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.     

Differential effects of conjugated linoleic acid isomers on macrophage glycerophospholipid metabolism

Conjugated linoleic acids (CLA) are dietary fatty acids. Whereas cis-9,trans-11-(c9,t11)-CLA can be found in meat and dairy products, trans-9,trans-11-(t9,t11)-CLA is a constituent of vegetable oils. Previous studies showed that these two isomers activate different nuclear receptors and, thus, expression of genes related to lipid metabolism. Here we show that these CLA isomers are differentially elongated and desaturated in primary monocyte-derived macrophages isolated from healthy volunteers by using gas chromatography-mass spectrometry (GC-MS). We further demonstrate that c9,t11-CLA incorporates in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species and activates de novo glycerophospholipid synthesis by quantitative electrospray ionization-tandem mass spectrometry (ESI-MS/MS). c9,t11-CLA leads to strong shifts of the species profiles to PC 18:2/18:2 and PE 18:2/18:2, which are due to de novo synthesis and fatty acid remodeling. In contrast, t9,t11-CLA is preferentially bound to neutral lipids, including triglycerides and cholesterol esters. Taken together our results show that c9,t11-CLA and t9,t11-CLA have differential effects on PC and PE metabolism. Moreover, these data demonstrate that the structure of fatty acids not only determines their incorporation into lipid classes but also modulates the kinetics of lipid metabolism, particularly PC synthesis.     

Gender differences in the cardiac response to dietary conjugated linoleic acid isomers

The present study was undertaken to assess the heart function, by the in vivo catheterization technique, of healthy male and female Sprague-Dawley rats fed different conjugated linoleic acid (CLA) isomers, (cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12)) individually and in combination (50:50 mix as triglyceride or fatty acids) from 4 to 20 weeks of age. Whereas the triglyceride form of the CLA isomer mix lowered the heart rate, the rate of contraction (+dP/dt) and rate of relaxation (-dP/dt), systolic and diastolic pressures, mean arterial pressure, and the left ventricular systolic pressure were higher in male rats as compared with all the other dietary groups. In contrast, there were no significant effects in the cardiac function of the female rats in response to the CLA isomer mix in triglyceride form. Whereas the heart rate, +dP/dt, and left ventricular systolic pressure were lower in male rats fed the t10,c12 CLA isomer alone, the heart rate of the female rats was higher, but the systolic pressure, +dP/dt, and mean arterial pressure were lower compared with the control group. Also, the left ventricular end-diastolic pressure was specifically higher in the female rats in response to free fatty acids-containing CLA mix. Furthermore, an additive effect of the free fatty acids-containing CLA mix was seen in the +dP/dt and -dP/dt of female rats compared with the control group. These results indicate that CLA isomers exert differential effects on heart function and suggest the need for a complete evaluation of the benefits, interactions, and potential side effects of each isomer.     

Purification of conjugated linoleic acid isomers through a process including lipase-catalyzed selective esterification

A mixture of conjugated linoleic acids (CLAs) was prepared by alkali conjugation of high purity linoleic acid. The preparation contained 45.1 wt% cis-9, trans-11 (c9,t11)-CLA, 46.8 wt% trans-10, cis-12 (t10,c12)-CLA, and 5.3 wt% other CLAs. A process comprising Candida rugosa lipase-catalyzed selective esterification with lauryl alcohol, molecular distillation, and urea adduct fractionation under strict conditions in ethanol was very effective for purification of c9,t11- and t10,c12-CLAs. In particular, the urea adduct fractionation efficiently eliminated CLAs except c9,t11- and t10,c12-isomers. Purification of c9,t11- and t10,c12-CLAs from 1.0 kg of the CLA mixture increased the c9,t11-CLA purity to 93.1% with 34% recovery of the initial content, and increased the t10,c12-CLA purity to 95.3% with 31% recovery.     

