Fatty acid ethyl esters in human mononuclear cells: Production by endogenous synthesis greatly exceeds the uptake of preformed ethyl esters

Background: Fatty acid ethyl esters (FAEE) are nonoxidative metabolites of ethanol. They are esterification products of ethanol and fatty acids. Fatty acid ethyl esters have been implicated as important mediators of ethanol-induced cytotoxicity, organ damage, and disease. In addition, they serve as specific and sensitive biomarkers for ethanol intake. Following ethanol consumption, FAEE are found in circulating blood bound to albumin or/and lipoproteins. Objectives: Using a mononuclear fraction of white blood cells (WBC) exposed to ethanol, we investigated FAEE synthesis. We then determined the amount of uptake of preformed FAEE presented to the cells and compared the amounts of FAEE within the cells that were derived from endogenous synthesis with the amount derived from uptake of exposure FAEE. We also measured the persistence of FAEE within these cells and assessed the fate of the FAEE-associated fatty acid upon FAEE hydrolysis. Methods: A mononuclear fraction of human WBC was incubated with 25, 50, or 100 mM ethanol for 0.08 to 120 minutes, and FAEE synthesis was measured by gas chromatography/mass spectrometry. In other experiments, mononuclear cells were incubated with 25, 50, and/or 100 μM [³H]ethyl oleate, a representative FAEE species, for 0.08-120 minutes, and FAEE uptake and hydrolysis were measured. Results: The total FAEE formed by treating the cells with 25 mM ethanol, which represents a physiologic dose achievable with excess alcohol intake, greatly exceeded the FAEE within cells derived from uptake of 100 μM ethyl oleate, which represents a supraphysiologic dose. There was hydrolysis of FAEE by human mononuclear cells, with free fatty acids as major metabolites of FAEE hydrolysis. Unlike any other cell type or homogenate studied, the only ethyl ester formed by human mononuclear cells exposed to ethanol was ethyl oleate. Conclusions: There is significant synthesis of FAEE by human mononuclear cells within seconds of exposure to physiologic doses of ethanol. The amount of FAEE in these cells derived from endogenous synthesis greatly exceeds the amount acquired by exogenous uptake.