Palmitic acid and linoleic acid metabolism in Caco-2 cells: different triglyceride synthesis and lipoprotein secretion.
Polarized monolayers of intestinal Caco-2 cells were used to study the effects of saturated palmitic acid (16:0) and polyunsaturated linoleic acid (18:2) on triglyceride synthesis and lipoprotein secretion. Monolayers were incubated for 24 h, at the apical or lumenal side, with palmitic acid (16:0) or linoleic acid (18:2) in physiological concentrations. Incubation with 1.0 mM 16:0 or 18:2 resulted in differences in the composition and amount of secreted lipoproteins. Radiolabeled lipids in the lipoproteins secreted during incubation with 18:2 were found in the chylomicron/VLDL (very low density lipoprotein) density whereas with 16:0 the secreted lipoproteins were in the intermediate density/low density lipoprotein (IDL/LDL) density range. More triglyceride was secreted into the (basolateral) medium during incubation with 1.0 mM 18:2 (41 +/- 12% of total triglyceride synthesized) than with 1.0 mM 16:0 (18 +/- 3% of total). The biochemical findings correlate with conspicuous morphological changes in the cells in the presence of 16:0, but not 18:2. Increasing concentrations of 16:0 (0.1-1.0 mM) caused gradual accumulation of intracellular membrane. Microvilli became strongly reduced in number. With 1.0 mM palmitic acid we found an increased incorporation of [1-14C]palmitic acid into phosphatidic acid (14.8% of total incorporation into phospholipid with 16:0 vs. < 0.5% with 18:2) and diacylglycerol (12.5% with 16:0 vs. < 0.5% with 18:2) and diacylglycerol (12.5% with 16:0 vs. 0.5% with 18:2) and the amount of intracellular phospholipid doubled. The morphological changes were completely reversed after 24 h with 1.0 mM 18:2. We conclude from our results that, compared to 18:2, 16:0 is not efficiently incorporated into triglycerides. 16:0 is incorporated into cellular phospholipids in a greater proportion than 18:2, causing accumulation of intracellular phospholipid and the precursors phosphatidic acid and diacylglycerol. Different processing of 18:2 and 16:0 by Caco-2 cells resulted in profound differences in triglyceride synthesis and lipoprotein composition and secretion.
van Greevenbroek
M M
MM
Department of Medicine, Faculty of Medicine, Utrecht University, The Netherlands.
Voorhout
W F
WF
Erkelens
D W
DW
van Meer
G
G
de Bruin
T W
TW
D002250:Carbon Radioisotopes; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D003110:Colonic Neoplasms; D005227:Fatty Acids / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects / Q000648:ultrastructure; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D008074:Lipoproteins / Q000378:metabolism*; D008854:Microscopy, Electron; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D010316:Particle Size; D014280:Triglycerides / Q000096:biosynthesis* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D002250:Carbon Radioisotopes; D005227:Fatty Acids; D008041:Linoleic Acids; D008074:Lipoproteins; D010169:Palmitic Acids; D014280:Triglycerides; D019308:Palmitic Acid; D019787:Linoleic Acid