Evidence that the trans-10,cis-12 isomer of conjugated linoleic acid induces body composition changes in mice

Dietary effect of pomegranate seed oil rich in 9cis, 11trans, 13cis conjugated linolenic acid on lipid metabolism in obese, hyperlipidemic OLETF rats

Conjugated fatty acid, the general term of positional and geometric isomers of polyunsaturated fatty acids with conjugated double bonds, has attracted considerable attention because of its potentially beneficial biological effects. In the present study, dietary effect of pomegranate seed oil rich in punicic acid (9cis, 11trans, 13cis-conjugated linolenic acid; 9c, 11t, 13c-CLNA) on lipid metabolism was investigated in obese, hyperlipidemic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. After 2 weeks feeding period, OLETF rats revealed obesity and hyperlipidemia compared with their progenitor LETO rats. Feeding of the diet supplemented with 9% safflower oil and 1% pomegranate seed oil (9c, 11t, 13c-CLNA diet) did not affect abdominal white adipose tissue weights and serum lipid levels compared with the diet supplemented with 10% safflower oil (control diet) in OLETF rats. However, the accumulated hepatic triacylglycerol was markedly decreased by 9c, 11t, 13c-CLNA diet in OLETF rats. Activities of hepatic enzymes related to fatty acid synthesis and fatty acid beta-oxidation were not altered by 9c, 11t, 13c-CLNA diet. Levels of monounsaturated fatty acid (MUFA), major storage form of fatty acid, in serum triacylglycerol were markedly higher in obese, hyperlipidemic OLETF rats than in lean LETO rats. In addition, 9c, 11t, 13c-CLNA diet significantly decreased MUFA levels in OLETF rats. This is the first study showing that 9c, 11t, 13c-CLNA suppresses delta-9 desaturation in vivo, and we suggest that the alleviation of hepatic triacylglycerol accumulation by 9c, 11t, 13c-CLNA diet was, at least in part, attributable to the suppression of delta-9 desaturation in OLETF rats.

Cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid isomers do not modify body composition in adult sedentary or exercised rats

Dietary CLA isomers were shown to reduce adipose tissues in growing animals, mainly in mice, but their effects in adult animals remain unclear. This study was conducted to determine whether these effects depend on the isomer fed, on physical activity, or on the initial level of body fat. Male Wistar rats (4 mo old) were fed for 6 wk diets containing either no CLA, the cis-9, trans-11 CLA isomer (10 g/kg), the trans-10, cis-12 CLA isomer (10 g/kg), or both isomers (10 g/kg each). Half of the rats were assigned to exercise by treadmill running (1 h/d, 22 m/min). The initial body fat level was normal (12.7%) in a first trial, and high (18.9%) in a second trial. Chemical and anatomical body compositions were determined by chemical analysis and organ dissection. In both trials, the CLA diets, whatever the isomer, had no effect on food intake and body weight changes, on body chemical composition (fat, protein and water contents or gains), or on the body anatomical composition (weights or gains in epididymal and perirenal adipose tissues, in liver and in 4 muscles). There was no interaction between CLA treatment and physical activity. In conclusion, adult male rats do not appear to be responsive to the fat-to-lean partitioning effect of CLA described in growing rats. This was not affected by exercise or initial body fat level.

Structure–activity relationship of conjugated linoleic acid and its cognates in inhibiting heparin-releasable lipoprotein lipase and glycerol release from fully differentiated 3T3-L1 adipocytes

Conjugated linoleic acid (CLA) reduces body fat in part by inhibiting the activity of heparin-releasable lipoprotein lipase (HR-LPL) activity in adipocytes, an effect that is induced by the trans-10,cis-12 CLA isomer. In this study we used a series of compounds that are structurally related to CLA (i.e., CLA cognates) to investigate the structural basis for this phenomenon. None of the 18:1 CLA cognates that were tested, nor trans-9,cis-12 18:2, cis-12-octadecen-10-ynoic acid (10y,cis-12) or 11-(2'-(n-pentyl)phenyl)-10-undecylenic acid (designated P-t10), exhibited any significant effect on HR-LPL activity. Among the CLA derivatives (alcohol, amide, and chloride) that were tested, only the alcohol form inhibited HR-LPL activity, although to a lesser extent than CLA itself. In addition, intracellular TG was reduced only by trans-10,cis-12 CLA and the alcohol form of CLA. Hence it appears that the trans-10,cis-12 conjugated double bond in conjunction with a carboxyl group at C-1 is required for inhibition of HR-LPL activity, and that an alcohol group can partially substitute for the carboxyl group. We also studied glycerol release from the cells, observing that this was enhanced by trans-10 18:1, trans-13 18:1, cis-12 18:1, cis-13 18:1, P-t10 but was reduced by cis-9 18:1, the alcohol and amide forms of CLA or 10y,cis-12. Accordingly the structural feature or features involved in regulating lipolysis appear to be more complex. Despite enhancing lipolysis in cultured 3T3-L1 adipocytes, trans-10 18:1 did not reduce body fat gain when fed to mice.

Opposing effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on blood lipids in healthy humans

BACKGROUND

Conjugated linoleic acid (CLA) is reported to have weight-reducing and antiatherogenic properties when fed to laboratory animals. However, the effects of CLA on human health and, in particular, the effects of individual CLA isomers are unclear.

OBJECTIVE

This study investigated the effects of 3 doses of highly enriched cis-9,trans-11 (0.59, 1.19, and 2.38 g/d) or trans-10,cis-12 (0.63, 1.26, and 2.52 g/d) CLA preparations on body composition, blood lipid profile, and markers of insulin resistance in healthy men.

DESIGN

Healthy men consumed 1, 2, and 4 capsules sequentially, containing either 80% cis-9,trans-11 CLA or 80% trans-10,cis-12 CLA for consecutive 8-wk periods. This phase was followed by a 6-wk washout and a crossover to the other isomer.

RESULTS

Body composition was not significantly affected by either isomer of CLA. Mean plasma triacylglycerol concentration was higher during supplementation with trans-10,cis-12 CLA than during that with cis-9,trans-11 CLA, although there was no influence of dose. There were significant effects of both isomer and dose on plasma total cholesterol and LDL-cholesterol concentrations but not on HDL-cholesterol concentration. The ratios of LDL to HDL cholesterol and of total to HDL cholesterol were higher during supplementation with trans-10,cis-12 CLA than during that with cis-9,trans-11 CLA. CLA supplementation had no significant effect on plasma insulin concentration, homeostasis model for insulin resistance, or revised quantitative insulin sensitivity check index.

CONCLUSION

Divergent effects of cis-9,trans-11 CLA and trans-10,cis-12 CLA appear on the blood lipid profile in healthy humans: trans-10,cis-12 CLA increases LDL:HDL cholesterol and total:HDL cholesterol, whereas cis-9,trans-11 CLA decreases them.

Effects of cis-9,trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men

BACKGROUND

We recently showed that trans-10,cis-12 (t10,c12) conjugated linoleic acid (CLA) causes insulin resistance in obese men. However, metabolic effects of the c9,t11 CLA isomer are still unknown in obese men. Because c9,t11 CLA is the predominant CLA isomer in foods and is included in dietary weight-loss products, it is important to conduct randomized controlled studies that use c9,t11 CLA preparations.

OBJECTIVE

We investigated the effects of c9,t11 CLA supplementation on insulin sensitivity, body composition, and lipid peroxidation in a group at high risk for cardiovascular disease.

DESIGN

In a randomized, double-blind, placebo-controlled study, 25 abdominally obese men received 3 g c9,t11 CLA/d or placebo (olive oil). Before and after 3 mo of supplementation, we assessed insulin sensitivity (hyperinsulinemic euglycemic clamp), lipid metabolism, body composition, and urinary 8-iso-prostaglandin F(2alpha) (a major F(2)-isoprostane) and 15-keto-dihydro-prostaglandin F(2alpha), markers of in vivo oxidative stress and inflammation, respectively.

RESULTS

All subjects completed the study. Compared with placebo, c9,t11 CLA decreased insulin sensitivity by 15% (P < 0.05) and increased 8-iso-prostaglandin F(2alpha) and 15-keto-dihydro-prostaglandin F(2alpha) excretion by 50% (P < 0.01) and 15% (P < 0.05), respectively. The decreased insulin sensitivity was independent of changes in serum lipids, glycemia, body mass index, and body fat but was abolished after adjustment for changes in 8-iso-prostaglandin F(2alpha) concentrations. There were no differences between groups in body composition.

