Cellular uptake of stearic, oleic, linoleic, and linolenic acid and their effects on synthesis and secretion of lipids in Hep-G2 cells

The present study was undertaken to examine the cellular uptake of stearic (18.0), oleic (18.1), linoleic (18.2), and linolenic acid (18:3). and their effects on synthesis and secretion of lipids in Hep-G2 cells. The cells were grown for 6 days in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum. On day 7, cells were incubated in a serum-fret DMEM containing 0.25-1.0 mM of 18.0. 18:1, 18.2 or 18:3. The cellular uptake of these fatty acids was almost linear during the 4 hr incubation period, and no significant differences were noted among the fatty acids tested, regardless of their degree of unsaturation. The treatment of cells with 1.0 mM of these fatty acids stimulated triglyceride (TG) synthesis nearly ten-fold and phospholipid (PL) synthesis approx, two-fold compared with those of the control. The lipoprotein-TG secretion also increased and was the highest with 18:1 followed in descending order by 18:2, 18.3, and 18:0. The fatty acid treatment of cells also significantly increased the incorporation of C-14-acetate into the cellular and lipoprotein cholesterol compared with that of the control (p < 0.05). In addition, notable changes occurred in the fatty acid composition of cellular and medium lipids, which were enriched with the particular fatty acid present in the incubation medium. The findings that 18:0, 18,1, 18:2, and 18:3 were taken up by Hep-G2 cells at almost identical rates demonstrate that differences in the cellular synthesis of lipids and their secretion are attributable to the metabolic specificity of those fatty acids, rather than variable rates of their uptake. (C) 1998 Elsevier Science Ltd. All rights reserved.