Effects of trans-10, cis-12 conjugated linoleic acid on body fat and serum lipids in young and adult hamsters

The aim of the present work was to determine whether t-10, c-12 conjugated linoleic acid (CLA) feeding was able to reduce body fat accumulation and improve the serum lipid profile in adult hamsters fed an atherogenic diet, in order to compare these effects with those observed in young growing hamsters. Young and adult hamsters were fed semi-purified atherogenic diets supplemented with 0.5 % linoleic acid or 0.5% t-10, c-12 CLA for 6 weeks. Body weight and food intake were measured every two days. Adipose tissue from different anatomical locations, liver and gastrocnemious muscle were dissected and weighed. Cholesterol, triacylglycerols, non-esterified fatty acids and proteins were determined spectrophotometrically and water content by gravimetry. In young hamsters, no significant differences were found in food intake, final body weight and gastrocnemious muscle weight. White adipose tissue weights were reduced, liver weight was increased and cholesterol and triacyl-glycerols in both serum and liver were reduced. In adult hamsters, CLA feeding decreased food intake and adipose tissue weights. No changes were observed in other parameters. The present study demonstrates that age has an influence in hamster responsiveness to t-10, c-12 CLA because, although when this isomer is added to an atherogenic diet it reduces body fat accumulation in both young and adults hamsters, the lessening of the effects on serum lipids brought about by atherogenic feeding is only observed in young animals. Moreover, it is clear that liver is a target for CLA in young but not in adult hamsters.     

The effects of t10,c12 CLA isomer compared with c9,t11 CLA isomer on lipid metabolism and body composition in hamsters

The objective of the present study was to examine the effects of two different isomers of conjugated linoleic acid (CLA), c9,t11 CLA and t10,c12 CLA, compared with linoleic acid (LA) used as control, on body composition, lipoprotein profile, hepatic lipids and fecal fat content in hamsters. Animals were assigned to the three diet groups (n=15) during 28 days. The diet was composed of 2% of the experimental fat, and throughout the experimental protocol, the hamsters experienced similar food intake. No significant differences were noted in body weight gain among the three diet groups. However, the t10,c12 CLA-fed animals showed higher low-density lipoprotein cholesterol (LDL-C) concentrations (0.9+/-0.1 mmol/L) than those who ingested either LA (0.6+/-0.1 mmol/L) or c9,t11 CLA isomer (0.7+/-0.1 mmol/L), although the t10,c12 CLA consumption decreased hepatic cholesterol and triglycerides and increased fecal fat content compared with the other two groups. Under the present experimental conditions, the dietary c9,t11 CLA isomer showed no positive beneficial effect on plasma lipids. Furthermore, the t10,c12 CLA isomer induced undesirable higher LDL-C, although it reduced hepatic lipids and fat digestibility in hamsters.     

Conjugated linoleic acid and atherosclerosis: studies in animal models

Conjugated linoleic acids (CLA) are isomeric forms of linoleic acid (LA) containing two conjugated sites of unsaturation. The most abundant dietary form of CLA is the cis-9,trans-11 (c-9,t-11) isomer that is found in the fatty tissues and milk of ruminant animals. CLA can also be acquired by ingestion of supplements, which are usually equimolar mixtures of the c-9,t-11 and t-10,c-12 CLA. For more than a decade, the potential for CLA to modify atherosclerosis in animal models has been examined. However, to date, the studies have failed to reach consensus on whether CLA can be effective in reducing the incidence or severity of atherosclerotic lesions, or whether or not plasma lipid and lipoprotein levels can be improved with CLA supplementation. This review will examine the evidence for and against a role for CLA in atherosclerosis, with a focus on the rabbit, the hamster, and the apoE-deficient mouse.     

