Conjugated Linoleic Acid Mixture Research Articles

Isomer-specific effects of CLA on gene expression in human adipose tissue depending on PPARγ2 P12A polymorphism: a double blind, randomized, controlled cross-over study

BackgroundPeroxisome proliferator-activated receptor (PPAR)γ is a key regulator in adipose tissue. The rare variant Pro12Ala of PPARγ2 is associated with a decreased risk of insulin resistance. Being dietary PPARγ 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.ResultsThe 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 PPARγ, 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 PPARγ and leptin genes depends on the PPARγ2 genotype.ConclusionThe data suggest that the isomer specific influence of CLA on glucose and lipid metabolism is genotype dependent and at least in part mediated by PPARγ.Trial registration: ISRCTN91188075

Chemometric deconvolution of gas chromatographic unresolved conjugated linoleic acid isomers triplet in milk samples

A generally known problem of GC separation of trans-7; cis-9; cis-9, trans-11; and trans-8, cis-10 CLA (conjugated linoleic acid) isomers was studied by GC–MS on 100 m capillary column coated with cyanopropyl silicone phase at isothermal column temperatures in a range of 140–170 °C. The resolution of these CLA isomers obtained at given conditions was not high enough for direct quantitative analysis, but it was, however, sufficient for the determination of their peak areas by commercial deconvolution software. Resolution factors of overlapped CLA isomers determined by the separation of a model CLA mixture prepared by mixing of a commercial CLA mixture and CLA isomer fraction obtained by the HPLC semi-preparative separation of milk fatty acids methyl esters were used to validate the deconvolution procedure. Developed deconvolution procedure allowed the determination of the content of studied CLA isomers in ewes’ and cows’ milk samples, where dominant isomer cis-9, trans-11 is eluted between two small isomers trans-7, cis-9 and trans-8, cis-10 (in the ratio up to 1:100).

Differential incorporation of dietary conjugated linolenic and linoleic acids into milk lipids and liver phospholipids in lactating and suckling rats

Interest in health benefits of conjugated fatty acids is growing. The present study compared the incorporation pattern of dietary conjugated linolenic acids (CLnA) into milk with that of conjugated linoleic acids (CLA). Lactating Sprague-Dawley rats (Day 1) were divided into five groups fed the control diet ( n=4) or one of four experimental diets supplemented with 1–2% CLA or CLnA mixture ( n=8 each). Supplementation of 1% and 2% CLA led to enrichment of 4.17% and 8.57% CLA, respectively, while supplementation of 1% and 2% CLnA resulted in enrichment of only 0.98% and 1.71% CLnA in the milk lipids, demonstrating the transfer of CLnA from maternal diet to milk was discriminated. When the lactating rats were given a diet containing a CLnA mixture of 9t,11t,13t-, 9c,11t,13t- and 9c,11t,13c-CLnA isomers, two CLA isomers, namely, 9t,11t (0.59–0.90%) and 9c,11t (1.21–1.96%), were found in the milk, suggesting that three CLnA isomers were Δ-13 saturated. Dietary CLnA at 1–2% had no effect on liver phospholipid (PL) fatty acid composition of both maternal and suckling rats, whereas dietary CLA increased docosahexaenoic acid ( 4c,7c,10c,13c,16c,19c-22:6) and palmitic acid (16:0) proportionally in the PL of maternal rats, but it suppressed 16:0 in the PL of suckling rats. It is concluded that maternal rats incorporate CLnA isomers into milk differently from that of CLA isomers. Most interesting is that maternal rats can metabolically convert CLnA to CLA.

The level of apoptotic protein is up‐regulated by conjugated linoleic acid (CLA) in the liver of chronically ethanol‐treated rats

The study was designed to observe the effect of conjugated linoleic acid (CLA) on the levels of apoptotic proteins in the liver of chronic ethanol-treated rat. Sixty Sprague Dawley male rats were divided into 3 groups (Control, EtOH, EtOH+CLA). All rats were fed Lieber-DeCarli liquid diet for 4 weeks by pair-feeding against the EtOH group. The liquid diet was supplemented with 1.77g CLA mixture per kg diet in the CLA-treated groups. For the groups of control isocaloric of maltose dextrin was added in replace of 50g ethanol (36%Kcal). Chronic ethanol ingestion significantly increased Bcl-2/Bax ratio and decreased Caspase-3 protein levels. CLA supplementation with ethanol significantly reduced Bcl-2/Bax ratio and increased Caspase-3 protein levels. Overall, CLA ingestion with chronic ethanol could significantly increase the level of apoptosis in the liver of chronically ethanol-treated rat.

