Comparison of the in fl uence of different chemical forms of selenium and the pro fi les of CLA isomers in the diet on the fatty acid and amino acid contents in the liver and femoral muscles of rats *

The infl uence of diets enriched in 2% CLA isomer mixture (as CLAmixA or CLAmixB) and/or Se as selenate (SeVI) or selenized yeast (Se-Y) on the concentration of fatty acids (FA) and amino acids (AA) in the liver and femoral muscles was studied on 8 groups of 7-8 rats aged 8 weeks. Rats were fed a basal diet for 29 days or diets enriched with two combinations of 2% CLAmixA with/without 2 ppm Se (as SeVI) or 2% CLAmixB with/without 1.2 ppm Se (as Se-Y). The dietary CLAmixB containing the higher concentration of trans10cis12CLA (t10c12CLA) resulted in a higher decrease of body weight gain (BWG) (P<0.1) than the dietary CLAmixA with the lower concentration of t10c12CLA. The diet enriched in SeVI reduced the BWG (P<0.05) in rats. The dietary CLAmixA lowered the concentration of saturated FA (SFA), atherogenic SFA and thrombogenic SFA in the liver and muscles. The value of the Δ9-desaturase index decreased in the liver and muscles of rats fed the diet enriched in CLAmixA or CLAmixB compared with that in the control rats. There were signifi cantly higher (P<0.01) concentrations of c9t11CLA, t10c12CLA, ccCLA and ttCLA in the muscles compared with the concentrations of these isomers in the liver of rats fed the diets enriched in CLAmixA or CLAmixB, regardless the presence of extra Se as Se VI or Se-Y. The ratio (Rt10c12/c9t11) of t10c12CLA and c9t11CLA in the liver and muscles of rats fed the diets enriched in CLA isomers was, regardless of the presence of Se, smaller compared with the values of Rt10c12/c9t11 in the dietary CLA isomers. The concentrations of CLA isomers tended to or signifi cantly increased in the liver and muscles of rats fed diets containing Se and CLA isomers compared with rats fed the diets enriched in CLA isomers. The concentrations of PUFAn-3, PUFAn-6, PUFA and the ratio of PUFA/SFA decreased in the muscles of rats fed the diet with CLAmixA. The results suggest that the dietary CLAmixA containing the higher concentration of ttCLA, regardless of the presence of SeVI, more effi ciently reduced the magnitude of lipoprotein synthesis in muscles than the diet containing CLAmixB with/without Se-Y, Journal of Animal and Feed Sciences, 16, 2007, 678–695 * Supported in part by the Ministry for Science and Information, Grant No. 2 P06Z 016 29 1 Corresponding author: e-mail: m.czauderna@ifzz.pan.pl 679 CZAUDERNA M. ET AL. while dietary Se-Y most effectively reduced the anti-obesity properties of CLA isomers in rats. The diets enriched in CLA isomers (as CLAmixA or CLAmixB), regardless of the presence of Se VI, led to a decrease in the concentration of methionine (Met) in the liver and the concentration of all amino acids in the muscles, while increasing the concentration of Met in muscles.


