Trans-10,cis-12 conjugated linoleic acid suppresses the desaturation of linoleic and alpha-linolenic acids in HepG2 cells.

The objective of this study was to determine the effects of cis-9,trans-11 and trans-10,cis-12 CLA on the fatty acid desaturation in a human hepatoma cell line, HepG2. Therefore, experiments were conducted in which HepG2 cells were incubated with various concentrations of those fatty acids and the concentrations of fatty acids in various lipid fractions of HepG2 cells were determined. In the presence of linoleic acid as substrate, cells treated with 25 micromol/L of trans-10,cis-12 CLA had lower ratios of dihomo-gamma-linoleic acid to linoleic acid and of arachidonic acid to linoleic acid in phospholipids than control cells; with alpha-linolenic acid as substrate, they had a lower ratio of eicosapentaenoic acid to alpha-linolenic acid in phospholipids than control cells. Cells treated with cis-9,trans-11 CLA did not differ in these ratios from control cells. Cells treated with trans-10,cis-12 CLA had also a markedly lower ratio of monounsaturated fatty acids (MUFA) to saturated fatty acids (SFA) in lipids than control cells; cells treated with cis-9,trans-11 CLA had a slightly lower MUFA:SFA ratio than control cells. These findings suggest that trans-10,cis-12 CLA suppresses Delta9-, Delta6- and Delta5-desaturation in HepG2 cells; cis-9,trans-11 CLA slightly reduces Delta9-desaturation but does not inhibit Delta6- and Delta5-desaturation. Moreover, HepG2 cells treated with 100 micromol/L of trans-10,cis-12 CLA released larger amounts of 6-keto-prostaglandin F(1alpha) and prostaglandin F(2alpha) than control cells. Treatment of cells with cis-9,trans-11 CLA did not alter the release of these eicosanoids compared with control cells. In conclusion, this study suggests that trans-10,cis-12 CLA has significant effects on the metabolism of essential fatty acids in HepG2 cells, whereas cis-9, trans-11 CLA does not have any effect in this respect.