The effect of conjugated linoleic acid (CLA) on the levels of apoptotic proteins and fatty acid ethyl esters (FAEEs) in the brain of chronic ethanol‐treated rat

SD rats were divided into three groups; Control, EtOH, EtOH+CLA. All rats were fed Lieber-DeCarli liquid diet (36%Kcal) for 4 wk by pair-feeding. Liquid diet of EtOH+CLA groups was supplemented with 1.77 g CLA mixture per kg diet. Chronic ethanol ingestion did not alter the levels of Bax and Bcl-2 proteins and FAEEs, but significantly increased the level of Caspase 3 protein by reducing the ratio of Bcl-2/Bax. Compared to the EtOH group, whereas, CLA supplementation significantly increased the content of 9,11-CLAEEs and thereby significantly increased the Bcl-2/Bax ratio, and consequently reduced the level of Caspase 3 protein. In conclusion, the biological functions and specific mechanism of CLAEEs are not yet fully understood. However, the increase of 9,11-CLAEEs in the brain may play an important role in reducing the level of apoptosis.

Dietary conjugated linoleic acid decreases adipocyte size and favorably modifies adipokine status and insulin sensitivity in obese, insulin-resistant rats

Conjugated linoleic acids (CLA) have been shown to alter adiposity in some species with varying effects on insulin resistance. The objective of this 8-week study was to investigate the effects of feeding a CLA mixture (1.5%, wt/wt) on adipocyte size, insulin sensitivity, adipokine status, and adipose lipid composition in fa/fa vs lean Zucker rats. The fa/fa CLA-fed rats had smaller adipocytes and improved insulin sensitivity compared with fa/fa rats fed the control diet. Conjugated linoleic acids did not affect select markers of adipose differentiation, lipid filling, lipid uptake, or oxidation. Dietary CLA, compared with the control diet, reduced circulating leptin and elevated fasting serum adiponectin concentrations in fa/fa rats. Adipose resistin messenger RNA levels were greater in fa/fa CLA-fed rats compared with fa/fa control rats. CLA did not markedly alter adipose phospholipid fatty acid composition, and the changes in the triacylglycerol fatty acid composition reflected a lower delta-9 desaturase index of CLA-fed vs control-fed rats. In conclusion, CLA reduced adipocyte size and favorably modified adipokine status and insulin sensitivity in fa/fa Zucker rats.

CLA differently regulates adipogenesis in stromal vascular cells from porcine subcutaneous adipose and skeletal muscle

Conjugated linoleic acid (CLA), a mixture of isomers of linoleic acid, has previously been shown to be able to decrease porcine subcutaneous (SC) adipose tissue levels while increasing the count of intramuscular (IM) adipose tissue in vivo. However, the underlying mechanisms through which it acts are poorly understood. The objective of this study was to investigate the different effects of CLA on adipogenesis in cultured SC adipose tissue and IM stromal vascular cells obtained from neonatal pigs. As shown here, trans-10, cis-12 CLA decreased the expression of adipocyte-specific genes as well as adipose precursor cell numbers and the accumulation of lipid in cultured SC adipose tissue stromal vascular cells. However, the cis-9, trans-11 CLA did not alter adipogenesis in SC cultures. On the other hand, both CLA isomers increased the expression of adipocyte-specific genes in IM cultures, together with the increasing accumulation of lipid and Oil Red O-stained cells. Collectively, these data show that CLA decreases SC adipose tissue but increases IM adipose tissue by different regulation of adipocyte-specific gene expression. These results suggest that adipogenesis in IM adipocytes differs from that in SC adipocytes.