CONCLUSIONS

A CLA preparation containing the purified c9,t11 CLA isomer increased insulin resistance and lipid peroxidation compared with placebo in obese men. Because c9,t11 CLA occurs in commercial supplements as well as in the diet, the present results should be confirmed in larger studies that also include women.

Differential inhibition of fatty acid transport in tissue-isolated steroid receptor negative human breast cancer xenografts perfused in situ with isomers of conjugated linoleic acid

In established rodent tumors and human cancer cell lines, conjugated dienoic isomers of linoleic acid (CLA) suppress the growth-stimulating effects of linoleic acid (LA) and its metabolism to the mitogenic agent, 13-hydroxyoctadecadienoic acid (13-HODE). Here, we compared the effects of three CLA isomers on LA uptake and metabolism, and growth in human breast xenografts perfused in situ in female nude rats. The results demonstrated that two CLA isomers [10t, 12c-CLA>9t, 11t-CLA] caused a dose-dependent inhibition of LA uptake, cAMP content, 13-HODE formation, Erk 1/2 activity, and [(3)H]thymidine incorporation into tumor DNA; 9c, 11t-CLA showed no effect. The inhibitory effect is reversible with either pertussis toxin (PTX) or 8-Br-cAMP suggesting that CLA isomers differentially inhibit LA uptake and metabolism and cell proliferation in human breast cancer in vivo via a receptor-mediated, PTX-sensitive pathway.

Conjugated linoleic acid and obesity control: efficacy and mechanisms

Obesity is associated with high blood cholesterol and high risk for developing diabetes and cardiovascular disease. Therefore, management of body weight and obesity are increasingly considered as an important approach to maintaining healthy cholesterol profiles and reducing cardiovascular risk. The present review addresses the effects of conjugated linoleic acid (CLA) on fat deposition, body weight and composition, safety, as well as mechanisms involved in animals and humans. Animal studies have shown promising effects of CLA on body weight and fat deposition. The majority of the animal studies have been conducted using CLA mixtures that contained approximately equal amounts of trans-10, cis-12 (t10c12) and cis-9, trans-11 (c9t11) isomers. Results of a few studies in mice fed CLA mixtures with different ratios of c9t11 and t10c12 isomers have indicated that the t10c12 isomer CLA may be the active form of CLA affecting weight gain and fat deposition. Inductions of leptin reduction and insulin resistance are the adverse effects of CLA observed in only mice. In pigs, the effects of CLA on weight gain and fat deposition are inconsistent, and no adverse effects of CLA have been reported. A number of human studies suggest that CLA supplementation has no effect on body weight and insulin sensitivity. Although it is suggested that the t10c12 CLA is the antiadipogenic isomer of CLA in humans, the effects of CLA on fat deposition are marginal and more equivocal as compared to results observed in animal studies. Mechanisms through which CLA reduces body weight and fat deposition remain to be fully understood. Proposed antiobesity mechanisms of CLA include decreased energy/food intake and increased energy expenditure, decreased preadipocyte differentiation and proliferation, decreased lipogenesis, and increased lipolysis and fat oxidation. In summary, CLA reduces weight gain and fat deposition in rodents, while produces less significant and inconsistent effects on body weight and composition in pigs and humans. New studies are required to examine isomer-specific effects and mechanisms of CLA in animals and humans using purified individual CLA isomers.

Conjugated linoleic acid isomer effects in atherosclerosis: Growth and regression of lesions

Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of octadecadienoic acid, has been shown to inhibit experimentally induced atherosclerosis in rabbits and also to cause significant regression of pre-established atheromatous lesions in rabbits. The two major CLA isomers (cis9,trans11 and trans10,cis12), now available at 90% purity, have been tested individually for their anti-atherogenic or lesion regression potency. The two major isomers and the mixture were fed for 90 d to rabbits fed 0.2% cholesterol. Atherosclerosis was inhibited significantly by all three preparations. The two CLA isomers and the isomer mix were also fed (1.0%) as part of a cholesterol-free diet for 90 d to rabbits bearing atheromatous lesions produced by feeding an atherogenic diet. A fourth group was maintained on a cholesterol-free diet. On the CLA-free diet atherosclerosis was exacerbated by 35%. Reduction of severity of atheromatous lesions was observed to the same extent in all three CLA-fed groups. The average reduction of severity in the three CLA-fed groups was 26 +/- 2% compared with the first control (atherogenic diet) and 46 +/- 1% compared with the regression diet. Insofar as individual effects on atherosclerosis were concerned, there was no difference between the CLA mix and the cis9,trans11 and trans10,cis12 isomers. They inhibit atherogenesis by 50% when fed as a component of a semipurified diet containing 0.2% cholesterol; and when fed as part of a cholesterol-free diet, they reduce established lesions by 26%. Reduction of atheromata to the observed extent by dietary means alone is noteworthy.

Selectively hydrogenated soybean oil with conjugated linoleic acid modifies body composition and plasma lipids in rats

The present study examined effects of a selectively hydrogenated soybean oil (SHSO) containing about 21% CLA on body composition, adipose depots and organ weights, and plasma lipid profiles in rats. Male Sprague Dawley rats were fed for 6 weeks a purified diet containing 0%, 1%, 3%, and 5% of SHSO. Different levels of SHSO supplementation did not significantly affect growth performance, although there was a trend toward decreased body weight gain with increasing dietary SHSO levels. The weights of inguinal, epididymal, and retroperitoneal adipose depot, but not mesenteric, were significantly influenced by dietary SHSO supplementation (P < 0.05, P < 0.01 and P < 0.001, respectively). Although the absolute weight of body protein in the control rats was higher in SHSO-fed rats, the effect on absolute weight of body protein is diluted and eliminated when the data are adjusted for eviscerated carcass weight as a percentage base. Therefore, as dietary SHSO level increased, body protein as a percentage of carcass weight increased (P < 0.05), although as dietary SHSO level increased, body fat proportion in carcass decreased (P < 0.01). Plasma triglycerides (TG) and total cholesterol (TC) concentrations were beneficially decreased, and HDL-cholesterol (HDL-C) to TC ratio was also beneficially increased by SHSO supplementation (P < 0.05, P < 0.001, and P < 0.01, respectively). However, plasma HDL-C concentration undesirably decreased with dietary SHSO supplementation (P < 0.05). The present study observed that body composition and plasma lipids were beneficially modulated by SHSO supplementation at least 3% levels (0.6% of CLA), and suggested that SHSO is a useful fat source because of the high level of CLA.

Role of nuclear receptors in the regulation of gene expression by dietary fatty acids (review)

Long chain fatty acids, derived either from endogenous metabolism or by nutritional sources play significant roles in important biological processes of membrane structure, production of biologically active compounds, and participation in cellular signaling processes. Recently, the structure of dietary fatty acids has become an important issue in human health because ingestion of saturated fats (containing triglycerides composed of saturated fatty acids) is considered harmful, while unsaturated fats are viewed as beneficial. It is important to note that the molecular reason for this dichotomy still remains elusive. Since fatty acids are important players in development of pathology of cardiovascular and endocrine system, understanding the key molecular targets of fatty acids, in particular those that discriminate between saturated and unsaturated fats, is much needed. Recently, insights have been gained on several fatty acid-activated nuclear receptors involved in gene expression. In other words, we can now envision long chain fatty acids as regulators of signal transduction processes and gene regulation, which in turn will dictate their roles in health and disease. In this review, we will discuss fatty acid-mediated regulation of nuclear receptors. We will focus on peroxisome proliferators-activated receptors (PPARs), liver X receptors (LXR), retinoid X receptors (RXRs), and Hepatocyte Nuclear Factor alpha (HNF-4alpha), all of which play pivotal roles in dietary fatty acid-mediated effects. Also, the regulation of gene expression by Conjugated Linoleic Acids (CLA), a family of dienoic fatty acids with a variety of beneficial effects, will be discussed.