The growth inhibitory effect of conjugated linoleic acid on a human hepatoma cell line, HepG2, is induced by a change in fatty acid metabolism, but not the facilitation of lipid peroxidation in the cells

We investigated the growth inhibitory effect of conjugated linoleic acid (CLA) on HepG2 (human hepatoma cell line), exploring whether the inhibitory action occurs via lipid peroxidation in the cells. When the cells were incubated up to 72 h with 5-40 microM of CLA (a mixture of 9c,11t-18:2 and 10t,12c-18:2), cell proliferation was clearly inhibited in a dose and time dependent manner but such an inhibition was not confirmed with linoleic acid (LA). In order to evaluate the possible contribution of lipid peroxidation exerted by CLA to cell growth inhibition, alpha-tocopherol (5-20 microM) and BHT (1-10 microM) as potent antioxidants were added to the medium with CLA (20 microM), which did not restore cell growth at all. Furthermore, after 72 h incubation, the membranous phospholipid hydroperoxide formation in the CLA-supplemented cells was suppressed respectively to 25% and 50% of that in LA-supplemented cells and control cells. No difference was observed by a conventional lipid peroxide assay, the TBA test, between CLA-supplemented cells and LA-supplemented cells. Although the cellular lipid peroxidation was not stimulated, lipid contents (triacylglycerol, total cholesterol and free cholesterol) and fatty acid contents (palmitic acid, palmitoleic acid and stearic acid) markedly increased in CLA-supplemented cells compared with LA-supplemented and control cells. Moreover, supplementation with 20 microM LA and 20 microM arachidonic acid profoundly interfered with the inhibitory effect of CLA in HepG2. These results suggest that the growth inhibitory effect of CLA on HepG2 is due to changes in fatty acid metabolism but not to lipid peroxidation.     

Biological effects of conjugated linoleic acids in health and disease

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of octadecadienoic acid [linoleic acid (LA), 18:2n-6] commonly found in beef, lamb and dairy products. The most abundant isomer of CLA in nature is the cis-9, trans-11 (c9t11) isomer. Commercially available CLA is usually a 1:1 mixture of c9t11 and trans-10, cis-12 (t10c12) isomers with other isomers as minor components. Conjugated LA isomer mixture and c9t11 and t10c12 isomers alone have been attributed to provide several health benefits that are largely based on animal and in vitro studies. Conjugated LA has been attributed many beneficial effects in prevention of atherosclerosis, different types of cancer, hypertension and also known to improve immune function. More recent literature with availability of purified c9t11 and t10c12 isomers suggests that t10c12 is the sole isomer involved in antiadipogenic role of CLA. Other studies in animals and cell lines suggest that the two isomers may act similarly or antagonistically to alter cellular function and metabolism, and may also act through different signaling pathways. The effect of CLA and individual isomers shows considerable variation between different strains (BALB/C mice vs. C57BL/6 mice) and species (e.g., rats vs. mice). The dramatic effects seen in animal studies have not been reflected in some clinical studies. This review comprehensively discusses the recent studies on the effects of CLA and individual isomers on body composition, cardiovascular disease, bone health, insulin resistance, mediators of inflammatory response and different types of cancer, obtained from both in vitro and animal studies. This review also discusses the latest available information from clinical studies in these areas of research.     

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

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

植物乳杆菌ZS2058在磷酸盐缓冲液体系中生物转化共轭亚油酸

植物乳杆菌ZS2058是从泡菜中筛选到一株具有转化共轭亚油酸能力的乳酸菌。该菌株在MRS培养基中经0.5mg/mL的亚油酸诱导培养后,所获得的菌体细胞具有较强的转化能力。文中就植物乳杆菌ZS2058水洗细胞在磷酸盐缓冲液体系中生物转化共轭亚油酸进行了深入研究。在非厌氧条件下,植物乳杆菌ZS2058在亚油酸浓度为1mg/mL,湿细胞质量浓度约为150mg/mL,120r/min、37℃的条件下反应24h后,能将亚油酸转化为共轭亚油酸和羟基脂肪酸,其中c9,t11-CLA占所产生的CLA总量的96.4%,产量可高达312.4μg/mL,说明该菌株有很强的专一性。随着反应进一步进行,反应至36h时,c9,t11-CLA含量逐渐减少,伴随着大量羟基脂肪酸的产生;并且,以CLA(c9,t11-CLA和t10,c12-CLA的混合样品)为底物进行反应时,c9,t11-CLA被转化为羟基脂肪酸。由此可知,c9,t11-CLA可能是该菌株生物转化LA过程中的一个中间产物。     