INTRODUCTION
Analyses of protein sequences, on a genomic scale, revealed a signifi cant number of proteins that bind micronutrients, including proteins that contain some trace elements (e.g., Se, I or B).Selenium, in particular, has been utilized by biological systems because it endows proteins with unique coordination, catalytic and electron transfer properties (Rowntree et al., 2004;Suzuki, 2005).These properties have been employed by organisms in key functions in a variety of pathways, resulting in dependence of organisms on the chemical form and level of Se in diets.In turn, Se and other nutrients important for health, e.g., conjugated linoleic acid (CLA) isomers, can govern an organism's nutritional strategies and its evolution (Combs, 2005;Rayman, 2005).Se occupies important sites in proteins, often being present as a catalytic species or serving key structural functions.Indeed, dietary Se is reduced to selenide for further excretion and/or utilization (Weiss and Hogan, 2005).Formed selenide is known to be utilized to synthesize proteins containing Se-cysteine (Se-Cys); these Se-Cys-proteins possess a specifi c codon.On the other hand, Semethionine (Se-Met), originated from e.g., selenized yeast (Rayman, 2004), does not have a specifi c codon and is incorporated into protein by the same codon as methionine.Moreover, Se-Met can also be transformed to Se-cysteine.
Numerous benefi cial regulatory effects of CLA isomers on immune functions, cytokines, immunoglobulin production, the ratio of protein to fat in mammal bodies (repartition), lipids and eicosanoid metabolism have been reported (Akahoshi et al., 2003(Akahoshi et al., , 2004;;Turpeinen et al., 2006).Moreover, CLA isomers can modulate the expression of numerous genes, either directly or through specifi c transcription factors involved in the many metabolic processes that they affect (Raes at al., 2004;Wahle et al., 2004).Fortunately in mammals, Se-proteins have important roles in protecting unsaturated fatty acids, including CLA isomers, from oxidative damage (Crespo et. al., 1995;Tapiero et al., 2003;Suzuki, 2005).Indeed, our studies documented that dietary selenate stimulated the accumulation of unsaturated fatty acids (UNFA) as well as affected the content of amino acids in rat bodies (Czauderna et al., 2004a,b;Niedźwiedzka et al., 2006a).
Therefore, the aim of the current study was to investigate the infl uence of various chemical forms of dietary Se on the magnitude of the accumulation of differ-ent geometrical and positional isomers of CLA, especially on the composition of long-chain polyunsaturated fatty acids (PUFA) in the liver and femoral muscles in rats.We intended especially to compare the effectiveness of dietary selenate (Se VI ) and high-selenized yeast (Se-Y) (Rayman, 2004) on the magnitude of the accumulation of cis9trans11CLA (c9t11CLA), trans10cis12CLA (t10c12CLA), n-3 long-chain PUFA (LPUFAn-3) and the ratio of PUFA to saturated fatty acids (PUFA/SFA) in the liver and muscles.

Animals, treatment and feeding
Sixty-one female rats (Wistar, Ifz: BOA), at 8 weeks of age, each weighing 201±1 g at the beginning of the experiment, were housed individually in plastic cages at a temperature of 22±1 o C with a 12 h light-dark cycle and relative humidity ~60%.Each group comprised 7-8 rats (Table 1).
The experimental protocol was approved by the Local Animal Care and Use Committee (The Agriculture University, Warsaw, Poland).During a one-week preliminary period the rats were fed the Labofeed H diet produced by the Feeds and Concentrates Production Plant in Kcynia (Poland) (Pastuszewska et al., 2000) given at a submaintenance level (9 g of Labofeed H diet/day/rat) to reduce the body fat of rats (Table 1).During that time the rats decreased body weight by about 10% of their initial weight.Afterwards for 29 days the rats were fed the experimental diets enriched with 2% of a mixture of CLA isomers (as CLAmix A or CLAmix B ), 2 ppm Se as Se VI (Se VI Experiment) or 1.2 ppm Se as the high-selenized yeast (Se-Y Experiment) (Table 1).The amount of the diet was adjusted each day to ensure an ad libitum feeding level.At the end of the experiment the rats were killed.The livers and femoral muscles were removed, weighed and frozen.Fatty acids (FA) in the livers and femoral muscles were analysed individually, while amino acids (AA) were analysed in pooled samples prepared by a combination of the livers or muscles from rats fed the same diet.

Reagents and chemicals
Sodium selenate and AA standards were provided by Sigma (USA), whereas absolute methanol, 99.9% acetonitrile and 95% heptane were HPLC grade and purchased from Lab-Scan (Ireland).The two CLA isomer mixtures (CLAmix A and CLAmix B ) were supplied by Larodan Fine Chemicals AB (Sweden).Composition details (Table 1) and the purities of CLA isomer standards and the dietary CLA isomer mixtures were examined using silver-liquid chromatography (Ag + -HPLC) with photodiode array detection (DAD) at 234 nm (Czauderna et al., 2003b) and 100 m capillary-column gas liquid-chromatography with fl ame-ionization detection (GLC-FID) (Czauderna et al., 2007).
All FA standards, 50% BF 3 in methanol and o-phthaldialdehyde (OPA) were provided by Sigma (USA) and Suppelco.Ethanethiol, tetrahydrofuran and sodium hypochlorite water solution (4% available Cl) were from Fluka.The high-selenized yeast (Se-Y) used was Sel-Plex (Alltech Inc., USA).Eighty-three per cent of the total Se content of Se-Y represent Se in the form of Se-methionine (Se-Met) incorporated into the proteins of Saccharomyces cerevisiae (Rayman, 2004).Other reagents, including dichloromethane (DCM), KOH, NaOH, Na 2 SO 4 and conc.HCl, were analytical grade and were purchased from POCh (Gliwice, Poland).