Effects of specific conjugated linoleic acid isomers on growth characteristics in obese Zucker rats

Growing female obese Zucker (fa/fa) rats were treated (via intragastric gavage) for 21 d with either a (i) vehicle [corn oil; 0.9 g/kg body weight (BW)], (ii) CLA mixture [50:50; trans-10, cis-12 and cis-9, trans-11 CLA], (iii) cis-9,trans-11 CLA, or (iv) trans- 10, cis-12 CLA (CLA treatments at 1.5 g CLA/kg BW). Compared with controls, average daily gain (g/d) was reduced 24 and 44% by the CLA mixture and trans-10, cis-12 CLA, respectively. There was no treatment effect on average whole-body (minus heart and liver) composition (dry matter basis): fat (70.2%), protein (21.0%), and ash (4.3%). Compared with animals treated with cis-9,trans-11 CLA, obese Zucker rats treated with trans-10, cis-12 and the CLA mixture had 7.8% more carcass water. Treatment had no effect on heart or liver weights or on heart or liver weights as a percentage of body weight, but compared with the other treatments trans-10, cis-12 CLA increased liver lipid content by 33%. Hepatic lipid ratios of 16:1/16:0 and 18:1/18:0 (a proxy for delta9-desaturase capability) were not affected by treatment (0.1 and 0.6, respectively). Similar to previous reports, CLA increased hepatic lipid content and altered both liver and carcass FA composition (i.e., reduced arachidonic acid content), but the ability of CLA to manipulate body composition in obese Zucker rats remains questionable.

Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans

BACKGROUND

Short-term trials showed that conjugated linoleic acid (CLA) may reduce body fat mass (BFM) and increase lean body mass (LBM), but the long-term effect of CLA was not examined.

OBJECTIVE

The objective of the study was to ascertain the 1-y effect of CLA on body composition and safety in healthy overweight adults consuming an ad libitum diet.

DESIGN

Male and female volunteers (n = 180) with body mass indexes (in kg/m(2)) of 25-30 were included in a double-blind, placebo-controlled study. Subjects were randomly assigned to 3 groups: CLA-free fatty acid (FFA), CLA-triacylglycerol, or placebo (olive oil). Change in BFM, as measured by dual-energy X-ray absorptiometry, was the primary outcome. Secondary outcomes included the effects of CLA on LBM, adverse events, and safety variables.

RESULTS

Mean (+/- SD) BFM in the CLA-triacylglycerol and CLA-FFA groups was 8.7 +/- 9.1% and 6.9 +/- 9.1%, respectively, lower than that in the placebo group (P < 0.001). Subjects receiving CLA-FFA had 1.8 +/- 4.3% greater LBM than did subjects receiving placebo (P = 0.002). These changes were not associated with diet or exercise. LDL increased in the CLA-FFA group (P = 0.008), HDL decreased in the CLA-triacylglycerol group (P = 0.003), and lipoprotein(a) increased in both CLA groups (P < 0.001) compared with month 0. Fasting blood glucose concentrations remained unchanged in all 3 groups. Glycated hemoglobin rose in all groups from month 0 concentrations, but there was no significant difference between groups. Adverse events did not differ significantly between groups.

CONCLUSION

Long-term supplementation with CLA-FFA or CLA-triacylglycerol reduces BFM in healthy overweight adults.

Perspective on the safety and effectiveness of conjugated linoleic acid

The amount of scientific literature on conjugated linoleic acid (CLA) is growing at a phenomenal rate. Animal studies and clinical trials indicate the possibility that CLA could be useful in improving human health in a number of areas, eg, controlling body fat gain and enhancing immunity while also reducing inflammation and other adverse effects typically associated with immune enhancement. The background of this growing research field and mechanistic insights from animal and cell culture experiments are briefly reviewed. Experimental and clinical data relating to the safety and effectiveness of CLA in humans are presented and discussed.

Trans10,cis12-18:2 is a more potent inhibitor of de novo fatty acid synthesis and desaturation than cis9,trans11-18:2 in the mammary gland of lactating mice

To investigate the effects of 2 conjugated linoleic acid (CLA) isomers and trans11-18:1 (TVA) on de novo lipogenesis and desaturation in liver and mammary gland, lactating mice were fed diets containing 3% canola oil (control) or 2% canola oil plus 1% stearic acid (SA), TVA, cis9,trans11 CLA (c9t11), or trans10,cis12 CLA (t10c12). In mammary tissue, TVA and CLA isomers reduced mRNA for acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) compared with control, but only c9t11 and t10c12 reduced mammary ACC activity. Of the 2 CLA isomers, t10c12 caused a greater reduction in mammary ACC activity. Hepatic ACC or FAS activity and mRNA abundance were not affected by dietary treatments. Feeding TVA, c9t11, or t10c12 reduced mammary stearoyl-CoA desaturase 1 (SCD) mRNA and activity. Reduction was greater due to feeding t10c12 compared with c9t11. Hepatic SCD mRNA was not affected by dietary treatments, but both CLA isomers depressed hepatic SCD activity. Results indicated that t10c12 is a more potent inhibitor of mammary lipogenesis and desaturation than is c9t11. A net gain of 77 and 1690 micro g of c9t11 in liver and mammary tissue, respectively, was found in the TVA-fed group over the control and SA-fed group. However, reduced mammary SCD mRNA or activity due to feeding TVA may indicate a limited capacity for desaturation of dietary TVA to c9t11 in vivo.

Photochemical production of conjugated linoleic acid from soybean oil

Conjugated linoleic acid (CLA), an anticarcinogenic compound with numerous other health benefits, is present mainly in dairy and beef lipids. The main CLA isomer present in dairy and beef lipids is cis 9, trans 11 CLA at a 0.5% concentration. The typical minimum human dietary intake of CLA is 10 times less than the 3 g/d suggested requirement that has been extrapolated from animal and cell-line studies. The objectives of this study were to produce CLA isomers from soybean oil by photoisomerization of soybean oil linoleic acid and to study the oxidation status of the oil. Refined, bleached, and deodorized soybean oil with added iodine concentrations of 0, 0.1, 0.25, and 0.5% was exposed to a 100-W mercury lamp for 0 to 120 h. An SP-2560 fused-silica capillary GC column with FID was used to analyze the esterified CLA isomers in the photoisomerized oil. The CLA content of the individual isomers was optimized by response surface methodology. Attenuated total reflectance (ATR)-FTIR spectra in the 3400 to 3600 cm(-1) range and 1H NMR spectra in the 8 to 12 ppm range of the photoisomerized soybean oil were obtained to follow hydroperoxide formation. The largest amount of cis 9, trans 11 CLA isomer in soybean oil was 0.6%, obtained with 0.25% iodine and 84 h of photoisomerization. Lipid hydroperoxide peaks in the ATR-FTIR spectra and aldehyde peaks in the 1H NMR spectra were not observed in the photoisomerized soybean oil, and the spectra were similar to that of fresh soybean oil. This study shows that CLA isomers can be produced simply and inexpensively from soybean oil by photoisomerization.

Dietary conjugated linoleic acid and body composition

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid. The major dietary source of CLA for humans is ruminant meats, such as beef and lamb, and dairy products, such as milk and cheese. The major isomer of CLA in natural food is cis-9,trans-11 (c9,t11). The commercial preparations contain approximately equal amounts of c9,t11 and trans-10,cis-12 (t10,c12) isomers. Studies have shown that CLA, specifically the t10,c12-isomer, can reduce fat tissue deposition and body lipid content but appears to induce insulin resistance and fatty liver and spleen in various animals. A few human studies suggest that CLA supplementation has no effect on body weight and could reduce body fat to a much lesser extent than in animals. To draw conclusions on this form of dietary supplementation and to ultimately make appropriate recommendations, further human studies are required. The postulated antiobesity mechanisms of CLA include decreased energy and food intakes, decreased lipogenesis, and increased energy expenditure, lipolysis, and fat oxidation. This review addresses recent studies of the effects of CLA on lipid metabolism, fat deposition, and body composition in both animals and humans as well as the mechanisms surrounding these effects.

