maintaining the lamellar structure and thus the barrier func-One of the functions of the intercellular lipids of the stratum tion has been investigated by 2 H NMR spectroscopy (6).
corneum is to control the permeation of molecules. Their main Wertz isolated, identified, and quantified six ceramides component being ceramides, the pseudo-ceramide sphingolipid E from human epidermal lipids (7). Even though ceramides (SLE), which is similar in structure to natural ceramide type constitute the major fraction of human epidermal lipids, they II, is considered a potential drug carrier. Therefore, the internal exist in nature only in trace amounts. To make them commerstructure of SLE was investigated. SLE by itself forms a metastable lamellar structure that gradually crystallizes out as con-cially available for skin treatment, Imokawa and co-workers firmed by X-ray analysis. With reference to naturally occurring synthesized a pseudo-ceramide, named sphingolipid E lamellar structures of intercellular lipids, stearic acid was found (SLE) ( 8), which has a molecular structure analogous to to be able to stabilize the lamellar structure of SLE, when added that of the naturally occurring ceramide type II (9).
within a defined concentration range. It was further demonstrated
The stratum corneum is considered the main barrier for that both the hydrophobic and the hydrophilic portions of the transdermal permeation. There are two potential routes for stearic acid molecule contribute to the stability. Short-chained drug permeation, between the cells (intercellular route) and fatty acids lacking a long hydrophobic chain resulted in unstable through the protein-filled cells (transcellular route) (10), the structures. Likewise, the addition of less polar derivatives of stearic acid (stearic alcohol and hexadecane, reps.) could not maintain a former being viewed as the main route (11-13). Chemical lamellar structure. Only the strong hydrogen bonds between the agents such as dimethyl sulfoxide (DMSO), urea, and carboxy group of stearic acid and the amido-carbonyl group of Azone (1-dodecylazacycloheptan-2-one) (14) impair the SLE produced a stable lamellar structure as was confirmed by FTstructure of the transepidermal barrier, thus allowing drugs IR analysis.