Analysis of in vitro release through reconstructed human epidermis and synthetic membranes of multi-vitamins from cosmetic formulations

A convenient method for in vitro investigation of the release of lipid- and water-soluble vitamins from cosmetic formulations was developed. The permeation of (d)-α-tocopherol (vitamin E), retinyl acetate (pro-vitamin A), ascorbic acid (vitamin C) and pyridoxine (vitamin B6) through SkinEthic® reconstructed human epidermis (RHE), and synthetic polyethersulfone and polycarbonate membranes was studied in vitro using a Franz-type diffusion apparatus, coupled either to a spectrophotometer for continuous reading (dynamic setting) or to HPLC-DAD analysis of the receptor medium (static setting). O/W and W/O emulsions were compared with simple aqueous solutions for their kinetic of vitamins release, to evaluate the influence of the cosmetic formulation on the bioavailability of active ingredients. Results indicate that synthetic membranes offer a limited barrier to the diffusion of vitamins, but may provide information on the release ability of the formulation. Penetration was more effective when water was the external phase of the formulation, i.e. W/O emulsions were less effective in the release of vitamins than O/W emulsion or aqueous solutions. RHE (17 days old) offered a significantly higher barrier to penetration of vitamins, as expected for native human epidermis. The relative ranking in coefficient of permeability (Ps (cm/h)) was: ascorbic acid > pyridoxine ≫ retinyl acetate > α-tocopherol ∼0, the absolute values depending on the formulation. The method herein described showed to be a practical and convenient tool for the quality-control and efficacy evaluation of cosmetic formulations.