FATTY-ACID UPTAKE AND METABOLISM IN CACO-2 CELLS - EICOSAPENTAENOIC ACID (20 5(N-3)) AND OLEIC ACID(18/1(N-9)) PRESENTED IN ASSOCIATION WITH MICELLES OR ALBUMIN/

In vivo, long-chain fatty acids are incorporated into bile salt micell es, which solubilize the hydrophobic fatty acids before they are trans ported across the unstirred water layer to the intestinal brush border membrane. In the present study we have used CaCo-2 cells, cultured on filter membranes as a model of human enterocytes, and compared presen tation of fatty acids bound to albumin with a micellar form. Absorptio n of eicosapentaenoic acid and oleic acid from micellar solutions was 4-times faster than from fatty acid-albumin complexes after 5 h incuba tion, and resulted in a corresponding increase in triacylglycerol synt hesis and secretion. Mass determination of newly synthesized, cell-ass ociated triacylglycerol after 5 h incubation, indicated a 5-fold incre ase in cells exposed to a micellar solution versus albumin-complexed f atty acids. A 2-fold larger fraction of the absorbed fatty acids was i ncorporated into triacylglycerol than into phospholipids when the fatt y acids were presented as micelles. Analysis by resistive pulse techni que showed that secreted lipoproteins of density less than 1.006 g/ml were in the same size-range as chylomicrons derived from human plasma. In spite of an increased amount of secreted triacylglycerol from cell s supplemented with micellar fatty acids, there was no increase in the mean size of these particles. Synthesis and secretion of triacylglyce rol in cells exposed to eicosapentaenoic acid and oleic acid were simi lar regardless of whether the fatty acids were presented to the cells associated with albumin or micelles, although the total amount of tria cylglycerol synthesized and secreted was highest with micelles. When i ncubating CaCo-2 monolayers with eicosapentaenoic acid or oleic acid b ound to albumin, a similar amount of radioactivity was released as CO2 and acid soluble products into the medium with less than 3% of the li pids being oxidized after 5 h of incubation. The oxidation rate of fat ty acids in cells incubated with micelles was increased 40 to 100%. In conclusion, micellar fatty acids are absorbed, metabolized and influe nce secretion of lipoprotein particles to a higher extent than albumin -bound fatty acids in CaCo-2 cells, and there is no major difference b etween eicosapentaenoic acid and oleic acid.