Chromatographic equipment and methods
An alliance separation module (model 2690, Waters) with a Waters 996 photodiode array detector and Waters 474 fl uorescence detectors were used for determination of the concentration of AA, CLA isomers and other fatty acids containing conjugated double bonds (CFA) in the livers and muscles of rats.The underivatized CLA isomers and CFA in the livers and muscles of rats were determined according to Czauderna et al., (2003b).Methylated non-CLA fatty acids in the livers and femoral muscles were determined using GLC-FID (Czauderna et al., 2007).Methylated nonadecanoic acid (C19:0) was used as the internal standard.

Statistical analysis
The results in Tables 1-5 are presented as means of 7-8 individually analysed concentrations of FA in the livers and femoral muscles of rats.Statistical analyses of the effects of the CLA isomer mixture (as CLAmix A or CLAmix B ) and/or Se (as Se VI or Se-Y) in the diets were conducted using the nonparametric Mann-Whitney U test (Statistica, 2002) for comparing pairs in an independent experimental group (one-factor analysis), while statistical analyses of the interaction between the CLA isomer mixture (as CLAmix A or CLAmix B ) and Se (as Se VI or Se-Y) were performed using two-factorial ANOVA analysis (CLA isomers × Se).The statistical analyses were performed using the Statistica v. 6 package (Statistica,       and Y, y, Ψ -for the liver and muscles, respectively 2002).Differences were considered signifi cant at the a,b -P<0.05 or A,B -P<0.01 levels, while a tendency was concluded at the α,β -P<0.1 level.Statistical analyses of the interaction between the CLA isomers and Se were performed using two factorial ANOVA analysis (the CLA isomers × Se).The interaction was considered statistically signifi cant at x,y -P<0.05,X,Y -P<0.01 or ψ -P<0.1 levels.

