Tea polyphenols, including (+)-catechin, (-)-epicatechin, and (-)-epigallocatechin-3-gallate (EGCG), have been shown to possess potent antioxidant and chemopreventive activities. The aim of this study was to assess the effects of electroporation, iontophoresis, and their combination on the transdermal delivery of tea catechins across porcine skin. The permeation characteristics were investigated using various analogues of catechins, pH values, and modes of electroporation and iontophoresis. The mechanisms by which these catechins were transported via the skin were elucidated by examining the electric conductivity, transepidermal water loss (TEWL), and fusion of stratum corneum lipid liposomes (SCLL). The isomers, (+)-catechin and (-)-epicatechin, showed different behaviors of skin permeation and local skin deposition with the electrically assisted methods. The results suggest evidence of selective skin absorption of (-)-epicatechin over (+)-catechin. A synergistic effect was detected for (+)-catechin but not for (-)-epicatechin after application of electroporation followed by iontophoresis. The presence of a gallic acid ester in the structure of EGCG significantly increased the skin uptake of catechins. However, a negligible amount of or no EGCG molecules permeated across the skin. The mechanisms involved in the enhancement of electroporation may be the skin reservoir effect and an increase in skin permeability. The TEWL profiles suggest that in addition to the force of electrorepulsion, the skin hydration effect and structural alterations may also have contributed to the enhancement by iontophoresis. Electroporation did not influence the skin barrier function, although the skin permeability increased according to the SCLL fusion study.
(c) 2006 S. Karger AG, Basel