Comparing the lipogenic and cholesterolgenic effects of individual trans-18:1 isomers in liver cells

The present study compared the lipogenic/cholesterolgenic effects of t6-, t9- (positive control), t10-, t11-, t13-, t14-, t15-18:1, cis(c)9-18:1 (cis control) or bovine serum albumin (BSA; negative control) in liver cells (HepG2). Fatty acids (100M) were complexed to BSA, and cells were incubated for 24h. Two wells of cells were cultured per treatment per experiment, and the experiment was repeated three times (n=6). The fatty acid treatments had no effect on cell viability compared to BSA. The content of triacylglycerol (TG) and cholesteryl esters (CE) were increased (P<0.05) when culturing with t6-, t9-, and t10-18:1 compared to BSA control, but were not affected (P>0.05) by other fatty acid treatments. Consistent with the effects on TG and CE, culturing cells with t6-, t9-, or t10-18:1 upregulated expression of several genes involved in fatty acid and cholesterol synthesis, and effects were most consistent for t6-18:1. Esterification of t18:1 isomers into TG was 1.7-fold greater when cells were cultured with t6-, t9-, and t10-18:1 compared to t11-, t13-, t14-, and t15-18:1. The results from the present study indicate t6-, t9-, and t10-18:1 induce lipogenic/cholesterolgenic gene expression resulting in increased cellular content of TG and CE, while t11-, t13-, t14-, and t15-18:1 responded similarly to c9-18:1 and control treatments. Practical application: Trans fatty acids have been associated with cardiovascular disease mainly through adverse effects on blood lipoprotein profiles. Several t18:1 isomers are found in foods, but studies on individual isomers have been mostly limited to t9- and t11-18:1. The isomer specific effects of other t18:1 isomers have been limited because of their lack of commercial availability. To investigate the effects of individual t18:1 isomers, we isolated and purified several isomers from beef fat using silver-ion chromatography techniques. We examined the effects of seven t18:1 isomers in liver cells on cellular triacylglycerol and cholesterol content, fatty acid composition, and expression of key genes involved in fatty acid and cholesterol syntheses. Our results indicate that the major t18:1 isomers found in partially hydrogenated vegetable oils, and ruminant fats when feeding grain based diets (i.e., t6- to t10-18:1) have more potent lipogenic/cholesterolgenic effects compared to isomers enriched in ruminant fats when feeding forage based diets (i.e., t11- to t15-18:1).