Rumenic Acid Significantly Reduces Plasma Levels of LDL and Small Dense LDL Cholesterol in Hamsters Fed a Cholesterol‐ and Lipid‐Enriched Semi‐Purified Diet

Conjugated linoleic acids (CLAs) consist of a series of positional and geometrical isomers of linoleic acid. CLA have been reported to beneficially affect cardiovascular risk factors in animal models. In order to assess the role of individual CLA isomers on lipoprotein cholesterol concentration, 30 hamsters were fed for 12 weeks an hyperlipidic diet containing pure cis-9,trans-11 CLA (c9,t11) or pure trans-10, cis-12 CLA (t10,c12) isomers given alone or as a mixture. Plasma total cholesterol, LDL and HDL cholesterol concentrations were significantly lower in the c9,t11 CLA isomer fed hamsters relative to the Control group, with the most substantially effect on LDL cholesterol (-56%; P < 0.05). Plasma triacylglycerol concentrations did not differ significantly regarding those two groups. Plasma cholesterol parameters showed a tendency to decrease in the t10,c12 CLA isomer and CLA mixture fed hamsters compared with the Control group, but differences were not significant. For the first time, the atherogenic fraction of small dense LDL was investigated. Plasma small dense LDL cholesterol concentration was lower in the c9,t11 CLA relative to Control, while the t10,c12 and CLA mixture groups showed only a non significant tendency to decrease. Taken together, these data indicate that feeding rumenic acid (c9,t11 CLA) may beneficially affect lipoprotein profile in hamster fed a cholesterol- and lipid-enriched semi-purified diet, when t10,c12 CLA isomer or CLA mixture would be less active.

Conjugated linoleic acid (CLA) effects on pups growth, milk composition and lipogenic enzymes in lactating rats

Conjugated linoleic acid (CLA) has a range of biological properties, including effects on lipid metabolism, milk and body composition in animals. This study investigated the effects of dietary CLA on lactating rats and development of the suckling pups. Dams were fed either a control diet or the same diet supplemented with 25 g/kg of a fat supplement containing 540 g CLA/kg (final concentration of 13.5 g CLA/kg diet) from parturition to the 15th day post-partum. The CLA mixture used in this study contained the following isomers (per 100 g): cis-9, trans-11 (24 g); cis-10, trans-12 (35 g); cis-8, trans-10 (15 g); cis-11, trans-13 (17 g) and others (9 g). On d 15 post partum, CLA supplementation reduced milk fat content by 33% and pup growth by 21%. The milk fatty acid profile, with decreased content of short and medium chain acids, suggests CLA inhibition was more pronounced for de novo lipid synthesis. Consistent with these results, activities of fatty acid synthase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were reduced by CLA treatment in the mammary gland and liver. In contrast, the activity of NADP-malate dehydrogenase was unchanged.

Maintenance of adiponectin attenuates insulin resistance induced by dietary conjugated linoleic acid in mice

Conjugated linoleic acid (CLA) causes insulin resistance and hepatic steatosis in conjunction with depletion of adipokines in some rodent models. Our objective was to determine whether the maintenance of adipokines, mainly leptin and adiponectin, by either removing CLA from diets or using an adiponectin enhancer, rosiglitazone (ROSI), could attenuate CLA-induced insulin resistance. Male C57BL/6 mice were consecutively fed two experimental diets containing 1.5% CLA mixed isomer for 4 weeks followed by a diet without CLA for 4 weeks. CLA significantly depleted adiponectin but not leptin and was accompanied by hepatic steatosis and insulin resistance. These effects were attenuated after switching mice to the diet without CLA along with restoration of adiponectin. To further elucidate the role of adiponectin in CLA-mediated insulin resistance, ROSI was used in a subsequent study in male ob/ob mice fed either control (CON) or CLA diet. ROSI maintained significantly higher adiponectin levels in CON- and CLA-fed mice and prevented the depletion of epididymal adipose tissue and the development of insulin resistance. In conclusion, we show that insulin resistance induced by CLA may be related more to adiponectin depletion than to leptin and that maintaining adiponectin levels alone either by removing CLA or using ROSI can attenuate these effects.

