Oxidation rate of conjugated linoleic acid and conjugated linolenic acid is slowed by triacylglycerol esterification and α-tocopherol

We have recently shown that α-eleostearic acid (α-ESA), a conjugated linolenic acid, has a stronger antitumor effect than conjugated linoleic acid (CLA), both in vitro and in vivo. In this study, the oxidative stability of α-ESA was examined compared with linoleic acid (LA), α-linolenic acid (LnA), and CLA. Thin layers of the FA (LA, 9Z, 11E-CLA, 10E,12Z-CLA, LnA, and α-ESA) were auto-oxidized at 37°C, and the FA remaining, the absorbed oxygen volume, the lipid hydroperoxide content, and the TBARS content were determined. The oxidation rate of α-ESA was faster than that of the unconjugated FA and CLA (9Z,11E-CLA and 10E,12Z-CLA). However, the lipid hydroperoxide and TBARS contents following α-ESA oxidation were low, suggesting production of only small amounts of rapid-reacting secondary oxidation products. Furthermore, the oxidative stability of conjugated FA (CLA and CLnA) in which the carboxylic acid group was esterified with triacylglycerol was greater than that of the FFA. Addition of an antioxidant (α-tocopherol) also increased the stability of the conjugated FA to a level similar to that of the unconjugated FA.     

Effects of margarine and butter consumption on distribution of trans-18∶1 fatty acid isomers and conjugated linoleic acid in major serum lipid classes in lactating women

Trans FA (TFA) have at least one trans double bond and comprise several isomers and types, including many of the CLA (e.g., c9, t11–18∶2 CLA). Some TFA may have adverse effects (e.g., cardiovascular disease), whereas some are though to have beneficial effects (e.g., anticarcinogenicity). The presence of TFA in human tissues and fluids is related to dietary intake, although this relationship is not completely understood—especially in regard to serum lipid fractions. This study was conducted as part of an investigation designed to test the influence of butter (B), “low TFA” margarine (LT), and regular margarine (RM) on milk fat content. Here we tested the secondary hypothesis that consumption of B, LT, and RM by lactating women would result in differential distribution of TFA and CLA in major serum lipid classes. Breastfeeding women (n=11) participated in this randomized Latinsquare study consisting of five periods: intervention I (5 d), washout I (7 d), intervention II (5 d), washout II (7 d), and intervention III (5 d). Extracted serum lipid was separated into cholesterol ester (CE), TAG, and phospholipid (PL) fractions and analyzed for total and isomeric TFA and CLA concentrations. Data indicate that TAG consistently contained the highest concentration of total t-18∶1. No interaction between treatment and fraction was found for any of the t-18∶1 isomers identified. Absolute concentration of each t-18∶1 isomer was greatest during the RM period, regardless of fraction. On a relative basis, concentrations of t10–18∶1 and t12–18∶1 were most responsive to treatment in the CE fraction. The concentration of c9, t11–18∶2 CLA was highest in the TAG fraction and lowest in the PL fraction, regardless of treatment. In summary, these results indicate (i) that there is a differential distribution of some isomeric TFA and CLA among human serum lipid fractions and (ii) that dietary TFA intake influences absolute and relative concentrations of some of the isomers in selected fractions.     

Inhibitory effect of linoleic acid on chain elongation and desaturation of 18∶2 c,t isomers in lactating and neonatal rats

The previous studies showed that dietary 18∶2 c,t isomers could be chain-elongated and desaturated to produce unusual 20∶4 isomers. The present study was undertaken to determine the minimal amount of 18∶2n−6 required to suppress the chain elongation and desaturation of 18∶2 c,t isomers in the lactating and neonatal rats when animals were fed 15% partially hydrogenated canola oil diet containing 1.72% energy as 18∶2 c,t isomers and varying amounts of free 18∶2n−6. These diets induced marginal essential fatty acid (EFA) deficiency states (0.56% energy 18∶2n−6) to EFA adequacy (2.56% energy 18∶2n−6). After feeding for 50 d, the female animals were mated with males by overnight pairing. After conception, the lactating rats were killed, together with one pup from each dam, at term and day 26 of lactation. Two unusual 20∶4 isomers in both maternal and neonatal liver phospholipids were identified as 20∶4Δ5c,8c,11c,14t and 20∶4Δ5c,8c,11c,15t, which were derived from 18∶2Δ9c,12t, and 18∶2Δ9c,13t, respectively. The results showed that 18∶2n−6 at about 2.0% of total energy in maternal diet was required to block the production of 20∶4Δ5c,8c,11c,14t and 20∶4Δ5c,8c,11c,15t in the maternal liver, whereas 18∶2n−6 at about 2.5% of total energy in maternal diet was required to suppress production of these unusual 20∶4 isomers in the neonatal liver.     