Combined effects of rosiglitazone and conjugated linoleic acid on adiposity, insulin sensitivity, and hepatic steatosis in high-fat-fed mice

Dysfunctional cross talk between adipose tissue and liver tissue results in metabolic and inflammatory disorders. As an insulin sensitizer, rosiglitazone (Rosi) improves insulin resistance yet causes increased adipose mass and weight gain in mice and humans. Conjugated linoleic acid (CLA) reduces adipose mass and body weight gain but induces hepatic steatosis in mice. We examined the combined effects of Rosi and CLA on adiposity, insulin sensitivity, and hepatic steatosis in high-fat-fed male C57Bl/6 mice. CLA alone suppressed weight gain and adipose mass but caused hepatic steatosis. Addition of Rosi attenuated CLA-induced insulin resistance and dysregulation of adipocytokines. In adipose, CLA significantly suppressed lipoprotein lipase and fatty acid translocase (FAT/CD36) mRNA, suggesting inhibition of fatty acid uptake into adipose; addition of Rosi completely rescued this effect. In addition, CLA alone increased markers of macrophage infiltration, F4/80, and CD68 mRNA levels, without inducing TNF-alpha in epididymal adipose tissue. The ratio of Bax to Bcl2, a marker of apoptosis, was significantly increased in adipose of the CLA-alone group and was partially prevented by treatment of Rosi. Immunohistochemistry of F4/80 demonstrates a proinflammatory response induced by CLA in epididymal adipose. In the liver, CLA alone induced microsteatotic liver but surprisingly increased the rate of very-low-density lipoprotein-triglyceride production without inducing inflammatory mediator-TNF-alpha and markers of macrophage infiltration. These changes were accompanied by significantly increased mRNA levels of stearoyl-CoA desaturase, FAT/CD36, and fatty acid synthase. The combined administration of CLA and Rosi reduced hepatic liver triglyceride content as well as lipogenic gene expression compared with CLA alone. In summary, dietary CLA prevented weight gain in Rosi-treated mice without attenuating the beneficial effects of Rosi on insulin sensitivity. Rosi ameliorated CLA-induced lipodystrophic disorders that occurred in parallel with rescued expression of adipocytokine and adipocytes-abundant genes.     

Effect of conjugated linoleic acid isomers on lipoproteins and atherosclerosis in the Syrian Golden hamster

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of linoleic acid (LA, C18:2 cis-9, cis-12) that are reported to have important biological activities, including protection against atherosclerosis. In this study, the potential role of the individual cis-9, trans-11 and trans-10, cis-12 isomers of CLA in atherogenesis were compared with LA in the Syrian Golden hamster. Supplementation of a high-fat, high-cholesterol diet (HFHC) with 1% (w/w) cis-9, trans-11 CLA or trans-10, cis-12 CLA did not significantly affect plasma cholesterol levels compared to supplementation with 1% (w/w) LA. Very low density lipoprotein cholesterol (VLDL-C) was lower and plasma triglycerides (TG) were higher in diets where C18:2 fatty acid was added to the HFHC diet, but neither the cis-9, trans-11 CLA group nor trans-10, cis-12 CLA group was significantly different from the LA control group. CLA supplementation did not significantly affect low density lipoprotein cholesterol (LDL-C). Trans-10, cis-12 CLA increased high density lipoprotein cholesterol (HDL-C) levels compared to LA or cis-9, trans-11 CLA (P<0.02), and although the ratio of non-HDL-C:HDL-C in the cis-9, trans-11 CLA group (1.11+/-0.54) and the trans-10, cis-12 CLA group (1.11+/-0.21) was lower than the LA group (1.29+/-0.45), the reduction did not reach statistical significance. Atherosclerosis was assessed in the ascending aorta by measuring the number of aortic cross-sections containing Oil Red O-stained intimal lesions. Compared to the LA group (60+/-11%), both the cis-9, trans-11 CLA group (38+/-8%) and the trans-10, cis-12 CLA group (28+/-7%) had fewer sections displaying a fatty streak lesion, although the differences did not reach statistical significance. These results suggest that individual CLA isomers may reduce atherosclerotic lesion development in the hamster, but when compared to LA, the apparent atheroprotective effects do not correlate with beneficial changes in lipoprotein profile.     