RESULTS AND DISCCUSION
Effects of the dietary CLA isomer mixtures, Se VI and Se-Y on the body weight gain in rats In the current study, no macroscopic lesions or pathological changes were found in the liver and femoral muscles or in any of the other organs of rats fed the diets enriched in the CLA isomer mixture (as CLAmix A or CLAmix B ) and/or selenium (as Se VI or Se-Y) (Czauderna et al., 2004a;Korniluk et al., 2006).There were no differences in the body weight gain (BWG) among the groups of rats fed the diets enriched in the CLA isomer mixture (as CLAmix A or CLAmix B ) and Se (as Se VI or Se-Y) compared with the appropriate control groups (Table 1).In contrast, BWG was numerically lower (-4.4%) and tended to be lower (-7.7%) in the group of rats fed the diet containing only CLAmix A or CLAmix B , respectively.Thus, in the current study the anti-obesity effect of CLA isomers, t10c12CLA in particularly, was confi rmed in all rats fed diets enriched in the CLA isomer mixture (as CLAmix A or CLAmix B ), regardless of the presence of the higher concentration of ccCLA and ttCLA isomers in the dietary CLAmix A than in the dietary CLAmix B .The obtained results suggest that the concentration of t10c12CLA in the dietary CLA isomer mixture determines the size of the anti-obesity effect of CLA isomers in rats.Consequently, the dietary CLAmix B containing the higher concentration of t10c12CLA (48.2%) resulted in a higher decrease of BWG than the dietary CLAmix A with the signifi cantly lower (28.0%)concentration of t10c12CLA.This conclusion is in agreement with results of our previous studies in which dietary t10c12CLA most effi ciently decreased BWG in rats (Czauderna et al., 2004a, b).On the other hand, recent investigations that have not documented a considerable reduction in BWG are usually those in which low concentrations of CLA isomers were used in diets (≤0.5%) or the dietary CLA isomer mixtures contained lower amounts of t10c12CLA (Sisk et al., 2001).Our results are also supported by several other investigations, which have indicated that the t10c12 isomer, due to its positional and geometric property, is the most potent CLA isomer in terms of antiobesity activity, thus the one which most effi ciently reduces feed intake (Czauderna et al., 2004a), body weight gain (Akahoshi et al., 2003(Akahoshi et al., , 2004)), concentration of plasma leptin and the abundance of sterol regulatory element-binding protein mRNA (Wang et al., 2004).
Our investigation confi rms the results of other studies in rodents documenting that CLA isomers lowered body fat content and energy retention, while increasing energy expenditure as well as faecal energy and fat excretion (Terpstra et al., 2002).Indeed, the sum of FA (ΣFA) concentrations numerically or statistically decreased in the liver and muscles of rats fed the diets enriched in the CLA isomer mixture (as CLAmix A or CLAmix B ; Tables 2 and 3).In addition, the dietary CLAmix A or CLAmix B numerically decreased the sum of protein amino acids (AA) in femoral muscles of rats (Tables 4 and 5).Interestingly, the dietary CLAmix B containing the higher 10c12CLA content also numerically lowered the concentration of AA in the liver of rats fed the diet enriched only in CLAmix B (Table 5).Surprisingly, addition of Se (as Se VI or Se-Y) to a diet enriched in a CLA isomer mixture (as CLAmix A or CLAmix B ) offset the decreasing effect of CLA isomer mixtures on BWG in rats.Therefore, we suggest that interactions between metabolites of CLA isomers and Se neutralized the anti-obesity properties of CLA isomers in rats.
As shown in Table 1, there was an obvious difference in the infl uence of dietary Se VI and Se-Y on BWG in rats.Se VI , the inorganic selenium compound, reduced BWG (P<0.05) in rats.In accordance with current observations, our previous studies also reported that dietary Se VI was most effi cient in decreasing the feed conversion effi ciency (FCE) in rats (Czauderna et al., 2003c).On the other hand, dosed Se-Y containing mainly seleno-methionine (~85%) (Rayman, 2004) resulted in a negligible infl uence on BWG in rats, which occurred concomitantly with the insignifi cant effect of dietary Se-Y on FCE in rats (Korniluk et al., 2006).

