cis-9,trans-11 and trans-10,cis-12 CLA affect lipid metabolism differently in primary white and brown adipocytes of Djungarian hamsters

We explored whether CLA isomers and other C₁₈ FA affect (i) lipid content and FA concentrations in total adipocyte lipids, (ii) FA synthesis from glucose in TAG and phospholipids of primary brown (BAT) and white adipocytes (WAT), and (iii) mRNA expression of uncoupling protein 1 (UCP1) in primary brown adipocytes of Djungarian hamsters (Phodopus sungorus). c9,t11-CLA, oleic, linoleic, and α-linolenic acid increased whereas t10,c12-CLA decreased lipid accumulation in both adipocyte types. t10,c12-CLA treatment affected FA composition mainly in BAT cells. CLA incorporation into lipids, in particular c9,t11-CLA, was higher in BAT. In both cell types, t10,c12-CLA treatment reduced the incorporation of glucose ¹³C carbon into FA of TAG and phospholipids, whereas c9,t11-CLA, linoleic, and α-linolenic acid either did not influence or dose-dependently increased glucose carbon incorporation into FA. UCP1 mRNA expression was inhibited by t10,c12-CLA but increased by c9,t11-CLA, linoleic, and α-linolenic acid. It is concluded that c9,t11-CLA and t10,c12-CLA have distinctly different effects on lipid metabolism in primary adipocytes. The effects of c9,t11-CLA are similar to those of other unsaturated C₁₈ FA. The opposite effects of c9,t11-CLA and t10,c12-CLA are evident in both WAT and BAT cultures; however, brown adipocytes seem to be more susceptible to CLA treatment.     

Contrasting effects of t10,c12- and c9,t11-conjugated linoleic acid isomers on the fatty acid profiles of mouse liver lipids

The purpose of this study was to examine the effects of two purified isomers of CLA (c9,t11-CLA and t10,c12-CLA) on the weights and FA compositions of hepatic TG, phospholipids, cholesterol esters, and FFA. Eight-week-old female mice (n=6/group) were fed either a control diet or diets supplemented with 0.5% c9,t11-CLA or t10, c12-CLA isomers for 8 wk. Weights of liver total lipids and those of individual lipid fractions. did not differ between the control and the c9,t11-CLA groups. Livers from animals fed the t10,c12-CLA diet contained four times more lipids than those of the control group; this was mainly due to an increase in the TG fractions (fivefold), but cholesterol (threefold), cholesterol esters (threefold), and FFA (twofold) were also significantly increased. Although c9,t11-CLA did not significantly alter the weights of liver lipids when compared with the control group, its intake was associated with significant reductions in the weight percentage (wt% of total FAME) of 18∶1n−9 and 18∶1n−7 in the TG fraction and with significant increases in the weight percentage of 18∶2n−6 in the TG, cholesterol ester, and phospholipid fractions. on the other hand, t10,c12-CLA intake was linked with a significant increase in the weight percentage of 18∶1n−9 and a decrease in that of 18∶2n−6 in all lipid fractions. These changes may be the result of alterations in the activity of Δ9-desaturase (stearoyl CoA desaturase) and the enzymes involved in the metabolism of 18∶2n−6. Thus, the two isomers differed not only in their effects on the weights of total liver lipids and lipid fractions but also on the FA profile of the lipid fractions.     

Modulation of body composition and immune cell functions by conjugated linoleic acid in humans and animal models: Benefits vs. risks