Dietary conjugated linoleic acid and insulin sensitivity and resistance in rodent models

Dietary conjugated linoleic acid (CLA) is being investigated for beneficial effects for disease prevention and treatment in a variety of experimental models, including obesity and type 2 diabetes. To date, rodent studies suggest that trans-10,cis-12 (t10,c12) CLA is associated with greater insulin resistance, despite lower body fat, and that a CLA mixture (and perhaps c9,t11) could be beneficial for the management of insulin resistance. Studies investigating the mechanisms by which CLA operates at the cellular level show that the primary targets for CLA are members of the nuclear receptor family, particularly the lipostat transcription factors peroxisome proliferator-activated receptor alpha (PPARalpha), PPARgamma, sterol regulatory element-binding protein 1c, and liver X receptor alpha. Consequently, the effects of CLA on glucose metabolism are likely secondary effects mediated through factors such as PPARgamma coactivator 1 that are controlled by these nuclear receptors. The different responses of normal compared with insulin-resistant obese rodents suggest that interactions of CLA isomers with the cellular components that contribute to development of metabolic syndrome require further investigation.

Metabolic syndrome and effects of conjugated linoleic acid in obesity and lipoprotein disorders: the Québec experience

The health hazards of obesity are well established. However, the fact that all obese individuals are not at equal risk of developing a disease is being increasingly recognized. The regional distribution of body fat has been identified as an important component of the obesity-related health hazards. Among obese individuals, those who accumulate fat predominantly in the abdominal area are more likely to present several metabolic perturbations of the metabolic syndrome, such as increased plasma triacylglycerol and apolipoprotein B concentrations, an elevated ratio of total cholesterol to HDL cholesterol, reduced plasma HDL-cholesterol concentrations, and small, dense LDL particles. This short review focuses on the risk associated with specific features of metabolic syndrome with use of data from the Québec Cardiovascular Study, an ongoing prospective study of traditional and nontraditional risk factors for ischemic heart disease in men. Recent data on the effect of conjugated linoleic acid on risk factors associated with metabolic syndrome are briefly reviewed. Data available to date suggest that conjugated linoleic acid might not be an appropriate dietary alternative for the treatment of metabolic syndrome and its complications.

Conjugated Linoleic Acid Improves Insulin Sensitivity in Young, Sedentary Humans

BACKGROUND

Preliminary evidence in obese diabetic rats suggests that conjugated linoleic acid (CLA) may have antidiabetic properties, based on reductions in fasting glucose and insulin concentrations. However, in lean rats, CLA causes hyperinsulinemia. Furthermore, experiments in humans also suggest that CLA may worsen insulin sensitivity.

OBJECTIVES

The present study examined whether CLA supplementation can improve insulin sensitivity in humans.

DESIGN

: Sixteen young sedentary individuals (age, 21.5 +/- 0.4 yr (mean +/- SEM); body mass, 77.6 +/- 3.4 kg) participated in this study. Ten subjects received 4 g x d of mixed CLA isomers (35.5%cis-9, trans-11; 36.8%trans-10, cis-12) for 8 wk, whereas six subjects received placebo (safflower oil). Oral glucose tolerance tests were performed at baseline (0), 4 and 8 wk of supplementation.

RESULTS

: After 8 wk of CLA supplementation, insulin sensitivity index (ISI) increased (14.4 +/- 1.0, 8 wk vs 11.3 +/- 1.3, 0 wk; P < 0.05), which corresponded to a decrease in fasting insulin concentrations. Six of the 10 subjects showed large increases in their ISI (range, +27 to 90%), whereas two demonstrated essential no change (+3 to 5%), and two had a decrease in insulin sensitivity (-12 to -13%). ISI was unchanged over 8 wk in the placebo group.

CONCLUSIONS

Our results indicate that a common dosage of a commercially available CLA supplement can improve ISI in young, sedentary individuals. However, there is considerable individual variability in the response. Additional studies are required to identify underlying metabolic changes in human skeletal muscle.

Conjugated linoleic acid induces human adipocyte delipidation: autocrine/paracrine regulation of MEK/ERK signaling by adipocytokines

Dietary conjugated linoleic acid (CLA) reduces body fat in animals and some humans. Here we show that trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, when added to cultures of stromal vascular cells containing newly differentiated human adipocytes, caused a time-dependent decrease in triglyceride content, insulin-stimulated glucose and fatty acid uptake, incorporation into lipid, and oxidation compared with controls. In parallel, gene expression of peroxisome proliferator-activated receptor-gamma and many of its downstream targets were diminished by trans-10, cis-12 CLA, whereas leptin gene expression was increased. Prior to changes in gene expression and metabolism, trans-10, cis-12 CLA caused a robust and sustained activation of mitogen-activated protein kinase kinase/extracellular signal-related kinase (MEK/ERK) signaling. Furthermore, the trans-10, cis-12 CLA-mediated activation of MEK/ERK could be attenuated by pretreatment with U0126 and pertussis toxin. In parallel, pretreatment with U0126 blocked the ability of trans-10, cis-12 CLA to alter gene expression and attenuate glucose and fatty acid uptake of the cultures. Intriguingly, the induction by CLA of MEK/ERK signaling was linked to hypersecretion of adipocytokines interleukin-6 and interleukin-8. Collectively, these data demonstrate for the first time that trans-10, cis-12 CLA decreases the triglyceride content of newly differentiated human adipocytes by inducing MEK/ERK signaling through the autocrine/paracrine actions of interleukins-6 and 8.

CLA isomers in milk fat from cows fed diets with high levels of unsaturated fatty acids

The concentrations of CLA isomers were determined by Ag+ -HPLC in the milk fat of cows fed a control diet consisting of hay ad libitum and 15 kg of fodder beets or this diet supplemented with oilseeds containing either high levels of oleic acid (rapeseed), linoleic acid (sunflower seed), or alphalinolenic acid (linseed). Highly significant (P < or = 0.001) correlations were found between the daily intakes of oleic acid and the concentration of the CLA isomer trans-7,cis-9 in milk fat; of linoleic acid and the CLA isomers trans-10,trans-12, trans-9,trans-11, trans-8,trans-10, trans-7,trans-9, trans-10,cis-12, cis-9,trans-11, trans-8,cis-10, and trans-7,cis-9; and of alpha-linolenic acid and the CLA isomers trans-12,trans-14, trans-11 ,trans-13, cis,trans/trans,cis-12,14, trans-11 ,cis-13, and cis-11 ,trans-13. CLA concentrations were also determined in the milk fat of cows grazing in the lowlands (600-650 m), the mountains (900-1210 m), and the highlands (1275-2120 m). The concentrations of many isomers were highest in milk fat from the highlands, but only three CLA isomers (cis-9,trans-11, trans-11 ,cis-13, and trans-8,cis-10) showed a nearly linear increase with elevation. Therefore, these three CLA isomers, and particularly the CLA isomer trans- 11,cis-13, the second-most important CLA in milk fat from cows grazing at the three altitudes, could be useful indicators of milk products of Alpine origin.

Incorporation of cis-9,trans-11 or trans-10,cis-12 conjugated linoleic acid into plasma and cellular lipids in healthy men

This study investigated the incorporation of cis-9,trans-11 conjugated linoleic acid (c9,t11 CLA) and trans-10,cis-12-CLA (t10,c12 CLA) into plasma and peripheral blood mononuclear cell (PBMC) lipids when consumed as supplements highly enriched in these isomers. Healthy men (n = 49, age 31 +/- 8 years) consumed one, two, and four capsules containing approximately 600 mg of either c9,t11 CLA or t10,c12 CLA per capsule for sequential 8 week periods followed by a 6 week washout before consuming the alternative isomer. Both isomers were incorporated in a dose-dependent manner into plasma phosphatidylcholine (PC) (c9,t11 CLA r = 0.779, t10,c12 CLA r = 0.738; P < 0.0001) and cholesteryl ester (CE) (c9,t11 CLA r = 0.706, t10,c12 CLA r = 0.788; P < 0.0001). Only t10,c12 CLA was enriched in plasma nonesterified fatty acids. Both c9,t11 CLA and t10,c12 CLA were incorporated linearly into PBMC total lipids (r = 0.285 and r = 0.273, respectively; P < 0.0005). The highest concentrations of c9,t11 CLA and t10,c12 CLA in PBMC lipids were 3- to 4-fold lower than those in plasma PC and CE. These data suggest that the level of intake is a major determinant of plasma and PBMC CLA content, although PBMCs appear to incorporate both CLA isomers less readily.

