Transdermal Delivery of Insulin in Mice by Using Lecithin Vesicles as a Carrier

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Abstract
The present study was undertaken to characterize the preparation of flexible lecithin vesicles containing insulin and to assess the enhancing effect of these flexible vesicles on the transdermal delivery of a hydrophilic protein. Both conventional and flexible vesicles were prepared by reverse-phase evaporation and treated further by sonication. The free drug was separated from vesicles by column chromatography and analyzed by HPLC. Both conventional and flexible vesicles were transparent colloidal dispersions. The particle size of the conventional and flexible vesicles was 73.5 nm and 87.1 nm with a polydispersity index of 44.5% and 15.6%, respectively. The entrapment efficiencies of conventional and flexible vesicles were 35% and 81%, respectively. When vesicles were nonocclusively applied onto the abdominal mice skin at a dose of 0.90 IU/cm2, in vivo hypoglycemic study showed the drop percentage of blood glucose by flexible vesicles was 21.42 plus/minus 10.19% at 1 hr, reached 61.48 plus/minus 8.97% at 5 hr, and was larger than 50% within 18 hr. Conventional vesicles, insulin solution, and saline had no hypoglycemic effect. Probably due to the incorporation or adsorption of a certain amount of insulin into the flexible vesicles during the mixing process, blank flexible vesicles mixed with insulin solution had a certain degree of hypoglycemic effect, though much less than the effect of flexible vesicles containing insulin (p < 0.05). Flexible vesicle may become a promising carrier for the transdermal delivery of hydrophilic polypeptides.