Effects of isomers of conjugated linoleic acid on porcine adipocyte growth and differentiation

Conjugated linoleic acids (CLAs) decrease fat deposition in mammals, including pigs. To determine mechanisms for CLA effects on adipocyte growth, porcine stromal-vascular cells (preadipocytes) were isolated and plated in medium containing 10% fetal bovine serum. After 24 h, differentiation factors (insulin + hydrocortisone + transferrin) were added. Oleic acid (200 microM) was added to some plates as a positive control. One of two isomers of CLA (50 microM cis 9, trans 11 or >50 microM trans 10, cis 12), or a mixture of the two isomers (25 microM each) was added to other plates. The cell number increased 7+ times in 7 days after initiation of differentiation, and was not different among treatment groups. By 7 days, Oil Red O-stained material (OROSM), expressed per cell, increased 10+ times in control cells and 64 times in oleic acid-treated cells. Addition of either isomer of CLA or the mixture caused OROSM/cell to increase 10+ times at 2 days, with no further increase at later times. In CLA-treated cells there was no increase in peroxisome proliferator-activated receptor gamma (PPARgamma) or lipoprotein lipase mRNA concentrations. The increased OROSM/cell may represent triacylglycerol synthesis from medium CLA using existing biosynthetic capacity or provision of a limiting ligand for PPARgamma already present. The results are different from those observed with rodent-derived clonal cells (3T3-L1 cells), wherein proliferation and differentiation are inhibited by CLAs, and the active isomer is trans 10, cis 12-CLA. The results suggest distinctions between clonal and primary preadipocytes, or species differences.     

Fatty acid composition and conjugated linoleic acid content of different tissues in rats fed individual conjugated linoleic acid isomers given as triacylglycerols small star,filled

HEAT TREATMENT OF VEGETABLE OILS GAVE RISE TO FOUR MAIN CONJUGATED LINOLEIC ACID (CLA) ISOMERS : the 9c,11t, 9t,11t, 10t,12c and 10t,12t. The diet of male Wistar rats was supplemented with 150 mg/day either 9c,11t-, 9t,11t-, 10t,12c- or 10t,12t CLA isomers for 6 days and their effects on lipid composition were investigated in liver, heart, skeletal muscle Gastrocnemius, kidneys, brain and adipose tissue. The incorporation of all isomers was low (< 1.4%) and the level was as follows : adipose tissue > Gastrocnemius > liver, kidneys > brain. The main changes in the overall lipid composition were observed in skeletal muscle (Gastrocnemius) and in heart and were associated with feeding the 10t,12c and 10t,12t isomers. The diet enriched in 10t,12t CLA decreased the total long chain polyunsaturated fatty acid proportion in Gastrocnemius (from 18.4% to 14.4%) and increased that of 20:4 n-6 in heart (from 16.9 to 19.3%). The diet enriched in 10t,12c CLA decreased the monounsaturated fatty acid proportion in Gastrocnemius (from 32.0 to 26.1%) and produced an effect similar to the 10t,12t in heart. By contrast, the 9c,11t and 9t,11t isomers did not affect fatty acid composition in all tissues and organs. We concluded that ingestion of 10t,12c and 10t,12t CLA present in oils and in CLA mixtures could change muscle lipid composition.     

High dietary levels of a conjugated linoleic acid mixture alter hepatic glycerophospholipid class profile and cholesterol-carrying serum lipoproteins of rats

