The effect of conjugated linoleic acid isomers on fatty acid profiles of liver and adipose tissues and their conversion to isomers of 16:2 and 18:3 conjugated fatty acids in rats

Conjugated Linolenic Acid (CLnA) vs Conjugated Linoleic Acid (CLA): A Comprehensive Review of Potential Advantages in Molecular Characteristics, Health Benefits, and Production Techniques

Conjugated linoleic acid (CLA) has been extensively characterized due to its many biological activities and health benefits, but conjugated linolenic acid (CLnA) is still not well understood. However, CLnA has shown to be more effective than CLA as a potential functional food ingredient. Current research has not thoroughly investigated the differences and advantages between CLnA and CLA. This article compares CLnA and CLA based on molecular characteristics, including structural, chemical, and metabolic characteristics. Then, the in vivo research evidence of CLnA on various health benefits is comprehensively reviewed and compared with CLA in terms of effectiveness and mechanism. Furthermore, the potential of CLnA in production technology and product protection is analyzed. In general, CLnA and CLA have similar physicochemical properties of conjugated molecules and share many similarities in regulation effects and pathways of various health benefits as well as in the production methods. However, their specific properties, regulatory capabilities, and unique mechanisms are different. The superior potential of CLnA must be specified according to the practical application patterns of isomers. Future research should focus more on the advantageous characteristics of different isomers, especially the effectiveness and safety in clinical applications in order to truly exert the potential value of CLnA.

Effects of in ovo feeding of t10,c12-conjugated linoleic acid on hepatic lipid metabolism and subcutaneous adipose tissue deposition in newly hatched broiler chicks

The purpose of this study was to investigate whether in ovo feeding of t10,c12-conjugated linoleic acid (CLA) could regulate hepatic lipid metabolism and decrease lipid accumulation in newly hatched chicks. Three hundred and sixty fertilely specific pathogen-free hatching eggs were selected and randomly divided into 6 groups. On embryonic day 11 of incubation (E11), 0, 1.5, 3.0, 4.5, 6.0, or 7.5 mg t10,c12-CLA were injected into the eggs. The results indicated that in ovo feeding of t10,c12-CLA significantly decreased the subcutaneous adipose tissue (SAT) mass and the relative SAT weight of newly hatched chicks in linear and quadratic manners (P < 0.05). In liver, the levels of triglycerides were reduced linearly and quadratically and total cholesterol were reduced quadratically as the dose of t10,c12-CLA increased (P < 0.05). Meanwhile, the hepatic carnitine palmitoyltransferase-1a (CPT1a) content and polyunsaturated fatty acid proportion were increased quadratically in t10,c12-CLA groups (P < 0.05), accompanied by the decrease of malondialdehyde level and the increase of glutathione peroxidase and total antioxidant capacity activities (P < 0.05). In addition, in ovo feeding of t10,c12-CLA decreased the mRNA expression levels of fatty acid synthase, acetyl-CoA carboxylase 1 in linear and quadratic manners (P < 0.05), and decreased the mRNA expression of adipose triacylglyceride lipase and stearoyl-CoA desaturase significantly in liver (P < 0.05), accompanied by upregulating the mRNA expression of CPT1a quadratically and AMP-activated protein kinase α linearly and quadratically (P < 0.05). In SAT, the mRNA expression of peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulatory element-binding protein-1c were decreased linearly and quadratically (P < 0.05), and the expression of PPARα and CPT1a genes were increased linearly and quadratically as the dose of t10,c12-CLA increased (P < 0.05). In conclusion, our findings demonstrate that in ovo feeding of t10,c12-CLA alleviates lipid accumulation in newly hatched chicks by suppressing fatty acid synthesis and stimulating lipolysis in the liver and inhibiting adipocyte differentiation in subcutaneous adipose tissue.

Conjugated linoleic acid ameliorates hepatic steatosis by modulating intestinal permeability and gut microbiota in ob/ob mice

Background

Conjugated linoleic acid (CLA) is an effective supplement for reducing fat mass, but its effect on hepatic steatosis remains controversial.

Objective

This study aims to evaluate the effect of CLA on liver fat accumulation, inflammation, gut microbiome, and intestinal barrier integrity.

Design

Wild-type (WT) mice and ob/ob (OB) mice were randomly divided into four groups according to the treatment with/without 1% CLA: WT, WT mice treated with CLA (WT-CLA), OB, and OB mice treated with CLA (OB-CLA). Lipid metabolism and hepatic fat accumulation were evaluated by changes in histological and biochemical parameters. Gene expressions related to liver inflammation and intestinal barrier integrity were examined. The effect of CLA on the gut microbiota population was investigated.

Results

The body weight, fatty tissue mass, and serum lipid levels of the WT-CLA group and OB-CLA group were separately lower than those of the WT group and OB group, but the livers of the WT-CLA group had more fatty lipids, higher triglyceride properties, and saturated fatty acid (FA) composition than those of the WT group, which was contrary to the effect of CLA on OB mice. Real time quantitative PCR results showed that CLA increased hepatic inflammation and intestinal permeability in the WT mice, while it significantly decreased the mRNA expression of liver TNF-α, IFN-γ, and IL-1β and markedly ameliorated intestinal tight junction proteins in the OB mice. The gut microbiota testing indicated a higher abundance of beneficial bacteria (e.g., Lachnoclostridium, Roseburia, Dubosiella, Oscillibacter, and Anaerostipes) and a lower abundance of pro-inflammatory bacteria (e.g., Tyzzerella and Alistipes) in the OB-CLA group than those of the OB group. Correlation analysis suggested that gut microbiota correlated with liver inflammation, intestinal permeability, and hepatic FA composition.

Conclusion

CLA potentially contributed to ameliorating hepatic steatosis in OB mice via modulating liver inflammation, intestinal permeability, and gut microbiota, which suggests CLA is more suitable for people with obesity or overweight.