Retraction: Are conjugated linoleic acid (CLA) isomers good or bad trans fats?

Even though trans fatty acids (TFAs) are present in natural sources such as foods from ruminant origins, the development of partially hydrogenated vegetable oil contributed to a significant increase in total TFAs consumption in humans. Currently, TFA consumption is considered to be a risk factor for coronary heart diseases. Researchers are now starting to discover that not all TFAs behave in a similar manner, that is, isomer specificity may be found. Among non‐conjugated TFAs, plant originated TFAs (mainly elaidic and linolelaidic acids) are particularly linked to increased risk for coronary heart diseases, while animal originated TFAs (mainly vaccenic acid) are not. Among conjugated TFAs, two major isomers of conjugated linoleic acid (CLA), cis‐9, trans‐11 and trans‐10, cis‐12, show distinctive biological activities. A number of clinical trials of CLA with effects on body composition have been reported, but effects on coronary heart disease risk factors have been inconsistent. Meanwhile, safety concerns regarding CLA, in particular isomer specificity, have also been raised. Thus, it is critical to identify isomer specific effects of TFAs on particular risk factors, to determine their health impact.     

Preparation, separation, and confirmation of the eight geometrical cis/trans conjugated linoleic acid isomers 8,10-through 11,13–18∶2

Conjugated linoleic acid (CLA) mixtures were isomerized with p-toluenesulfinic acid or I₂ catalyst. The resultant mixtures of the eight cis/trans geometric isomers of 8,10-, 9,11-, 10,12-, and 11,13-octadecadienoic (18∶2) acid methyl esters were separated by silver ion-high-performance liquid chromatography (Ag⁺-HPLC) and gas chromatography (GC). Ag⁺-HPLC allowed the separation of all positional CLA isomers and geometric cis/trans CLA isomers except 10,12–18∶2. However, one of the 8,10 isomers (8cis, 10trans-18∶2) coeluted with the 9trans,11cis18∶2 isomer. There were differences in the elution order of the pairs of geometric CLA isomers resolved by Ag⁺-HPLC. For the 8,10 and 9,11 CLA isomers, cis,trans eluted before trans,cis, whereas the opposite elution pattern was observed for the 11,13–18∶2 geometric isomers (trans,cis before cis,trans). All eight cis/trans CLA isomers were separated by GC on long polar capillary columns only when their relative concentrations were about equal. Large differences in the relative concentration of the CLA isomers found in natural products obscured the resolution and identification of a number of minor CLA isomers. In such cases, GC-mass spectrometry of the dimethyloxazoline derivatives was used to identify and confirm coeluting CLA isomers. For the same positional isomer, the cis,trans consistently eluted before the trans,cis CLA isomers by GC. High resolution mass spectrometry (MS) selected ion recording (SIR) of the molecular ions of the 18∶1 18∶2, and 18∶3 fatty acid methyl esters served as an independent and highly sensitive method to confirm CLA methyl ester peak assignments in GC chromatograms obtained from food samples by flame-ionization detection. The high-resolution MS data were used to correct for the nonselectivity of the flame-ionization detector.     

Gas chromatography—High resolution selected-ion mass spectrometric identification of trace 21∶0 and 20∶2 fatty acids eluting with conjugated linoleic acid isomers

High-resolution selected-ion recording (SIR) of the exact molecular ion mass was used to confirm unambiguously the presence of conjugated linoleic acid (CLA) derivatives in biological matrices and standard mixtures and to differentiate non-CLA derivatives from CLA derivatives in the CLA region of the gas chromatogram. The success of this method was based on the selectivity of the SIR technique and its sensitivity, which was comparable to that of flame-ionization detection. A minor fatty acid methyl ester (FAME) was identified as methyl heneicosanoate (21∶0), and six isomers of 20∶2 FAME were found to elute in the CLA region. Isomerization of a standard CLA mixture resulted in a non-CLA flame-ionization response eluting in the CLA region of the gas chromatogram. It is therefore recommended that the identification of minor CLA isomers in natural products of biological matrices should include their direct confirmation by mass spectrometry     

Geometry of conjugated double bonds of CLA isomers in a commercial mixture and in their hepatic 20∶4 metabolites