To investigate the body composition, hepatic lipids, and serum lipoproteins in response to graded levels of a conjugated linoleic acid (CLA) mixture added to a high linoleate diet, adult male Sprague-Dawley rats were randomly assigned into four dietary groups of 10 rats each and fed for 5 weeks controlled amounts of diets containing 0%, 1%, 3%, or 5% of a CLA mixture in exchange for sunflower oil. The various dietary lipid treatments did not significantly influence growth and body partitioning, although there was a trend toward decreased contents of extractable lipids in carcass (whole bled body without liver and gut) with increasing CLA. When carcass lipids of CLA-treated rats were extracted, a distinct accumulation of total CLA was observed. A dietary level of 1% CLA mixture exhibited only weak effects on hepatic glycerophospholipid levels. CLA levels of 3% and 5% caused distinct changes in phospholipid subclass distribution. These changes were reduced levels of lysophosphatidylethanolamine (LPE) and ethanolamine plasmalogen (EPL) and increased levels of phosphatidylcholine (PC). Further, a 5% level of CLA increased the hepatic concentration of phosphatidylserine (PS) compared with the other treatments. The incorporation of total CLA into individual phospholipids followed a dose-responsive manner. The extent of incorporation of CLA was not the same among the glycerophospholipid species analyzed, the order being cardiolipin > phosphatidylethanolamine and PC > LPE/EPL > phosphatidylinositol > PS. Further, CLA increased the proportions of n-3 fatty acids in the individual glycerophospholipids. High CLA diets containing 3% and 5% of a CLA mixture were associated with increased activity of catalase in the peroxisome-enriched cell fraction of liver and exhibited marked reductions of cholesterol in the low and high density lipoproteins relative to rats receiving no CLA.     

Effect of a conjugated linoleic acid and omega-3 fatty acid mixture on body composition and adiponectin

This study aimed to determine the effect of supplementation with conjugated linoleic acids (CLAs) plus n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) on body composition, adiposity, and hormone levels in young and older, lean and obese men. Young (31.4+/-3.9 years) lean (BMI, 23.6+/-1.5 kg/m2; n=13) and obese (BMI, 32.4+/-1.9 kg/m2; n=12) and older (56.5+/-4.6 years) lean (BMI, 23.6+/-1.5 kg/m2; n=20) and obese (BMI, 32.0+/-1.6 kg/m2; n=14) men participated in a double-blind placebo-controlled, randomized crossover study. Subjects received either 6 g/day control fat or 3 g/day CLA (50:50 cis-9, trans-11:trans-10, cis-12) and 3 g/day n-3 LC-PUFA for 12 weeks with a 12-week wash-out period between crossovers. Body composition was assessed by dual-energy X-ray absorptiometry. Fasting adiponectin, leptin, glucose, and insulin concentrations were measured and insulin resistance estimated by homeostasis model assessment for insulin resistance (HOMA-IR). In the younger obese subjects, CLA plus n-3 LC-PUFA supplementation compared with control fat did not result in increased abdominal fat and raised both fat-free mass (2.4%) and adiponectin levels (12%). CLA plus n-3 LC-PUFA showed no significant effects on HOMA-IR in any group but did increase fasting glucose in older obese subjects. In summary, supplementation with CLA plus n-3 LC-PUFA prevents increased abdominal fat mass and raises fat-free mass and adiponectin levels in younger obese individuals without deleteriously affecting insulin sensitivity, whereas these parameters in young and older lean and older obese individuals were unaffected, apart from increased fasting glucose in older obese men.     

Gender differences in the modulation of cardiac gene expression by dietary conjugated linoleic acid isomers

In an earlier study, we showed that dietary conjugated linoleic acid (CLA) isomers can exert differential effects on heart function in male and female rats, but the underlying mechanisms for these actions are not known. Cardiomyocyte Ca2+ cycling is a key event in normal cardiac contractile function and defects in Ca2+ cycling are associated with cardiac dysfunction and heart disease. We therefore hypothesized that abnormalities in the sarcolemmal (SL) and sarcoplasmic reticulum (SR)-mediated regulation of intracellular Ca2+ contribute to altered cardiac contractile function of male and female rats owing to dietary CLA isomers. Healthy male and female Sprague-Dawley rats were fed different CLA isomers, (cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12)) individually and in combination (50:50 mix as triglyceride or fatty acids) from 4 to 20 weeks of age. We determined the mRNA levels of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) 2a, ryanodine receptor, phospholamban, calsequestrin, Na+-Ca2+-exchanger (NCX), and L-type Ca2+ channel in the left ventricle (LV) by RT-PCR. The SR function was assessed by measurement of Ca2+-uptake and -release. Significant gender differences were seen in the LV NCX, L-type Ca2+ channel, and ryanodine receptor mRNA expression levels in control male and female rats. Dietary CLA isomers in the various forms induced changes in the mRNA levels of SERCA 2a, NCX, and L-type Ca2+ channel in the LV of both male and female hearts. Whereas protein contents of the Ca2+ cycling proteins were altered, changes in SR Ca2+-uptake and -release were also detected in both male and female rats in response to dietary CLA. The results of this study demonstrate that long-term dietary supplementation can modulate cardiac gene expression and SR function in a gender-related manner and may, in part, contribute to altered cardiac contractility.     

