Various kinds of double-chained cationic surfactants have been shown to form bilayer vesicles (cationic liposomes) and have been applied to gene delivery.1,2) Cationic vesicles designed for that purpose are generally intrinsically unstable. 3,4) Although application of cationic liposomes has also been anticipated for the delivery of drugs, peptides, vitamins and lipids and other biologically active compounds to biological cells and tissues, liposomes used for that purpose need to be intrinsically stable in order to retain their contents. 5) In a previous study we revealed that phosphatidylcholines enriched with unsaturated acyl chains stabilized the liposomes of dimethyldialkylammoniums such as dimethyldipalmitylammonium at physiological temperature.6) In contrast, 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) formed stable vesicles at physiological temperature with phosphatidylcholines containing either saturated acyl chains such as dimyristoylphosphatidylcholine (DMPC) or unsaturated acyl chains such as dilinoleoylphosphatidylcholine (DLPC). 7) We also revealed that these cationic liposomes interacted with erythrocytes as cationic vesicles and induced the formation of tightly aggregated structures of several erythrocytes which might also induce fusion of the erythrocytes.
6,7)The lipid lamella of the stratum corneum of the skin contains a high ratio of negatively charged lipids, 8) which are expected to interact with cationic liposomes. Transfer of some of the bilayer components of the liposomes to the skin is then possibly induced. Therefore, in this work we prepared cationic liposomes containing retinoic acid (all-trans-retinoic acid) as a bilayer component, and examined the incorporation of retinoic acid into skin by the cationic liposomes. Although topical retinoic acid has been clinically used with success for the treatment of several cutaneous diseases such as psoriasis or ichthyosis and mild acne, 9) its efficient delivery into skin has not been established yet. We compared the incorporation efficiency by cationic liposomes with those by electrically neutral liposomes and elastic liposomes as well as that by an organic solvent solution.
ExperimentalMaterials Chloride salt of DOTAP was purchased from Avanti Polar Lipids (Alabaster, AL, U.S.A.). Bromide salt of dimethyldipalmitylammonium was purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Dimyristoryphosphatidylcholine (DMPC, L-a -phosphatidylcholine dimyristoyl) and Dipalmitoylphosphatidylcholine (DPPC, L-a -phosphatidylcholine dipalmitoyl) were from Sigma Chemical Co. (St. Louis, MO, U.S.A.). All-trans-retinoic acid, egg yolk phosphatidylcholine (egg yolk PC), heptaethylene glycol mono-n-dodecyl ether and all other reagents were from Wako Pure Chemical Industries, Ltd. (Osaka, Japan).Preparation of Sonicated Liposomes Consisting of Phosphatidylcholines, Double-Chained Cationic Surfactants and Retinoic Acid Liposomes consisting of phosphatidylcholines, DOTAP (or dimethyldipalmitylammonium) and retinoic acid were prepared as described ...