Dietary conjugated linoleic acid isomers and selenium affect the fatty acid profile in rat liver *

The influence of dietary conjugated linoleic acid (CLA) isomers and/or Se (as Na2Se04) on the content of CLA isomers and other fatty acids (FAs) in rat liver was investigated. Feeding CLA isomers resulted in an elevated hepatic CLA isomer content. The diet with Se and cis9trans11 CLA most effectively elevated the liver content of cis9 trans11, cis,tras/trans,cis, the sum of CLA isomers, C20:4 and C20:6. Adding Se, cis9trans11CLA or a CLA isomer mixture decreased the capacity of Δ6-, Δ5-desaturases and elongase, while trans10cis12 had the opposite effect. Feeding Se or CLA isomers reduced Δ9-desaturase capacity.


INTRODUCTION
Numerous investigations have demonstrated that CLA isomers alter lipid metabolism in the liver and adipose tissue.Indeed, PUFA have been shown to decrease SREBP-1 mRNA2 in liver, therefore leading to reduced lipogenic gene expression.Moreover, in some studies it has been reported that dietary CLA isomers can modify the oxidation of fatty acids (FAs).
Therefore, the aim of this study was to investigate the CLA isomer profile and composition of other FAs in the liver of rats fed a mixture of CLA isomers: cis9,trans11 (c9,t11), trans10,cis12 (t10,c12) and/or 2 ppm Se (as Na 2 SeO 4 ).

MATERIAL AND METHODS
Ten groups of 7-8 female rats each (Wistar, Ifz: BOA), 8 weeks of age and an initial body mass ~200 g were housed individually as described previously (Czauderna et al., 2004).Rats were fed the Labofeed diet or one enriched in 1-2% CLA isomers, 2 ppm Se (as Na 2 SeO 4 ) (Table 1), ad libitum.After 28 days the rats were killed by CO 2 and their livers were removed and freeze-dried.
All reagents used and the saponification methylation methods were as previously described (Czauderna et al., 2005).CLA isomers and other FAs containing conjugated double bonds (CFA) were determined using ion (Ag+) liquid chromatography (Ag + -HPLC), while analysis of all FAs in rat liver was carried out using GLC (Czauderna et al., 2005).
The effects of CLA isomers or Se treatments were subjected to statistical analysis using the nonparametric Mann-Whitney U test, while the simultaneous Se and CLA treatment was analysed by two-factorial analysis.Statistica (ver. 6) and Excel 2000 were used.

RESULTS AND DISCUSSION
No lesions or symptoms of harmful effects of Se were found in rats fed diets with Se.The FA composition in rat liver was altered by the treatment with CLA isomers and/or Se (Table 1).Incorporation of isomers c9t11 and t10c12 and t,t was found to be selective; in particular, the percentage contribution of t,t isomers in liver was relatively higher compared with their share (~15%) in the dietary CLA isomer mixture.The t,t isomers are catabolized more slowly and are poor species for β-oxidation; they are more efficiently accumulated into liver membrane phospholipids due to their geometrical configuration.On the other hand, the percentage contribution of c9t11and t10c12 was lower than in the administered CLA isomer mixture and the content ratio of t10c12 to c9t11 in the liver was smaller than in the CLA isomer mixture.The c9t11 and c11,t13 isomers were preferentially metabolized (like other c,t/t,c isomers) to form CFA (i.e.C18:3, C20:3, C20:4), while t10c12, t10t12 and t8c10 isomers were more efficiently driven through β-oxidation than their 9,11 homologues.Se most efficiently elevated the content of c9t11 (285%), c,t/t,c (286%), the sum of CLA isomers (281%), C20:4 and C20:6 in the liver of rats simultaneously fed Se and c9t11 CLA (positive interaction).Our recent study has also indicated that dietary Se increased the c6 C18:1 content in the liver of rats fed Se and c9t11 or other CLA isomers, probably due to stimulation of Δ6-desaturase capacity (a positive interaction).These results suggest that dietary Se and isomer c9t11 most efficiently stimulated the capacity of Δ6-, Δ5desaturases and elongase; so feeding diet 8 +Se increased the content of CFA, C20:4 and C22:6 in the liver.This effect may be also attributed to the ability of dietary Se 8.9 5.7 d 1 analysis was performed using GLC as described previously (Czauderna et al., 2005); results are presented as mean values 2 Δ9-desaturase index: (cis9C16:1 + cis9C18:1)/ (cis9C16:1 + cis9C18:1 + C16:0 + C18:0) 3 a diet with 1% CLA isomer mixture (the profile of CLA isomer mixture was presented previously, Czauderna et al., 2003) 4 a diet with 1% cis9trans11CLA (c9,t11) 5 a diet with 1% trans10cis12CLA (t10,c12) 6 a diet with 2% CLA isomer mixture 7 analysis performed using GLC and Ag + -HPLC as described previously (Czauderna et al., 2005); results are mean values obtained from GLC and Ag + -HPLC 8 t,t CLA: trans,trans -11/13, 10/12, 9/11 or 8/10 CLA isomers (~15% trans,trans CLA isomers in dietary CLA isomer mixture; Czauderna et al., 2004) 9 c,t/t,c CLA: c,t/tc -11/13,10/12, 9/11 or 8/10 CLA isomers; main CLA isomers ( ~80%) in the dietary CLA isomer mixture; Czauderna et al., 2003Czauderna et al., , 2004 10 MUFA -c9C16:1; t11C18:1; c9C18:1; c11C18:1.PUFA -c9c12C18:2; c9c12c15C18:3; c5c8c11c14C20:4; c5c8c11c14c17C20:5; c7c10c13c16c19C22:5; c4c7c10c13c16c19C22:6; SFA -C16:0; C17:0; C18:0 11 the ratio (R) of the concentration of t10c12CLA to c9t11CLA in liver of rats fed a diet with CLA isomer mixture; the ratio of the concentration of t10c12CLA to c9t11CLA in dietary CLA isomer mixture: 1.0242 (Czauderna et al., 2003) to diminish the efficiency of β-oxidation of administered CLA isomers, particularly c9t11CLA, as well as other non-CLA FAs in liver.These results suggest that Se, c9t11 or the CLA isomer mixture decreased the capacity of Δ6-, Δ5-desaturases and elongase3 (negative interaction), while t10 c12CLA increased the capacity of these enzymes.Feeding Se or CLA isomers probably caused reduction of Δ9-desaturase capacity (most effectively t10c12CLA regardless of Se presence), while Se in the diet with CLA isomers slightly stimulated the capacity of this enzyme (positive interaction).Consequently, the hepatic MUFA and PUFA contents of rats fed Se or CLA isomers numerically or statistically decreased, while extra Se in the diet with CLA isomers usually slightly elevated the content of MUFA in liver (positive interaction).

CONCLUSIONS
Our results indicate that CLA isomers (especially c9t11) decreased Δ9-, Δ6and Δ5-desaturase capacity.Therefore, finding that CLA isomers, especially c9t11, modify arachidonate metabolism with concurrent reduction of arachidonatederived eisosanoid biosynthesis (cancer stimulating metabolites) and increase the level of c9t114 and other conjugated fatty acids in the animal body confirm the particular importance of our program of developing functional food by feeding domestic animals a diet enriched in CLA isomers.