Effect of dietary conjugated linoleic acid isomers on water and glycerol permeability of kidney membranes

Conjugated linoleic acid (CLA) refers to a group of positional and geometrical isomers of linoleic acid in which the double bonds are conjugated. Dietary CLA has been associated with various health benefits although details of its molecular mode of action remain elusive. The effect of CLA supplemented to palm oil-based diets in Wistar rats, as a mixture of both or isolated c9,t11 and t10,c12 isomers, was examined on water and glycerol membrane permeability of kidney proximal tubule. Although water permeability was unaltered, an increase in glycerol permeability was obtained for the group supplemented with CLA mixture, even though the activation energy for glycerol permeation remained high. This effect was correlated with an increased CLA isomeric membrane incorporation for the same dietary group. These results suggest that diet supplementation with CLA mixture, in contrast to its individual isomers, may enhance membrane fluidity subsequently raising kidney glycerol reabsorption.     

Effects of conjugated linoleic acid isomers on monocyte, macrophage and foam cell phenotype in atherosclerosis

Conjugated linoleic acid (CLA) is a generic term denoting a group of naturally occurring isomers of linoleic acid (18:2, n6) that differ in the position or geometry (i.e. cis or trans) of their double bonds. The predominant isomers in ruminant fats are cis-9,trans-11 CLA (c9,t11-CLA), and trans-10,cis-12 CLA (t10,c12-CLA). The biological activities of CLA have received considerable attention because of its protective effects in cancer, immune function, obesity and atherosclerosis. Importantly, dietary administration of a blend of the two most abundant isomers of CLA, has been shown to inhibit the progression and induce the regression of pre-established atherosclerosis in the ApoE?/? murine model. Studies investigating the mechanisms involved in CLA induced protective effects are continually emerging with results from both in vitro and in vivo models yielding confounding and often inconsistent results depending on both the isomer of CLA and the species under investigation. The purpose of this review is to comprehensively discuss the effects of CLA on monocyte/macrophage function in atherosclerosis. This review also discusses the possible mechanisms through which CLA mediates its atheroprotective effects with a particular emphasis on the migratory capacity of the monocyte and the inflammatory and cholesterol homeostasis of the macrophage.     

Influence of conjugated linoleic acid isomers on the metastasis of colon cancer cells in vitro and in vivo

This study investigated the isomer-specific effects of cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12) conjugated linoleic acid (CLA) on the metastasis of colon cancer cells in vitro and in vivo. Cell migration was examined by a Boyden chamber assay in SW480 cells. MMP-9 activity was monitored by gelatin zymography, and MMP-9 protein and mRNA levels were determined by Western blot and RT-PCR analysis, respectively, in SW480 cells. For the experimental metastasis, BALB/c mice were injected intravenously with CT-26 cells in the tail vein. Mice were fed a diet containing either no CLA or 0.1% c9,t11 or t10,c12 CLA for 4 weeks. In experimental metastasis, the numbers of pulmonary nodules were significantly lower in mice fed CLA isomers than in mice fed a control diet (P<.05). Results from the Boyden chamber assay revealed that c9,t11 CLA significantly inhibited cell migration (P<.05), whereas t10,c12 CLA had no effect on cell migration. The activity of MMP-9 was significantly inhibited by c9,t11 CLA (P<.05) but not by t10,c12 CLA. However, neither MMP-9 protein nor mRNA levels were altered by either of these CLA isomers. We have demonstrated that diets containing 0.1% c9,t11 and t10,c12 CLA were equally effective in inhibiting colon cancer cell metastasis in vivo. However, in vitro, only c9,t11 but not t10,c12 inhibited colon cancer cell migration and MMP-9 activity.     