We have reviewed the published literature regarding the effects of CLA on body composition and immune cell functions in humans and in animal models. Results from studies in mice, hamsters, rats, and pigs generally support the notion that CLA reduced depot fat in the normal or lean strains. However, in obese rats, it increased body fat or decreased it less than in the corresponding lean controls. These studies also indicate that t10,c12-CLA was the isomer that reduced adipose fat; however, it also increased the fat content of several other tissues and increased circulating insulin and the saturated FA content of adipose tissue and muscle. Four of the eight published human studies found small but significant reductions in body fat with CLA supplementation; however, the reductions were smaller than the prediction errors for the methods used. The other four human studies found no change in body fat with CLA supplementation. These studies also report that CLA supplementation increased the risk factors for diabetes and cardiovascular disease including increased blood glucose, insulin, insulin resistance, VLDL, C-reactive protein, lipid peroxidation, and decreased HDL. Most studies regarding the effects of CLA on immune cell functions have been conducted with a mixture of isomers, and the results have been variable. One study conducted in mice with the purified c9,t11-CLA and t10,c12-CLA isomers indicated that the two isomers have similar effects on immune cell functions. Some of the reasons for the discrepancies between the effects of CLA in published reports are discussed. Although significant benefit to humans from CLA supplementation is questionable, it may create several health risks in both humans and animals. On the basis of the published data, CLA supplementation of adult human diets to improve body composition or enhance immune functions cannot be recommended at this time.     

Fractionation and enrichment of CLA isomers by selective esterification with Candida rugosa lipase

A commercial product of CLA contains almost equal amounts of cis-9,trans-11 (c9,t11)-CLA and trans-10,cis-12 (t10,c12)-CLA. We attempted to enrich the two isomers by a two-step selective esterification using Candida rugosa lipase that acted on c9,t11-CLA more strongly than on t10,c12-CLA. An FFA mixture containing CLA isomers was esterified with an equimolar amount of lauryl alcohol in a mixture of 20% water and the lipase. When the esterification of total FA reached 50%, two isomers were fractionated in a good yield: t10,c12-CLA was enriched in FFA, and c9,t11-CLA was recovered in lauryl esters. The FFA were esterified again to enrich t10,c12-CLA. At 27.3% esterification of total FA, the t10,c12-CLA content in FFA increased to 64.8 wt% with 89.3% recovery: The ratio of the content of t10,c12-CLA to that of two isomers was 95.9%. Lauryl esters obtained by the single esterification were employed for enrichment of c9,t11-CLA. After the esters were hydrolyzed, the resulting FFA were esterified again with lauryl alcohol. At 62.0% esterification of total FA, the c9,t11-CLA content in lauryl esters increased to 73.3 wt% with 79.4% recovery: The ratio of the content of c9,t11-CLA to that of two isomers was 95.6%. In a 600-g-scale purification, molecular distillation was effective in separating the reaction mixture into lauryl alcohol, FFA, and lauryl ester fractions.     

Conjugated Linoleic Acid Reduces Hepatic Steatosis and Restores Liver Triacylglycerol Secretion and the Fatty Acid Profile During Protein Repletion in Rats

Protein depletion is associated with hepatic steatosis and decreased circulating triacylglycerol (TAG). Since conjugated linoleic acid (CLA) increases lean body mass, protects against muscle catabolism, and modulates lipid metabolism, the aim of this work was to investigate the effects of CLA with two different amounts of dietary fat on the regulation of plasma and hepatic TAG concentration, and its possible connections with changes in fatty acid (FA) profile in plasma, liver and adipose tissue and hepatic oxidative status during protein repletion. Rats were fed a low protein diet (14 days) and then a protein repletion diet (30 days), supplemented or not with CLA, containing 7% (w/w) or 20% (w/w) of fat. Hepatic TAG secretion and removal by muscle and adipose tissue lipoprotein lipase, FA profile and liver oxidative status were evaluated. Protein depletion affected hepatic TAG secretion and peripheral removal, decreasing plasma and increasing liver TAG concentration, whereas protein repletion with CLA improved these abnormalities independently of the amount of dietary fat by increasing hepatic TAG secretion. This prevention in the absence of CLA was not observed. CLA was incorporated in plasma and tissues (adipose > liver > plasma, and c9,t11-CLA > t10,c12-CLA), accompanied by alterations in FA composition, mainly in adipose tissue. The hepatic oxidative stress was overcome by protein repletion. CLA had a beneficial impact on TAG metabolism in protein repleted animals, preventing hepatic steatosis through higher hepatic TAG secretion.     