The infl uence of the diets on the concentration of saturated and monounsaturated fatty acids and CLA isomers in the liver and muscles
On analysing the concentration of saturated fatty acids (SFA), differences were found in the liver and muscles of rats fed the experimental diets.The dietary CLAmix A lowered the concentration of SFA, atherogenic SFA (A-SFA: the sum of C12:0, C14:0 and C16:0) and thrombogenic SFA (T-SFA: the sum of C14:0, C16:0 and C18:0) in the liver and muscles (Table 2).This additive in the diet also decreased the concentration of C18:0 in the liver, while only numerically lowering it in the muscles.In contrast, the diet enriched in CLAmix B usually less effectively decreased the concentration of these fatty acids in the liver and muscles of rats (Table 3) compared with the dietary CLAmix A .Indeed, CLAmix B containing the higher concentration of t10c12CLA (48.2%) than CLAmix A (i.e.t10c12CLA -28.0%) caused a stronger reduction of the desaturation capacity through Δ9-desaturase.So, the current results are consistent with other studies in which dietary individual t10c12CLA or mixtures of t10c12CLA with other CLA isomers caused a reduction in Δ9-desaturase capacity, inhibited steaoryl-CoA desaturase mRNA expression and fatty acid synthesis (Czauderna et al., 2004a,b;Raes et al., 2004;Wang at al., 2004).Therefore, the values of the Δ9-desaturase index (Δ9-index) decreased in the liver and muscles of rats fed the diet enriched in CLAmix A or CLAmix B compared with that in the control rats (Tables 4 and 5).Moreover, the highest decrease of the Δ9-index value in the liver of rats fed the diet enriched in CLAmix B was accompanied by the highest increase of the liver concentration of C18:0 and SFA.Therefore, as shown in Tables 2 and 3, there was an obvious decrease in the concentration of oleic acid (c9C18:1) and monounsaturated fatty acids (MUFA) (Tables 4 and 5) in the liver and muscles of rats fed the diet containing CLAmix A or CLAmix B .
The diet enriched in CLAmix A and Se VI decreased the concentration of C18:0, T-SFA, SFA, c9C18:1 and ∆9-index in the liver (the interaction signifi cances: P<0.05 and P<0.1), while numerically lowering the liver concentrations of A-SFA and MUFA.There was only a numerical decrease in the concentration of A-SFA, c9C18:1, MUFA and the ∆9-index in the muscles (interaction P>0.05) of rats fed this diet.Surprisingly, simultaneous addition of CLAmix B and Se-Y to the diet caused a numerical increase of the concentration of C18:0, A-SFA, T-SFA and SFA in the liver, whereas in muscles no consistent differences were observed.There was a numerical decrease in the value of the ∆9-index and the concentration of MUFA and c9C18:1 in the liver and muscles of rats fed the diet enriched in CLAmix B and Se-Y (Tables 3 and 5).
Fortunately, the diet enriched in Se VI decreased the concentrations of C18:0, A-SFA, T-SFA and SFA in the liver, while there were no noticeable or consistent differences in the muscles.On the other hand, the dietary Se-Y increased the concentration of A-SFA (P<0.01),T-SFA (P<0.05),SFA (P<0.05),c9C18:1 (P<0.01),MUFA (P<0.05) and the value of the ∆9-index (P<0.1) in the liver, while only numerically decreasing the concentrations of these fatty acids and the value of the ∆9-index in the muscles (Tables 3 and 5).A considerable infl uence of dietary Se VI on the ∆9-index values and the concentration of c9C18:1 and MUFA in the liver and muscles was not found.However, this additive numerically decreased the concentration of MUFA and the ∆9-index value in the liver and muscles, while a statistically signifi cant decrease was observed only for the concentration of c9C18:1 in the liver (P<0.05).
The addition of CLAmix A or CLAmix B to the diet induced a signifi cant increase in the concentrations of c9t11CLA, t10c12CLA, ccCLA and ttCLA in the liver and muscles of rats.As shown in Tables 2 and 3, there were signifi cantly higher (P<0.01)concentrations of CLA isomers in the muscles compared with the concentrations of CLA isomers in the liver of rats fed the diets enriched in CLAmix A or CLAmix B , regardless of the presence of extra Se as Se VI or Se-Y.The current study also investigated the relationship between the experimental diets and preferential accumulation of t10c12CLA and c9t11CLA in the liver and muscles (Tables 2 and  3).The present results clearly demonstrated that the concentration ratios (R t10c12/ c9t11 ) of t10c12CLA and c9t11CLA in the liver and muscles of rats fed the diets enriched in CLAmix A or CLAmix B were, regardless of the presence of Se (as Se VI or Se-Y), smaller compared with the values of R t10c12/c9t11 of these isomers in CLAmix A (R t10c12/c9t11 = 1.0242) and CLAmix B (R t10c12/c9t11 = 0.9813) added to the rat diets (i.e. in the liver, muscles: 0.6863, 0.6678 and 0.6405, 0.6247, respectively; Tables 2  and 3).Thus, our results are in agreement with the studies of Alasnier et al. (2002) in which t10c12CLA and t10t12CLA were also more effi ciently driven through β-oxidation in the cells of the liver, muscles, kidneys or adipose tissue compared with their 9,11 homologues.Moreover, based on the concentration sums of all assayed fatty acids (ΣFA) in the liver and muscles (Tables 2 and 3) and other studies (Alasnier et al., 2002;Akahoshi et al., 2003), we suggest that CLAmix A and CLAmix B added to the rat diet stimulated FA oxidation in rats.
The results summarized in Tables 2 and 3 suggest that the addition of Se (as Se VI or Se-Y) to the diet enriched in CLAmix A or CLAmix B affected the capacity of β-oxidation of CLA isomers.In our studies, the values of R t10c12/c9t11 were higher in the liver and muscles of rats fed the diet containing Se (as Se VI or Se-Y) and the CLA isomer mixture (as CLAmix A or CLAmix B ) compared with the R t10c12/c9t11 values in the liver and muscles of rats fed the diet enriched in only the CLA isomer mixture.Moreover, we suggest that adding Se-Y to the diet containing CLAmix B more effi ciently reduced the β-oxidation of t10c12CLA in the liver and muscles than the diet enriched in Se VI and CLAmix A .Therefore, in the liver and muscles, Se-Y in the diet with CLAmix B gave a higher value of R t10c12/c9t11 in comparison with the values of R t10c12/c9t11 in the liver and muscles of rats fed the diet containing Se VI and CLAmix A (i.e.0.8171 vs 0.7450 and 0.8429 vs 0.6868, respectively; see Tables 2 and 3).The present results on this subject also reinforce the hypothesis that the CLAmix B × Se-Y interaction more effi ciently diminished the yield of FA oxidation than the dietary CLAmix A and Se VI (Tables 2 and  3).Therefore, BWG, concentrations of ΣFA and the percentage contributions of t10c12CLA in the liver and muscles of the CLA Se-YB rats' group are more similar to the ones in the control rats.Concomitantly, stronger effects of the CLAmix A × Se VI interaction on BWG, the sum of concentrations of all assayed fatty acids (ΣFA) and the abundance of the t10c12 isomer were observed in rats fed the diet enriched in CLAmix A and Se VI .
The concentrations of c9t11CLA, t10c12CLA, ccCLA and ttCLA numerically or signifi cantly (P<0.05 or P<0.01) increased in the liver and muscles of rats fed diets containing Se (as Se VI or Se-Y) and the CLA isomer mixture (as CLAmix A or CLAmix B ) compared with rats fed the diets enriched in CLAmix A or CLAmix B .For the concentration of t10c12CLA in the liver, interactions of CLAmix A x Se VI and CLAmix B x Se-Y interactions were found (P<0.05), while for the concentration of c9t11CLA in the liver, there a CLAmix A x Se VI interaction was observed (P<0.1).It is well established that dietary supplementation of both selenate and Se-Y results in increased activities of glutathione peroxidases and other specifi c selenoproteins.Thus, we hypothesized that both chemical forms of Se are effective in maintaining the antioxidant Se status in rats.