Supplementing conjugated linoleic acid (CLA) in breeder hens diet increased CLA incorporation in liver and alters hepatic lipid metabolism in chick offspring

This experiment was designed to investigate the effect of supplementing conjugated linoleic acid (CLA) in breeder hens diet on development and hepatic lipid metabolism of chick offspring. Hy-Line Brown breeder hens were allocated into two groups, supplemented with 0 (CT) or 0.5% CLA for 8 weeks. Offspring chicks were grouped according to the mother generation and fed for 7 days. CLA treatment had no significant influence on development, egg quality, and fertility of breeder hens, but darkened the egg yolks in shade and increased yolk sac mass compared to CT group. Addition of CLA resulted in increased body mass and liver mass, and decreased deposition of subcutaneous adipose tissue in chick offspring. The serum triglyceride (TG) and cholesterol (TC) levels of chick offspring were decreased in CLA group. CLA treatment increased the incorporation of both CLA isomers (c9t11 and t10c12) in liver of chick offspring, accompanied by the decreased hepatic TG levels, related to the significant reduction of fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) enzyme activities and the increased of carnitine palmitoyltransferase-1 (CPT1) enzyme activity. Meanwhile, CLA treatment reduced the mRNA expression of genes related to fatty acid biosynthesis (FAS, ACC, and sterol regulatory element-binding protein-1c), and induced the expression of genes related to β-oxidative (CPT1, AMP-activated protein kinase, and peroxisome proliferator-activated receptor α) in chick offspring liver. In summary, the addition of CLA in breeder hens diet significantly increased incorporation of CLA in liver of chick offspring, which further regulate hepatic lipid metabolism.

Structure determination of conjugated linoleic and linolenic acids

Conjugated linoleic and linolenic acids (CLA and CLnA) can be found in dairy, ruminant meat and oilseeds, these types of unsaturated fatty acids consist of various positional and geometrical isomers, and have demonstrated health-promoting potential for human beings. Extensive reviews have reported the physiological effects of CLA, CLnA, while little is known regarding their isomer-specific effects. However, the isomers are difficult to identify, owing to (i) the similar retention time in common chromatographic methods; and (ii) the isomers are highly sensitive to high temperature, pH changes, and oxidation. The uncertainties in molecular structure have hindered investigations on the physiological effects of CLA and CLnA. Therefore, this review presents a summary of the currently available technologies for the structural determination of CLA and CLnA, including the presence confirmation, double bond position determination, and the potential stereo-isomer determination. Special focus has been projected to the novel techniques for structure determination of CLA and CLnA. Some possible future directions are also proposed.

Trans-palmitoleic acid (trans-9-C16:1, or trans-C16:1 n-7): Nutritional impacts, metabolism, origin, compositional data, analytical methods and chemical synthesis. A review

Since the early 2010s, dietary trans-palmitoleic acid (trans-9-hexadecenoic acid, trans-9-C16:1 in the Δ-nomenclature, trans-C16:1 n-7 in the Ω-nomenclature, TPA) has been epidemiologically associated with a lower risk of type 2 diabetes in humans. Thanks to these findings, TPA has become a nutrient of interest. However, there is a lot of unresolved crucial questions about this dietary fatty acid. Is TPA a natural trans fatty acid? What kind of foods ensures intakes in TPA? What about its metabolism? How does dietary TPA act to prevent type 2 diabetes? What are the biological mechanisms involved in this physiological effect? Clearly, it is high time to answer all these questions with the very first review specifically dedicated to this intriguing fatty acid. Aiming at getting an overview, we shall try to give an answer to all these questions, relying on appropriate and accurate scientific results. Briefly, this review underlines that TPA is indeed a natural trans fatty acid which is metabolically linked to other well-known natural trans fatty acids. Knowledge on physiological impacts of dietary TPA is limited so far to epidemiological data, awaiting for supplementation studies. In this multidisciplinary review, we also emphasize on methodological topics related to TPA, particularly when it comes to the quantification of TPA in foods and human plasma. As a conclusion, we highlight promising health benefits of dietary TPA; however, there is a strong lack in well-designed studies in both the nutritional and the analytical area.

Production of conjugated fatty acids: A review of recent advances

Conjugated fatty acids (CFAs) have received a deal of attention due to the increasing understanding of their beneficial physiological effects, especially the anti-cancer effects and metabolism-regulation activities. However, the production of CFAs is generally difficult. Several challenges are the low CFAs content in natural sources, the difficulty to chemically synthesize target CFA isomers in high purity, and the sensitive characteristics of CFAs. In this article, the current technologies to produce CFAs, including physical, chemical, and biotechnical approaches were summarized, with a focus on the conjugated linoleic acids (CLAs) and conjugated linolenic acids (CLNAs) which are the most common investigated CFAs. CFAs usually demonstrate stronger physiological effects than other non-conjugated fatty acids; however, they are more sensitive to heat and oxidation. Consequently, the quality control throughout the entire production process of CFAs is significant. Special attention was given to the micro- or nano-encapsulation which presented as an emerging technique to improve the bioavailability and storage stability of CFAs. The current applications of CFAs and the potential research directions were also discussed.

Maternal conjugated linoleic acid modulates TAG metabolism in adult rat offspring

Conjugated linoleic acid (CLA) might regulate the lipid depots in liver and adipose tissue. As there is an association between maternal nutrition, fat depots and risk of offspring chronic disease, the aim was to investigate the effect of maternal CLA consumption on TAG regulation and some inflammatory parameters in adult male rat offspring receiving or not receiving CLA. Female Wistar rats were fed control (C) or CLA-supplemented (1 %, w/w) diets during 4 weeks before and throughout pregnancy and lactation. After weaning, male offspring of CLA rats were fed C or CLA diets (CLA/C and CLA/CLA groups, respectively), whereas C male rat offspring were fed a C diet (C/C group) for 9 weeks. Serum TAG levels were increased in the CLA/CLA and CLA/C groups, associated with a reduction of lipoprotein lipase activity and weights of adipose tissue. The liver TAG levels were decreased in the CLA/CLA group, related to a significant reduction of fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC) and glucose-6-phosphate dehydrogenase enzyme activities, as well as to the mRNA levels of FAS, ACC, stearoyl-CoA desaturase-1 and sterol regulatory element-binding protein-1c. Even though normal TAG levels were found in the liver of CLA/C rats, a reduction of lipogenesis was also observed. Thus, these results demonstrated a programming effect of CLA on the lipid metabolic pathways leading to a preventive effect on the TAG accretion in adipose tissue and the liver of male rat offspring. This knowledge could be important to develop some dietary strategies leading to a reduced incidence of obesity and fatty acid liver disease in humans.

