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.     

Chronic but not acute treatment with conjugated linoleic acid (CLA) isomers (trans-10, cis-12 CLA and cis-9, trans-11 CLA) affects lipid metabolism in Caco-2 cells

Conjugated linoleic acid (CLA) has profound effects on hepatic and adipocyte lipid metabolism, but little is known about its effects on intestinal lipid metabolism. We investigated the acute (22 h) and acute-after-chronic (22 h after 19 d) effects of trans-10, cis-12 CLA (t10,c12-CLA) and cis-9, trans-11 CLA (c9, t11-CLA) on triacylglycerol (TAG)-rich lipoprotein (TRL) metabolism, de novo TAG, phospholipid (PL) ((14)C-glycerol) and apolipoprotein B (apoB) ((35)S-methionine) synthesis and secretion, in the colon carcinoma (Caco-2) cell model of intestinal lipoprotein metabolism. Acute treatment with either CLA isomer did not affect TRL metabolism. However, chronic t10,c12-CLA and c9,t11-CLA supplementation followed by acute palmitic acid (PA) treatment increased the ratio of cellular to secreted de novo TAG (cTAG/sTAG) (P < or = 0.03) as a result of increased cellular de novo TAG levels. Chronic Caco-2 cell t10,c12-CLA supplementation, prior to the acute oleic acid (OA) treatment, significantly increased (P = 0.005) the ratio of cellular de novo TAG to de novo PL (cTAG/cPL), to a greater extent than that following chronic linoleic acid (LA) (P = 0.001) or c9,t11-CLA supplementation (P = 0.005). Again, this effect was attributed to increased cellular de novo TAG synthesis. Neither CLA isomer affected the ratio of secreted de novo TAG to de novo PL (sTAG/sPL). No effects on Caco-2 cell apoB synthesis and secretion were observed after acute or chronic CLA treatments. In conclusion, chronic t10,c12-CLA supplementation modulated intestinal TRL metabolism, by increasing cellular de novo TAG synthesis but had no effect on de novo TAG secretion in Caco-2 cells.     

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

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

trans-11 18:1 Vaccenic Acid (TVA) Has a Direct Anti-Carcinogenic Effect on MCF-7 Human Mammary Adenocarcinoma Cells

Trans vaccenic acid (TVA; trans-11 18:1) is a positional and geometric isomer of oleic acid and it is the predominant trans isomer found in ruminant fats. TVA can be converted into cis-9, trans-11 conjugated linoleic acid (c9, t11-CLA), a CLA isomer that has many beneficial effects, by stearoyl CoA desaturase 1 (SCD1) in the mammary gland. The health benefits associated with CLA are well documented, but it is unclear whether trans fatty acids (TFAs) from ruminant products have healthy effects. Therefore, the effects of TVA on the proliferation of MCF-7 human breast adenocarcinoma cells and MCF-10A human breast epithelial cells were investigated in the present study. Results showed that TVA inhibited the proliferation of MCF-7 cells but not MCF-10A cells by down-regulating the expression of Bcl-2 as well as procaspase-9. In addition, the suppressive effect of TVA was confirmed in SCD1-depleted MCF-7 cells. Our results suggested that TVA exerts a direct anti-carcinogenic effect on MCF-7 cells. These findings provided a better understanding of the research on the anti-carcinogenic effects of TVA and this may facilitate the manufacture of TVA/c9, t11-CLA fortified ruminant products.     

Antiproliferative effects of conjugated linoleic acid on human colon adenocarcinoma cell line Caco-2

Conjugated linoleic acid (CLA) reduces body fat reserves, and reduces atherogenesis and type II diabetes in animal experiments. It has been reported that CLA have isomeric-specificity, such as c9, t11 CLA with anticancer activity. The antiproliferative effects of two isomers of CLA (c9, t11-CLA, t9, t11-CLA) and their mixture on the human colon adenocarcinoma cell line Caco-2 were investigated in this paper. Caco-2 were incubated in serum-free medium. The antiproliferative effects of different concentrations (0, 25, 50, 100, 200 micromol/L) of linoleic acid (LA), c9, t11-CLA, t9, t11-CLA (the purity of LA and CLA was 96%) and a mixture of c9, t11-CLA and t9, t11- CLA (1:1 v/v) on caco-2 in various action time (1d, 2d, 3d, 4d) were tested in the present study. The antiproliferative effects of four substances in the same concentration and with the same action time were compared. All substances tested could inhibit Caco-2 cell proliferation. The higher anti-proliferation activity in the four materials is the mixture of CLA, then is t9,t11-CLA, c9,t11-CLA, and linoleic acid respectively. The activity is closely related to treatment time and concentration. The isomer t9, t11-CLA itself was found to have antiproliferative activity.     

