Interaction of fish oil and conjugated linoleic acid in affecting hepatic activity of lipogenic enzymes and gene expression in liver and adipose tissue

The interaction of dietary fish oil and conjugated linoleic acid (CLA) in affecting the activity of hepatic lipogenic enzymes and gene expression in liver and adipose tissue was examined in mice. A diet containing 1.0% CLA, mainly composed of 9cis,11trans- and 10trans,12cis-octadecadienoic acids at equivalent amounts, greatly decreased adipose tissue weight and serum concentrations of leptin and adiponectin and was accompanied by a downregulation of the expression of various adipocyte-abundant genes in epididymal adipose tissue. However, CLA increased the serum insulin concentration fourfold, and it caused hepatomegaly, with huge increases in the triacylglycerol level and the activity and mRNA levels of hepatic lipogenic enzymes. Different amounts (1.5, 3, and 6%) of fish oil added to CLA-containing diets dose-dependently downregulated parameters of lipogenesis and were accompanied by a parallel decrease in the triacylglycerol level in the liver. The supplementation of CLA-containing diets with fish oil was also associated with an increase in fat pad mass and mRNA levels of many adipocyte-abundant genes in epididymal adipose tissue along with a normalization of serum concentrations of leptin and adiponectin in a dose-dependent manner. However, in mice fed a diet containing 1.5% fish oil and CLA in whom fat pad mass was still low and comparable to that in the animals fed CLA alone, the serum insulin concentration greatly exceeded (twofold) the value observed in mice fed CLA alone, indicating an aggravation of insulin resistance. This hyperinsulinemia was ameliorated with increasing amounts of fish oil in the diets. Apparently, many of the physiological effects of CLA can be reversed by fish oil.