Vitamin A uptake by human skin in vitro.

Results are presented establishing that epidermis accumulates vitamin A from serum retinol-binding protein (RBP). Strips of human breast skin (0.2-0.3-mm thick) were incubated in a serum-free medium. From the rate of glucose oxidation, the tissue was viable for at least 48 h at 32 degrees C in 5% CO2 air. [3H]-Retinol-RBP (10(-6) M) was added to the medium for 1-24 h, after which epidermis and dermis were split and separately extracted with hexane after saponification. [3H]-Retinol was isolated by high performance liquid chromatography (HPLC). Epidermis had 6-7 times higher affinity for [3H]-retinol than dermis. The uptake could be saturated by substrate and was inhibited with unlabelled retinol-RBP but not with serum albumin. Furthermore, although the uptake was temperature-dependent, it seemed independent of cellular energy production. The epidermal accumulation of [3H]-retinol was reduced by the filtering action of dermis. On the basis of these observations, an in vitro model for the delivery of vitamin A to human skin has been proposed.