[The potential effects of linalool on enantioselective skin permeation of norgestrel]

The purpose of this study is to investigate the enantioselectivity of norgestrel (NG) transdermal permeation and the potential influence of linalool and lipids on the enantioselectivity. In vitro skin permeation studies of NG across the excised rat skins were performed with Valia-Chien diffusion cells, and the permeation samples were analyzed by enantioselective HPLC. The possible enantioselective permeation of NG across intact rat back skin and lipids extracted rat back skin and the influence of linalool were evaluated. The skin permeation rate of dl-NG was two times higher than that of l-NG when donor solutions (EtOH/H2O 2 : 8, v/v) containing l-NG or dl-NG. It may be mainly attributed to the solubility discrepancy between enantiomer and racemate. The enantioselective permeation of dl-NG across intact rat skin was observed when the donor solutions containing dl-linalool. The permeation flux of l-NG was 22% higher than that of d-NG. But interestingly, the enantioselective permeation of dl-NG disappeared under the same experimental condition except that the lipid extracted rat skin was used. Attenuated total reflection-fourier transform infrared spectroscopy analysis of stratum corneum showed that the wave number for asymmetric CH2 stretching vibrations of lipids treated with dl-linalool was greater than that of the control. The results indicated that the enantioselective permeation of NG may be contributed by the interaction between dl-linalool and lipids. More than half of lipids were composed of ceramides. The stereospecific interaction maybe existed among chiral enhancer (linalool), lipids (ceramides) and/or chiral drugs (NG).