Nutrient Regulation: Conjugated Linoleic Acid's Inflammatory and Browning Properties in Adipose Tissue

Obesity is the most widespread nutritional disease in the United States. Developing effective and safe strategies to manage excess body weight is therefore of paramount importance. One potential strategy to reduce obesity is to consume conjugated linoleic acid (CLA) supplements containing isomers cis-9, trans-11 and trans-10, cis-12, or trans-10, cis-12 alone. Proposed antiobesity mechanisms of CLA include regulation of (a) adipogenesis, (b) lipid metabolism, (c) inflammation, (d) adipocyte apoptosis, (e) browning or beiging of adipose tissue, and (f) energy metabolism. However, causality of CLA-mediated responses to body fat loss, particularly the linkage between inflammation, thermogenesis, and energy metabolism, is unclear. This review examines whether CLA's antiobesity properties are due to inflammatory signaling and considers CLA's linkage with lipogenesis, lipolysis, thermogenesis, and browning of white and brown adipose tissue. We propose a series of questions and studies to interrogate the role of the sympathetic nervous system in mediating CLA's antiobesity properties.

Individual CLA Isomers, c9t11 and t10c12, Prevent Excess Liver Glycogen Storage and Inhibit Lipogenic Genes Expression Induced by High-Fructose Diet in Rats

This study assessed the effects of individual conjugated linoleic acid isomers, c9t11-CLA and t10c12-CLA, on nonalcoholic fatty liver disease (NAFLD) and systemic endothelial dysfunction in rats fed for four weeks with control or high-fructose diet. The high-fructose diet hampered body weight gain (without influencing food intake), increased liver weight and glycogen storage in hepatocytes, upregulated expression of fatty acid synthase (FAS) and stearoyl-CoA desaturase-1 (SCD-1), and increased saturated fatty acid (SFA) content in the liver. Both CLA isomers prevented excessive accumulation of glycogen in the liver. Specifically, t10c12-CLA decreased concentration of serum triacylglycerols and LDL + VLDL cholesterol, increased HDL cholesterol, and affected liver lipid content and fatty acid composition by downregulation of liver SCD-1 and FAS expression. In turn, the c9t11-CLA decreased LDL+VLDL cholesterol in the control group and downregulated liver expression of FAS without significant effects on liver weight, lipid content, and fatty acid composition. In summary, feeding rats with a high-fructose diet resulted in increased liver glycogen storage, indicating the induction of gluconeogenesis despite simultaneous upregulation of genes involved in de novo lipogenesis. Although both CLA isomers (c9t11 and t10c12) display hepatoprotective activity, the hypolipemic action of the t10c12-CLA isomer proved to be more pronounced than that of c9t11-CLA.

Rosiglitazone, a PPAR-γ agonist, fails to attenuate CLA-induced milk fat depression and hepatic lipid accumulation in lactating mice

Our objective was to investigate the combination of rosiglitazone (ROSI) and conjugated linoleic acid (CLA) on mammary and hepatic lipogenesis in lactating C57Bl/6 J mice. Twenty-four lactating mice were randomly assigned to one of four treatments applied from postpartum day 6 to day 10. Treatments included: (1) control diet, (2) control plus 1.5 % dietary CLA (CLA) substituted for soybean oil, (3) control plus daily intra-peritoneal (IP) rosiglitazone injections (10 mg/kg body weight) (ROSI), and (4) CLA plus ROSI (CLA-ROSI). Dam food intake and milk fat concentration were depressed with CLA. However, no effects were observed with ROSI. The CLA-induced milk fat depression was due to reduced expression for mammary lipogenic genes involved in de-novo fatty acid (FA) synthesis, FA uptake and desaturation, and triacyglycerol synthesis. Liver weight (g/100 g body weight) was increased by CLA due to an increase in lipid accumulation triggering a compensatory reduction in mRNA abundance of hepatic lipogenic enzymes, including acetyl-CoA carboxylase I and stearoyl-CoA desaturase I. On the contrary, no effects were observed with ROSI on hepatic and mammary lipogenic gene and enzyme expression. Overall, feeding CLA to lactating mice induced milk fat depression and increased hepatic lipid accumulation, probably due to the presence of trans-10, cis-12 CLA isomer, while ROSI failed to significantly attenuate both hepatic steatosis and reduction in milk fat content.

Dietary conjugated linoleic Acid and hepatic steatosis: species-specific effects on liver and adipose lipid metabolism and gene expression

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms. Methods. Sixty-four published experiments were summarized in which trans-10, cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared. Summary and Conclusions. Dietary trans-10, cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

Conjugated double bonds in lipid bilayers: a molecular dynamics simulation study

Conjugated linoleic acids (CLA) are found naturally in dairy products. Two isomers of CLA, that differ only in the location of cis and trans double bonds, are found to have distinct and different biological effects. The cis 9 trans 11 (C9T11) isomer is attributed to have the anti-carcinogenic effects, while the trans 10 cis 12 (T10C12) isomer is believed to be responsible for the anti-obesity effects. Since dietary CLA are incorporated into membrane phospholipids, we have used Molecular Dynamics (MD) simulations to investigate the comparative effects of the two isomers on lipid bilayer structure. Specifically, simulations of phosphatidylcholine lipid bilayers in which the sn-2 chains contained one of the two isomers of CLA were performed. Force field parameters for the torsional potential of double bonds were obtained from ab initio calculations. From the MD trajectories we calculated and compared structural properties of the two lipid bilayers, including areas per molecule, density profiles, thickness of bilayers, tilt angle of tail chains, order parameters profiles, radial distribution function (RDF) and lateral pressure profiles. The main differences found between bilayers of the two CLA isomers, are (1) the order parameter profile for C9T11 has a dip in the middle of sn-2 chain while the profile for T10C12 has a deeper dip close to terminal of sn-2 chain, and (2) the lateral pressure profiles show differences between the two isomers. Our simulation results reveal localized physical structural differences between bilayers of the two CLA isomers that may contribute to different biological effects through differential interactions with membrane proteins or cholesterol.