Rats were fed a fat-free diet for 2 wk. After this period, while maintaining the animals on the same diet, the rats were given intragastrically 180 mg per day of a mixture of conjugated linoleic acids (CLA) as triacylglycerols. Gas chromatography-mass spectrometry (GC-MS) analyses of this mixture, as well as hydrazine reduction and GC-MS and GC-Fourier transform infrared analyses of the resulting monoenes, revealed the presence of two major isomers, the 9c, 11t-and the 10t, 12c-18∶2 accompanied by smaller amounts of the 8t, 10c and the 11c,13t−18∶2 isomers. Minor quantities of cis,cis and trans,trans conjugated isomers also were detected. The total fatty acid methyl esters from the liver lipids were fractionated by reversed-phase high-performance liquid chromatography, and the fraction containing the 20∶4 isomers was further fractionated by silver nitrate thin-layer chromatography. A band containing two 20∶4 conjugated isomers was submitted to hydrazine reduction and the resulting monoenes analyzed by GC-MS as dimethyl-oxazoline derivatives. The two conjugated isomers were tentatively identified as 5c,8c,11c,13t–20∶4 and 5c,8c,12t,14c−20∶4. These could be formed by desaturation and elongation of the 9c,11t-and 10t,12c−18∶2 present in the commerical CLA mixture.     

Effects of ψ-linolenic acid and docosahexaenoic acid in formulae on brain fatty acid composition in artificially reared rats

This study evaluated the effects of dietary supple-mentation with ψ-linolenic acid (GLA, 18∶3n−6) and docosahexaenoic acid (DHA, 22∶6n−3) on the fatty acid composition of the neonatal brain in gastrostomized rat pups reared artificially from days 5–18. These pups were fed rat milk substitutes containing fats that provided 10% linoleic acid and 1% α-linolenic acid (% fatty acids) and, using a 2×3 factorial design, one of two levels of DHA (0.5 and 2.5%), and one of three levels of GLA (0.5, 1.0, and 3.0%). A seventh artificially reared groups served as a reference group and was fed 0.5% DHA and 0.5% arachidonic acid (AA, 20∶4n−6); these levels are within the range of those found in rat milk. The eighth group, the suckled control group, was reared by nursing dams fed a standard American Institute of Nutrition 93M chow. The fatty acid composition of the phosphatidylethanolamine, phosphatidyl-choline, and phosphatidylserine/phosphatidylinositol membrane fractions of the forebrain on day 18 reflected the dietary composition in that high levels of dietary DHA resulted in increases in DHA but decreases in 22∶4n−6 and 22∶5n−6 in brain. High levels of GLA increased 22∶4n−6 but, in contrast to previous findings with high levels of AA, did not decrease levels of DHA. These results suggest that dietary GLA, during development, differs from high dietary levels of AA in that it does not lead to reductions in brain DHA.     

Effects of conjugated linoleic acid, fish oil and soybean oil on PPARs (α & γ) mRNA expression in broiler chickens and their relation to body fat deposits

An experiment was conducted on broiler chickens to study the effects of different dietary fats (Conjugated linoleic acid (CLA), fish oil, soybean oil, or their mixtures, as well as palm oil, as a more saturated fat), with a as fed dose of 7% for single fat and 3.5 + 3.5% for the mixtures, on Peroxisome Proliferator-Activated Receptors (PPARs) gene expression and its relation with body fat deposits. The CLA used in this experiment was CLA LUTA60 which contained 60% CLA, so 7% and 3.5% dietary inclusions of CLA LUTA60 were equal to 4.2% and 2.1% CLA, respectively. Higher abdominal fat pad was found in broiler chickens fed with a diet containing palm oil compared to chickens in the other experimental groups (P ≤ 0.05). The diets containing CLA resulted in an increased fat deposition in the liver of broiler chickens (P ≤ 0.05). The only exception was related to the birds fed with diets containing palm oil or fish oil + soybean oil, where contents of liver fat were compared to the CLA + fish oil treatment. PPARγ gene in adipose tissue of chickens fed with palm oil diet was up-regulated compared to other treatments (P ≤ 0.001), whereas no significant differences were found in adipose PPARγ gene expression between chickens fed with diets containing CLA, fish oil, soybean oil or the mixture of these fats. On the other hand, the PPARα gene expression in liver tissue was up-regulated in response to the dietary fish oil inclusion and the differences were also significant for both fish oil and CLA + fish oil diets compared to the diets with palm oil, soybean oil or CLA as the only oil source (P ≤ 0.001). In conclusion, the results of present study showed that there was a relationship between the adipose PPARγ gene up-regulation and abdominal fat pad deposition for birds fed with palm oil diet, while no deference was detected in n-3 and n-6 fatty acids, as well as CLA on PPARγ down regulation in comparison to a more saturated fat. When used on its own, fish oil was found to be a more effective fat in up-regulating hepatic PPARα gene expression and this effect was related to a less fat deposition in liver tissue. A negative correlation coefficient (-0.3) between PPARα relative gene expression and liver tissue fat content confirm the anti-lipogenic effect of PPARα, however, the change in these parameters was not completely parallel.     