<Emphasis Type="Italic">t</Emphasis>10,<Emphasis Type="Italic">c</Emphasis>12-18:2-Induced Milk Fat Depression is Less Pronounced in Cows Fed High-Concentrate Diets

In intensively reared dairy cows, milk fat secretion is reduced in response to high-concentrate diets and it is often referred to as the “milk fat depression” (MFD) syndrome. Some trans fatty acid (FA) isomers produced in the rumen of the cows, including t10,c12-18:2, are known for their inhibitory effect on mammary lipogenesis. To study whether this effect depends on the basal diet, duodenal infusions of t10,c12-18:2 were performed on cows fed four different diets (a factorial arrangement of forage:concentrate ratio and linseed oil supplementation). The overall response obtained with t10,c12-18:2 infusion was consistent with previous studies: a decrease in milk fat content and yield without significant variations in milk yield. Mean transfer efficiency of infused t10,c12-18:2 was 19.6%. However, the decrease in milk fat and FA yields (both de novo synthesis and preformed long-chain FA) was less pronounced in cows fed high-concentrate diets (−27% of the initial level), compared with cows fed low-concentrate diets (−42% of initial level). This difference was independent of dietary oil supplementation and milk FA yield before infusion. Results pertaining to effects of dietary forage:concentrate ratio were confirmed by statistical meta-analysis of data from previously published t10,c12-18:2 infusion experiments. This study shows that in cows fed MFD diets the mammary gland becomes more resistant to or experiences a lower response potential to further inhibition of lipogenesis and/or delta-9 desaturation of FA.     

High intake,but not low intake,of CLA impairs weight gain in growing mice

CLA has a range of biological properties, including effects on lipid metabolism and body composition in experimental animals. The prevalent isomer of CLA found in the human diet is 9c, 11t-CLA, and it is predominantly found in products containing fat from ruminant animals. This study investigated the effect of dietary CLA on energy balance in mice. Synthetic CLA reduced body fat in growing male BAI B/c mice in a dose-dependent manner over the range 0.25–1.0% w/w CLA in the diet. Weight gain was also reduced at the highest levels of dietary CLA, being only 5.88±2.68 g/4 mice (mean±1 SD) after 4 wk of 2.0% CLA in the diet, compared with weight groups. There was no significant effect on weight gain if diets contained 0.5% synthetic CLA or less. These results suggest that high levels of a synthetic mixture of CLA isomers modify energy metabolism and body composition and that high levels of synthetic CLA impair weight gain and reduce body fat pad mass in growing mice.     

Selective Enrichment of Conjugated Linoleic Acid Isomers in Their Mixtures Using Combined Chemical and Enzymatic Methods

The aim of this study was to selectively enrich t10,c12-conjugated linoleic acid (t10,c12-CLA) and c9,t11-CLA in commercial CLA mixtures using a combination of urea crystallization and lipase-catalyzed esterification. The objective of the urea fractionation is to remove saturated and monounsaturated fatty acids (FA) from the CLA mixtures. CLA-enriched free FA (FFA) mixtures containing 53.8 wt% t10,c12-CLA and 39.1 wt% c9,t11-CLA were produced from the CLA mixtures containing ~34 wt% each of the two CLA isomers by a urea crystallization using methanol and the urea-to-FA weight ratio of 2.5:1. The CLA-enriched FFA mixtures were partially esterified with dodecan-1-ol in a recirculating packed-bed reactor using an immobilized lipase from Candida rugosa to further enrich the t10,c12-CLA and c9,t11-CLA in an FFA fraction and an FA dodecyl ester fraction, respectively, under the optimal conditions, i.e., temperature, 20 °C; FA-to-dodecan-1-ol molar ratio, 1:1; water content, 2 wt% of total substrates; residence time, 5 min; and reaction time, 24 h (for t10,c12-CLA enrichment) and 12 h (for c9,t11-CLA enrichment). After the reaction, an FFA fraction with 72.6 wt% t10,c12-CLA was obtained. Another FFA fraction with 62.0 wt% c9,t11-CLA was recovered after the saponification of the FA dodecyl ester fraction. The yields of t10,c12-CLA and c9,t11-CLA in the FFA fractions were 43.6 and 21.5 wt%, respectively, based on their initial weights in the CLA mixtures.     

