intraperitoneal injection, the hair from the back of the animals was clipped and then shaved with an electric razor. The rats were treated on the back with 10% OA/PG-soaked cotton balls. The other group serving as a control was treated with PG-soaked cotton balls. Each was rolled gently on the skin surface for 2 h at 5-min intervals, and neither OA nor PG application produced damage to the stratum corneum. MATERIALS AND METHODS MaterialsElectron Microscopy Samples were taken from the flanks of animals for electron microscopy after either OA or PG treatment. Briefly, samples were fixed in modified Karnovsky's fixative overnight at 4°C, which contained 2% paraformaldehyde, 2% glutaraldehyde, 0.06% CaCl 2 , in 0.1 M cacodylate buffer, pH 7.4. The tissues were then washed in 0.1 M cacoylate buffer, postfixed in either 0.25% ruthenium tetroxide (RuO 4 ) in 0.1 M cacodylate for 45 min in the dark at room temp...

Overcoming the Stratum Corneum: The Modulation of Skin Penetration

“…The results showed that oleic acid might increase the epidermal per-meability via a mechanism involving perturbation of stratum corneum lipid bilayers and lacunae formation as penetration enhancing effects [74] . Butyl paraben, methyl paraben and caffeine were used as model penetrants to test the effects of unsaturated fatty acids in benzyl alcohol on percutaneous drug permeation.…”

Innovative Strategies for Enhancing Topical and Transdermal Drug Delivery

“…The bent structure of the enhancer disrupts intercellular lipid packing, facilitating enhanced drug mobility. Disruption of lipid bilayers was also proposed by Jiang and Zhou [156] who used electron microscopy to examine structural alterations induced by oleic acid.…”

OCT image contrast improvement of skin tissue by using oleic acid as an enhancer

“…Oleic acid(OA), as an enhancer, has been widely used in the field of drug delivery [20][21][22] . It is a mono-unsaturated fatty acid and is Generally Recognized As Safe(GRAS) 23 .…”