Hepatic steatosis is not due to impaired fatty acid oxidation capacities in C57BL/6J mice fed the conjugated trans-10,cis-12-isomer of linoleic acid

Decreased body fat mass and liver steatosis have been reported in mice fed diets containing the conjugated linoleic acid trans-10,cis-12-C18:2 (CLA2), but not in those fed diets containing cis-9,trans-11-C18:2 (CLA1). Because the decrease in fatty acid (FA) oxidation may cause fat accumulation, we questioned whether the effects of both CLAs on enzyme activities and mRNA expression were related to liver FA oxidation. To address this question, 7-wk-old male C57BL/6J mice were fed for 4 wk a diet supplemented with 1% CLA1, CLA2, or cis-9-C18:1 (control) esterified as triacylglycerols. In CLA2-fed mice, the proportions of CLA2 in the total FA of liver lipids were substantially lower than those of CLA1 in mice fed CLA1. The mitochondrial protein content per total liver was about 56% greater in CLA2-fed mice than in CLA1-fed mice and controls. Mitochondrial carnitine palmitoyltransferase I (CPT I) and carnitine-dependent palmitate oxidation activities were also significantly greater in CLA2-fed mice than in the two other groups. The amounts of malonyl-CoA per gram of liver and the sensitivity of CPT I to malonyl-CoA inhibition were greater in both groups of CLA-fed mice than in the controls. L-CPT I mRNA expression doubled in CLA2-fed mice and was 3 and 2 times greater for M-CPT I in the CLA1 and CLA2 groups, respectively, compared with controls. Peroxisomal FA oxidation-related activities and acyl-CoA oxidase mRNA expression were increased in CLA1-fed mice, and to a larger extent in CLA2-fed mice, relative to controls. These data indicate that FA oxidation capacities were increased in mice fed CLA2, but were likely depressed in vivo through malonyl-CoA inhibition.

Evidence that the anti-obesity effect of conjugated linoleic acid is independent of effects on stearoyl-CoA desaturase1 expression and enzyme activity

The trans-10,cis-12 isomer of conjugated linoleic acid (CLA) reduces body fat gain in animals and inhibits stearoyl-CoA desaturase (SCD) activity in 3T3-L1 adipocytes. To test whether CLA's body fat reduction is mediated by SCD1, wild-type and SCD1-null mice were fed diet supplemented with 0.2% trans-10,cis-12 (t10c12) CLA for 4 weeks. The t10c12 CLA-supplemented diet significantly reduced body fat mass in both wild type and SCD1-null mice. Similarly, t10c12 CLA diet decreased blood triglyceride and free fatty acid levels regardless of SCD1 genotypes. Mice fed t10c12 CLA exhibited increased mRNA expression of fatty acid synthase and uncoupling protein 2 in both genotypes. Taken together, the effects of t10c12 CLA on reduction of body fat gain, blood parameters, and mRNA expression in both SCD1-null mice and wild-type mice were similar, indicating that the anti-obesity effect of t10c12 CLA may be independent of the effects of this CLA isomer on SCD1 gene expression and enzyme activity.

Effect of conjugated linoleic acid supplementation after weight loss on appetite and food intake in overweight subjects

OBJECTIVE

To study the effects of 13 weeks conjugated linoleic acid (CLA) supplementation in overweight subjects on body-weight maintenance, parameters of appetite and energy intake (EI) at breakfast after weight loss.

DESIGN

This study had a double-blind, placebo-controlled randomized design.

SUBJECTS

A total of 26 men and 28 women (age 37.8+/-7.7 y; body mass index 27.8+/-1.5 kg/m(2)).

INTERVENTIONS

Subjects were first submitted to a very-low-calorie diet (VLCD; 2.1 MJ/day) for 3 weeks after which they started with the 13-week intervention period. They either received 1.8 g CLA or placebo per day or 3.6 g CLA or placebo per day. Additionally, subjects of the high dosage intervention replaced their habitual lunch by one meal of a protein-rich, low-energy supplement. EI was measured at breakfast and appetite profile after an overnight fast.

RESULTS

The mean body weight loss was 6.9+/-1.7% of their original body weight. Multiple regression analysis showed that at the end of the 13-week intervention, CLA did not have an effect on body weight regain. Feelings of fullness and satiety were increased and feelings of hunger were decreased after 13 weeks intervention by CLA compared to placebo, independent of %body weight regain. However, EI measured at breakfast was not affected by CLA.

CONCLUSION

Appetite (hunger, satiety and fullness) was favorably, dose-independently affected by a 13-week consumption of 1.8 or 3.6 g CLA/day. This did not result in a lower EI at breakfast or an improved body-weight maintenance after weight loss.

Conjugated linoleic acid blocks estrogen signaling in human breast cancer cells

Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of linoleic acid found in dairy products and meat from ruminants, has been widely shown to possess anticarcinogenic activity against breast cancer both in vitro and in animal models. However, little information is available concerning the mechanisms of the antitumor effects of these compounds. In this study, we investigated whether CLA has direct antiestrogenic activity in estrogen receptor positive (ER+) breast cancer cells. Treatment of the ER+ cell line, MCF-7, with 5 purified CLA isomers as well as "mixed" CLA showed a dose-dependent growth inhibition with the 9cis,11cis and 9cis,11trans being the most and least potent isomers, respectively. In assessing effects on a number of variables that play obligatory roles in the estrogen signaling pathway, we determined that CLA treatment downregulated ERalpha expression at both mRNA and protein levels and decreased binding activity of nuclear protein to a canonical estrogen response element (ERE(v)). Using a reporter gene construct (ERE(v)-tk-Luc) that was transiently transfected into MCF-7 cells, we also demonstrated inhibition of promoter activity by CLA that was directly mediated by blockage of activity through the ERE. The results indicated that the order of potency of the CLA isomers for inhibiting activation of ERE(v) was similar to that demonstrated for their antiproliferative activity on MCF-7 cells. Taken together, these findings demonstrate that CLA compounds possess potent antiestrogenic properties that may at least partly account for their antitumor activity on breast cancer cells.

Role of fatty acids in adipocyte growth and development1,2

Fat is typically added to diets as a source of energy. The alternative aspects considered here are the use of specific fats to alter the fatty acid profile of adipose tissue toward creation of value-added products and the potential for individual fatty acids to alter gene expression and control adipose tissue development. Emphasis is placed on the omega-3 fatty acids, such as those found in fish oil, and on CLA. The most common association of fatty acids with adipose tissue is related to their storage as triglycerides in mature adipocytes and the consequences of excess accumulation in obesity. Fatty acids and their derivatives also can have hormone-like effects and have been be shown to regulate gene expression in preadipocytes, which ultimately effects their proliferation and differentiation. Long-chain, saturated, and polyunsaturated fatty acids have been shown to regulate transcription factors, such as CCAAT/enhancer binding protein, peroxisome proliferator activated receptor, and other adipose-specific genes, very early in adipocyte development. These effects have the potential to affect fat cell number at maturity. Specifically, there is evidence that the fatty acids in fish oil, such as docosahexaenoic and eicosopentaenoic acids, and fatty acids in the CLA series, decrease preadipocyte proliferation in cell lines and reduce adiposity in rodents. There is little direct evidence of the ability of fatty acids to manipulate adipocyte development in non-rodent species. The genetic, nutritional, and pharmacological manipulation of adipose tissue in meat animals has long been of interest to animal scientists. An understanding of the ability of fatty acids to regulate factors such as adipocyte size and number, particularly in meat animals, would be of great interest. The evidence for regulatory roles of fatty acids in development from rodent and in vitro studies and their potential application to meat animals are reviewed.

Effect of conjugated linoleic acid on body composition and plasma lipids in humans: an overview of the literature

Studies in mice have indicated that feeding diets containing 0.5-1% conjugated linoleic acid (CLA) considerably reduces body fat. These findings have attracted much interest because of the potential use of CLA as a tool to promote weight loss in humans. Several CLA studies in humans have now been published, and the objective of the present review was to give an overview of these experiments. Most of the studies were done in free-living subjects and were not strictly controlled for nutrient and energy intakes. None of the studies found a significant reduction in body weight, and only 2 studies showed a significant but relatively small body fat-lowering effect. Some studies suggested that CLA may have a tendency to increase lean body mass. Furthermore, there are indications from animal studies that CLA may have effects on plasma lipids. However, only one study in humans showed a significant HDL-cholesterol-lowering effect of CLA; in all the other studies, there were no significant effects on plasma total, LDL-, and HDL-cholesterol concentrations or on plasma triacylglycerol concentrations. Thus, the results of the studies in humans indicate that the effect of CLA on body fat is considerably less than that anticipated from mice studies and that CLA has no major effect on plasma lipids.