<Emphasis Type="Italic">9-trans,11-trans</Emphasis>-CLA: Antiproliferative and proapoptotic effects on bovine endothelial cells

Endothelial cell function can be influenced by nutrition, especially dietary FA and antioxidants. One class of dietary FA that is found in meat and dairy products derived from ruminant animals is conjugated linoleic acids (CLA). We have examined the effects of several CLA isomers on endothelial cell proliferation. 9t,11t-CLA was the only isomer that inhibited bovine arotic endothelial cell (BAEC) [³H]methylthymidine incorporation (I₅₀=35 μM), and this antiproliferative effect was time-dependent. A small decrease (20%) in cell number was observed only at the highest concentration (60 μM) tested. The 9c,11t-, 9c,11c-, 10t 12c-, and 11c,13t-CLA isomers did not exhibit any antiproliferative effects over a 5–60 μM concentration range. α-Tocopherol and BHT decreased BAEC proliferation, but pretreatment of cells with either of these antioxidants substantially attenuated the antiproliferative effect of 9t,11t-CLA. No difference in lipid peroxidation, as measured by the thiobarbituric acid assay for malondialdehyde, was observed on treatment of endothelial cells with either 9t,11t- or 9c,11t-CLA. However, a 43% increase in caspase-3 activity was observed after incubating BAEC with 9t,11t-CLA, suggesting that the antiproliferative effect of this isomer is partially due to an apoptotic pathway. In contrast to the above results with normal endothelial cells, these five CLA isomers all inhibited proliferation of the human leukemic cell line THP-1, with the 9t,11t isomer again being the most (I₅₀=60 μM) effective. These results confirm that different CLA isomers have different inhibitory potencies on the proliferation of normal and leukemic cells.     

Comparison of body weight and adipose tissue in male C57BI/6J mice fed diets with and withouttrans fatty acids

The effect of a diet containingtrans-fatty acids (tFA) on the fatty acid composition and fat accumulation in adipose tissue was investigated in mice. Male C57BI/6J mice were fed Control or Trans Diets that were similar, except that 50% of the 18∶1, which was allcis in the Control Diet, was replaced bytFA in the Trans Diet. At selected ages, body weight, epididymal fat pad weight, perirenal fat yield, adipose tissue cellularity and fatty acid composition were examined. Over the time period studied (2–24 mon), the proportion of 18∶0 and 16∶0 tended to decrease whilecis-18∶1 levels increased. Compared to the Control Diet, the Trans Diet resulted in adipose tissue lipids with higher percentages of 14∶0 and 18∶2n−6 and lower percentages ofcis-18∶1 and 20∶4n−6. In polar lipids,tFA replaced saturated fatty acids, whereastFA replacedcis-18∶1 in the nonpolar lipids. Body weights at 16 and 24 mon of age and epididymal fat pad weights at 8–24 mon of age were lower in mice fed the Trans Diet as compared to those fed the Control Diet. At the ages studied, the Trans Diet also resulted in lower values for perirenal fat weights, triacylglycerol to polar lipid ratios, and adipose cell size. The data suggest that chronic consumption oftFA affects lipid metabolism and results in decreased fat accumulation in murine adipose tissue.     

Dietary fats and energy levels differently affect tissue lipogenic enzyme activity in finishing pigs

