β-Carotene Uptake and Bioconversion to Retinol Differ Between Human Melanocytes and Keratinocytes

Abstract

β-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 β-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 [¹⁴C]β-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 β-carotene incubation. The conversion of [C]β-carotene to [¹⁴C]retinol peaked at 24 hours of incubation in keratinocytes and melanocytes. The results suggest that β-carotene can function as a local supply of vitamin A in the skin and that melanocytes are especially likely to store β-carotene.