Contrasting effects oft10,c12- andc9,t11-conjugated linoleic acid isomers on the fatty acid profiles of mouse liver lipids

The purpose of this study was to examine the effects of two purified isomers of CLA (c9,t11-CLA and t10,c12-CLA) on the weights and FA compositions of hepatic TG, phospholipids, cholesterol esters, and FFA. Eight-week-old female mice (n = 6/group) were fed either a control diet or diets supplemented with 0.5% c9,t11-CLA or t10,c12-CLA isomers for 8 wk. Weights of liver total lipids and those of individual lipid fractions did not differ between the control and the c9,t11-CLA groups. Livers from animals fed the t10, c12-CLA diet contained four times more lipids than those of the control group; this was mainly due to an increase in the TG fractions (fivefold), but cholesterol (threefold), cholesterol esters (threefold), and FFA (twofold) were also significantly increased. Although c9,t11-CLA did not significantly alter the weights of liver lipids when compared with the control group, its intake was associated with significant reductions in the weight percentage (wt% of total FAME) of 18:1n-9 and 18:1n-7 in the TG fraction and with significant increases in the weight percentage of 18:2n-6 in the TG, cholesterol ester, and phospholipid fractions. On the other hand, t10,c12-CLA intake was linked with a significant increase in the weight percentage of 18:1n-9 and a decrease in that of 18:2n-6 in all lipid fractions. These changes may be the result of alterations in the activity of delta9-desaturase (stearoyl CoA desaturase) and the enzymes involved in the metabolism of 18:2n-6. Thus, the two isomers differed not only in their effects on the weights of total liver lipids and lipid fractions but also on the FA profile of the lipid fractions.

Isomers of conjugated linoleic acid differ in their effects on angiogenesis and survival of mouse mammary adipose vasculature

Dietary conjugated linoleic acid (CLA) is a cancer chemopreventive agent that has been shown to inhibit angiogenesis in vivo and in vitro, and to decrease vascular endothelial growth factor (VEGF) and Flk-1 concentrations in the mouse mammary gland. To determine which isomer mediates the antiangiogenic effects of CLA in vivo, the effects of diets supplemented with 5 or 10 g/kg c9,t11- or t10,c12-CLA isomers were compared in CD2F1Cr mice. Both isomers inhibited functional vascularization of a matrigel pellet in vivo and decreased serum VEGF concentrations; the t10,c12 isomer also decreased the proangiogenic hormone leptin (P < 0.05). Additionally, the t10,c12 isomer, but not c9,t11-CLA, rapidly induced apoptosis of the white and brown adipocytes as well as the preexisting supporting vasculature of the mammary fat pad (P < 0.05). Independent of this isomer-specific adipose apoptotic effect, both isomers induced a rapid and reversible decrease in the diameter of the unilocular adipocytes (P < 0.05). The ability of both CLA isomers to inhibit angiogenesis in vivo may contribute to their ability to inhibit carcinogenesis. Moreover, we propose that each CLA isomer uniquely modifies the mammary stromal "soil" in a manner that is useful for chemoprevention of breast cancer.

An enriched mixture of trans-10,cis-12-CLA inhibits linoleic acid metabolism and PGE2 synthesis in MDA-MB-231 cells

Conjugated linoleic acid (CLA) isomers are potent inhibitors of mammary tumor cell growth. Evidence suggests that CLA modulates essential fatty acid (EFA) metabolism; however, it is not clear which parts of this pathway are important regulatory points modulated by CLA. Enriched mixtures of D9-cis,11-trans (D9c,11t)- and D10-trans,12-cis (D10t,12c)-18:2 were used to assess outcome measures of EFA metabolism pertaining to membrane phospholipid incorporation, tumor cell growth, and prostaglandin E2 (PGE2) synthesis in the MDA-MB-231 mammary tumor cell line. Tumor cells were treated with linoleic acid (LA), an equal mixture (Mix), or enriched preparations of D9c,11t- or D10t,12c-18:2. Treatment with Mix or the enriched mixture of D10t,12c-18:2 significantly inhibited the synthesis of arachidonic acid (AA) from LA, resulting in increased levels of LA and decreased levels of AA in membrane phosphatidylcholine and phosphatidylethanolamine (P < 0.05). LA and AA levels were not altered in cells treated with enriched D9c,11t-18:2 and were similar to those in LA control treated cells. All CLA treatments reduced [3H]thymidine uptake, an indicator of tumor cell growth, by more than one-half relative to LA controls. MDA-MB-231 cells challenged with AA in the presence of all CLA mixtures resulted in significantly reduced PGE2 synthesis relative to controls treated with LA (P < 0.05). It is evident that individual isomers exert inhibitory effects at specific steps of EFA metabolism, which correspondingly leads to a reduction in PGE2 synthesis and, ultimately, tumor growth.

The Position of Rumenic Acid on Triacylglycerols Alters Its Bioavailability in Rats

The metabolic fate of rumenic acid (9cis,11trans-octadecenoic acid) related to its position on the glycerol moiety has not yet been studied. In the present work, synthetic triacylglycerols (TAG) esterified with oleic and rumenic acids were prepared. Rats were force-fed synthetic dioleyl monorumenyl glycerol with (14)C labeled rumenic acid in the internal (sn-2) or in the external position (sn-1 or sn-3). Rats were then placed in metabolic cages for 16 h. At the end of the experiment, the radioactivity in tissues, carcass and expired CO(2) was measured. Rumenic acid that was esterified at the external positions on the TAG was better absorbed and oxidized to a greater extent than when esterified at the internal position. The fatty acid from the 2-TAG form was also better incorporated into the rat carcass. In the liver, rumenic acid appeared mainly in TAG (50%) and to a lesser extent in phospholipids (33%) whatever its dietary form. Moreover, analyses of lipids from Camembert cheese and butter revealed that rumenic acid was located mainly on the sn-1 or sn-3 positions (74%). Taken together, these data suggest that rumenic acid from dairy fat may be well absorbed and used extensively for energy production.

Effects of lipid-esterified conjugated linoleic acid isomers on platelet function: evidence for stimulation of platelet phospholipase activity

The effects of four conjugated linoleic acid (CLA) isomers on in vitro collagen-induced human platelet aggregation and thromboxane (TXB(2), the inactive metabolite of the proaggregatory TXA(2)) production were examined. As the free fatty acid (FFA), 9t, 11t-CLA was the most effective inhibitor of these two processes (I(50)s of 2.2 and 4 microM, respectively) and the 9c, 11c-CLA was the least effective (I(50)s of 8.3 and 37 microM) of the isomers tested. When platelets were preesterified with either 25 microM 9t, 11t-CLA or 9c, 11c-CLA, CLA incorporation in total platelet lipids increased from 0.24% to 0.31% and 0.38%, and most of this increase was found to be in the phosphatidyl choline and phosphatidyl ethanolamine subclasses. The decrease in arachidonic acid (AA) content in total fatty acids or phospholipids was an order of magnitude greater. Furthermore, no significant differences between platelets prelabeled with either 9t, 11t- or 9c, 11c-CLA in the inhibition of collagen-induced aggregation and TXB(2) formation were observed. However, platelets prelabeled with 9c, 11c-CLA stimulated basal TXB(2) production (4-fold) which was not observed with platelets pretreated with either 9t, 11t-CLA, linoleic acid or stearic acid. This enhancement was associated with a 2.4-5-fold increase in the release of endogenous AA. Our results suggest that the presence of a conjugated cis, cis double bond appears to change the lipid environment sufficiently to stimulate the basal platelet phospholipase activity, which in turn increases the formation of TXB(2).