The aim of the present study was to determine the relationship between high and low digestible energy levels (9.5 vs. 15.4 MJ ME/kg) and either tallow or soy oil supplementation (5%rpar; on lipogenic activities and fatty acid profile of the backfat tissue outer layer and liver tissue in finishing pigs. Twenty Large White pigs averaging 30 (initial) to 106 kg (final) live weight were allocated into four dietary groups and fed the diets ad libitum. The lipid content and fatty acid composition of the tissues were determined and glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME), and fatty acid synthase (FAS) activity were measured. Growth performance and carcass measurements were affected by the dietary energy levels but not by the fat sources. Lipid deposition rate of animals fed the low energy diets was lowered regardless whether tallow or soy oil was supplemented. Unlike lipid deposition, fatty acid profile was influenced by both dietary factors. Pigs fed the low energy diet supplemented with soy oil exhibited the lowest level of saturated (P<0.001), monounsaturated (P<0.001), and the highest level of polyenic fatty acids in the backfat, the opposite was the case for the pigs fed the high energy diet supplemented with beef tallow. The fatty acid profile of the adipose tissue of animals fed the other two diets were intermediate, but clear distinction of the profile due to diets was visible. Independent of dietary treatments, lipogenic activities were up to 10 times higher in the backfat than in the liver. G6PDH activity was higher (P<0.05) due to high energy diet, whereas the activities of ME and FAS were not affected. Animals fed the high energy diet either supplemented with tallow or soy oil exhibited higher ME activity lpar;P<0.05) in the backfat, without any effects on G6PDH activity. In contrast, dietary fat sources affected the FAS activity, with lower activity lpar;P<0.05) exhibited in the backfat of animals fed the soy oil diets. The present results indicate that dietary manipulation, which change the flux through the pathway of lipogenesis and pentose-phosphate must affect differently the activities of the involved enzymes. The effect of the dietary energy level was stronger and overwhelmed the inducing effect of the PUFA on the activities of the collateral enzymes. In contrast the immediately involved lipogenic enzyme FAS responded more to dietary PUFA stimulation than to the energy supply.     

Dietary sandalwood seed oil modifies fatty acid composition of mouse adipose tissue, brain, and liver

Sandalwood (Santalum spicatum) seed oil, which occurs to about 50% of the weight of the seed kernels, contains 30–35% of total fatty acids (FA) as ximenynic acid (XMYA). This study was designed to obtain basic information on changes in tissue FA composition and on the metabolic fate of XMYA in mice fed a sandalwood seed oil (SWSO)-enriched diet. Female mice were randomly divided into three groups, each receiving different semisynthetic diets containing 5.2% (w/w) fat (standard laboratory diet), 15% canola oil, or 15% SWSO for 8 wk. The effects of SWSO as a dietary fat on the FA composition of adipose tissue, brain, and liver lipids were determined by analyses of FA methyl ester derivatives of extracted total lipid. The FA compositions of the liver and adipose tissue were markedly altered by the dietary fats, and mice fed on a SWSO-enriched diet were found to contain XMYA but only in low concentration (0.3 3%) in these tissues; XMYA was not detected in brain. Oleic acid was suggested to be a principal XMYA biotransformation product. The results were interpreted to suggest that the metabolism of XMYA may involve both biohydrogenation and oxidation reactions.     

Determination of <Emphasis Type="Italic">c</Emphasis>9,<Emphasis Type="Italic">t</Emphasis>11-CLA in major human plasma lipid classes using a combination of methylating methodologies

Isomeric CLA exhibit several significant biological activities in animals and humans and are easily isomerized to their corresponding t,t-CLA isomers during methylation with various acid-catalyzed reagents. To minimize such isomerization and provide a valid quantification of human plasma CLA content, several methylation methods were tested. Plasma neutral lipid, nonesterified FA (NEFA), and polar lipid classes were separated into the following fractions: (i) cholesteryl ester (CE, 1.2 mg/12 mL, 37.5% lipids), (ii) TAG (0.8 mg/12 mL, 25% lipids), (iii) NFFA (0.2 mg/12 mL, 6.2% lipids), (iv) MAG/DAG/cholesterol (0.3 mg/12 mL, 9.4% lipids), and (v) phospholipid (PL, 0.5 mg/20 mL, 15.6% lipids). Data showed that c9,t11-CLA found in TAG, MAG/DAG/cholesterol, and PL fractions were converted to methyl esters with sodium methoxide within 2 h at 55°C. However, the c9,t11-CLA in the CE fraction could not be completely converted to methyl esters by sodium methoxide/acetylchloride in methanol or methanolic KOH; instead, CE was treated with sodium methoxide and methyl acetate in diethyl ether for 1 h. NEFA were converted to methyl esters with trimethylsilyldiazomethane (TMSDAM). All reaction mixtures were monitored by TLC prior to GLC analysis. The highest enrichment of c9,t11-18∶2 (% FA) was in TAG (0.31%), followed by CE (0.14%) and PL (0.13%). The above methylation methods were then applied to a small subset (n=10) of nonfasting plasma lipid fractions to confirm the applicability of these data. Results from this subset of samples also indicated that the greatest enrichment of c9,t11-CLA was present in the TAG fraction (0.39%), followed by CE (0.27%) and PL (0.22%). These data indicate that different plasma fractions have different c9,t11-CLA contents.     

