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

Conjugated linoleic acid supplementation in humans: effects on circulating leptin concentrations and appetite

Conjugated linoleic acid (CLA) has been demonstrated to reduce body fat in animals. However, the mechanism by which this reduction occurs is unknown. Leptin may mediate the effect of CLA to decrease body fat. We assessed the effects of 64 d of CLA supplementation (3 g/d) on circulating leptin, insulin, glucose, and lactate concentrations in healthy women. Appetite was assessed as a physiological correlate of changes in circulating leptin levels. Analysis of plasma leptin concentrations adjusted for adiposity by using fat mass as a covariate showed that CLA supplementation significantly decreased circulating leptin concentrations in the absence of any changes of fat mass. Mean leptin levels decreased over the first 7 wk and then returned to baseline levels over the last 2 wk of the study in the CLA-treated group. Appetite parameters measured at around the time when the greatest decreases in leptin levels were observed showed no significant differences between supplementation and baseline determinations in the CLA-supplemented group or between the CLA and placebo-supplemented groups. There was a nonsignificant trend for mean insulin levels to increase toward the end of the supplementation period in CLA-treated subjects. CLA did not affect plasma glucose and lactate over the treatment period. Thus, 64 d of CLA supplementation in women produced a transient decrease in leptin levels but did not alter appetite. CLA did not affect these parameters in a manner that promoted decreases of adiposity.

Conjugated linoleic acids exhibit a strong fat-to-lean partitioning effect, reduce serum VLDL lipids and redistribute tissue lipids in food-restricted rats

Effects of conjugated linoleic acids (CLA) on a series of metabolic events are expected to depend on the feeding regimen and levels of energy ingested. This study was the first examining the mode of action of CLA on body composition, tissue lipids, lipoproteins and hepatic enzymes in situations of enhanced fat store mobilization. Two groups of male growing Sprague-Dawley rats were fed for 3 wk a diet containing 0 (control group) or 3 g/100 g of a CLA mixture at the expense of sunflower oil, and were then subjected to a weight-loss feeding regimen for another 18 d. Rats fed the CLA-fortified diet gained 11% less weight than the control rats (P<0.05). Rats fed the high CLA diet had less body fat (1.47+/-0.16 vs. 1.07+/-0.09 g/100g, P<0.05) and a higher lean deposition (25.6+/-0.2 vs. 28.4+/-0.3 g/100 g, P<0.05) than control rats. CLA-fed rats had a 41% lower cholesterol concentration in liver than the control rats (P<0.05). Some differences in glycerophospholipid subclass profile of liver and erythrocyte membrane were observed; the hepatic concentrations of phosphatidylethanolamine (4.76+/-0.46 vs. 6.86+/-0.99 micromol/g, P = 0.07) and phosphatidylcholine (12.9+/-0.5 vs. 15.3+/-1.2 micromol/g, P = 0.09) tended to be greater and the level of phosphatidylcholine in erythrocyte membranes was significantly greater (1.40+/-0.12 vs. 1.83 +/-0.16 micromol/g, P<0.05) in the CLA-treated group than in the control group. The activities of catalase and ornithine decarboxylase in liver did not differ between the groups. Further, CLA-treated rats had significantly lower serum concentrations of VLDL lipids than control rats, whereas concentrations of LDL and HDL lipids were unaffected. The results indicate that a high dose of a CLA mixture is a strong repartitioning agent and a modulator of lipid metabolism under conditions of enhanced fat store mobilization in rats.

Do conjugated eicosapentaenoic acid and conjugated docosahexaenoic acid induce apoptosis via lipid peroxidation in cultured human tumor cells?

