Conjugated linoleic acid isomers' roles in the regulation of PPARγ and NF-κB DNA binding and subsequent expression of antioxidant enzymes in human umbilical vein endothelial cells

Department of Nutrition and Environmental Sciences, University of Nevada, Reno, USA.
Nutrition (Impact Factor: 2.93). 04/2009; 25(7-8):800-11. DOI: 10.1016/j.nut.2009.01.003
Source: PubMed


Conjugated linoleic acid (CLA) isomers have shown health benefits. Because CLA isomers may act as activators for peroxisome proliferator-activated receptors and may induce antioxidant enzymes, this study was conducted to examine the effects of CLA isomers on the gene expression of antioxidant enzymes, copper/zinc superoxide dismutase, and catalase in human umbilical vein endothelial cells.
Human umbilical vein endothelial cells were treated with graded concentrations of the 9-cis, 11-trans or the 10-trans, 12-cis-CLA isomer for 24 h.
The 9-cis, 11-trans-CLA treatments resulted in increases in transcription factor DNA binding activities and expression of antioxidant enzymes at 0-25 micromol/L and an increase in lipid peroxidation only at the lowest concentrations (5 micromol/L). The 10-trans, 12-cis-CLA treatments resulted in increases in transcription factor DNA binding activities at 0-25 micromol/L and highest levels of mRNA of both antioxidant enzymes, superoxide dismutase protein, and lipid peroxidation only at the lowest concentrations (5 micromol/L). The 9-cis, 11-trans-CLA treatments produced expression of antioxidant enzymes, except catalase protein, that were positively correlated with lipid peroxidation. Positive correlations were found between expression of antioxidant enzymes, except catalase protein, and lipid peroxidation for 10-trans, 12-cis-CLA treatments. Although CLA isomers exhibit mostly stimulatory effects in expression of antioxidant enzymes, interestingly, the lowest concentrations of both CLA isomers resulted in increases in thiobarbituric acid-reactive substance levels.
An understanding of the optimal concentrations of CLA isomers, which stimulate the benefits of antioxidant enzyme induction, may require careful CLA titration to determine predictable and dependable therapeutic strategies against adverse effects, such as pro-oxidants.

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    • "Very recent studies on PPARγ-DNA binding activity in human umbilical vein endothelial cells after treatment with the individual CLA isomers showed that the concentration determines whether CLA isomers exert inhibitory or a stimulatory effects in inflammatory and atherogenic processes, and that microenvironments also influence CLA effects [45]. The tissue dependent differences of action were also evident in mice; t10c12 CLA induced loss of adipose tissue but at the same time decreased fatty acid oxidation and increased fatty acid synthesis in liver [46]. "
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    ABSTRACT: Peroxisome proliferator-activated receptor (PPAR)gamma is a key regulator in adipose tissue. The rare variant Pro12Ala of PPARgamma2 is associated with a decreased risk of insulin resistance. Being dietary PPARgamma ligands, conjugated linoleic acids (CLAs) received considerable attention because of their effects on body composition, cancer, atherosclerosis, diabetes, obesity and inflammation, although some effects were only demonstrated in animal trials and the results in human studies were not always consistent. In the present study effects of CLA supplementation on genome wide gene expression in adipose tissue biopsies from 11 Ala12Ala and 23 Pro12Pro men were investigated. Subjects underwent four intervention periods (4 wk) in a randomized double blind cross-over design receiving 4.25 g/d of either cis-9, trans-11 CLA, trans-10,cis-12 CLA, 1:1 mixture of both isomers or a reference linoleic acid oil preparation. After each intervention biopsies were taken, whole genome expression microarrays were applied, and genes of interest were verified by realtime PCR. The following genes of lipid metabolism were regulated by CLA: LDLR, FASN, SCD, FADS1 and UCP2 were induced, while ABCA1, CD36 and CA3 were repressed. Transcription factors PPARgamma, NFAT5, CREB5 and EBF1, the adipokine NAMPT, members of the insulin signaling cascade SORBS1 and IGF1 and IL6ST were repressed, while the adipokine THBS1 and GLUT4 involved in insulin signaling were induced. Compared to trans-10,cis-12 CLA and the CLA mixture the cis-9, trans-11 CLA isomer exerted weaker effects. Only CD36 (-1.2 fold) and THBS1 (1.5 fold) were regulated. The CLA effect on expression of PPARgamma and leptin genes depends on the PPARgamma2 genotype. The data suggest that the isomer specific influence of CLA on glucose and lipid metabolism is genotype dependent and at least in part mediated by PPARgamma. ISRCTN91188075.
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