Dietary conjugated linoleic acid isomers change the unsaturation degree of hepatic fatty acids in neutral lipids but not in polar lipids

The fatty acid composition of phospholipids plays a key role in the structural and functional properties of cellular membrane. In this study, it was hypothesized that conjugated linoleic acid (CLA) isomer supplementation changes the unsaturation degree of the fatty acids of neutral lipids (NLs) but not those of polar lipids (PLs). Thus, the main goal was to determine the pattern of fatty acid incorporation into hepatic PL and NL fractions. Wistar male rats were fed cis(c)9,trans(t)11 and t10,c12 CLA isomers, separately or as a mixture. Whereas the t10,c12 isomer incorporation in the PL fraction was similar when supplemented either individually or as a mixture, the c9,t11 isomer reached the highest values of incorporation when combined with t10,c12. In the PL fraction, the linoleic acid did not change; but the arachidonic acid decreased, especially in the rats given the mixture. Also in this fraction, the t10,c12 isomer, either separately or as a mixture, decreased the amounts of n-6 long-chain (LC) polyunsaturated fatty acids (PUFA) and increased those of the n-3 LC PUFA relative to the control. In the NL fraction, linoleic acid incorporation followed the diet composition, whereas the arachidonic acid was similar among treatments. Facing CLA isomer supplementation, the present study suggests that fatty acid incorporation into phospholipids, through the balance between n-6 and n-3 LC PUFA, is dependent upon maintaining the unsaturation degree of cellular membrane.

Metabolism and actions of conjugated linoleic acids on atherosclerosis-related events in vascular endothelial cells and smooth muscle cells

Conjugated linoleic acids (CLAs) are biologically highly active lipid compounds that have attracted great scientific interest due to their ability to cause either inhibition of atherosclerotic plaque development or even regression of pre-established atherosclerotic plaques in mice, hamsters and rabbits. The underlying mechanisms of action, however, are only poorly understood. Since cell culture experiments are appropriate to gain insight into the mechanisms of action of a compound, the present review summarizes data from cell culture studies about the metabolism and the actions of CLAs on atherosclerosis-related events in endothelial cells (ECs) and smooth muscle cells (SMCs), which are important cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLAs exert several beneficial actions including inhibition of inflammatory and vasoactive mediator release from ECs and SMCs, which may help explain the anti-atherogenic effect of CLAs observed in vivo. The observation that significant levels of CLA metabolites, which have been reported to have significant biological activities, are well detectable in ECs and SMCs indicates that the anti-atherogenic effects observed with CLAs are presumably mediated not only by CLAs themselves but also by their metabolites.

Differential effects of conjugated linoleic acid isomers on the biophysical and biochemical properties of model membranes

Conjugated linoleic acids (CLA) are known to exert several isomer-specific biological effects, but their mechanisms of action are unclear. In order to determine whether the physicochemical effects of CLA on membranes play a role in their isomer-specific effects, we synthesized phosphatidylcholines (PCs) with 16:0 at sn-1 position and one of four CLA isomers (trans 10 cis 12 (A), trans 9 trans 11 (B), cis 9 trans 11 (C), and cis 9 cis 11 (D)) at sn-2, and determined their biophysical properties in monolayers and bilayers. The surface areas of the PCs with the two natural CLA (A and C) were similar at all pressures, but they differed significantly in the presence of cholesterol, with PC-A condensing more than PC-C. Liposomes of PC-A similarly showed increased binding of cholesterol compared to PC-C liposomes. PC-A liposomes were less permeable to carboxyfluorescein compared to PC-C liposomes. The PC with two trans double bonds (B) showed the highest affinity to cholesterol and lowest permeability. The two natural CLA-PCs (A and C) stimulated lecithin-cholesterol acyltransferase activity by 2-fold, whereas the unnatural CLA-PCs (B and D) were inhibitory. These results suggest that the differences in the biophysical properties of CLA isomers A and C may partly contribute to the known differences in their biological effects.

Influence of conjugated linoleic acids on functional properties of vascular cells

Conjugated linoleic acids (CLA) are biologically highly active lipid compounds that inhibit the development of atherosclerotic plaques in experimental animals. The underlying mechanisms of action, however, are only poorly understood. Since cell-culture experiments are appropriate to provide a detailed view into the mechanisms of action of a compound, the present review summarises results fromin vitrostudies dealing with the effects of CLA isomers and CLA mixtures on functional properties of cells of the vascular wall, such as endothelial cells, smooth muscle cells and monocyte-derived macrophages, which are amongst the major cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLA exert several beneficial actions in cells of the vascular wall through the activation of nuclear PPAR. These actions of CLA, which may, at least partially, explain the inhibition of atherogenesis by dietary CLA, include modulation of vasoactive mediator release from endothelial cells, inhibition of inflammatory and fibrotic processes in activated smooth muscle cells, abrogation of inflammatory responses in activated macrophages, and reduction of cholesterol accumulation in macrophage-derived foam cells.

Trans-10, cis-12-conjugated linoleic acid reduces the hepatic triacylglycerol content and the leptin mRNA level in adipose tissue in obese Zucker fa/fa rats

Conjugated linoleic acid (CLA) isomers have been reported to reduce body weight and beneficially affect glucose metabolism in animals, but the results are inconsistent and seem to depend on animal model and type of CLA isomer. In the present study, feeding male Zucker fa/fa rats diets supplemented with 1% trans-10, cis-12-CLA for 10 d reduced the liver TAG content without improving the overall adiposity, and enhanced hepatic mitochondrial and peroxisomal beta-oxidation. The increased carnitine palmitoyltransferase (CPT)-I activity and mRNA level as well as the increased n-3:n-6 PUFA ratio in liver suggest that trans-10, cis-12-CLA increased the hepatic beta-oxidation by stimulation of PPARalpha. The reduced hepatic TAG content may be partly due to lower activity of stearoyl-CoA desaturase, as the ratios of 18 : 1n-9:18 : 0 and 16 : 1n-7:16 : 0 were reduced in liver. Trans-10, cis-12-CLA increased the CPT-I mRNA in retroperitoneal white adipose tissue (WAT), and increased uncoupling protein-2 mRNA in epididymal and inguinal WAT depots. Leptin mRNA level was decreased in all examined WAT depots, implying reduced insulin sensitivity. The resistin mRNA level was increased in all WAT depots, whereas adiponectin mRNA was reduced in inguinal and retroperitoneal WAT. The present results suggest that dietary supplementation with trans-10, cis-12-CLA may increase the catabolism of lipids in liver and adipose tissue. Moreover, we provide new data suggesting that trans-10, cis-12-CLA modulates the expression of resistin and adiponectin inversely in adipose tissue. Hence, the present results suggest that trans-10, cis-12-CLA may have some beneficial effects on lipid metabolism and adiposity but possibly reduces insulin sensitivity.

