EFFECTS OF SATURATED, MONOUNSATURATED, AND POLYUNSATURATED FATTY-ACIDS ON THE SECRETION OF APO-B CONTAINING LIPOPROTEINS BY CACO-2 CELLS

We studied the effects of addition of physiological concentrations (0. 5 mM) of fatty acids i.e., palmitic (16:0), stearic (18:0), oleic (18: 1) and linoleic acid (18:2) on lipoprotein secretion by polarized Caco -2 cells. With saturated fatty acids, secreted lipoproteins were at ID L/LDL density, 1.009 < d < 1.068 g/ml. The numbers of secreted lipopro teins, expressed as secreted apolipoprotein (ape) B, were comparable t o control without Fatty acid (palmitic acid, 551 +/- 185; stearic acid , 629 +/- 304 and control, 504 +/- 176 ng apo B/4.7 cm(2) filter). Wit h unsaturated fatty acids, apo B containing lipoproteins were secreted at chylomicron/VLDL density (d < 1.006 g/ml). Oleic acid caused a two -fold higher secretion of apo B than control (1058 +/- 87 vs. 504 +/- 176 ng/4.7 cm(2) filter, P < 0.001). The increase in apo B secretion w as attributed to a specific increase in apo B-48. Unsaturated fatty ac id caused a two-fold higher secretion of triglyceride than saturated f atty acids but incorporation of newly synthesized lipid into the secre ted lipoproteins, measured by incorporation of a fatty acid marker, wa s 10- to 20-fold higher, indicating preferential translocation of unsa turated triglycerides into lipoproteins. Mixtures rich in either polyu nsaturated, monounsaturated, or saturated fatty acids, resembling nutr itional fat and oils, were capable of a two-fold stimulation of secret ion of apo B containing triglyceride-rich lipoproteins. The triglyceri de/apo B ratio in the basolateral medium was higher with the monounsat urated 'olive oil' mixture (12 250 +/- 2000 mol/mol) than with the pol yunsaturated 'corn oil' mixture (7830 +/- 2480 mol/mol) and incorporat ion of newly synthesized lipid into the secreted lipoproteins was 1.5- fold higher as well. In conclusion, unsaturated fatty acids were most potent in stimulating the secretion of apo B by specifically increasin g apo B-48 secretion. Unsaturated triglycerides, that contain mainly o leic acid, were more efficiently incorporated into lipoproteins than s aturated triglycerides, suggesting preferential translocation by micro somal triglyceride transfer protein.