Effect of conjugated linoleic acid isomers on insulin resistance and mRNA levels of genes regulating energy metabolism in high-fat–fed rats

Objective We investigated the effects of specific conjugated linoleic acid (CLA) isomers on glucose metabolism and insulin resistance and on mRNA levels of genes important in glucose and lipid metabolism. Methods Sprague-Dawley rats were fed for 8 wk on a high-fat diet (45% kcal from fat) or one of three CLA-supplemented diets (1% CLA) containing differing isomers of CLA, including a mixture of CLAs (CLA mix), cis-9, trans-11-CLA (C9,T11-CLA), or trans-10, cis-12-CLA (T10,C12-CLA). Results Compared with the high-fat group, all the CLA groups had enhanced glucose tolerance. Insulin resistance index was significantly lower in the CLA-treated groups. No significant difference could be observed in the level of serum lipids between groups and in the activities of phosphoenolpyruvate carboxylase, glucose-6-phosphatase, and glucokinase. However, C9,T11-CLA and T10,C12-CLA significantly increased acyl coenzyme A oxidase mRNA in skeletal muscle. In addition, C9,T11-CLA increased hepatic acyl coenzyme A oxidase mRNA and skeletal muscle uncoupling protein-2 mRNA. The CLA mix showed intermediate effects on the levels of these genes. Conclusions The addition of all types of CLA to Sprague-Dawley rats fed a high-fat diet can decrease insulin resistance. Possible mechanisms are increased fat oxidation and energy expenditure by increasing acyl coenzyme A oxidase and uncoupling protein-2 mRNA in the liver and/or skeletal muscle.