Effect of linseed oil supplementation on concentrations of (n-3) polyunsaturated fatty acids in liver phospholipids of rats fed diets containing either an oil rich in conjugated linoleic acids, sunflower oil or high-oleic acid sunflower oil

This study investigated the metabolism of alpha-linolenic acid and the formation of eicosanoids in rats fed diets with three different dietary fats (30 g/kg diet): either a conjugated linoleic acid (CLA) preparation with a high concentration of cis-9, trans-11 CLA (32.2 g/100 g) and trans-10, cis-12 CLA (33.3 g/100 g) and a low concentration of linoleic acid (0.5 g/100 g), sunflower oil (SFO) with a high concentration of linoleic acid or high-oleic acid sunflower oil (HO-SFO) with a high concentration of oleic acid. Basal diets with those oils were fed for 4 weeks. In the fifth week, the same diets supplemented with 50 g of linseed oil/kg as a source of alpha-linolenic acid were fed. To study the effect of the oils on the metabolism of alpha-linolenic acid, the amounts of individual (n-3) polyunsaturated fatty acids (PUFA) in liver phospholipids (phosphatidyl choline and phosphatidyl ethanolamine) were determined; to study the effect on eicosanoid formation, the concentrations of various two-series eicosanoids in liver and plasma, the activity of the secretory phospholipase A2 and the relative mRNA concentrations of cyclooxygenases-1 and 2 in the liver were measured. Rats fed the CLA diets had the highest concentrations of long chain (n-3) PUFA deriving from delta6, delta5 and 14-desaturation of alpha-linolenic acid in liver phospholipids; rats fed the SFO diet had the lowest concentrations of those fatty acids. The concentration of arachidonic acid in liver phospholipids and the concentrations of eicosanoids in liver and plasma were lowest in rats fed the CLA diet and highest in the rats fed the SFO diet. Moreover, rats fed the CLA diet had a higher gene expression of delta6-desaturase in the liver than the other two groups of rats. The results show that feeding the CLA oil reduced the formation of arachidonic acid and eicosanoids but enhanced the formation of long chain (n-3) PUFA and their incorporation into tissue lipids when compared with feeding SFO or HO-SFO.

Conjugated linoleic acid isomers: differences in metabolism and biological effects

The term conjugated linoleic acid (CLA) refers to a mixture of linoleic acid positional and geometric isomers, characterized by having conjugated double bonds, not separated by a methylene group as in linoleic acid. CLA isomers appear as a minor component of the lipid fraction, found mainly in meat and dairy products from cows and sheep. The most abundant isomer is cis-9,trans-11, which represents up to 80% of total CLA in food. These isomers are metabolized in the body through different metabolic pathways, but important differences, that can have physiological consequences, are observed between the two main isomers. The trans-10,cis-12 isomer is more efficiently oxidized than the cis-9,trans-11 isomer, due to the position of its double bounds. Interest in CLA arose in its anticarcinogenic action but there is an increasing amount of specific scientific literature concerning the biological effects and properties of CLA. Numerous biological effects of CLA are due to the separate action of the most studied isomers, cis-9,trans-11 and trans-10,cis-12. It is also likely that some effects are induced and/or enhanced by these isomers acting synergistically. Although the cis-9,trans-11 isomer is mainly responsible for the anticarcinogenic effect, the trans-10,cis-12 isomer reduces body fat and it is referred as the most effective isomer affecting blood lipids. As far as insulin function is concerned, both isomers seem to be responsible for insulin resistance in humans. Finally, with regard to the immune system it is not clear whether individual isomers of CLA could act similarly or differently.

Conjugated linoleic acid-induced fat loss dependence on Delta6-desaturase or cyclooxygenase

OBJECTIVE

To determine whether conjugated linoleic acid (CLA)-induced body fat loss is dependent upon metabolism of CLA by Delta6-desaturase, cyclooxygenase, or lipoxygenase.

METHODS AND PROCEDURES

Mice were fed diets with or without CLA and inhibitors to either Delta6-desaturase (SC-26196), cyclooxygenase (aspirin), or lipoxygenase (nordihydroguaiaretic acid (NDGA)) for 2 weeks. Body fat percent, lean mass, fat pad weights, liver weight, and fatty acid concentrations were determined. A Delta6-desaturase index was calculated, and adipose tissue prostaglandin E(2) (PGE(2)) and leukotriene B(4) (LTB(4)) concentrations were determined to confirm enzyme inhibition.

RESULTS

Inhibition of Delta6-desaturase and cyclooxygenase were confirmed. CLA caused a loss of body fat (P < 0.001). The body fat loss was blocked (P = 0.08) by the Delta6-desaturase inhibitor at a dose that decreased (P < 0.05) the calculated index. Aspirin and NDGA had no effect on body fat and did not interact with CLA.

DISCUSSION

Inhibition of Delta6-desaturase prevented CLA from being able to cause a body fat loss. Therefore, a desaturated metabolite of CLA appears to be involved in the CLA antiobesity effect. This effect of CLA does not seem dependent upon cyclooxygenase. Because lipoxygenase activity was not blocked by NDGA, we cannot draw conclusions about its importance in mediating the antiobesity effect of CLA.

Conjugated linoleic acid isomers and cancer

We reviewed the literature regarding the effects of conjugated linoleic acid (CLA) preparations enriched in specific isomers, cis9, trans11-CLA (c9, t11-CLA) or trans10, cis12-CLA (t10, c12-CLA), on tumorigenesis in vivo and growth of tumor cell lines in vitro. We also examined the potential mechanisms by which CLA isomers may alter the incidence of cancer. We found no published reports that examined the effects of purified CLA isomers on human cancer in vivo. Incidence of rat mammary tumors induced by methylnitrosourea was decreased by c9, t11-CLA in all studies and by t10, c12-CLA in just a few that included it. Those 2 isomers decreased the incidence of forestomach tumors induced by benzo (a) pyrene in mice. Both isomers reduced breast and forestomach tumorigenesis. The c9, t11-CLA isomer did not affect the development of spontaneous tumors of the intestine or mammary gland, whereas t10, c12-CLA increased development of genetically induced mammary and intestinal tumors. In vitro, t10, c12-CLA inhibited the growth of mammary, colon, colorectal, gastric, prostate, and hepatoma cell lines. These 2 CLA isomers may regulate tumor growth through different mechanisms, because they have markedly different effects on lipid metabolism and regulation of oncogenes. In addition, c9, t11-CLA inhibited the cyclooxygenase-2 pathway and t10, c12-CLA inhibited the lipooxygenase pathway. The t10, c12-CLA isomer induced the expression of apoptotic genes, whereas c9, t11-CLA did not increase apoptosis in most of the studies that assessed it. Several minor isomers including t9, t11-CLA; c11, t13-CLA; c9, c11-CLA; and t7, c11-CLA were more effective than c9, t11-CLA or t10, c12-CLA in inhibiting cell growth in vitro. Additional studies with purified isomers are needed to establish the health benefit and risk ratios of each isomer in humans.