Acute-on-chronic effects of fatty acids on intestinal triacylglycerol-rich lipoprotein metabolism

Postprandial triacylglycerol (TAG) metabolism is an important metabolic state that has been associated with cardiovascular disease. The magnitude of the postprandial TAG response is determined by dietary fat composition, which alters intestinal and hepatic TAG-rich lipoprotein (TRL) metabolism. Caco-2 cell monolayers are morphologically and physiologically similar to the human intestinal enterocytes, hence they are a good model to study intestinal lipoprotein metabolism. To date only the acute effect of fatty acid composition on intestinal TRL metabolism in Caco-2 cells has been investigated. Little is known of the effect of habitual, or chronic, dietary fat composition on intestinal TRL metabolism. Using the Caco-2 cell model, the present study investigated the acute-on-chronic effect of fatty acid composition on TRL metabolism. Caco-2 cells were grown in the presence of 0.05 mm-palmitic acid (PA; 16 : 0), -oleic acid (OA; 18 : 1n-9),-eicosapentaenoic acid (EPA; 20 : 5n-3) or no fatty acid (control) for 19 d, then one of four acute treatments (control (bovine serum albumin (BSA; 5 g/l)) or BSA (5 g/l) plus 0.5 mm-PA, -OA or -EPA) were administered for 22 h. Significant acutexchronic interactions for the effect of fatty acid composition on cellular TAG:secreted de novo TAG, and cellular de novo TAG:de novo phospholipid were observed. Thus the effect of a fatty acid was determined by the duration of exposure to the fatty acid intervention. Acute PA treatment increased de novo TAG synthesis, but chronic PA supplementation did not. Acute and chronic OA treatments increased de novo TAG secretion. For EPA, chronic supplementation had the greatest effect on TAG synthesis and secretion. The acute-on-chronic effects of fatty acids on apolipoprotein B metabolism were relatively minor compared with the changes noted for TRL lipid composition. The present study shows that the Caco-2 cell model is valuable for studying intestinal TRL metabolism and that fatty acids modulate this process, the nature of which can be determined by the length of exposure of the cell to the fatty acid.     

Conjugated linoleic acid isomers and trans fatty acids inhibit fatty acid transport in hepatoma 7288CTC and inguinal fat pads in Buffalo rats

Conjugated linoleic acid (CLA) and some trans fatty acids (FA) decrease tumor growth and alter tumor and host lipid uptake and storage. The goal of this study was to test the hypothesis that the acute inhibitory effects of CLA isomers and trans FAs on FA transport in tumors and white adipose tissue are mediated via an inhibitory G-protein coupled (GPC), FFA receptor (FFAR). Experiments were performed in hepatoma 7288CTC and inguinal fat pads in Buffalo rats during perfusion in situ. CLA isomers and trans FAs (0.03-0.4 mmol/L, in plasma) were added to the arterial blood, and FA uptake or release was measured by arterial minus venous difference. In hepatoma 7288CTC, the CLA isomers, t10,c12-CLA > (+/-)-9-HODE [13-(S)-hydroxyoctadecadienoic acid] > t9,t11-CLA, and the trans FAs, linolelaidic = vaccenic > elaidic, decreased cAMP content and inhibited FA uptake, 13(S)-HODE release, extracellular signal-regulated kinase p44/p42 phosphorylation, and [(3)H]thymidine incorporation. Other CLA isomers, c9,t11-CLA, 13-(S)-HODE, c9,c11-CLA, and c11,t13-CLA, had no effect. In inguinal fat pads, FA transport was inhibited by t10,c12-CLA = linolelaidic acid > trans vaccenic acid, whereas c9,t11-CLA had no effect. In both hepatoma 7288CTC and inguinal fat pad, addition of either pertussis toxin or 8-Br-cAMP to the arterial blood reversed the inhibitions of FA transport. These results support the idea that an inhibitory GPC FFAR reduces cAMP and controls FA transport by CLA isomers and trans FAs. Ligand activity is conferred by the presence of a trans double bond proximal to the carboxyl group.     