Dietary conjugated linoleic acid preserves pancreatic function and reduces inflammatory markers in obese, insulin-resistant rats

Pancreatic preservation is an important part of diabetes management that may occur with improved peripheral insulin sensitivity and attenuated low-grade adipose tissue inflammation. The objective of the current study was to determine the response of obese, insulin-resistant fa/fa Zucker rats vs lean controls to dietary conjugated linoleic acid (CLA) supplementation with respect to pancreatic islet size, insulin resistance, and markers of inflammation and adipose glucose uptake. Six-week-old fa/fa and lean Zucker rats (n = 20 per genotype) were fed either a 1.5% CLA mixture or control diet for 8 weeks. Oral glucose tolerance testing was conducted at 7.5 weeks. Fasting serum haptoglobin, insulin, and C-peptide were assayed, and select messenger RNA (mRNA) and protein markers of inflammation and glucose metabolism were measured in adipose and liver tissues. CLA-fed fa/fa Zucker rats had smaller islet cell size, improved oral glucose tolerance and insulinemia, and attenuated serum haptoglobin levels compared with control-fed fa/fa Zucker rats, despite no differences in body weight and a slightly higher visceral adipose mass. CLA did not alter insulin sensitivity or islet size in lean Zucker rats. The CLA-fed fa/fa rats also had greater adipose glucose transporter-4 mRNA and less adipose tumor necrosis factor α mRNA and protein compared with control-fed fa/fa rats. In contrast, other markers of inflammation and glucose metabolism including adipose macrophage inflammatory factor, macrophage inflammatory protein-2, and liver pyruvate carboxylase and pyruvate dehydrogenase kinase 4 were not significantly changed. These results suggest that CLA supplementation preserved pancreatic function in conjunction with improved peripheral glucose use and reduced inflammation in fa/fa Zucker rats.

Elucidation of Structural Isomers from the Homogeneous Rhodium-Catalyzed Isomerization of Vegetable Oils

The structural isomers formed by the homogeneous rhodium-catalyzed isomerization of several vegetable oils have been elucidated. A detailed study of the isomerization of the model compound methyl linoleate has been performed to correlate the distribution of conjugated isomers, the reaction kinetics, and the mechanism of the reaction. It has been shown that [RhCl(C8H8)2]2 is a highly efficient and selective isomerization catalyst for the production of highly conjugated vegetable oils with a high conjugated linoleic acid (CLA) content, which is highly desirable in the food industry. The combined fraction of the two major CLA isomers [(9Z,11E)-CLA and (10E,12Z)-CLA] in the overall CLA mixture is in the range from 76.2% to 93.4%. The high efficiency and selectivity of this isomerization method along with the straightforward purification process render this approach highly promising for the preparation of conjugated oils and CLA. Proposed improvements in catalyst recovery and reusability will only make this method more appealing to the food, paint, coating, and polymer industries in the future.

Dietary Conjugated Linoleic Acid Does Not Adversely Affect Bone Mass in Obese fa/fa or Lean Zucker Rats

Conjugated linoleic acid (CLA) elevates body ash in healthy animals. The objective of the present study was to determine if single or mixed CLA isomers improve bone mass in an obese and hyperinsulinemic state. Male (n = 120) lean and obese fa/fa Zucker rats (age, 6 weeks) were randomized to 8 weeks on a control diet or to 0.4% (w/w) cis-9, trans-11 CLA (Group 1); 0.4% (w/w) trans-10, cis-12 CLA (Group 2); 0.4% (w/w) cis-9, trans-11 CLA and 0.4% (w/w) trans-10, cis-12 CLA (Group 3); 0.4% (w/w) cis-9, trans-11 CLA, 0.4% (w/w) trans-10, cis-12 CLA, and traces of other CLA isomers (Group 4); and 0.4% (w/w) cis-9, trans-11 CLA, 0.4% (w/w) trans-10, cis-12 CLA, and 0.3% (w/w) other CLA isomers (Group 5). Bone area (BA), bone mineral content (BMC), and bone mineral density (BMD) of the whole body, spine, and femur were measured at baseline (6 weeks) and at 14 weeks of age. Effects of genotype, diet, and genotype x diet interactions were assessed using factorial analysis of variance. At 6 and 14 weeks, whole-body BA and BMC were lower in lean rats compared with fa/fa rats. Similarly, at 14 weeks, fa/fa rats had a higher spine and femur BMD despite a lower femur weight. The fa/fa rats in Groups 4 and 5 had higher adjusted whole-body BMC compared with Group 3, but not with Group 1, Group 2, or the control. In lean rats, Group 3 had a greater adjusted whole-body BMC than Groups 1 and 2, but not Group 4, Group 5, or the control. Thus, commercially available CLA mixtures and single CLA isomers do not affect bone mass in a hyperinsulinemic, obese state.

Trans-10, cis-12 conjugated linoleic acid inhibits prolactin-induced cytosolic NADP+ -dependent isocitrate dehydrogenase expression in bovine mammary epithelial cells.

