Enhancement of the skin penetration of alkannin/shikonin enantiomers by Tooki extract

This study investigated the effectiveness of Tooki extract (Angelica sinensis) to enhance the skin penetration of alkannin/shikonin enantiomers (A/S). An 0.1 % suspension of A/S was compounded with or without different concentrations of Tooki extract and used in skin penetration studies in a Franz cell apparatus at 32 °C and a 500-rpm stirring rate. Fresh full-thickness skin from the abdominal region of Wistar rats was used as the penetration barrier. Addition of Tooki extract at concentrations of 0.25 %, 0.5 %, and 1% significantly increased the penetration rate of A/S by 1.62, 1.83, and 2.33 fold, respectively. Tooki extract also decreased penetration lag times. Enhancement of the A/S penetration rate was correlated with reduced rigidity of lipid matrices in the stratum corneum and enlarged hair follicles. Skin irritation studies in rabbits demonstrated that Tooki extract did not produce gross skin irritation with a primary irritation index of 0, and showed only slight dermal inflammatory effects upon histopathological examination.