Effect of dietary conjugated linoleic acid isomers on lipid metabolism in hamsters fed high-carbohydrate and high-fat diets

Dietary conjugated linoleic acids (CLA) have been reported to have a number of isomer-dependent effects on lipid metabolism including reduction in adipose tissue deposition, changes in plasma lipoprotein concentrations and hepatic lipid accumulation. The aim of this study was to compare the effect of individual CLA isomers against lipogenic and high 'Western' fat background diets. Golden Syrian hamsters were fed a high-carbohydrate rodent chow or chow supplemented with 17.25 % fat formulated to represent the type and amount of fatty acids found in a typical 'Western' diet (including 0.2 % cholesterol). Diets were further supplemented with 0.25 % (w/w) rapeseed oil, cis9, trans11 (c9,t11)-CLA or trans10, cis12 (t10,c12)-CLA. Neither isomer had a significant impact on plasma lipid or lipoprotein concentrations. The t10,c12-CLA isomer significantly reduced perirenal adipose tissue depot mass. While adipose tissue acetyl CoA carboxylase and fatty acid synthase mRNA concentrations (as measured by quantitative PCR) were unaffected by CLA, lipoprotein lipase mRNA was specifically reduced by t10,c12-CLA, on both background diets (P < 0.001). This was associated with a specific reduction of sterol regulatory element binding protein 1c expression in perirenal adipose tissue (P = 0.018). The isomers appear to have divergent effects on liver TAG content with c9,t11-CLA producing lower concentrations than t10,c12-CLA. We conclude that t10,c12-CLA modestly reduces adipose tissue deposition in the Golden Syrian hamster independently of background diet and this may possibly result from reduced uptake of lipoprotein fatty acids, as a consequence of reduced lipoprotein lipase gene expression.     

The conjugated linoleic acid (CLA) isomer,t10c12-CLA,is inversely associated with changes in body weight and serum leptin in subjects with type 2 diabetes mellitus

Isomers of conjugated linoleic acid (CLA) are found in beef, lamb and dairy products. Diets containing CLA reduce adipose mass in various depots of experimental animals. In addition, CLA delays the onset of diabetes in the ZDF rat model for obesity-linked type 2 diabetes mellitus. We hypothesize that there would be an inverse association of CLA with body weight and serum leptin in subjects with type 2 diabetes mellitus. In this double-blind study, subjects with type 2 diabetes mellitus were randomized into one of two groups receiving either a supplement containing mixed CLA isomers (CLA-mix; 8.0 g daily, 76% pure CLA; n = 12) or a supplement containing safflower oil (placebo; 8.0 g daily safflower oil, n = 9) for 8 wk. The isomers of CLA in the CLA-mix supplement were primarily c9t11-CLA ( approximately 37%) and t10c12-CLA ( approximately 39%) in free fatty acid form. Plasma levels of CLA were inversely associated with body weight (P < 0.05) and serum leptin levels (P < 0.05). When levels of plasma t10c12-CLA isomer were correlated with changes in body weight or serum leptin, t10c12-CLA, but not c9t11-CLA, was inversely associated with body weights (P < 0.05) and serum leptin (P < 0.02). These findings strongly suggest that the t10c12-CLA isomer may be the bioactive isomer of CLA to influence the body weight changes observed in subjects with type 2 diabetes. Future studies are needed to determine a causal relationship, if any, of t10c12-CLA or c9t11-CLA to modulate body weight and composition in subjects with type 2 diabetes. Furthermore, determining the ability of CLA isomers to influence glucose and lipid metabolism as well as markers of insulin sensitivity is imperative to understanding the role of CLA to aid in the management of type 2 diabetes and other related conditions of insulin resistance.     