Enrichment of CLA isomers by selective esterification with l-menthol using Candida rugosa lipase

Commercially available preparations of CLA are composed of almost equal amounts of 9-cis,11-trans (9c,11t)-CLA and 10-trans,12-cis (10t,12c)-CLA. Each isomer was fractionated and enriched, for availability as a food supplement, by a process comprising selective esterification with l-menthol by Candida rugosa lipase, distillation, and n-hexane extraction. The first selective esterification of CLA isomers was conducted with an equimolar amount of l-menthol of 30°C. The oil phase of the reaction mixture was fractionated into an l-menthyl ester fraction (9c,11t-CLA rich) and an FFA fraction (10t,12c-CLA rich) by distillation. The FFA fraction was esterified again with an equimolar amount of l-menthol to enrich 10t,12c-CLA. The 10t,12c-CLA preparation was obtained as the resulting FFA fraction by distillation. 10t,12c-CLA was enriched to 91% with 40% recovery. To enrich 9c,11t-CLA, the l-menthyl ester fraction in the first esterification was chemically hydrolyzed, and the resulting FFA were esterified again with an equimolar amount of l-menthol. The 9c, 11t-CLA preparation was obtained by chemical hydrolysis of the resulting l-methyl ester fraction, followed by n-hexane extraction. 9c,11t-CLA was enriched to 94% with 42% recovery. This effective process for purification of CLA isomers using l-methol is applicable to the production of food supplements.     

Dietary CLA Combined with Palm Oil or Ovine Fat Differentially Influences Fatty Acid Deposition in Tissues of Obese Zucker Rats

The effect of dietary conjugated linoleic acid (CLA) supplementation in combination with fat from vegetable versus animal origin on the fatty acid deposition, including that of individual 18:1 and 18:2 (conjugated and non-conjugated) isomers, in the liver and muscle of obese rats was investigated. For this purpose, 32 male Zucker rats were randomly assigned to one of four diets containing palm oil or ovine fat, supplemented or not with 1% of 1:1 cis(c)9,trans(t)11 and t10,c12 CLA isomers mixture. Total fatty acid content decreased in the liver and muscle of CLA-fed rats. In the liver, CLA increased saturated fatty acids (SFA) in 11.9% and decreased monounsaturated fatty acids (MUFA) in 6.5%. n-3 Polyunsaturated fatty acids (PUFA) relative proportions were increased in 30.6% by CLA when supplemented to the ovine fat diet. In the muscle, CLA did not affect SFA but decreased MUFA and PUFA percentages. The estimation of Δ9-indices 16 and 18 suggested that CLA inhibited the stearoyl-CoA desaturase activity in the liver (a decrease of 13–38%), in particular when supplemented to the ovine fat diet. Concerning CLA supplementation, the t10,c12 isomer percentage was 60–80% higher in the muscle than in the liver. It is of relevance that rats fed ovine fat, containing bio-formed CLA, had more c9,t11 CLA isomer deposited in both tissues than rats fed palm oil plus synthetic CLA. These results highlight the importance to further clarify the biological effects of consuming foods naturally enriched in CLA, alternatively to CLA dietary supplementation.     

