β-carotene uptake and bioconversion to retinol differ between human melanocytes and keratinocytes

beta -Carotene is one of the carotenoids that has been considered to play a role in the natural defense against ultraviolet-induced skin cancer. It is not known whether epidermal cells are able to accumulate beta -carotene and, subsequently, convert it to vitamin A. We used normal cultured human keratinocytes and melanocytes to study the uptake, and possible bioconversion to retinol, of authentic or [C-14]beta -carotene. The uptake was much higher in melanocytes than in keratinocytes, corresponding to a fivefold difference in the intracellular fraction after two days of incubation. An increased level of cellular retinol was noted after one day of beta -carotene incubation. The conversion of [C-14]beta -carotene to [C-14]retinol peaked at 24 hours of incubation in keratinocytes and melanocytes. The results suggest that beta -carotene can function as a local supply of vitamin A in the skin and that melanocytes are especially likely to store beta -carotene.