The infl uence of diets on the concentration of PUFA in the liver and muscles
The concentration of PUFAn-3 (P<0.01),PUFAn-6 (P<0.1),PUFA (P<0.1) and the value of the concentration ratio of PUFA and SFA (PUFA/SFA) decreased in the muscles of rats fed the diet containing CLAmin A (Table 4).Similar changes were observed in the muscles of rats fed the diet enriched in CLAmix B , however, the decrease was not statistically signifi cant (0.10<P<0.17;Table 5).Moreover, this diet resulted in a decrease in the concentrations of these fatty acids and the ratios of PUFAn-6/PUFAn-3 and PUFA/SFA in the liver.Surprisingly, the diet containing CLAmix A increased the concentrations of PUFAn-3, PUFAn-6, PUFA and the value of PUFA/SFA in the liver.
No consistent differences in the concentrations of PUFAn-3, PUFAn-6, PUFA and the ratio value of PUFA/SFA, were observed in the liver and muscles of rats fed the diet enriched in Se VI and Se-Y.On the other hand, as shown in Table 4, the diet enriched in CLAmix A or Se VI increased the concentration of PUFAn-3, PUFAn-6, PUFA and the ratio of PUFA/SFA in the liver, while there was decrease in the concentration of PUFAn-3, PUFAn-6 and PUFA in the muscles.For these fatty acids and the ratio of PUFA/SFA, there were no signifi cant CLA isomer (as CLAmix A and CLAmix B ) x Se (as Se VI and Se-Y) interactions in the liver and muscles, with the exception of the ratio of PUFA/SFA (P<0.1) in the muscles of rats fed the diet containing CLAmix B and Se-Y.
The concentrations of linoleic (LA), linolenic (αLNA) and arachidonic (ArA) acids were statistically or numerically lower in the muscles of rats fed the diet containing CLAmix A (P<0.05, P<0.05 and P<0.01, respectively) or CLAmix B (P=0.22, P=0.22 and P<0.01, respectively) (Tables 2 and 3).Unexpectedly, the concentrations of these fatty acids in the liver showed no signifi cant changes (P>0.05) with the exception of the level of ArA in the liver of rats fed the diet enriched in CLAmix B (P<0.05).So, the current study demonstrates that the dietary CLA isomer mixture containing higher concentrations of c9t11CLA (47.3%) and t10c12CLA (48.2%) (i.e.CLAmix B ) more effi ciently decreased the accumulation of AAs than the dietary CLAmix A possessing lower concentrations of c9t11CLA and t10c12CLA (i.e.28.6 and 28.0%, respectively).Thus, the present results are consistent with other studies showing that dietary c9t11CLA and t10c12CLA decreased the concentration of LA (i.e.PUFAn-6 in particularly) and its metabolites (e.g., C18:3n-6, C20:3n-6 and ArA) in animals (Wang et al., 2004;Korniluk et al., 2006).The current results documented that dietary c9t11CLA and t10c12CLA resulted in dose-dependent interference in the conversion of LA to anabolites by competing for the same enzymes (the ∆6-, ∆5-, ∆4-desaturases and elongase) (Alasnier et al., 2002;Korniluk et al., 2006).These CLA isomers also modifi ed the metabolism of αLNA (PUFAn-3), however, the effects of CLA isomers are weaker and less consistent than on the metabolism of LA (Tables 2 and 3).On the other hand, no consistent differences were observed in the concentrations of LA, αLNA and AAs in the liver and muscles of rats fed the diet containing Se VI or Se-Y.Similarly, for these fatty acids in the liver and muscles, there also were no signifi cant CLA isomer mixture (as CLAmix A or CLAmix B ) × Se (as Se VI or Se-Y) interactions, although the diet enriched in CLAmix B and Se-Y resulted in a numerical decrease of the LA, αLNA and AAs in the liver and muscles, while CLAmix A x Se VI treatment numerically lowered the levels of these fatty acids only in the muscles.
The concentration of c11c14C20:2 in the liver and muscles usually numerically or signifi cantly (P<0.01 and P<0.05) increased in rats fed the diet enriched in CLAmix A or CLAmix B , respectively (Tables 4 and 5).Therefore, we suggest that dietary c9t11CLA and t10c12CLA tended to increase elongase capacity, particularly in the liver.On the other hand, for the capacity of elongase, there were no signifi cant CLA isomer (as CLAmix A or CLAmix B ) x Se (as Se VI or Se-Y) interactions.
The stimulatory effect of c9t11CLA and t10c12CLA on elongase capacity as well as ∆4-desaturase in the liver was confi rmed by the increase of the c7c10c13c16c19C22:5 (C22:5n-3) and c4c7c10c13c16c19C22:6 (C22:6n-3) concentrations of in the liver of rats supplemented with CLAmix A or CLAmix B in the liver of rats (Tables 4 and 5).For these fatty acids, a similar effect was observed in the liver of rats fed the diet enriched in both CLAmix A and Se VI .Unexpectedly, the products of elongase and ∆4-desaturase (i.e.C22:5n-3 and C22:6n-6) were less effi ciently accumulated in the muscles of rats fed the diets containing CLAmix A or CLAmix B compared with the control rats.Moreover, no consistent effects of Se VI and Se-Y on C22:5n-3 and C22:6n-6 in the liver and muscles were found.