Conjugated eicosapentaenoic acid (CEPA) and conjugated docosahexaenoic acid (CDHA) with triene structure, isomerized by alkaline treatment, showed intensive cytotoxicity with LD(50) at 12 and 16 microM, respectively, in DLD-1 cells (colorectal adenocarcinoma), while they had no effect on normal human fibroblast cell lines such as MRC-5, TIG-103, and KMS-6 cells. Cytotoxic action of CEPA and CDHA was also demonstrated in other tumor cell lines including HepG2, A549, MCF-7, and MKN-7 cells. alpha-Tocopherol suppressed cytotoxicity of CEPA and CDHA in tumor cells, and the cytotoxicity involved membrane phospholipid peroxidation. CEPA and CDHA induced DNA condensation and fragmentation in DLD-1 cells, indicating the involvement of apoptosis in this cytotoxic mechanism. Furthermore, previous reports have shown that lipid peroxidation product induces cell death, including apoptotic cell death in different cell lines. CEPA and CDHA have been demonstrated in cultured cells to cause cell death via lipid peroxidation and apoptosis in the absence of alpha-tocopherol.

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.

Reduction of murine mammary tumor metastasis by conjugated linoleic acid

Recent studies have shown that conjugated linoleic acid (CLA) can inhibit the initiation and thus, incidence of mammary tumors in rodents. The concentration of CLA required for these effects was as low as 0.1% of the diet, with no increased effects above 1%. To date, there is little evidence that CLA has any effect on growth or metastasis of mammary tumors. In this report, we demonstrate that CLA, at the concentrations used in previous studies, had a significant effect on the latency, metastasis, and pulmonary tumor burden of transplantable murine mammary tumors grown in mice fed 20% fat diets. The latency of tumors from mice fed CLA was significantly increased when compared with the 0% CLA control diet. The volume of pulmonary tumor burden, as a result of spontaneous metastasis, decreased proportionately with increasing concentrations of dietary CLA. With 0.5 and 1% CLA, pulmonary tumor burden was significantly decreased compared to mice treated with the eicosanoid inhibitor, indomethacin and fed diets containing no CLA. Tumors of mice fed as little as 0.1% CLA and as much as 1% had significantly decreased numbers of pulmonary nodules when compared with diets containing no CLA. The decrease in the number of pulmonary nodules by CLA was nearly as effective as indomethacin, a known suppressor of tumor growth and metastasis in this malignant model. These data suggest that effects of CLA on mammary tumorigenesis may go beyond the reported alterations in tumor incidence and effect later stages, especially metastasis.

Trans-vaccenic acid is desaturated to conjugated linoleic acid in mice

Mice were fed pure trans11 octadecenoic acid (trans-vaccenic acid; TVA) to determine whether it is desaturated to cis9, trans11 octadecadienoic acid, a predominant isomer of conjugated linoleic acid (CLA). In a preliminary trial, 12% of the TVA consumed during a 2-wk feeding period was recovered in the carcass as CLA. As a proportion of TVA in the tissues available for bioconversion, 48.8% was desaturated. We tested whether desaturation could be modified by supplementing no modifier, 0.5% clofibric acid to stimulate desaturation, or increasing the polyunsaturated fatty acids (PUFA) (10% corn oil vs. 4% corn oil) to inhibit desaturation in diets with or without 1% TVA. These diets were fed to six groups of mice in a 3x2 factorial arrangement of treatments. Feeding 1% TVA with 10% corn oil decreased feed intake (2.70 vs. 3.73 g/d, SEM 0.23; P<0.05). Bioconversion of dietary TVA was 12.0, 7.5 and 5.1% for mice fed no modifier of desaturation, clofibrate and increased PUFA, respectively. Conversion based on TVA available for desaturation was 52.6, 55.5 and 37.0%, respectively. Thus, clofibrate did not increase bioconversion, but increasing PUFA decreased conversion by 30%. To test whether TVA decreases food intake directly or after conversion to CLA, four groups of mice were fed diets containing 1% stearic, TVA, elaidic or conjugated linoleic acid. Dietary CLA decreased food intake and body fat, but did not change body protein. CLA was found in the carcass only when TVA or CLA was fed. CLA was found in both triacylglycerol and phospholipids when CLA was fed, but only in triacylglycerol when TVA was fed, suggesting that bioconversion occurred in the adipose tissue. In three trials, conversion of dietary TVA to CLA was 11.4+/-1.25%; conversion of stored TVA was 50.8+/-1.91%. Similar bioconversion of TVA in humans would increase current estimates of CLA available for the general population by 6- to 10-fold.