Creatine monohydrate and conjugated linoleic acid improve strength and body composition following resistance exercise in older adults

Aging is associated with lower muscle mass and an increase in body fat. We examined whether creatine monohydrate (CrM) and conjugated linoleic acid (CLA) could enhance strength gains and improve body composition (i.e., increase fat-free mass (FFM); decrease body fat) following resistance exercise training in older adults (>65 y). Men (N = 19) and women (N = 20) completed six months of resistance exercise training with CrM (5g/d)+CLA (6g/d) or placebo with randomized, double blind, allocation. Outcomes included: strength and muscular endurance, functional tasks, body composition (DEXA scan), blood tests (lipids, liver function, CK, glucose, systemic inflammation markers (IL-6, C-reactive protein)), urinary markers of compliance (creatine/creatinine), oxidative stress (8-OH-2dG, 8-isoP) and bone resorption (Ν-telopeptides). Exercise training improved all measurements of functional capacity (P<0.05) and strength (P<0.001), with greater improvement for the CrM+CLA group in most measurements of muscular endurance, isokinetic knee extension strength, FFM, and lower fat mass (P<0.05). Plasma creatinine (P<0.05), but not creatinine clearance, increased for CrM+CLA, with no changes in serum CK activity or liver function tests. Together, this data confirms that supervised resistance exercise training is safe and effective for increasing strength in older adults and that a combination of CrM and CLA can enhance some of the beneficial effects of training over a six-month period. Trial Registration. ClinicalTrials.gov NCT00473902

Evaluation of the Mechanism of Action of Conjugated Linoleic Acid Isomers on Reproduction in Dairy Cows

The objective of this study was to evaluate the mechanism of action through which conjugated linoleic acid (CLA) beneficially affects reproduction. Lactating Holstein cows (n = 45, 20 +/- 1 DIM) were assigned to 1 of 3 treatments: 70 g/d of Ca salts of tallow (control); 63 g/d of lipid-encapsulated CLA providing 7.1 g/d of cis-9, trans-11 CLA and 2.4 g/d of trans-10, cis-12 CLA (CLA 75:25); or 76 g/d of lipid-encapsulated CLA providing 7.1 g/d each of cis-9, trans-11 and trans-10, cis-12 CLA (CLA 50:50). Supplements were top-dressed for 37 d, milk production and DMI were recorded daily, and blood samples were taken 3 times per week. At 30 +/- 3 DIM, ovulation was synchronized in all cows with a modified Ovsynch protocol, and on d 15 of the cycle cows received an oxytocin injection; blood samples were obtained frequently to measure 13,14 dihydro, 15-keto PGF2alpha. On d 16 of the cycle cows received a PGF2alpha injection and ovarian follicular aspiration was performed 54 h later. Follicular fluid was analyzed for fatty acids, progesterone, and estradiol. Endometrial biopsies were taken before and again near the end of the supplementation period for fatty acid analysis. The CLA resulted in decreased milk fat content of 14.1 and 6.1% at wk 5 of treatment of CLA 50:50 and CLA 75:25, respectively. There were no differences in energy balance or plasma nonesterified fatty acids; however, plasma IGF-I was greater in cows supplemented with CLA 50:50. The CLA isomers were not detectable in endometrial tissue, but cis-9, trans-11 CLA tended to be greater in follicular fluid of supplemented cows. Response to the oxytocin challenge was not different among treatments. Progesterone during the early luteal phase and the estradiol:progesterone ratio in follicular fluid tended to be greater in cows supplemented with CLA 50:50. Overall, these results indicate that short periods of CLA supplementation do not alter uterine secretion of PGF2alpha. The mechanism through which CLA affects reproduction may involve improved ovarian follicular steroidogenesis and increased circulating concentrations of IGF-I.

Effects of conjugated linoleic acid on linoleic and linolenic acid metabolism in man

Evidence from animal studies suggests that conjugated linoleic acid (CLA) modulates plasma and tissue appearance of newly synthesized PUFA. The effects of a 1·2g (0·5% energy) daily intake of thecis-9,trans-11 (c9,t11) isomer of CLA,trans-10,cis-12 (t10,c12) isomer of CLA or olive oil (placebo) on linoleic acid (LA) and linolenic acid (LNA) metabolism in healthy human volunteers was investigated. Fifteen subjects were fed an experimental diet and supplemented withc9,t11-CLA,t10,c12-CLA or placebo for 7d before consuming a tracer dose of U-[13C]La (50%Mg) And U-[13C]Lna (50Mg). Blood Samples Were Taken At 0, 2, 4, 6, 8, 24, 48, 72 and 168%h and analysed using high-precision MS. No differences between the groups in peak plasma [13C]LA (10·3–11·6% of dose), [13C]LNA (2·5–2·9% of dose), [13C]arachidonic acid (0·09–0·12% of dose), [13C]EPA (0·04–0·06% of dose) or [13C]Dha (0c·06–0·10% of dose) were detected. ConcentrationV. time curves (area under the curve) also showed no significant differences between groups. This suggests that, in healthy human subjects consuming a diet with adequate intake of essential fatty acids, CLA does not affect metabolism of LA or LNA

Incorporation ofcis-9,trans-11 conjugated linoleic acid and vaccenic acid (trans-11 18:1) into plasma and leucocyte lipids in healthy men consuming dairy products naturally enriched in these fatty acids