Effects of pH and Concentrations of Linoleic and Linolenic Acids on Extent and Intermediates of Ruminal Biohydrogenation in Vitro

Three experiments were conducted by in vitro incubations in ruminal fluid to investigate the effects of pH and amounts of linoleic and linolenic acids on the extent of their biohydrogenation, the proportions of conjugated linoleic acid (CLA) and trans-C18:1 as intermediates, and the ratio trans-10:trans-11 intermediates. The effects of pH and amount of linoleic acid were investigated in kinetic studies, and effects of the amount of linolenic acid were studied with 6-h incubations. With identical initial amounts of linoleic acid, its disappearance declined when the mean pH during incubation was under 6.0 compared with a mean pH over 6.5, and when the amount of linolenic acid increased from 10 to 180 mg/160-ml flask, suggesting an inhibition of the isomerization step of the biohydrogenation. Low pH decreased the ratio of trans-10:trans-11 intermediates. With initial amounts of linoleic acid increasing from 100 to 300 mg, the percentage of linoleic acid disappearance declined, but the amount that disappeared increased, without modification of the trans-10:trans-11 ratio, suggesting a maximal capacity of isomerization rather than an inhibition. Moreover, increasing initial linoleic acid resulted in high amounts of trans-C18:1 and an increase of C18:0 that was a linear function of time, suggesting a maximal capacity for the second reduction step of biohydrogenation. High amounts of initial linolenic acid did not affect the amounts of CLA, trans-C18:1, or the ratio trans-10:trans-11. Based on these experiments, a ruminal pH near neutrality with high amount of dietary linoleic acid should modulate the reactions of biohydrogenation in a way that supports CLA and trans-11C18:1 in the rumen.

Efficacy and safety of dietary supplements containing CLA for the treatment of obesity: evidence from animal and human studies

Dietary supplements containing conjugated linoleic acid (CLA) are widely promoted as weight loss agents available over the counter and via the Internet. In this review, we evaluate the efficacy and safety of CLA supplementation based on peer-reviewed published results from randomized, placebo-controlled, human intervention trials lasting more than 4 weeks. We also review findings from experimental studies in animals and studies performed in vitro. CLA appears to produce loss of fat mass and increase of lean tissue mass in rodents, but the results from 13 randomized, controlled, short-term (<6 months) trials in humans find little evidence to support that CLA reduces body weight or promotes repartitioning of body fat and fat-free mass in man. However, there is increasing evidence from mice and human studies that the CLA isomer trans-10, cis-12 may produce liver hypertrophy and insulin resistance via a redistribution of fat deposition that resembles lipodystrophy. CLA also decreases the fat content of both human and bovine milk. In conclusion, although CLA appears to attenuate increases in body weight and body fat in several animal models, CLA isomers sold as dietary supplements are not effective as weight loss agents in humans and may actually have adverse effects on human health.

Herbal preparations for obesity: are they useful?

The opportunities for additional research in this area are plentiful. Unfortunately, there has been relatively limited funding for research on herbal supplements compared with the amount of funding that is available for research on pharmaceuticals. Botanical dietary supplements often contain complex mixtures of phytochemicals that have additive or synergistic interactions. For example, the tea catechins include a group of related compounds with effects that are demonstrable beyond those that are seen with epigallocatechin gallate, the most potent catechin. The metabolism of families of related compounds may be different than the metabolism of purified crystallized compounds. In some cases, herbal medicines may simply be less purified forms of single active ingredients, but in other cases they represent unique formulations of multiple, related compounds that may have superior safety and efficacy compared with single ingredients. Obesity is a global epidemic, and traditional herbal medicines may have more acceptance than prescription drugs in many cultures with emerging epidemics of obesity. Several ethnobotanical studies found herbal treatments for diabetes, and similar surveys, termed bioprospecting, for obesity treatments may be productive. Beyond increasing thermogenesis, there are other biological rationales for the actions of several different alternative medical and herbal approaches to weight loss. For example, several supplements and herbs claim to result in nutrient partitioning so that ingested calories will be directed to muscle, rather than fat. These include an herb (Garcinia cambogia), and a lipid which is the product of bacterial metabolism (conjugated linoleic acid). Moreover, a series of approaches attempt to physically affect gastric satiety by filling the stomach. Fiber swells after ingestion and has was found to result in increased satiety. A binding resin (Chitosan) has the ability to precipitate fat in the laboratory and is touted for its ability to bind fat in the intestines so that it is not absorbed. In double-blind studies, however, this approach was found to be ineffective. There are two key attractions of alternative treatments to obese patients. First, they are viewed as being natural and are assumed by patients to be safer than prescription drugs. Second, there is no perceived need for professional assistance with these approaches. For obese individuals who cannot afford to see a physician, these approaches often represent a more accessible solution. Finally, for many others, these approaches represent alternatives to failed attempts at weight loss with the use of more conventional approaches. These consumers are often discouraged by previous failures, and are likely to combine approaches or use these supplements at doses higher than are recommended. It is vital that the primary care physician is aware of the herbal preparations that are being used by patients so that any potential interaction with prescription drugs or underlying medical conditions can be anticipated. Unfortunately, there have been several instances where unscrupulous profiteers have plundered the resources of the obese public. Although Americans spend $30 billion per year on weight loss aids, our regulatory and monitoring capability as a society are woefully inadequate. Without adequate resources, the FDA resorted to "guilt by association" adverse events reporting, which often results in the loss of potentially helpful therapies without adequate investigation of the real causes of the adverse events that are reported. Scientific investigations of herbal and alternative therapies represent a potentially important source for new discoveries in obesity treatment and prevention. Cooperative interactions in research between the Office of Dietary Supplements, the National Center for Complementary and Alternative Medicine, and the FDA could lead to major advances in research on the efficacy and safety of the most promising of these alternative approaches.

cis-9,trans-11 and trans-10,cis-12 CLA affect lipid metabolism differently in primary white and brown adipocytes of djungarian hamsters

We explored whether CLA isomers and other C18 FA affect (i) lipid content and FA concentrations in total adipocyte lipids, (ii) FA synthesis from glucose in TAG and phospholipids of primary brown (BAT) and white adipocytes (WAT), and (iii) mRNA expression of uncoupling protein 1 (UCP1) in primary brown adipocytes of Djungarian hamsters (Phodopus sungorus). c9,t11-CLA, oleic, linoleic, and alpha-linolenic acid increased whereas t10,c12-CLA decreased lipid accumulation in both adipocyte types. t10,c12-CLA treatment affected FA composition mainly in BAT cells. CLA incorporation into lipids, in particular c9,t11-CLA, was higher in BAT. In both cell types, t10,c12-CLA treatment reduced the incorporation of glucose 13C carbon into FA of TAG and phospholipids, whereas c9,t11-CLA, linoleic, and alpha-linolenic acid either did not influence or dose-dependently increased glucose carbon incorporation into FA. UCP1 mRNA expression was inhibited by t10,c12-CLA but increased by c9,t11-CLA, linoleic, and alpha-linolenic acid. It is concluded that c9,t11-CLA and t10,c12-CLA have distinctly different effects on lipid metabolism in primary adipocytes. The effects of c9,t11-CLA are similar to those of other unsaturated C18 FA. The opposite effects of c9,t11-CLA and t10,c12-CLA are evident in both WAT and BAT cultures; however, brown adipocytes seem to be more susceptible to CLA treatment.