Inhibition of Stearoyl-CoA Desaturase 1 Reduces Lipogenesis in Primary Bovine Adipocytes

The objectives were to determine the effect of stearoyl-CoA desaturase (SCD1) inhibition on adipocyte proliferation, differentiation and cellular lipid metabolism in bovine primary adipocytes. Inhibition of SCD1 activity by sterculic acid (SA) or conjugated linoleic acid, trans-10 cis-12 isomer, (t10, c12-CLA) did not alter adipocyte cellular proliferation, viability or differentiation. In 1,2-[¹³C]-acetate supplemented cells, the mass isotopomer distribution analysis showed that the fractional synthesis rate of [¹³C]-16:0 was reduced (P < 0.01) in SA and t10, c12-CLA treatments compared to control. Of the lipogenic genes, t10, c12-CLA treatment decreased (P < 0.05) the expression of SCD1, acetyl-CoA carboxylase (ACC), fatty acid synthase; whereas SA supplementation decreased (P < 0.05) the expression of ACC. Both SA and t10, c12-CLA increased (P < 0.05) the expression of hormone-sensitive lipase and carnitine palmitoyl transferase involved in lipolysis and oxidation. Inhibition of SCD1 in bovine adipocytes decreases de novo fatty acid synthesis by down-regulating genes involved in lipogenesis and up-regulating genes involved in lipolysis and oxidation.     

Changes in body composition in mice during feeding and withdrawal of conjugated linoleic acid

Two experiments were conducted. In Experiment 1, 8-wk-old mice were fed control diet or diet supplemented with 0.5% conjugated linoleic acid (CLA) to study the effect of CLA on body composition (CLA: 40.8–41.1% c-9,t-11 isomer, 43.5–44.9% t-10,c-12 isomer). The data for CLA-fed mice vs. controls described parallel but significantly distinct responses for both absolute and relative changes in body fat mass (reduced in CLA-fed mice) and for relative changes in whole body protein and whole body water (both of which were increased in CLA-fed mice). In the CLA-fed mice, the effect on whole body protein appeared to precede the reduction in body fat mass. In Experiment 2, weanling mice were fed control diet or diet supplemented with 0.5% CLA for 4 wk (test group), at which time all mice were fed control diet devoid of added CLA. The test group exhibited significantly reduced body fat and significantly enhanced whole body water relative to controls at the time of diet change. Time trends for changes in relative body composition were described by parallel lines where the test group exhibited significantly less body fat but significantly more whole body protein, whole body water, and whole body ash than controls. Tissue CLA levels declined following the withdrawal of CLA from the diet. In skeletal muscle of mice fed CLA-supplemented diet, the t-10,c-12 isomer was cleared significantly faster than the c-9,t-11 CLA isomer.     

Effects of trans‐10,cis‐12 and cis‐9,trans‐11 CLA on atherosclerosis in apoE/LDLR−/− mice