The present study investigated whether consuming dairy products naturally enriched incis-9,trans-11 (c9,t11) conjugated linoleic acid (CLA) by modification of cattle feed increases the concentration of this isomer in plasma and cellular lipids in healthy men. The study had a double-blind cross-over design. Subjects aged 34–60 years consumed dairy products available from food retailers for 1 week and then either control (0·17 gc9,t11 CLA/d; 0·31 gtrans-vaccenic acid (tVA)/d) or CLA-enriched (1·43 gc9,t11 CLA/d; 4·71 gtVA/d) dairy products for 6 weeks. After 7 weeks washout, this was repeated with the alternate products.c9,t11 CLA concentration in plasma lipids was lower after consuming the control products, which may reflect the two-fold greaterc9,t11 CLA content of the commercial products. Consuming the CLA-enriched dairy products increased thec9,t11 CLA concentration in plasma phosphatidylcholine (PC) (38%;P=0·035), triacylglycerol (TAG) (22%;P<0·0001) and cholesteryl esters (205%;P<0·0001), and in peripheral blood mononuclear cells (PBMC) (238%;P<0·0001), whiletVA concentration was greater in plasma PC (65%;P=0·035), TAG (98%;P=0·001) and PBMC (84%;P=0·004). Overall, the present study shows that consumption of naturally enriched dairy products in amounts similar to habitual intakes of these foods increased thec9,t11 CLA content of plasma and cellular lipids.

Failure of conjugated linoleic acid supplementation to enhance biosynthesis of docosahexaenoic acid from alpha-linolenic acid in healthy human volunteers

A rate-limiting step in docosahexaenoic acid (DHA) formation from alpha-linolenic acid (ALA) involves peroxisomal oxidation of 24:6n-3 to DHA. The aim of the study was to determine whether conjugated linoleic acid (CLA) would enhance conversion of ALA to DHA in humans on an ALA-supplemented diet. The subjects (n=8 per group) received daily supplementation of ALA (11g) and either CLA (3.2g) or placebo for 8 weeks. At baseline, 4 and 8 weeks, blood was collected for plasma fatty acid analysis and a number of physiological measures were examined. The ALA-supplemented diet increased plasma levels of ALA and eicosapentaenoic acid (EPA). The addition of CLA to the ALA diet resulted in increased plasma levels of CLA, as well as ALA and EPA. Plasma level of DHA was not increased with either the ALA alone or ALA plus CLA supplementation. The results demonstrated that CLA was not effective in enhancing DHA levels in plasma in healthy volunteers.

Effect of conjugated linoleic acid type, treatment period, and dosage on differentiation of 3T3 cells

This study was conducted to determine effect of CLA and linoleic acid (LA) on cell differentiation, cellular glycerol-3-phosphate dehydrogenase (GPDH) activity, and FA accumulation in differentiating 3T3-L1 cells (3 isomers x 3 treatment periods x 4 doses). The cells were cultured in 24-well plates for proliferation until confluence. Then they were treated with media containing 0, 10, 35, or 70 mg/L (0, 35, 125, or 250 mmol/L, respectively) of LA, cis9,trans11- or trans10,cis12-CLA during early (day 0-2), intermediate and late (day 3-8), or overall (day 0-8) differentiation periods. Dexamethasone, methyl-isobutylxanthine, and insulin were supplemented to the media only for the early period to induce the differentiation. On day 8 of postconfluence the cells were harvested for Oil Red O staining, analysis of GPDH activity, and determination of the FA Concentration. Cellular LA or CLA was found to accumulate in a dose-response manner, mainly during the intermediate/late period. Treatment with trans10,cis12-CLA lowered (P < 0.05) GPDH activity and the concentration of FA including palmitic acid (16:0) and palmitoleic acid (16:1), especially during the intermediate/late and overall periods, or whenever a high dose of 70 mg/L was applied. This also resulted in a higher (P < 0.05) ratio of saturated FA to monounsaturated FA. Treatment with LA or cis9,trans11-CLA lowered cellular FA only when they applied during the early period at a dose of 70 mg/L. The results demonstrated that the inhibitory effects of CLA on differentiation, GPDH activity, and FA accumulation of 3T3-L1 cells are dependent on the isomer type, treatment period, and dose.

Effects of cis-9, trans-11 and trans-10, cis-12 CLA isomers on liver and adipose tissue fatty acid profile in hamsters

The aim of the present study was to investigate the effect of cis-9,trans-11 and trans-10,cis-12 CLA on FA composition of TAG in epididymal adipose tissue and liver, and of hepatic phospholipids PL. Twenty-four Syrian Golden hamsters were randomly divided into three groups of eight animals each and fed semipurified atherogenic diets supplemented with either 0.5 g/100 g diet of linoleic acid or cis-9,trans-11 or trans-12,cis-9 CLA for 6 wk. Total lipids were extracted, and TAG and PL were separated by TLC. FA profile in lipid species from liver and adipose tissue, as well as in feces, was determined by GC. Trans-10,cis-12 CLA feeding significantly reduced linoleic and linolenic acids in TAG from both tissues, leading to reduced total PUFA content. Moreover, in the epididymal adipose tissue docosenoic and arachidonic acids were significantly increased. In liver PL, although no changes in individual FA were observed, total saturated FA (SFA) were decreased. No changes in TAG and PL FA profiles were induced by the cis-9,trans-11 CLA. TAG and PL incorporated cis-9,trans-11 more readily than trans-10,cis-12 CLA. This difference was not due to differential intestinal absorption, as shown by the analysis of feces. We concluded that only trans-10,cis-12 CLA induces changes in FA composition. Whereas increased PUFA content was observed in either liver or adipose tissue TAG, decreased SFA were found in liver PL. Incorporation of cis-9,trans-11 CLA in TAG is greater than that of trans-10,cis-12 CLA, but this is not due to differences in intestinal absorption.