Conjugated linoleic acid (CLA) has been found to exert beneficial effects on lipid profile and repress de novo fatty acid synthesis in mammary gland during lactation. However, the underlying mechanisms responsible for the antilipogenic effects of CLA have not been established. The cytosolic NADP+ -dependent isocitrate dehydrogenase (IDH1) plays a critical role in cholesterol and fatty acid biosynthesis by providing reducing equivalents as NADPH. In previous studies, we documented that the expression of IDH1 in bovine mammary epithelium was modulated by regulators of mammary differentiation and metabolic effectors. In this study, we investigated the short-term effects of prolactin (PRL) and CLA on IDH1 expression in BME-UV bovine mammary epithelial cells. In time-course experiments, we found that the treatment with PRL for 60 and 90 min elicited a significant increase in IDH1 transcript levels. Conversely, the cotreatment of BME-UV cells with PRL plus a CLA mixture for 90 min prevented the accumulation of IDH1 mRNA induced by PRL. In addition, we found that the trans-10, cis-12 CLA, but not the cis-9, trans-11 CLA isomer, inhibited basal- and PRL-induced IDH1 mRNA expression. The inhibitory effects of the trans-10, cis-12 CLA isomer on PRL-induced IDH1 expression accumulation were confirmed by quantitative real time PCR and western-blotting analysis. We propose that the inhibitory effects of CLA on milk fat synthesis in mammary epithelial cells may derive, at least in part, from repression of IDH1 expression.

CLA and n-3 PUFA differentially modulate clinical activity and colonic PPAR-responsive gene expression in a pig model of experimental IBD

Conjugated linoleic acid (CLA) and n-3 polyunsaturated fatty acids (PUFA) have been proposed as important pharmaco-nutrients for modulating mucosal immunity and therapeutic responses in patients with inflammatory bowel disease (IBD). We evaluated the ability of CLA and n-3 PUFA alone or in combination to modulate IBD in a pig model of dextran sodium sulfate (DSS)-induced colitis. Sixty-four, 15-day-old pigs were used to evaluate the effect of CLA, n-3 PUFA and a 50:50 mixture of CLA and n-3 PUFA on growth, clinical activity and colonic PPAR-responsive gene expression. Diets were formulated to contain: 1.33% soybean oil (control); 1.33% CLA; 1.33% fish oil; or 1.33% of a 50:50 mixture of CLA and fish oil. Intestinal inflammation was induced by an intragastric challenge with DSS on day 42 of dietary supplementation. The colonic expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma), PPAR gamma- and delta-responsive genes, keratinocyte growth factor (KGF) and tumor necrosis factor (TNF-alpha) were assayed by quantitative RT-PCR. The onset of IBD was delayed, colitis less severe and growth suppression attenuated in pigs fed CLA, which correlated with induction of colonic PPAR gamma and its responsive gene PPAR gamma-coactivator-1alpha (PGC1-alpha) and downregulation of TNF-alpha. However, dietary supplementation with n-3 PUFA alone or in combination with CLA resulted in an early onset of disease (i.e., day 2) and faster recovery on days 6 and 7, which correlated with a marked induction of the PPAR delta-responsive gene uncoupling protein 3 (UCP3). CLA and n-3 PUFA acted synergistically to upregulate colonic KGF expression in DSS-challenged pigs but n-3 PUFA blocked CLA-induced PPAR gamma activation. Dietary CLA-supplementation upregulated colonic PPAR gamma expression and contributed to delaying the onset of experimental IBD, whereas n-3 PUFA failed to protect from IBD, although it accelerated colonic regeneration and clinical remission by activating PPAR delta.