The metabolism and distribution of docosapentaenoic acid (n−6) in rats and rat hepatocytes

In this study, a new marine oil that contains 45% docosahexaenoic acid (DHA, 22∶6n−3) and 13% docosapentaenoic acid (DPA, 22∶5n−6) was administered to rats. The metabolism and distribution of DPA in rats was investigated. In experiment 1, the effects of DHA and n−6 fatty acids (linoleic acid, I A; arachidonic acid, AA; and DPA) on AA contents were investigated in vivo. LA group: LA 25%, DHA 30%; LA-DPA group: LA 15%, DPA 10%, DHA 35%; LA-AA-DPA group: LA 10%, AA 5%, DPA 10%, DHA 35% were administered to rats for 4 wk. In the liver, the AA content in the LA-DPA and LA-AA-DPA groups was significantly higher than in the LA group. The decreased AA contents in the LA group might be caused by DHA administration. Although DHA also was administered in the LA-DPA and LA-AA-DPA groups, the AA contents in these two groups did not decrease. These results suggested that DPA retroconverted to AA, blunting the decrease in AA content caused by DHA administration. To conduct a detailed investigation on DPA metabolism and its relation with AA and DHA, rat hepatocytes were cultured with pruified DPA and DHA for 24 h. We discovered the retroconversion of DPA to AA occurred only when AA content was decreased by a high DHA administration; it did not occur when AA content was maintained at a normal level.     

Dietary comparison of conjugated linolenic acid (9 cis, 11 trans, 13 trans) and α-tocopherol effects on blood lipids and lipid peroxidation in alloxan-induced diabetes mellitus in rats

The present study investigated the dietary effect of conjugated linolenic acid (CLnA) on lipid profiles and lipid peroxidations in alloxan-induced diabetes mellitus in rats. Diabetic rats were fed with 20% sunflower oil (diabetic control), sunflower oil supplemented with 0.5% CLnA, sunflower oil supplemented with 0.15% α-tocopherol, and sunflower oil containing 0.25% CLnA+0.15% α-tocopherol. The results demonstrated that 0.5% CLnA, 0.15% α-tocopherol, and 0.25% CLnA+0.15% α-tocopherol each on supplementation significantly lowered total cholesterol and non-HDL-cholesterol in comparison with the diabetic control group. The TAG level was significantly lowered in both the 0.15% α-tocopherol and 0.25% CLnA+0.15% α-tocopherol groups. LDL lipid peroxidation and erythrocyte membrane lipid peroxidation were reduced significantly in each of the experimental groups vs. the control group. The CLnA+α-tocopherol diet induced a greater reduction in membrane lipid and liver lipid peroxidation than the α-tocopherol diet alone. In conclusion, dietary CLnA exerts antioxidant activity as evidenced by reduced lipid peroxidation in chemically induced diabetes mellitus.     

The effect of α-linolenic acid and linoleic acid on the growth and development of formula-fed infants: A systematic review and meta-analysis of randomized controlled trials

This systematic review and meta-analysis aimed to evaluate the effect of modifying 18-carbon PUFA [18-C PUFA: α-linolenic acid (ALA, 18∶3n−3) and linoleic acid (LA, 18∶2n−6)] in the diets of term and preterm infants on DHA (22∶6n−3) status, growth, and developmental outcomes. Only randomized controlled trials (RCT) involving formula-fed term and preterm infants, in which the 18-C PUFA composition of the formula was changed and growth or developmental outcomes were measured, were included. Differences were presented as control (standard formula) and treatment (18-C PUFA-supplemented formula). Primary analyses for term infants were 4 and 12 mon and for preterm infants 37–42 and 57 wk postmenstrual age. Five RCT involving term infants and three RCT involving preterm infants were included in the systematic review. Infants fed ALA-supplemented formula had significantly higher plasma and erythrocyte phospholipid DHA levels than control infants. There was no effect of ALA supplementation on the growth of preterm infants. In term infants, ALA supplementation was associated with increased weight and length at 12 mon, which was at least 4 mon after the end of dietary intervention. Developmental indices of term infants did not differ between groups. There was a transient improvement in the retinal function of preterm infants fed ALA-supplemented diets compared with controls. The findings suggest that ALA-supplemented diets improve the DHA status of infants. Further studies are needed to provide convincing evidence regarding the effects of ALA supplementation of formula on infant growth and development.     

