beta-Carotene uptake and effects on intracellular levels of retinol in vitro.

The purpose of the present study was to determine beta-carotene uptake and resultant effects on intracellular levels of retinol in cell lines of varied origin. Human skin fibroblasts, mouse embryonic fibroblasts, rabbit corneal epithelial cells, and rat liver cells were studied. Cells were cultured in medium supplemented with beta-carotene in a water-dispersible beadlet formulation. At selected intervals, cells and media were sampled and analyzed by high-performance liquid chromatography for beta-carotene and retinol content. beta-Carotene was taken up by all four cell lines. An increase in the intracellular levels of retinol was concomitant with beta-carotene uptake in all cell lines. The uptake of beta-carotene and the increase in intracellular retinol were highest in the two fibroblast cell lines. Incubation with media supplemented with crystalline beta-carotene, dissolved in tetrahydrofuran, resulted in significantly lower beta-carotene uptake and intracellular retinol levels. We view these results as a demonstration that a wide variety of cells, cultured in vitro, are able to convert beta-carotene to retinol. Therefore, beta-carotene's provitamin A activity should be carefully considered when the protective effects of beta-carotene in vitro are interpreted.