Beef conjugated linoleic acid isomers reduce human cancer cell growth even when associated with other beef fatty acids

Although many data are available concerning anticarcinogenic effects of industrial conjugated linoleic acid (CLA), few studies have reported the antitumour properties of CLA mixtures originating from ruminant products. The aim of the present study was to investigate the in vitro antiproliferative effects of beef CLA mixtures on breast, lung, colon, melanoma and ovarian human cancer cell lines. For this purpose, four fatty acid (FA) extracts prepared from beef lipid and varying in their CLA composition, their corresponding purified CLA-enriched fractions, and mixtures of pure synthetic CLA, the composition of which reproduced that of the four selected beef samples, were tested on cancer cell lines. Cancer cells were exposed for 48 h to medium containing 100 microm-FA and their proliferation was determined by quantifying cellular DNA content (Hoechst 33342 dye). Compared with cells incubated without FA, the number of cancer cells was reduced from 25 to 67 % (P<0.0001) following FA treatment. Antiproliferative effects of CLA mixtures varied in magnitude according to the source of FA, the CLA composition and the cell lines. CLA mixtures naturally present in beef inhibited the proliferation of human cancer cell lines, a high content in cis-trans isomers allowing the most important antiproliferative effect. Beef total FA exhibited a greater growth-inhibitory activity than their corresponding CLA-enriched fractions. These results suggested that either beef FA other than beef CLA could possess antiproliferative properties and/or the existence of complementary effects of non-conjugated FA and CLA, which could favour the antiproliferative properties of beef total FA.

Enrichment of conjugated linoleic acid (CLA) in the eggs of laying hens fed pure isomers of CLA or vaccenic acid

Conjugated linoleic acid (CLA) is a complex mixture of positional and geometric conjugated isomersof linoleic acid. Dairy products are the major dietary source of CLA and cis-9, trans-11 CLA (9,11CLA) is the predominant isomer resulting from the specific metabolism of feed derived fatty acids inthe rumen. Recent studies suggest endogenous synthesis of CLA by action of Δ-9 desaturase on trans-11 18:1 fatty acid (vaccenic acid, VA) is more important than ruminal production. In view of potentialhuman health benefits, several studies have attempted to enrich eggs with CLA by supplementing thediets of laying hen with mixtures of CLA. This has resulted in marked enrichment but also negativeeffects on egg quality and loss of hatchability of the eggs with concurrent increase in saturated fattyacid content in egg yolk. Such changes are consistent with Δ-9 desaturase inhibition especially associatedwith the presence of the trans-10, cis-12 CLA isomer (10,12 CLA) in the CLA mixtures. It istherefore worthwhile to determine which of the major CLA isomers present in the CLA mixtures, 9,11CLA or 10,12 CLA, is associated with the negative effects on egg quality. This was done by supplementingthe diets of laying hen with relatively pure forms of 9,11 CLA and 10,12 CLA. Furthermore,using relatively pure forms of 9,11 CLA and 10,12 CLA allowed us to determine the transfer efficiencyof 9,11 CLA and 10,12 CLA into egg yolk. In addition, endogenous conversion of VA to 9,11CLA in hens and deposition in egg yolk was examined.Experimental treatments consisted of diets supplemented with 0, 0.5, 1.0 and 1.5 g/d of CLA orVA. CLA isomer content (% of total fatty acids) of the materials was 83 and 7% (9,11 CLA), 9 and85% (10,12 CLA), 35 and 35% (Mix CLA) of 9,11 CLA and 10, 12 CLA, respectively. VA was suppliedin the form of dehydrated hydroxy stearic acid with trans-11 C18:1 content of 28%. The othermajor isomers in this product were cis-11, trans-12 and cis-12 C18:1 (28, 11 and 11%, respectively).There were three hens in each treatment and experimental diets were fed for 21 days. When dietswere supplemented with 9,11 CLA, 10,12 CLA and Mix CLA the transfer efficiencies (percentageof dietary CLA recovered in the egg) of 9,11 CLA and 10,12 CLA in egg yolk total lipids were 21 and&lt;1%, 24 and 12%, 20 and 9%, respectively. Dietary VA was efficiently converted to 9,11 CLA anddeposited in the yolk. The slope of linear regression of VA plus 9,11 CLA versus 9,11 CLA in the eggyolk total lipids represents an estimate of the average conversion over the range of VA intakes studied.In this study 74% of VA available for desaturation was converted to 9,11 CLA. The transfer efficiencyof VA (percentage of dietary VA recovered as VA plus 9,11 CLA in the egg) was 14%. Dietary vaccenicacid in hens is efficiently converted to 9,11 CLA, but the overall efficiency of dietary VA use forCLA enrichment is quite low. Further studies examining the limitations of VA transfer to the liver andavailability for conversion by Δ-9 desaturase should be examined.

