Objective: Conjugated linoleic acid (CLA) decreases adipose mass and increases vitamin E levels in the liver and adipose tissue in mice. The aim of the present study was to examine the mechanism by which CLA alters vitamin E levels in tissues and antioxidant activity in mice.
Methods: C57BL/6J mice were divided into three groups and fed 5% lipid as soybean oil alone (control group), 4% soybean oil supplemented with 1% CLA (CLA group), or 5% lipid with a vitamin E supplement (VE group) for 4 wk.
Results: The CLA and VE diets resulted in a significant increase in the α-tocopherol concentration in all tissues examined, i.e., the liver, kidney, testis, spleen, heart, lung, and adipose tissue (P < 0.05). Levels of thiobarbituric acid-reactive substances in the kidney, testis, heart, lung, and adipose tissue were lower in the CLA and VE groups than in the control group (P < 0.05). CLA did not alter the absorption rate of vitamin E or α-carboxyethyl hydroxychromans levels in the liver and plasma. The CLA diet induced a significant increase in α-tocopherol transfer protein and mRNA levels in the liver. CLA resulted in a decrease in catalase and glutathione peroxidase activities and peroxisome proliferator α mRNA levels but had no effect on levels of mRNAs for other nuclear transcription factors in the liver.
Conclusion: The increase in vitamin E status in CLA-fed mice is not due to altered absorption and metabolism of vitamin E but might be related to the induction of α-tocopherol transfer protein expression in the liver. The regulation of the activities of catalase and glutathione peroxidase by CLA is not mediated by vitamin E accumulation in the liver.
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