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

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

Mechanisms of action of conjugated linoleic acid: evidence and speculation

Conjugated linoleic acid (CLA) has been shown to inhibit carcinogenesis and atherosclerosis, enhance immunologic function while protecting against the catabolic effects of immune stimulation, affect body composition change (reducing body fat gain while enhancing lean body mass gain), and stimulate the growth of young rats. We discuss possible biochemical mechanisms that underlie these physiological effects. We emphasize the importance of considering the effects, both individually and combined, of the two CLA isomers (cis-9, trans-11 CLA and trans-10, cis-12 CLA) that have been shown to exhibit biological activity and which appear to exert their effects via different biochemical mechanisms.

An isomeric mixture of conjugated linoleic acids but not pure cis-9, trans-11-octadecadienoic acid affects body weight gain and plasma lipids in hamsters

We report the effect of an atherogenic diet supplemented with cis-9, trans-11-octadecadienoic acid (c9t11), linoleic acid (LA) or an isomeric mixture of conjugated linoleic acids (CLA) on plasma lipids, weight gain and food intake of male Golden Syrian hamsters. Animals were assigned to three diet groups (n = 10), and fed nonpurified diet, supplemented with 10% hydrogenated coconut oil and 0.05% cholesterol for 6 wk. The first diet group was further supplemented with 1% CLA (CLA group), the second diet group with 0.2% c9t11 (c9t11 group) and the third group with 0.2% LA (LA group). The diets were designed to have equivalent levels of c9t11 in the CLA and c9t11 groups. At 2 and 6 wk of feeding, the CLA group had significantly lower plasma triglyceride and total cholesterol concentrations than either the c9t11 or the LA groups. HDL-cholesterol did not differ among diet groups. The CLA group had significantly lower weight gain but greater food intake than either the c9t11 or the LA groups. There were no significant differences between the c9t11 and the LA groups in any of the variables measured. We conclude that under our experimental conditions of short-term feeding, c9t11, thought to be the active compound in CLA, does not produce the same effect as the isomer mixture.

Species differences in the metabolism and regulation of gene expression by conjugated linoleic acid

Conjugated linoleic acid (CLA) inhibits carcinogenesis and atherosclerotic plaque formation and delays the onset of diabetes in experimental animals. Whereas a plethora of data has demonstrated beneficial effects in rodent models, little work has been done to determine the role of dietary CLA in human health. The ability of CLA to modulate lipid metabolism appears to be a pivotal mechanism of CLA's beneficial effects in mice and rats. In particular, dietary CLA induces the expression of genes dependent in part on the transcription factor, peroxisome proliferator-activated receptor (PPAR). Furthermore, several CLA isomers are high-affinity ligands and activators for PPAR alpha. Within various rodent species and strains, dietary CLA exerts varying potencies; therefore, the differences in species' sensitivities are of great importance when trying to extrapolate the rodent data to be relevant in humans. This review presents the latest findings of the ability of CLA to alter lipid metabolism and gene expression in several different strains of mice and rats and speculates on the implications of these findings for human health.

