Metabolic regulation of active retinoid concentrations in cultured human epidermal keratinocytes by exogenous fatty acids

Retinol metabolism was examined in cultured human epidermal keratinocytes incubated with medium containing physiological concentrations of bovine serum albumin-free fatty acid complexes and [³H]retinol. Unsaturated 16- and 18-carbon fatty acids: (1) promoted up to a 60% increase in the steady state total cell retinoid mass which was accounted for as retinyl ester corresponding to the added fatty acid, (2) decreased the rate of endogenous retinyl ester utilization up to 80%, (3) decreased the steady state cellular concentrations of retinol, 3, 4-didehydroretinol and their respective carboxylic acids up to 80%, and (4) did not alter the rate of retinoic acid metabolism. Increasing the medium retinol concentration augmented the fatty acid-stimulated increase in esters and blunted the extent of decrease in alcohols and acids. Saturated fatty acids with 14, 16, 17, and 18 carbons also reduced the rate of retinyl ester utilization and the cellular concentrations of the retinoid alcohols and acids but had little to no effect on retinyl ester synthesis. The data demonstrate that exogenous fatty acids possess the capacity to regulate the cellular concentrations of substrate retinoid alcohols, active retinoid acids, and the overall rate of retinol metabolism via substrate-mediated stimulation of retinol esterification and decreasing retinyl ester utilization. Fatty acids thus possess the potential to play a physiological role in modulating retinoid signaling in keratinocytes by regulating cellular concentrations of active retinoids.