Effects of conjugated linoleic acid isomers on lipid-metabolizing enzymes in male rats

Male weanling Wistar rats (n = 15), weighing 200-220 g, were allocated for 6 wk to diets containing 1% (by weight) of conjugated linoleic acid (CLA), either as the 9c,11 t-isomer, the 10t, 12c-isomer, or as a mixture containing 45% of each of these isomers. The five rats of the control group received 1% of oleic acid,instead. Selected enzyme activities were determined indifferent tissues after cellular subfractionation. None of the CLA-diet induced a hepatic peroxisome-proliferation response, as evidenced by a lack of change in the activity of some characteristic enzymes [i.e., acyl-CoA oxidase, CYP4A1, but also carnitine palmitoyltransferase-1 (CPT-I)] or enzyme affected by peroxisome-proliferators (glutathione S-transferase). In addition to the liver,;the activity of the rate-limiting beta-oxidation enzyme in mitochondria, CPT-I, did not change either in skeletal muscle or in heart. Conversely, its activity increased more than 30% in:the control value in epididymal adipose tissue of the animals fed the CLA-diets containing the 10t, 12c-isomer. Conversely, the activity of phosphatidate phosphohydrolase, a rate-limiting enzyme in glycerolipid neosynthesis, remained unchanged in adipose tissue. Kinetic studies conducted on hepatic CPT-I and peroxisomal acyl-CoA oxidase with CoA derivatives predicted a different channeling of CLA isomers through the mitochondrial or the peroxisomal oxidation pathways. In conclusion, the 10t, 12c-CLA isomer seems to be more efficiently utilized by the cells than its 9c,11 t homolog, though the Wistar rat species appeared to be poorly responsive to CLA diets for the effects measured.