The objective of our studies was to verify the potential health‐related, anti‐atherogenic potency of CLA isomers, fed to apolipoprotein E and LDL receptor double knockout mice (apoE/LDLR^?/?), representing a reliable model of atherogenesis. Additionally, the effect of CLA isomers on liver steatosis was observed. In a “long experiment” (LONG), 2‐month‐old mice with no atherosclerosis were randomly assigned to three experimental groups and fed for the next 4 months. In a “short experiment” (SHORT), 4‐month‐old mice, with pre‐established atherosclerosis, were randomly assigned to three experimental groups and fed for the next 2 months. The experimental diets were: AIN‐93G (control), AIN‐93G + 0.5% trans‐10,cis‐12 CLA (t10,c12), and AIN‐93G + 0.5% cis9,trans‐11 CLA (c9,t11). In both experiments, c9,t11 CLA increased mice body weight. In mice fed t10,c12 CLA weight of liver was threefold (p<0.05) increased what was linked with hepatic steatosis observed in LONG and SHORT experiment. In LONG experiment, t10,c12 CLA significantly (p<0.05) increased plasma TAGs, whereas no such effect was observed in SHORT one. In mice receiving the CLA isomers the level of PPARα and SREBP‐1 mRNA in liver were significantly decreased. The expression of their target genes like ACO (PPARα) or FAS (SREBP‐1) were not changed. Only c9,t11 increased ACO level in LONG experiment. There were no isomer‐specific effects of CLA isomers on the area of atherosclerotic plaque. In conclusion, our results do not support the notion that CLA isomers supplementation to the diet has anti‐atherosclerotic effects. CLA isomers have no effect on atherosclerosis in apoE/LDLR^?/? mice. Practical applications: CLAs have been shown to occur naturally in food. In the last 10 years, attempts have been made to enrich animal‐derived foods in CLA isomers through animal nutrition strategies. Indeed, these attempts resulted in production of functional food such as CLA‐enriched milk (butter and cheese), ruminant and non‐ruminant meat, as well as eggs. In addition to natural foodstuff, dietary CLA supplements can also contribute to CLA intake in humans. Commercial CLA preparations, fed to laboratory animals, showed several health‐related properties, including anti‐adipogenic, anti‐carcinogenic, anti‐atherogenic, and anti‐inflammatory effects. The underlying mechanisms of action, however, are only poorly understood. The major objective of our studies was to verify the potential health‐related, namely anti‐atherogenic potency of CLA isomers, fed to apoE/LDLR^?/? mice, representing unique and reliable model of atherogenesis. Additionally, effect of CLA isomers on steatosis was observed.     

Comparison of Postprandial Oleic Acid, 9<Emphasis Type="Italic">c,</Emphasis>11<Emphasis Type="Italic">t</Emphasis> CLA and 10<Emphasis Type="Italic">t,</Emphasis>12<Emphasis Type="Italic">c</Emphasis> CLA Oxidation in Healthy Moderately Overweight Subjects

Few studies report the individual effect of 9c,11t- and 10t,12c-CLA on human energy metabolism. We compared the postprandial oxidative metabolism of 9c,11t- and 10t,12c-CLA and oleic acid (9c-18:1) in 22 healthy moderately overweight volunteers. After 24 weeks supplementation with 9c,11t-, 10t,12c-CLA or 9c-18:1 (3 g/day), subjects consumed a single oral bolus of the appropriate [1-¹³C]-labeled fatty acid. 8 h post-dose, cumulative oxidation was similar for 9c-18:1 and 10t,12c (P = 0.66), but significantly higher for 9c,11t (P < 0.01).     

Effects of conjugated linoleic acid isomers on lipid-metabolizing enzymes in male rats

Male weanling Wistar rats (n=15), weighing 200–220 g, were allocated for 6 wk to diets containing 1% (by weight) of conjugated linoleic acid (CLA), either as the 9c,11t-isomer, the 10t,12c-isomer, or as a mixture containing 45% of each of these isomers. The five rats of the control group received 1% of oleic acid instead. Selected enzyme activities were determined in different tissues after cellular subfractionation. None of the CLA-diet induced a hepatic peroxisome-proliferation response, as evidenced by a lack of change in the activity of some characteristic enzymes [i.e., acyl-CoA oxidase, CYP4A1, but also carnitine palmitoyltransferase-I (CPT-I)] or enzyme affected by peroxisome-proliferators (glutathione S-transferase). In addition to the liver, the activity of the rate-limiting β-oxidation enzyme in mitochondria, CPT-I, did not change either in skeletal muscle or in heart. Conversely, its activity increased more than 30% in the control value in epididymal adipose tissue of the animals fed the CLA-diets containing the 10t,12c-isomer. Conversely, the activity of phosphatidate phosphohydrolase, a rate-limiting enzyme in glycerolipid neosynthesis, remained unchanged in adipose tissue. Kinetic studies conducted on hepatic CPT-I and peroxisomal acyl-CoA oxidase with CoA derivatives predicted a different channeling of CLA isomers through the mitochondrial or the peroxisomal oxidation pathways. In conclusion, the 10t,12c-CLA isomer seems to be more efficiently utilized by the cells than its 9c,11t homolog, though the Wistar rat species appeared to be poorly responsive to CLA diets for the effects measured.