Enhanced skin delivery of genistein and other two isoflavones by microemulsion and prevention against UV irradiation-induced erythema formation.

To improve the efficiency of the intradermal delivery of genistein and other two isoflavones (daidzein and biochanin A), we tried to clarify the usefulness of microemulsion by in vitro study on excised guinea pig dorsal skin and Yucatan micropig skin. Using microemulsion consisting of isopropyl myristate (IPM), 150 mM NaCl solution, Tween 80 and ethanol as a vehicle, the solubility of all the isoflavones markedly increased and significant amounts of isoflavones were delivered to the skin. The effect of water-in-oil (w/o)-type microemulsion D was larger than that of oil-in-water (o/w)-type microemulsion A. Among three isoflavones tested, the increase of genistein was most marked on both solubility and skin accumulation. Genistein retained in the skin significantly inhibited lipid peroxidation in vitro dose-dependently. Furthermore, pretreatment of guinea pig dorsal skin with genistein containing gel-like microemulsion D prevented UV irradiation-induced erythema formation. These findings indicate the potential use of w/o-type microemulsion for the delivery of genistein to protect skin against UV-induced oxidative damage.