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

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

Production of conjugated linoleic acids through KOH-catalyzed dehydration of ricinoleic acid

Production of conjugated linoleic acids (CLA) using castor oil as starting material involves conversion of ricinoleic acid to methyl 12-mesyloxy-octadec-9-enoate (MMOE) followed by dehydration. This process usually uses 1,8-diazabicyclo-(5.4.0)-undec-7-ene (DBU) as an expensive dehydrating reagent. The present study reports that potassium hydroxide (KOH) can serve as a dehydrating reagent in replacement of DBU. The results showed that conversion of MMOE to CLA catalyzed by KOH was an efficient reaction, with a 77% conversion efficiency at 80 degrees C. The CLA isomeric profile produced in KOH-catalyzed dehydration reaction was similar to that catalyzed by DBU. The CLA mixture produced in KOH-catalyzed dehydration of MMOE at 80 degrees C contained 72% 9c,11t-18:2 and 26% 9c,11c-18:2 while in that catalyzed by DBU, 9c,11t-18:2 and 9c,11c-18:2 accounted for 78 and 16%, respectively. It was found that the temperature of dehydration was an important factor in the determination of CLA isomer composition and yield of conversion. Elevating the temperature from 78 to 180 degrees C decreased not only the conversion efficiency but also production of total c,t-18:2 and c,c-18:2 isomers regardless of dehydration catalyzed by either DBU or KOH. It is concluded that KOH may replace DBU as a dehydrating reagent in conversion of MMOE to CLA when the reaction conditions are optimized.     

Antiplatelet effects of conjugated linoleic acid isomers

Conjugated diene isomers of linoleic acid (CLA) are normal constituents of certain foods and exhibit anticarcinogenic and antiatherogenic properties. In the present study, the effects of several CLA isomers on human platelet aggregation and arachidonic acid metabolism were examined. It was found that 9c,11t-CLA, 10t, 12c-CLA and 13-hydroxy-9c,11t-octadecadienoic acid (13-HODE) inhibited arachidonic acid- and collagen-induced platelet aggregation with I50s in the 5-7 microM range. The nonconjugated 9c, 12c-LA was about 300% and 50%, respectively, less potent an inhibitor with these aggregating agents. Using either thrombin or the calcium ionophore A23187 as aggregating agents, a CLA isomer mix was also found to be more inhibitory than 9c,12c-LA. The 9c,11t- and 10t,12c-CLA isomers as well as the CLA isomer mix inhibited formation of the proaggregatory cyclooxygenase-catalyzed product TXA2, as measured by decreased production of its inactive metabolite [14C]TXB2 from exogenously added [14C]arachidonic acid (I50s=9-16 microM). None of the CLA isomers tested inhibited production of the platelet lipoxygenase metabolite [14C]12-HETE. The additional presence of a hydroxyl group gave opposite results: 13-HODE (I50=3 microM) was about 4-fold more potent a cyclooxygenase inhibitor than the 9c,11t-CLA isomer but 9-HODE was 2- to 3-fold less effective an inhibitor (I50=34 microM) of [14C]TXB2 formation than the corresponding 10t,12c-CLA. In both the aggregation and arachidonic acid metabolism experiments, the inhibitory effects of CLA on platelets were reversible and dependent on the time of addition of either the aggregating agent or the [14C]arachidonic acid substrate. These studies suggest that CLA isomers may also possess antithrombotic properties.     