Infl uence of the diets on the concentration of amino acids in the liver and muscles
It has been shown that the diet enriched in the CLA isomer mixture (as CLAmix A or CLAmix B ), regardless of the presence of Se as Se VI (Tables 4 and 5), leads to a decrease in the concentration of methionine (Met) in the liver and the sum of all amino acid (AA) concentrations in the muscles, while increasing the concentration of Met in the muscles.The presented data suggested that dietary CLAmix A containing the higher concentration of ttCLA, regardless of Se VI supplementation, more effi ciently reduced lipoprotein synthesis in the muscles of rats than the diet with CLAmin B , regardless of the presence of Se-Y.Consequently, the sums of AA concentrations (Tables 4 and 5) and ΣFA (Tables 2 and 3) in the muscles decreased in rats fed the diet containing CLAmix A or CLAmix B , although the addition of Se VI and especially Se-Y to the diet containing CLA isomers reduced the effect of CLAmix A and CLAmix B .We also hypothesize that dietary Se VI and, particularly, Se-Y, reduced the metabolism of Met in the muscles, while stimulating the catabolism or/and transfer of liver Met to other organs and tissues of rats (e.g., into muscles).Indeed, the concentration of Met (P<0.05) and the sum of AA (P<0.05)increased in the blood plasma of rats fed the diet enriched in 2% CLAmix A (Niedźwiedzka et al., 2006a).Interestingly, the diet containing only Se VI resulted in a considerable decrease in the sum of AA concentrations in the liver and, especially, in the muscles, concomitantly with a lower BWG (Table 1).On the other hand, Se-Y added to the diet enriched in CLAmix B most effi ciently elevated the concentrations of AA, Met and cysteine in the muscles (Table 5).Moreover, addition of Se-Y to the diet with CLAmix B most effi ciently diminished the ability of CLAmix B to decrease the value of BWG and the concentration of ΣFA in the muscles.Therefore, we suggest that Se-Y most effectively reduced the anti-obesity property of CLA isomers.
No consistent effects were observed on the content of cysteine in the liver and muscles of rats fed the diets enriched in CLA isomers (CLAmix A or CLAmix B ) or/and Se (as Se VI or Se-Y).

