Transdermal delivery of tea catechins by electrically assisted methods.

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.

Ionic mechanisms of tetrandrine in cultured rat aortic smooth muscle cells.

The ionic mechanism of tetrandrine, an alkaloid extracted from the Chinese medicinal herb Radix stephania tetrandrae, was investigated in A7r5 vascular smooth muscle cells. The nystatin-perforated whole-cell voltage-clamp technique was performed to examine the effects of tetrandrine on ionic currents. Tetrandrine (1-100 microM) reversibly caused an inhibition of L-type voltage-dependent Ca2+ current (I(Ca,L)) in a concentration-dependent manner. Tetrandrine did not cause any change in the overall shape of the current-voltage relationship of I(Ca,L). The IC50 value of tetrandrine-induced inhibition of I(Ca,L) was 5 microM. In the presence of Bay K 8644 (3 microM) or cyclopiazonic acid (30 microM), tetrandrine still produced a significant inhibition of I(Ca,L). The inhibitory effects of tetrandrine on I(Ca,L) exhibited tonic and use-dependent characteristics. Moreover. tetrandrine (3 microM) shifted the steady-state inactivation curve of I(Ca,L) to more negative membrane potentials by approximately -15 mV. These results indicate that tetrandrine directly inhibits the voltage-dependent L-type Ca2+ current in vascular smooth muscle cells, which may predominantly contribute to the vasodilatory actions of tetrandrine.