In vivo distribution and turnover of trans- and cis-10-octadecenoic acid isomers in human plasma lipids

Triacylglycerols containing deuterium-labeled trans-10- and cis-10-octadecenoic acid (10t-18:1, 10c-18:1) plus the triacylglycerol of deuterated cis-9-octadecenoic acid (9c-18:1) were fed as a mixture to two young, adult male subjects. Analysis by mass spectroscopy of the labeled fats in blood samples collected periodically for 48 h allowed the uptake, distribution and turnover of both 10-octadecenoic acid isomers to be directly compared to 9c-18:1. A feature of this study is that actual weight data for the labeled fats were obtained. These data allowed plasma triacylglycerol turnover rates of 3.47-5.13 mg/min per kg to be estimated. Plasma and chylomicron triacylglycerol data also provided evidence that absorption of the deuterated fats mobilized 10-12 g of a triacylglycerol pool present in the intestinal cells. Other results are summarized as follows: the 10t-, 10c- and 9c-18:1 fatty acids were equally well absorbed, both delta 10-18:1 isomers were oxidized more rapidly than 9c-18:1, conversion of the delta 10-18:1 isomers into their corresponding 16:1 isomers was about 3-times faster than for 9c-18:1, the delta 10-18:1 isomers were preferentially incorporated at the 1-acyl and excluded from the 2-acyl position of phosphatidylcholine, esterification of cholesterol with the delta 10-18:1 fatty acids was 2.5-4.3-times slower than for 9c-18:1 and desaturation and elongation rates for the delta 10-18:1 acids were very low.     

Influence of different CLA isomers on insulin resistance and adipocytokines in pre-diabetic, middle-aged men with PPARγ2 Pro12Ala polymorphism

Conjugated linoleic acids (CLAs) are natural PPARγ ligands, which showed conflicting effects on metabolism in humans. We examined metabolic effects of different isomers of CLA in subjects with PPARγ2 Pro12Ala polymorphisms. A total of 35 men underwent four intervention periods in a crossover study design: subjects with either genotypes received c9, t11 CLA or t10, c12 CLA, a commercially available 1:1 mix of both isomers or reference oil (linoleic acid (LA)). Adipocytokines, insulin, glucose and triglycerides were assessed in the fasting state and after a standardized mixed meal. Across all genotypes, there was a significant (p = 0.025) CLA treatment effect upon postprandial (pp) HOMA-IR values, with c9, t11 CLA and CLA isomer mix improving, but t10, c12 CLA isomer worsening. In Ala12Ala subjects, the t10, c12 isomer caused weight gain (p = 0.03) and tended to increase postprandial insulin levels (p = 0.05). In Pro12Pro subjects, t10, c12 resulted in reduction in waist circumference (p = 0.03). The comparison of the different genotype groups revealed statistically different changes in fasting and postprandial insulin, HOMA-IR and leptin after intervention. c9, t11 CLA and the commercial CLA mix showed beneficial effects on insulin sensitivity compared with LA, while t10, c12 CLA adversely affects body weight and insulin sensitivity in different PPAR genotypes. CLA isomers have different effects on metabolism in Ala and Pro carriers.     

The biologically active isomers of conjugated linoleic acid.

Numerous physiological effects are attributed to conjugated linoleic acid (CLA). The purpose of this presentation is to consider these effects with respect to the cis-9,trans-11 and trans-10,cis-12 CLA isomers. We review previously published data and present new findings that relate to underlying biochemical mechanisms of action. Both isomers are natural products. The cis-9,trans-11 isomer is the principal dietary form of CLA, but the concentrations of this isomer and the trans-10,cis-12 isomer in dairy products or beef vary depending on the diet fed to cows or steers, respectively. The trans-10,cis-12 CLA isomer exerts specific effects on adipocytes, in particular reducing the uptake of lipid by inhibiting the activities of lipoprotein lipase and stearoyl-CoA desaturase. The trans-10,cis-12 CLA isomer also affects lipid metabolism in cultured Hep-G2 human liver cells, whereas both the cis-9,trans-11 and trans-10,cis-12 CLA isomers appear to be active in inhibiting carcinogenesis in animal models. We present new findings indicating that the cis-9,trans-11 CLA isomer enhances growth and probably feed efficiency in young rodents. Accordingly, the effects of CLA on body composition (induced by trans-10,cis-12 CLA) and growth/feed efficiency (induced by cis-9,trans-11 CLA) appear to be due to separate biochemical mechanisms. We also show that a 19-carbon CLA cognate (conjugated nonadecadienoic acid, CNA) inhibits lipoprotein lipase activity as effectively as CLA in cultured 3T3-L1 adipocytes. Presumably, CNA is metabolized differently than the 18-carbon CLA isomers, so this finding indicates direct activity of the administered compound as opposed to acting via a metabolite.     