CONCLUSIONS
For monogastric animals both dietary CLA isomer mixtures, regardless of the different content of t,t and c,c isomers of CLA, seem to be an effi cient way of increasing the deposition of c9t11CLA and t10c12CLA in the liver and muscles, as well as of DPA and DHA in the liver.The mixture of c9t11CLA t10c12CLA considerably decreased the abundance of A-SFA and T-SFA in the liver and muscles, so, we suggest that the diets enriched in these CLA isomers improve the nutritional properties of meat derived from monogastric animals.Selenate added to the diet with CLAmix A more effi ciently decreased the concentration of A-SFA and T-SFA as well as other SFA in the liver and muscles than the diet enriched in CLAmix B and Se-Y.
In a fi nal conclusion, dietary Se-Y and Se VI were shown to produce generally different effects on body weight gain of rats and FA profi les in the animals' bodies, regardless of the presence of CLA isomers in the diet.

Table 1
, CLA isomers, oleic acid (c9C18:1), linoleic acid (LA), c9c12c15C18:3 (αLNA), c5c8c11c14C20:4 (ArA) and the concentration sum of all fatty acids (ΣFA) in the liver and femoral muscles of rats fed the control diet and the experimental diet enriched in the CLA isomer mixture (CLAmix A ) and/or selenate (Se VI A CLA SeVI 9

Table 3
. The concentration of saturated fatty acids (SFA), CLA isomers, oleic acid (c9C18:1), linoleic acid (LA), c9c12c15C18:3 (αLNA) c5c8c11c14C20:4 (ArA) and the concentration sum of all fatty acids (ΣFA) in the liver and femoral muscles of rats fed the control diet and the experimental diet enriched in the CLA isomer mixture (CLAmix B ) and/or the high-selenized yeast (Se-Y) 1

Table 4 .
The ∆9 desaturase index, the concentrations of unsaturated fatty acids and amino acids in the liver and femoral muscles of rats fed the control diet and the experimental diet enriched in the CLA isomer mixture (CLAmix

Table 5 .
The ∆9 desaturase index, the concentrations of unsaturated fatty acids and amino acids in the liver and femoral muscles of rats fed the control diet and the experimental diets enriched in the CLA isomer mixture (CLAmix