Evaluation of the influence of diet supplementation with conjugated linoleic acid isomers on elemental composition in the cardio-oncological nutritional programming rat’ model

BackgroundThe ‘developmental origin of health and disease’ (DOHaD) hypothesis assumes that due to the action of some stimuli during fetal life the long-term physiological changes occurs and may affects the risk of various diseases. The main aim of this study was to assess impact of supplementation of maternal’ and early postnatal diet with conjugated linoleic acids (CLA) isomers on selected elements content in hearts of their female offspring with chemically induced breast cancer.MethodsElemental composition was determined by quadrupole mass spectrometer with inductively coupled plasma ionization (ICP-MS).ResultsThe effect of maternal’ diet on the elements content was more pronounced than the progeny diet modifications. Significant correlations among determined elements, especially macroelements, and lipidomic parameters, in the experimental factors dependent manner were observed. It can be concluded that supplementation of maternal and progeny diets with CLA isomers may significantly influence the contents of both macro- and microelements in cardiac tissue of newborns.ConclusionOur results also indicate, that dynamic and intricate balance among various elements in body may be affected by the lipid dietary supplements also in the pathological state. Utility of cardio-oncological approach in developmental programming study was confirmed.     

Effect of conjugated linoleic acid mixture supplemented daily after carcinogen application on linoleic and arachidonic acid metabolites in rat serum and induced tumours

Conjugated linoleic acid (CLA) is thought to exert anticarcinogenic, antiatherogenic, anti-inflammatory and weight loss effects. The impact on eicosanoid biosynthesis may be one of the mechanisms of its action. The aim of this study was to establish whether CLA mixture supplemented daily after administration of carcinogen (7, 12-dimethylbenz[a]anthracene, DMBA) influenced the concentration of linoleic and arachidonic acid metabolites: 13- or 9-hydroxyoctadecadienoic acids (13-, 9-HODE) and 15-, 12- or 5-hydroxyeicosatetraenoic acids (15-, 12- or 5-HETE) and prostaglandin E₂ (PGE₂) in rat serum and DMBA-induced tumours. The correlations between polyunsaturated fatty acids (PUFA) and HETE and HODE contents in serum were also investigated.Female Sprague–Dawley rats divided into three groups according to the diet (1% Bio-C.L.A., 2% Bio-C.L.A. and plant oil in the control group) were used in the study. On the 50th day of life some of the animals in every dietary group were administered DMBA to induce tumours. Since that day, the rats were fed one of the above-mentioned diets. After 15 weeks the animals were sacrificed and blood and tumours were collected. HETE and HODE were extracted using a solid-phase extraction (SPE) method on C18 columns and analysed with LC-MS/MS.The results of our study showed that CLA daily supplementation after carcinogen administration influence LA and AA metabolite levels in serum and tumours. However, the ratios of eicosanoids having opposite effects (e.g. 12-HETE/15-HETE), not concentrations of particular compounds, appear to be better indicators of pathological processes.     

Incorporation profiles of conjugated linoleic acid isomers in cell membranes and their positional distribution in phospholipids

Although the conjugated linoleic acids (CLA) have several isomer-specific biological effects including anti-carcinogenic and anti-adipogenic effects, their mechanisms of action remain unclear. To determine their potential effects on membrane structure and function, we studied the incorporation profiles 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)) in CHO and HepG2 cells. All four isomers were incorporated into cellular lipids as efficiently as linoleic acid (LA), with the majority of the incorporated CLA present in membrane rafts. Of the four isomers, only CLA-A increased the cholesterol content of the raft fraction. Over 50% of the incorporated CLAs were recovered in phosphatidylcholine of CHO cells, but in HepG2 the neutral lipids contained the majority of CLA. The desaturation index (18:1/18:0 and 16:1/16:0) was reduced by CLA-A, but increased by CLA-B, the effects being apparent mostly in raft lipids. The Δ? desaturase activity was inhibited by CLAs A and C. Unlike LA, which was mostly found in the sn-2 position of phospholipids, most CLAs were also incorporated significantly into the sn-1 position in both cell types. These studies show that the incorporation profiles of CLA isomers differ significantly from that of LA, and this could lead to alterations in membrane function, especially in the raft-associated proteins.