Dose Response of Milk Fat to Intravenous Administration of the trans-10, cis-12 Isomer of Conjugated Linoleic Acid

Intravenous infusion of conjugated linoleic acid (CLA) was evaluated as a simpler method than abomasal infusion and the feeding of calcium salts to examine milk fat depression. The objectives were to determine the dose-dependent response of milk fat and plasma metabolites to intravenous administration of the trans-10, cis-12 isomer of CLA, an isomer identified to possess an inhibitory effect on milk fat synthesis. Four multiparous Holstein cows averaging 123 +/- 30 d in milk were randomly assigned to treatments in a 4 x 4 Latin square design. Catheters were inserted into the jugular vein for infusions and blood sampling. Treatments consisted of intravenous infusions of 0, 2, 4, and 6 g/d CLA (> 95% trans-10, cis-12 CLA). Infusates contained 72 g/d of a parenteral solution, saline, and CLA to 90 ml. Periods were of 5 d duration with a 7 d wash out. Milk was sampled at each milking and analyzed for fat, protein, and fatty acids. Blood samples were obtained on the last day of each period. Dry matter intake (22.4 +/- 2.4 kg/d), milk yield (28.5 +/- 3.3 kg/d), and protein percent (3.26 +/- 0.08%) of cows were not affected by treatment. However, milk fat percentage was reduced linearly with increasing doses of CLA. Milk fat percentage was 4.17, 3.53, 3.29, and 2.92% on d 5 for treatments 0, 2, 4, and 6 g/d CLA, respectively. Concentrations (4.2 mg/g of fat) of cis-9, trans-11 CLA in milk fat were not affected by treatment. However, an increase in the trans-10, cis-12 CLA content of milk fat was observed. Milk fat contained 0.00, 0.02, 0.06, and 0.10 mg of trans-10, cis-12 CLA per g of fat (SEM = 0.065) for treatments 0, 2, 4, and 6 g/d CLA, respectively. Plasma NEFA concentration increased linearly with the dose of the trans-10, cis-12 CLA. Intravenous infusion of the trans-10, cis-12 isomer of CLA depressed milk fat in a linear manner over the range of infusion studied and, therefore, is an alternative to abomasal infusion.

Validation and calibration of DEXA body composition in mice

Validated methods of determining murine body composition are required for studies of obesity in mice. Dual-energy X-ray absorptiometry (DEXA) provides a noninvasive approach to assess body fat and lean tissue contents. Similar to DEXA analyses in other species, body fat measurements in mice show acceptable precision but suffer from poor accuracy. Because fat and lean tissues each contain various components, these inaccuracies likely result from selection of inappropriate calibration standards. Analysis of solvents showed that the PIXImus2 DEXA gave results consistent with theoretical calculations. Male mice weighing 26-60 g and having body fat percentages ranging from 3 to 49% were analyzed by both PIXImus2 DEXA and chemical carcass analysis. DEXA overestimated mouse fat content by an average of 3.3 g, and algorithms were generated to calculate body fat from both measured body fat values and the measured ratio of high- to low-energy X-ray attenuations. With calibration to mouse body fat content measured by carcass analysis, the PIXImus2 DEXA gives accurate body composition values in mice.

Interactions of conjugated linoleic acid and lipoic acid on insulin action in the obese Zucker rat

The fatty acid conjugated linoleic acid (CLA) and the antioxidant R-(+)-alpha-lipoic acid (R-ALA) individually enhance glucose tolerance and insulin action on skeletal muscle glucose transport in the insulin-resistant obese Zucker rat. To date, no study has assessed the potential interactions between these 2 interventions in treating insulin resistance. The present study was designed to determine whether chronic treatment with CLA and R-ALA in combination would enhance skeletal muscle glucose transport to a greater extent than either intervention individually. CLA, R-ALA, or a combination treatment of R-ALA and CLA were administered to female obese Zucker rats for 20 days at low or high doses. Whereas low-dose R-ALA (10 mg/kg body weight) alone did not alter muscle glucose transport, low-dose CLA (0.3 g/kg) induced a significant increase (38%, P <.05) in insulin-mediated glucose transport in epitrochlearis, but not in soleus. Low-dose combination therapy brought about the greatest enhancement of insulin-mediated glucose transport in epitrochlearis (77%) and soleus (54%), with the latter effect being associated with a 50% reduction in protein carbonyls (an index of tissue oxidative stress) and a 33% diminution in muscle triglycerides. High-dose treatments with CLA (1.5 g/kg), R-ALA (50 mg/kg), and the combination of CLA and R-ALA elicited increases in insulin-mediated glucose transport in epitrochlearis (57%, 58%, and 77%) and soleus (32%, 35%, and 54%). However, whereas the individual high-dose treatments with CLA and R-ALA reduced protein carbonyls (63% and 49%) and triglycerides (29% and 28%) in soleus, no further reductions were observed with the high-dose combination treatment groups. These findings support a significant interaction between low doses of CLA and R-ALA for enhancement of insulin action on skeletal muscle glucose transport, possibly via reductions in muscle oxidative stress and in lipid storage.

Effect of conjugated FA on feed intake, body composition, and liver FA in mice

CLA is a generic term describing different isomers of linoleic acid with two conjugated double bonds. Various metabolic effects have been demonstrated following administration of CLA, including a change in body composition in animals. However, the effects of pure CLA isomers are not fully understood. In addition, conjugated octadecatrienoic acids such as calendic acid have not been extensively investigated. In this study, male and female ICR mice were fed pure CLA isomers (cis9,trans11 or trans10,cis12) or calendic acid (trans8,trans10,cis12) as their ethyl esters for 6 wk. Body protein content was significantly increased after feeding CLA isomers, either as pure isomers or as a mixture. Calendic acid significantly decreased body fat content in males. CLA (pure isomers or a mixture) significantly decreased body fat in both males and females, with the trans10,cis12 isomer being the most effective. The effect of the cis9,trans11 isomer was more pronounced in females than in males. It was concluded that the trans10,cis12 CLA isomer was mainly responsible for the decrease in fat content in mice, without a significant modification of feed efficiency, and that it was more effective than calendic acid.

Trans10, cis12-conjugated linoleic acid prevents triacylglycerol accumulation in adipocytes by acting as a PPARgamma modulator

A group of polyunsaturated fatty acids called conjugated linoleic acids (CLAs) are found in ruminant products, where the most common isomers are cis9, trans11 (c 9,t11) and trans10, cis12 (t10,c12) CLA. A crude mixture of these isomers has been shown in animal studies to alter body composition by a reduction in body fat mass as well as an increase in lean body mass, with the t10,c12 isomer having the most pronounced effect. The objective of this study was to establish the molecular mechanisms by which t10,c12 CLA affects lipid accumulation in adipocytes. We have shown that t10,c12 CLA prevents lipid accumulation in human and mouse adipocytes at concentrations as low as 5 microM and 25 microM, respectively. t10,c12 CLA fails to activate peroxisome proliferator-activated receptor gamma (PPARgamma) but selectively inhibits thiazolidinedione-induced PPARgamma activation in 3T3-L1 adipocytes. Treatment of mature adipocytes with t10,c12 CLA alone or in combination with Darglitazone down-regulates the mRNA expression of PPARgamma as well as its target genes, fatty acid binding protein (aP2) and liver X receptor alpha (LXRalpha). Taken together, our results suggest that the trans10, cis12 CLA isomer prevents lipid accumulation in adipocytes by acting as a PPARgamma modulator.

Conjugated linoleic acid isomers and mammary cancer prevention

There is increasing evidence that individual isomers of conjugated linoleic acid (CLA) may have unique biological or biochemical effects. A primary objective of this study was to determine whether there might be differences in the anticancer activity of 9,11-CLA and 10,12-CLA. This was achieved by evaluating the reduction in premalignant lesions and carcinomas in the mammary gland of rats that had been treated with a single dose of methylnitrosourea and given 0.5% of either highly purified CLA isomer in the diet. Our results showed that the anticancer efficacies of the two isomers were very similar. At 6 wk after carcinogen administration, the total number of premalignant lesions was reduced by 33-36%. At 24 wk, the total number of mammary carcinomas was reduced by 35-40%. The concentration of each CLA isomer and its respective metabolites was analyzed in the mammary fat pad. Tissue level of 10,12-CLA was much lower than that of 9,11-CLA. The pool of metabolites from each isomer was very similar between the two groups and represented only a small fraction of total conjugated diene fatty acids. Feeding of 9,11-CLA resulted in minimal changes in other unsaturated fatty acids. In contrast, feeding of 10,12-CLA produced a wider spectrum of perturbations. Small but significant increases in 16:1 and 16:2 were detected; these were accompanied by decreases in 20:2, 20:3, 20:4, 22:4, and 22:6. The above observation suggests that 10,12-CLA might be more potent than 9,11-CLA in interfering with elongation and desaturation of linoleic and linolenic acids. In summary, our study showed that, at the 0.5% dose level, the anticancer activity of 9,11-CLA and 10,12-CLA was very similar, even though accumulation of 10,12-CLA in the mammary tissue was considerably less than that of 9,11-CLA. These confounding changes of the other unsaturated fatty acids in contributing to the effect of 10,12-CLA need to be clarified.