Conjugated Linoleic Acid Impairs Endothelial Function

To determine the effect of dietary supplementation with conjugated linoleic acid (CLA) on body mass index (BMI), body fat distribution, endothelial function, and markers of cardiovascular risk. Forty healthy volunteers with BMI >27 kg/m2 were randomized to receive a CLA isomeric mixture or olive oil in a 12-week double-blind study. Subcutaneous body fat and abdominal/hepatic fat content were assessed using skin-fold thicknesses and computed tomography scanning, respectively. Endothelial function was assessed by brachial artery flow-mediated dilatation (FMD). Plasma isoprostanes were measured as an index of oxidative stress. CLA supplementation did not result in a significant change in BMI index or total body fat. There was a significant decrease in limb (-7.8 mm, P<0.001), but not torso skin-fold thicknesses or abdominal or liver fat content. Brachial artery FMD declined (-1.3%, P=0.013), and plasma F2-isoprostanes increased (+91 pg/mL, P=0.042). A CLA isomeric mixture had at most modest effects on adiposity and worsened endothelial function. On the basis of these results, the use of the isomeric mixture of CLA as an aid to weight loss cannot be recommended.

Effect of dietary conjugated linoleic acid on muscle, liver and visceral lipid deposition in rainbow trout juveniles ( Oncorhynchus mykiss)

Some of the conjugated linoleic acids (CLA), cis-9, trans-11 and trans-10, cis-12 isomers, may present a wide range of health benefits. Taking into account these beneficial effects and the relative low amounts of CLA in fish products, commercial diets for juvenile rainbow trout were supplemented with graded levels (0, 0.5, 0.75, 1 and 2%) of CLA. Duplicated groups of 5.3 g fish were fed to satiation, twice a day, over a period of 12 weeks with a CLA mixture, containing mainly the bioactive cis-9, trans-11 and trans-10, cis-12 isomers. The increase of dietary CLA levels did not affect growth performance, feed conversion ratio (FCR), hepatosomatic index (HSI) or viscerosomatic index (VSI) of the rainbow trout juveniles. Total lipids in muscle and liver were similar among treatments. In viscera, CLA supplementation reduced total lipids, but only the 0.5% CLA treatment differed significantly from the control. The fatty acid profile was affected by the dietary inclusion of CLA, resulting in a significant increase of the saturated and polyunsaturated fractions and a general decrease of the monounsaturated one, in both muscle and viscera. Nevertheless, in liver only fish fed 1% CLA had a significantly higher saturated fraction. The general decreases of monounsaturated fatty acid level in tissues with the saturated increase suggest a reduction of Δ-9 desaturase activity. CLA was deposited in all tissues and reflected the dietary CLA level. The highest concentration was attained when the 2% diet was used (6.9 g/100 g lipids in muscle). In conclusion, rainbow trout are capable of incorporating CLA in muscle, liver and viscera better than any other vertebrate, showing that this species is a potential route to increase human CLA ingestion.

Effects of trans-10, cis-12 conjugated linoleic acid and cognates on apolipoprotein B secretion in HepG2 cells

Conjugated linoleic acid (CLA) has been shown to decrease apolipoprotein B (apoB) secretion in HepG2 cells. The purpose of this study was to determine the activity of individual CLA isomers—and to test cognates that are structurally related to CLA—with regard to apoB secretion. Trans-10, cis-12 CLA decreased apoB secretion whereas cis-9, trans-11, cis-9, cis-11, trans-9, trans-11, and the chloride, alcohol, or amide forms of CLA had no effect on apoB secretion. Trans-9, cis-12 octadecadienoic acid had no effect whereas cis-9, cis-12 octadecadienoic acid (linoleic acid) enhanced apoB secretion. Among 18-carbon monounsaturated fatty acids tested, only trans-10 octadecenoic acid decreased apoB secretion. Trans-11, trans-12, trans-13, cis-9 , cis-11, and cis-13 octadecenoic acids increased apoB secretion whereas trans-9 and cis-12 octadecenoic acids were without effect. None of the 20-carbon compounds tested or cis-12 octadecen-10-ynoic acid had an effect on apoB secretion. Conjugated nonadecadienoic acid decreased apoB secretion whereas cis-10, cis-13 nonadecadienoic acid did not. The reduction of apoB secretion by CLA mixture is caused by the unique structural features of trans-10, cis-12 CLA. A trans double bond at the 10th position appears to be a key structure involved in the inhibition of apoB secretion.