Release and in vitro skin permeation of polyphenols from cosmetic emulsions

Objective: Polyphenols are natural antioxidants, which can inhibit oxidative chain reactions in human skin and prevent therefore some skin diseases and premature ageing. A prerequisite of this behaviour is their permeation through the skin barrier, in particular the stratum corneum (SC). In this study, we investigated the skin permeation kinetic of polyphenols, incorporated to semisolid emulsions, and the release of polyphenols from the emulsions. Methods: Mixtures of model substances, consisting of catechin, epigallocatechin gallate (EGCG), resveratrol, quercetin, rutin and protocatechuic acid (PCA), were formulated into o/w emulsions with different oil phase content. The in vitro experiments were carried out in Franz-type diffusion cells by means of ex vivo pig skin and a cellulose membrane. Results: The increased oil content in the emulsion led to a significant decrease in initial release coefficients (Kr), diffusion coefficients within the formulation (Dv) and skin permeation coefficients (Kp), respectively. The study considered the dependence of Kr on molecular weight and lipophilicity of polyphenolics. For both more hydrophilic and more lipophilic substance groups, the values for Kr were inverse proportional to molecular weight. For catechin, quercetin, rutin, resveratrol and PCA, a good correlation between Kp and Kr parameters was obtained. The most permeable substance was PCA (Kp = 1.2·10-3 cm h-1), and the least permeable was quercetin (Kp = 1.5·10-5 cm h-1). Conclusion: All substances could pass the SC barrier and were found mostly in the epidermis and dermis, confirming the potential of polyphenols as anti-ageing active cosmetic ingredients.