Conjugated linoleic acid isomers have differential effects on triglyceride secretion in Hep G2 cells

Abstract The effect of different conjugated linoleic acid (CLA) isomers ( trans -10, cis -12 ( t10 , c12 )-CLA and cis -9, trans -11 ( c9 , t11 )-CLA), compared with oleic acid (OA) and linoleic acid (LA), on hepatic lipid synthesis and secretion were investigated in Hep G2 cells. The cells were incubated in a medium containing 1 mmol/l fatty acid–bovine serum albumin (BSA) complex for 5 h, with BSA alone as control. [ 3 H]Glycerol and [ 14 C]acetate were used to monitor lipid synthesis and secretion. The results show that cellular uptake rates of these fatty acids were similar. Incubation with OA, t10 , c12 -CLA, c9 , t11 -CLA and LA resulted in 6-, 4-, 2- and 1.8-fold increases in intracellular [ 3 H]triglyceride ([ 3 H]TG) compared with incubation with BSA alone. OA, LA and c9 , t11 -CLA increased [ 3 H]TG secretion 3.6-, 2.5- and 1.2-fold above the control, whereas t10 , c12 -CLA markedly suppressed the secretion of [ 3 H]TG. Hepatic secretion of TG mass increased 3.5-, 3.3-, 2.7- and 1.5-fold in the cells incubated with OA, LA, c9 , t11 -CLA and t10 , c12 -CLA, respectively. Since the secreted TG is mainly contained in very low density lipoproteins (VLDL), the decreased ([ 3 H])TG secretion by t10 , c12 -CLA reflects a diminished secretion of VLDL. With respect to cholesterol synthesis OA was more effective in stimulating the incorporation of [ 14 C]acetate into cellular total cholesterol followed in descending order by LA, c9 , t11 -CLA and t10 , c12 -CLA. In conclusion, the biological properties of 18-carbon fatty acids are clearly influenced by both the number and (geometric) positions of their double bonds. Furthermore t10 , c12 -CLA is more effective than c9 , t11 -CLA on suppressing hepatic TG secretion in vitro.