Comparison of growth and fatty acid metabolism in rats fed diets containing equal levels of γ-linolenic acid from high γ-linolenic acid canola oil or borage oil

We have utilized transgenic technology to develop a new source of γ-linolenic acid (GLA) using the canola plant as a host. The aim of the present study was to compare the growth and fatty acid metabolism in rats fed equal amounts of GLA obtained from the transgenic canola plant relative to GLA from the borage plant. Young male Sprague-Dawley rats (n=10/group) were randomized and fed a purified AIN93G diet (10% lipid by weight) containing either a mixture of high GLA canola oil (HGCO) and corn oil or a control diet containing borage oil (BO) for 6 wk. GLA accounted for 23% of the triglyceride fatty acids in both diets. Growth and diet consumption were monitored every 2–3 d throughout the study. At study termination, the fatty acid composition of the liver and plasma phospholipids was analyzed by gas chromatography. The growth and diet consumption of the HGCO group were similar to the BO group. There were no adverse effects of either diet on the general health or appearance of the rats, or on the morphology of the major organs. There was no significant difference between the diet groups for total percentage of n−6 polyunsaturated fatty acids present in either the total or individual phospholipid fractions of liver or plasma. The relative percentage of GLA and its main metabolite, arachidonic acid, in each phospholipid fraction of liver or plasma were also similar between groups. The percentage of 18∶2n−6 in liver phosphatidylethanolamine and phosphatidylinositol/serine was higher (P<0.05) and 22∶5n−6 was lower in the HGCO group than the BO group. This finding could be attributed to the higher 18∶3n−3 content in the HGCO diet than the BO diet. Results from this long-term feeding study of rats show for the first time that a diet containing transgenically modified canola oil was well-tolerated, and had similar biological effects, i.e., growth characteristics and hepatic metabolism of n−6 fatty acids, as a diet containing borage oil.     

Formation of 8-oxo-2′-deoxyguanosine in the DNA of human diploid fibroblasts by treatment with linoleic acid hydroperoxide and ferric ion

Lipid peroxides are suggested to be related to the occurrence of a variety of diseases including cancer and atherosclerosis. We examined whether lipid peroxides cause oxidative damage to DNA in intact cells. Linoleic acid hydroperoxide (LOOH) and ferric chloride were used at concentrations at which separate treatment had no effect on the formation of 8-oxo-2′-deoxyguanosine (8-oxodG) in DNA or the survival rate of cultured human diploid fibroblasts, TIG-7. The amount of 8-oxodG in the cellular DNA increased significantly when TIG-7 cells were treated concurrently with LOOH and ferric chloride. In a LOOH concentration-dependent manner 8-oxodG was formed. However, no significant induction of the activities of superoxide dismutases, catalase, or glutathione peroxidase was observed under these conditions. The formation of 8-oxodG by lipid hydroperoxides seems to be due to the generation of reactive species other than superoxide radicals and hydrogen peroxide. These results indicate that some species formed during the reaction of lipid hydroperoxides with ferric ion can cause oxidative damage to DNA.     

Effects of Cα -Oxidation in the Fungal Metabolism of Lignin

C_α-Oxidation (benzyl alcohol oxidation) is a prominent reaction in the degradation of lignin by white-rot fungi. This study showed that such oxidation markedly retards metabolism of a nonphenolic β-O-4 model compound, 1-(3-methoxy-4-ethoxyphenyl)-2-(o-methoxyphenoxy)propane-1,3-diol, by cultures of Phanerochaete chrysosporium Burds. Surprisingly, however, selective chemical C_α -oxidation of spruce lignins enhanced their depolymerization by the cultures. Thus the decrease in intrinsic degradability of substructures is more than compensated by another effect of C_α-oxidation in lignin. One possibility is that the oxidation increases the accessibility of the lignin to enzymes by decreasing its steric complexity. This study also revealed that the β-O-4 model, like lignin in wood, is degraded in part via C_α-oxidation by P. chrysosporium. Reduction of the α-carbonyl groups thus formed does not occur. Addition of L-glutamate to ligninolytic cultures completely suppresses their competence to degrade the model compound, as it does their ability to oxidize lignin to CO₂. This result strengthens past evidence indicating that substructure models are metabolized by the same enzyme system as lignin.     