Effect of dietary conjugated linoleic acid on the composition of egg yolk lipids

Forty-eight 27-wk-old White Leghorn hens were assigned randomly to four diets containing 0, 1.25, 2.5, or 5.0% conjugated linoleic acid (CLA). Hens were fed the CLA diets for 2 wk before eggs were collected for the study. Classes of egg yolk lipids were separated, and fatty acid concentrations in total lipid, triglyceride (TG), phosphatidylethanolamine (PE), and phosphatidylcholine (PC) were analyzed to determine the incorporation of dietary CLA isomers into different classes of egg yolk lipids. The amounts of CLA incorporated into lipid, PC, PE, and TG of egg yolk were proportional to the levels of CLA in the diet. However, more CLA was incorporated in TG than in PC and PE. The incorporation rates of different CLA isomers into different classes of lipids also were significantly different: cis-9, trans-11 and cis-10, trans-12 CLA were deposited more in TG, but cis-11, trans-13 CLA deposition in TG was significantly less. There were large differences in the concentrations of cis-8, trans-10 CLA in PC and PE. The inclusion of CLA into the diet influenced the metabolism of polyunsaturated fatty acids. The contents of 5,8,11,14-eicosatetraenoic, 9,12-octadecadienoic, and 9,12,15-octadecatrienoic acids were decreased as dietary CLA increased. Three isomers of hexadecadienoic acid were found in egg yolk lipids from hens fed 5% dietary CLA. The detection of hexadecadienoic acid isomers in lipid indicates that the utilization of CLA as an energy source after the first round of beta-oxidation may be less favorable than that of 9,12-octadecadienoic acid.

Dietary conjugated linoleic acids increase lean tissue and decrease fat deposition in growing pigs

Conjugated linoleic acids (CLA) decrease the body fat content of rodents; the aim of this study was to determine whether dietary CLA altered carcass composition of pigs. Female Large White x Landrace pigs (n = 66) were used in this study. To obtain initial body composition, six pigs were slaughtered at 57 kg live weight, whereas the remaining pigs were allocated to one of six dietary treatments (0, 1.25, 2.5, 5.0, 7.5 and 10.0 g/kg CLA, containing 55% of CLA isomers). The diets, containing 14.3 MJ digestible energy (DE) and 9. 3 g available lysine per kg, were fed ad libitum for 8 wk. Dietary CLA had no significant effect on average daily gain (861 vs. 911 g/d for pigs fed diets with and without CLA, P = 0.15) or feed intake (2. 83 vs. 2.80 kg/d, P = 0.74). The gain to feed ratio was increased by dietary CLA by 6.3% (0.328 vs. 0.348, P = 0.009). Fat deposition decreased linearly (-8.2 +/- 2.09 g/d for each gram per kilogram increase in CLA concentration; P < 0.001) with increasing inclusion of CLA. At the highest level of CLA inclusion, fat deposition was decreased by 88 g/d (-31%). Similarly, the ratio of fat to lean tissue deposition decreased linearly (-0.093 +/- 0.0216 for each gram per kilogram increase in CLA concentration; P < 0.001) with increasing dietary CLA. The carcass lean tissue deposition response to dietary CLA was quadratic in nature and was maximized (+25%) at 5. 0 g/kg dietary CLA. Overall, dietary CLA increased the gain to feed ratio and lean tissue deposition and decreased fat deposition in finisher pigs.

Recent advances in conjugated linoleic acid research

New results on the physiological properties of conjugated linoleic acid have been published by several working groups, especially showing the effects of single conjugated linoleic acid isomers on carcinogenesis and body composition. Recently, other studies have shown that conjugated linoleic acid has an influence on diabetes mellitus, platelet aggregation and the immune system. Conjugated linoleic acid was found to modify prostaglandin metabolism and delta9-desaturase activity and influence apoptosis. Furthermore, improved analytical methods using 13C nuclear magnetic resonance and silver ion high performance liquid chromatography are available to investigate the composition of conjugated linoleic acid mixtures and the exact structure of separated isomers. Also, the synthesis of isolated isomers is described, as published by different authors, in order to determine further the effects of each single conjugated linoleic acid isomer. In addition, new data on the contents of conjugated linoleic acid in foods, human adipose tissue and fluids are given in this review. More data need to be obtained using isolated isomers, with particular emphasis on studies in humans.