Upregulation of liver VLDL receptor and FAT/CD36 expression in LDLR-/- apoB100/100 mice fed trans-10,cis-12 conjugated linoleic acid

This study explores the mechanisms responsible for the fatty liver setup in mice fed trans-10,cis-12 conjugated linoleic acid (t10c12 CLA), hypothesizing that an induction of low density lipoprotein receptor (LDLR) expression is associated with lipid accumulation. To this end, the effects of t10c12 CLA treatment on lipid parameters, serum lipoproteins, and expression of liver lipid receptors were measured in LDLR(-/-) apoB(100/100) mice as a model of human familial hypercholesterolemia itself depleted of LDLR. Mice were fed t10c12 CLA over 2 or 4 weeks. We first observed that the treatment induced liver steatosis, even in the absence of LDLR. Mice treated for 2 weeks exhibited hypertriglyceridemia with high levels of VLDL and HDL, whereas a 4 week treatment inversely induced a reduction of serum triglycerides (TGs), essentially through a decrease in VLDL levels. In the absence of LDLR, the mRNA levels of other proteins, such as VLDL receptor, lipoprotein lipase, and fatty acid translocase, usually not expressed in the liver, were upregulated, suggesting their involvement in the steatosis setup and lipoprotein clearance. The data also suggest that the TG-lowering effect induced by t10c12 CLA treatment was attributable to both the reduction of circulating free fatty acids in response to the severe lipoatrophy and the high capacity of liver to clear off plasma lipids.

Fatty acid composition of liver, adipose tissue, spleen, and heart of mice fed diets containing t10, c12-, and c9, t11-conjugated linoleic acid

Conjugated linoleic acid (CLA) isomers have unique effects on tissue lipids. Here we investigated the influence of individual CLA isomers on the lipid weight and fatty acid composition of lipid metabolizing (i.e. liver and retroperitoneal adipose) and lipid sensitive (i.e. spleen and heart) tissues. Female mice (8 week old; n=6/group) were fed either a control or one of the two CLA isomer supplemented (0.5%) diets for 8 weeks. The cis-9, trans-11-CLA diet reduced the 18:1n-9 wt% by 20-50% in liver, adipose tissue, and spleen, reduced the spleen n-3 polyunsaturated fatty acid (PUFA) by 90%, and increased the n-6 PUFA wt% by 20-50% in all tissues except heart. The trans-10, cis-12-CLA reduced both the n-6 and n-3 PUFA wt% in liver (>50%), reduced the heart n-3 PUFA wt% by 25%, and increased the wt% of spleen n-3 PUFA by 700%. The functional consequences of such changes in tissue fatty acid composition need to be investigated.

Detection of conjugated dienoic fatty acids in human vascular smooth muscle cells treated with conjugated linoleic acid

Conjugated linoleic acids (CLA) have attracted scientific interest due to their potential beneficial effects on atherosclerosis. Recent studies demonstrated that conjugated metabolites of CLA are found in tissues of CLA-fed animals and cultured cells treated with CLA. This observation has gained in importance since it has recently been shown that these metabolites of CLA exert specific biological activities. Therefore, the present study aimed to explore the potential formation of metabolites of cis-9, trans-11 CLA, trans-10, cis-12 CLA and trans-9, trans-11 CLA in cells of the vascular wall, which has not yet been shown. Examination of fatty acid composition of total cell lipids using Ag+-HPLC, GC-FID and GC-MS analysis revealed a significant isomer-specific formation of conjugated metabolites of CLA such as CD16:2, CD20:2 and CD22:2 in human coronary artery smooth muscle cells treated with various CLA isomers. Different CD16:2/CLA ratios between various CLA isomers as observed in the present study indicate that fatty acid metabolism is differently affected by the configuration of the double bonds. In conclusion, the observation from the present study suggests that the effects of CLA in vascular cells might not only be mediated by CLA itself but also by its conjugated metabolites. Future studies using highly purified conjugated metabolites of CLA are necessary to study their role in mediating biological effects of CLA in cell culture systems.

In vitro metabolism of rumenic acid in bovine liver slices

Ruminant products are the major source of CLA for humans. However, during periods of fat mobilization, the liver might play an important role in CLA metabolism which would limit the availability of the latter for muscles and milk. In this context, rumenic acid (cis-9, trans-11 CLA) metabolism in the bovine liver (n = 5) was compared to that of oleic acid (n = 3) by using the in vitro liver slice method. Liver slices were incubated for 17 h in a medium containing 0.75 mM of FA mixture and 55 microM of either [1-(14)C] rumenic acid or [1-(14)C] oleic acid at 37 degrees C under an atmosphere of 95% O(2)-5% CO(2). Rumenic acid uptake by liver slices was twice (P = 0.009) that of oleic acid. Hepatic oxidation of both FA (> 50% of incorporated FA) led essentially to the production of acid-soluble products and to a lower extent to CO(2) production. Rumenic acid was partly converted (> 12% of incorporated rumenic acid) into conjugated C18:3. CLA and its conjugated derivatives were mainly esterified into polar lipids (71.7%), whereas oleic acid was preferentially esterified into neutral lipids (59.8%). Rumenic acid secretion as part of VLDL particles was very low and was one-fourth lower than that of oleic acid. In conclusion, rumenic acid was highly metabolized by bovine hepatocytes, especially by the oxidation pathway and by its conversion into conjugated C18:3 for which the biological properties need to be elucidated.

In sacco studies of conjugated linoleic acid production from various oils in the rumen of sheep

In this experiment sunflower oil, soybean oil and fish oil were incubated in rumen-fistulated adult ewes (n = 5) to study conjugated linoleic acid (CLA) production in the rumen. The individual oils were incubated in nylon bags in the rumen on perlite carrier (40% oil, 60% carrier) over a period of 2, 4, 6, 8, 10 and 12 h for all treatments. During the incubation of each oil primarily the formation of the cis-9, trans-11 isomer of CLA could be observed. Both sunflower and soybean oils showed similar changes in the rumen. After the incubation of these two vegetable oils the proportion of linoleic acid decreased significantly as the duration of incubation increased in the rumen. These changes were accompanied by a significant increase in the amount of cis-9, trans-11 CLA. However, in the case of sunflower oil the rate of formation of the cis-9, trans-11 CLA isomer was significantly higher after the different incubation times as compared to soybean oil. Much lower amounts of CLA were formed when fish oil was incubated in the rumen. The level of cis-9, trans-11 isomer produced during these treatments was 10% less than the amount obtained with the other two oils of vegetable origin. Besides the cis-9, trans-11 isomer, trans-10, cis-12 CLA could also be detected during the incubation of the different oils in the rumen. However, the level of this isomer was low and did not show consistent differences among the treatments. The results of this experiment indicate that the fatty acid composition of the oils and the duration of incubation collectively determine the amount of CLA produced in the first compartment of the forestomach of ruminants.