Preparation and fractionation of conjugated trienes from α-linolenic acid and their growth-inhibitory effects on human tumor cells and fibroblasts

Conjugated α-linolenic acid (ClnA) was prepared from α-linolenic acid (9,12,15–18∶3n−3, LnA) by alkaline treatment; we fractionated CLnA into three peaks by reversed-phase column-HPLC as evidenced by monitoring absorbance at 205, 235, and 268 nm. Peak I was a conjugated dienoic FA derived from LnA, whereas Peaks II and III were conjugated trienoic LnA. Proton NMR analysis showed that Peak III consisted of the all-trans isomer. The methylated Peak III was further divided into five peaks (Peaks IV–VIII) by silver ion column-HPLC. Peak V, a major constituent in the Peak III fraction, was identified as conjugated 10t,12t,14t-LnA by GC-EIMS and ¹H NMR analysis. Peaks III and V, which consisted of conjugated all-trans trienoic LnA, had stronger growth-inhibitory effects on human tumor cell lines than the other collected peaks and strongly induced lipid peroxidation as compared with Peaks I, II, and LnA. We propose that conjugated all-trans trienoic FA have the strongest growth-inhibitory effect among the conjugated trienoic acids and conjugated dienoic acids produced by alkaline treatment of α-LnA, and that this effect is mediated by lipid peroxidation.     

Trans-10,Cis-12 conjugated linoleic acid reduces triglyceride content while differentially affecting peroxisome proliferator activated receptor γ2 and aP2 expression in 3T3-L1 preadipocytes

A series of experiments was conducted using 3T3-L1 preadipocytes as the cell model to determine: (i) whether the triglyceride (TG)-lowering effects of a crude mixture of conjugated linoleic acid (CLA) isomers were due to a specific isomer of CLA and the timing of treatment, (ii) if CLA reduced TG content by inhibiting a key regulator of adipogenesis, (iii) if CLA incorporated into either neutral lipid or phospholipid cell fractions, and (iv) whether the effects of CLA treatment were reversible. Trans-10,cis-12 CLA reduced TG content, whereas the cis-9,trans-11 isomer increased TG content compared to vehicle [bovine serum albumin (BSA)] controls. Treatment with 50 μM trans-10,cis-12 CLA during the entire 6 d of differentiation reduced TG content to a greater extent than treatment during either the first 3 d or last 3 d of differentiation. Trans-10,cis-12 CLA treatment of preadipocyte cultures for 48 h increased peroxisome proliferator activated receptor γ2 (PPARγ2) protein expression compared to cultures treated with linoleic acid (LA) or the BSA controls. CLA had no effect on adipose P2 (aP2), a fatty acid-binding protein regulated by PPARγ2. Both the cis-9,trans-11 and the trans-10,cis-12 isomers of CLA were incorporated into neutral lipids and phospholipids. However, cis-9,trans-11 CLA levels were one- to twofold higher than trans-10,cis-12 CLA levels. Moreover, trans-10,cis-12 CLA treatment reduced cis-11 18∶1 concentrations in both neutral lipids and phospholipids while increasing cis-9 18∶1 and 18∶2 concentrations. Palmitoleic acid (16∶1) levels were also lower in the neutral lipid fraction of cultures treated with trans-10,cis-12 CLA. Supplementing trans-10,cis-12 CLA-treated cultures (50 μM) with increasing levels of LA resulted in a dose-dependent increase in TG content compared to cultures treated with 50 μM CLA alone. LA supplementation also prevented some of the morphological changes associated with trans-10,cis-12 CLA treatment as seen with scanning electron microscopy. Treatment with 50μM trans-10,cis-12 CLA for 6 d decreased PPARγ2 levels, and supplementation of CLA-treated cultures with LA increased PPARγ2 levels compared with cultures treated with CLA alone. Taken together, these data indicate that in cultures of 3T3-L1 preadipocytes: (i) trans-10,cis-12 CLA is the TG-lowering isomer of CLA, and its effects are dependent on dose, duration of treatment, and the amount of LA in the cultures; (ii) trans-10,cis-12 CLA treatment alters the monounsaturated fatty acid profile of neutral- and phospholipids of the cultures; and (iii) although acute (2−d) trans-10,cis-12 CLA treatment increased PPARγ2 protein levels, chronic (6−d) treatment decreased PPARγ2 levels.