Isomers of conjugated linoleic acid decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in post-prandial adult sedentary or trained Wistar rat

The respective effects and interactions of supplementation with two conjugated linoleic acid (CLA) isomers and exercise on plasma metabolic profile, activity of lipogenic enzymes and cellularity in two adipose tissue sites, those of the liver and heart, were examined in adult Wistar rats. Rats that were either sedentary or exercise-trained by treadmill running were fed one of four diets: a diet without CLA; a diet with either 1% cis 9, trans 11 CLA or 1% trans 10, cis 12 CLA; or a mixture of both isomers (1% of each) for 6 weeks. We observed that the exercise decreased lipogenic enzyme activities in epididymal and perirenal adipose tissue. Plasma cholesterol, insulin, and leptin concentrations were lower in exercise-trained rats than in sedentary rats. The ingestion of either CLA mixture or the trans 10, cis 12 CLA increased lipogenic enzyme activities in epididymal tissue and more markedly in perirenal adipose tissue, especially in sedentary rats, and without affecting adipose tissue weight or cellularity. A similar effect of trans 10, cis 12 CLA was observed in regard to malic enzyme activity in the liver. In addition, this isomer decreased plasma lipid and urea concentrations and increased plasma 3-hydroxybutyrate levels. The ingestion of cis 9, trans 11 CLA increased fatty acid synthase activity in perirenal adipose tissue in sedentary rats and decreased plasma cholesterol and leptin concentrations. These results show that isomers of CLA decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in adult sedentary or exercise-trained rat, thus suggesting a stimulation of adipose tissue turnover.     

Antioxidant activity of conjugated linoleic acid isomers, linoleic acid and its methyl ester determined by photoemission and DPPH techniques

The chemiluminescent response of conjugated linoleic acid isomers (CLAs), linoleic acid (LA) and methyl linoleate (LAME) against the prooxidant t-butyl hydroperoxide (tBHP) was analyzed. The c9, t11-CLA and t10, c12-CLA isomers showed significant photoemission at the highest concentration used, while photoemission was not detected at any concentration of LA and LAME analyzed. These results show that CLAs are more susceptible to peroxidation than LA and LAME. Likewise, the effect of CLA, LA and LAME on lipid peroxidation of triglycerides rich in C20:5 omega3 and C22:6 omega3 (Tg omega3-PUFAs) was investigated. For that, chemiluminescence produced by triglycerides in the presence of tBHP, previously incubated with different concentrations of CLAs, LA and LAME (from 1 to 200 mM) was registered for 60 min. Triglycerides in the presence of t-BHP produced a peak of light emission (3151+/-134 RLUs) 5 min after addition. CLAs produced significant inhibition on photoemission, t10, c12-CLA being more effective than the c9, t11-CLA isomer. LA and LAME did not have an effect on lipid peroxidation of Tg omega3-PUFAs. CLA isomers, LA and LAME were also investigated for free radical scavenging properties against the stable radical (DPPH()). Both CLA isomers reacted and quenched DPPH() at all tested levels (from 5 to 25 mM), while LA and LAME did not show radical quenching activity even at the highest concentration tested. These data indicate that CLAs would provide protection against free radicals, but LA and LAME cannot.     

