Submitted to: Lipids Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2003
Publication Date: 5/1/2003
Citation: Warren, J.M., Simon, V.A., Bartolini, G.L., Erickson, K.L., Mackey, B.E., Kelley, D.S. 2003. TRANS-10, CIS-12 CONJUGATED LINOLEIC ACID INCREASES LIVER AND DECREASES ADIPOSE TISSUE LIPIDS IN MICE: POSSIBLE ROLE OF SPECIFIC LIPID METABOLISM GENES. Lipids Journal. 38(5):497-504, 2003. Interpretive Summary: One of the forms (c9, t11-CLA) of conjugated linoleic acid or CLA is naturally found in beef and dairy products; while several other forms, including t10, c12-CLA are produced during the processing and partial hydrogenation of vegetable oils. Feeding a mixture of CLA isomers has been reported to have several health effects in animal models, including a reduction in adipose fat and an increase in liver fat. Which of the CLA isomers causes these changes in body fat and the mechanisms associated with it are not known. We fed diets containing two purified isomer of CLA (c9, t11 and t10, c12, 0.5%) to mice for eight weeks. The c9, t11-CLA did not alter body, liver or adipose tissue weights, while the c10, t 12-CLA reduced body and adipose tissue weights but it caused a five fold increase in liver lipids. These changes in body fat were associated with decreases in the message RNA for adipose tissue hormones leptin and adiponectin. These results suggest that changes in adiponectin and leptin may mediate the effects of CLA on lipid metabolism. Our results show that the CLA found naturally did not have any harmful effects, but that formed through the processing of vegetable oils can be potentially harmful.
Technical Abstract: While consumption of conjugated linoleic acid (CLA) mixtures has been associated with several health effects, less is known about the actions of specific CLA isomers. There is evidence that the t10, c12-CLA isomer is associated with alterations in body and tissue weights in animals fed CLA, but the mechanisms leading to these changes are unclear. The purpose of this study was to determine the effects of two commonly occurring isomers of CLA on body composition and the transcription of genes associated with lipid metabolism. Female mice were fed either a control diet, or diets supplemented with 0.5% c9, t11-CLA or t10, c12-CLA isomers or 0.2% of the PPAR alpha agonist fenofibrate for eight weeks. Body and adipose tissue weights were significantly less, and liver weights were significantly greater in the t10, c12-CLA and the fenofibrate groups, compared with the other two groups. Livers from animals in the t10, c12-CLA group contained 5 times more lipids than in the control group, while the lipid content of the fenofibrate group did not differ from that in the control group. While fenofibrate increased the mRNA for PPAR alpha,t10, c12-CLA decreased it. These results suggest that PPAR alpha did not mediate the effects of t10, c12-CLA on body composition. The CLA isomers and fenofibrate altered mRNA levels for several proteins involved in lipid metabolism, but the most striking difference was the reduction of mRNA for leptin and adiponectin in the t10, c12-CLA group. These initial results suggest that changes associated with energy homeostasis and insulin action may mediate the effects of t10, c12-CLA on lipid metabolism.