Enhanced skin delivery of polyphenols by microemulsion and prevention against UV irradiation-induced erythema formation

Polyphenols have been applied for topical purposes such as photoprotection against UV-induced skin damage. However, intradermal delivery of most polyphenols is inefficient. To improve the efficiency, we tried to clarify the usefulness of microemulsion using excised guinea pig dorsal skin and Yucatan micropig skin. We used two types of microemulsions consisting of isopropyl myristate (IPM), 150 mM NaCl solution, Tween 80 and ethanol. Weight ratio of IPM, 150 mM NaCl solution, Tween 80 and ethanol was 8:25:20:47 in microemulsion A, and 33:7:30:30 in microemulsion D. By using these microemulsions solubility and skin delivery of polyphenols such as genistein and chlorogenic acid were markedly improved. For example, solubility of genistein in 150 mM NaCl was only 0.059 mM, it increased to 80 mM in o/w-type microemulsion A, and further increased to 140 mM in w/o-type microemulsion D. Skin delivery of genistein also increased 36 times using microemulsion A and further increased about 60 times using microemulsion D at saturated concentration. On the other hand, enhancement effect of microemulsion A was larger than that of microemulsion D for skin accumulation of hydrophilic chlorogenic acid. Genistein and chlorogenic acid retained in the skin significantly inhibited lipid peroxidation dose-dependently in vitro. When genistein was applied with microemulsion D at saturated concentration (140 mM), lipid peroxidation tested by ammonium iron (II) sulfate and sodium citrate decreased to less than 10%. We furthermore revealed that pretreatment of guinea pig dorsal skin with microemulsion gel which contains either genistein or chlorogenic acid prevented UV-irradiation-induced erythema formation. These findings revealed the potential use of microemulsion for the delivery of these polyphenols to protect skin against UV-irradiation-induced damage.