Long-term effects of cis and trans monounsaturated (18 : 1) and saturated (16 : 0) fatty acids on the synthesis and secretion of apolipoprotein A-I- and apolipoprotein B containing lipoproteins in HepG2 cells

The objective of this study was to compare the long-term effects of oleic ( cis 18:1), elaidic (trans 18:1), and palmitic (16:0) acids on hepatic lipop rotein production, using HepG2 cells as an experimental model. The net accu mulation in the medium of apolipoprotein A-I (apoiA-I) was not significantl y altered by fatty acids, whereas that of apoB was increased with oleic and elaidic acids. Oleic acid, and to a lesser extent elaidic and palmitic aci ds, increased the mass of triglycerides in the medium and the incorporation of [H-3]glycerol into secreted triglycerides. The incorporation of [C-14]a cetate into cellular and secreted total cholesterol was stimulated by 96% a nd 83%, respectively, with elaidic acid but was not significantly modified by oleic or palmitic acid. Relative to oleic acid, the secretion of C-14-la beled phospholipids and triglycerides was decreased 28% to 31% with elaidic and palmitic acids whereas that of free cholesterol and cholesteryl esters was enhanced 93% and 73%, respectively, with elaidic acid but remained unc hanged with palmitic acid. Compared with oleic acid, elaidic acid stimulate d the secretion of very low density lipoprotein cholesterol (VLDL-Chol), lo w density lipoprotein cholesterol (LDL-Chol), and high density lipoprotein cholesterol (HDL-Chol) by 43%, 70%, and 34%, respectively, whereas palmitic acid decreased VLDL-Chol but had no significant effect on LDL-Chol and HDL -Chol. The ratios of total cholesterol to HDL-Chol were 3.17, 3.60, and 3.2 5 with oleic, elaidic, and palmitic acids, respectively; the corresponding ratios of LDL-Chol to HDL-Chol were 0.87, 1.10, and 0.93, respectively. Com pared with oleic and palmitic acids, the LDL and HDL particles secreted in the presence of elaidic acid contained higher levels of free cholesterol an d cholesteryl esters and a lower content of phospholipids. The phospholipid -to-total cholesterol ratios of HDL were 1.05, 0.40, and 0.76 with oleic, e laidic, and palmitic acids, respectively. Our results indicate that in comp arison with cis monounsaturated and saturated fatty acids, trans fatty acid s have more adverse effects on the concentration and composition of lipopro teins secreted by HepG2 cells.