Quantitative gas chromatographic method for the analysis of cis-9, trans-11 and trans-10, cis-12 isomers of the conjugated linoleic acid in liver

A quantitative GC method for conjugated linoleic acid (CLA) isomers of physiological significance (cis-9, trans-11 CLA and trans-10, cis-12 CLA) as non-esterified fatty acids (NEFA) or triacylglycerols (TAG) was developed. Furthermore, the effect of the internal standard addition point (sample or fat extract) was studied. Response linearity, recovery and precision assays, detection and quantification limits were determined. Linearity was demonstrated over a range from 0.1 to 10 microg/mL. When CLA isomers were present as NEFA, the recovery significantly decreased (P< or =0.05) from 76% to 27.1% (cis-9, trans-11 CLA) and 28.5% (trans-10, cis-12 CLA) when the standards were added to the fat extract or to the initial tissue, respectively. As an application, liver samples from hamsters fed a diet supplemented with both CLA isomers were analyzed. The CLA isomers in liver samples were detected with reasonable reproducibility.     

Conjugated linoleic acids promote human fat cell apoptosis.

Conjugated linoleic acids (CLAs) are conjugated dienoic isomers of linoleic acid. Some isomers have been shown to reduce fat mass in animal and cell culture models. However, controversial results were obtained in studies of supplementation of CLAs in human subjects. In order to get more insights into the direct effects of CLAs on human fat cells, we have studied the influence of cis-9, trans-11 CLA and trans-10, cis-12 CLA on the biology of human SGBS preadipocytes and adipocytes. Both CLA isomers equally inhibited the proliferation of preadipocytes in a dose-dependent manner. Continuous treatment with 1-10 microM trans-10, cis-12 CLA, and to a weaker extent cis-9, trans-11 CLA, inhibited accumulation of lipids during adipogenic differentiation. Treatment with higher doses of CLA induced apoptosis in preadipocytes, in differentiating cells, and adipocytes. The trans-10, cis-12 isomer had a higher apoptotic potency in adipocytes than cis-9, trans-11 CLA. Taken together, the treatment of human preadipocytes and adipocytes with physiological relevant concentrations of CLAs resulted in an impairment of proliferation and differentiation and induction of apoptosis. The trans-10, cis-12 isomer was more potent than the cis-9, trans-11 isomer. Further clinical studies are needed to evaluate the effects of CLAs on human fat mass and metabolism in vivo.     

Dietary conjugated linoleic acid has limited effects on tissue protein anabolism in sedentary and exercising adult rats

The effects of conjugated linoleic acid isomers (CLA) and endurance training on lean body mass are expected to result from their action on tissue protein metabolism. The aim of this study was to analyze their effects on protein metabolism in 2 muscles, the small intestine and liver of adult rats. Four-month-old male Wistar rats were fed diets containing either no CLA, cis-9, trans-11 CLA isomer (1 g.100 g(-1)), trans-10, cis-12 CLA isomer (1 g.100 g(-1)) or both isomers (1 g.100 g(-1) each) for 6 weeks. Half of the rats were subjected to endurance training by running on a treadmill. At the end of this period, the rats were injected with a flooding dose of (13)C-valine to determine protein synthesis rates in the post-absorptive (experiment 1) and in the post-prandial (experiment 2) states. No effect of CLA or endurance training were detected in the small intestine. Training reduced food intake and protein synthesis rates in the liver but no effect was found on the protein synthesis rates in muscles. In the post-absorptive state, protein synthesis rate was increased by feeding the trans-10, cis-12 CLA isomer alone in the liver (+9%) or in combination with the cis-9, trans-11 isomer in the gastrocnemius (+30%), mostly in sedentary rats. In the post-prandial state, the cis-9, trans-11 CLA isomer tended to reduce the protein synthesis rate in the gastrocnemius muscle. However, no effect of CLA was found on muscle protein amounts. In conclusion, CLA isomers would have limited but differential effects on tissue protein metabolism in adult rats.