t10,c12-共轭亚油酸对骨骼肌细胞脂肪酸代谢的影响

目的通过研究t10,c12-共轭亚油酸(t10,c12-CLA)对高游离脂肪酸环境中骨骼肌细胞脂肪酸代谢的影响,探讨t10,c12-CLA改善脂代谢的作用机制。方法体外培养成熟的C2C12骨骼肌细胞,通过施加软脂酸在体外模拟高游离脂肪酸环境,再给予不同浓度的t10,c12-CLA(20、30和40μmol/L),通过荧光免疫法利用激光共聚焦显微镜观察t10,c12-CLA对细胞脂肪酸转运蛋白(FAT/CD36)的影响,应用Western blot法检测t10,c12-CLA对C2C12细胞脂肪酸代谢相关酶及AMP激活的蛋白激酶(AMPK)的作用。结果t10,c12-CLA剂量依赖性的增加了高游离脂肪酸环境中细胞对脂肪酸的摄取,抑制了乙酰辅酶A羧化酶(ACC)的活性,增加了肉碱酰基转移酶-1(CPT-1)的表达,并且激活了AMPK。结论t10,c12-CLA可通过激活AMPK增强细胞对脂肪酸的氧化代谢。     

Conjugated linoleic acid isomers and cancer

We reviewed the literature regarding the effects of conjugated linoleic acid (CLA) preparations enriched in specific isomers, cis9, trans11-CLA (c9, t11-CLA) or trans10, cis12-CLA (t10, c12-CLA), on tumorigenesis in vivo and growth of tumor cell lines in vitro. We also examined the potential mechanisms by which CLA isomers may alter the incidence of cancer. We found no published reports that examined the effects of purified CLA isomers on human cancer in vivo. Incidence of rat mammary tumors induced by methylnitrosourea was decreased by c9, t11-CLA in all studies and by t10, c12-CLA in just a few that included it. Those 2 isomers decreased the incidence of forestomach tumors induced by benzo (a) pyrene in mice. Both isomers reduced breast and forestomach tumorigenesis. The c9, t11-CLA isomer did not affect the development of spontaneous tumors of the intestine or mammary gland, whereas t10, c12-CLA increased development of genetically induced mammary and intestinal tumors. In vitro, t10, c12-CLA inhibited the growth of mammary, colon, colorectal, gastric, prostate, and hepatoma cell lines. These 2 CLA isomers may regulate tumor growth through different mechanisms, because they have markedly different effects on lipid metabolism and regulation of oncogenes. In addition, c9, t11-CLA inhibited the cyclooxygenase-2 pathway and t10, c12-CLA inhibited the lipooxygenase pathway. The t10, c12-CLA isomer induced the expression of apoptotic genes, whereas c9, t11-CLA did not increase apoptosis in most of the studies that assessed it. Several minor isomers including t9, t11-CLA; c11, t13-CLA; c9, c11-CLA; and t7, c11-CLA were more effective than c9, t11-CLA or t10, c12-CLA in inhibiting cell growth in vitro. Additional studies with purified isomers are needed to establish the health benefit and risk ratios of each isomer in humans.     

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.     

Conjugated linoleic acid (CLA)-enriched milk fat inhibits growth and modulates CLA-responsive biomarkers in MCF-7 and SW480 human cancer cell lines

Milk enriched in conjugated linoleic acid (CLA) was obtained from cows on pasture supplemented with full-fat rapeseeds (FFR; 2.26 g cis 9, trans 11 (c9,t11)-CLA/100 g fatty acid methyl esters) and full-fat soyabeans (1.83 g c9,t11-CLA100 g fatty acid methyl esters). A control milk fat (1.69 g c9,t11-CLA/100 g fatty acid methyl esters) was obtained from cows fed on pasture only. The present study assessed the potency of the CLA-enriched milk fats to modulate biomarkers that had previously been observed to respond to c9,t11-CLA in the MCF-7 and SW480 cell lines. Cell numbers decreased (P<0.05) by up to 61 and 58% following the incubation of MCF-7 and SW480 cells, respectively, for 4 d with milk fats (yielding CLA concentrations between 60.2 and 80.6 microM). The FFR milk fat, containing the highest CLA content, increased (P<0.05) [14C]arachidonic acid (AA) uptake into the monoacylglycerol fraction of MCF-7 and SW480 cells while it decreased (P<0.05) uptake into the phospholipid fraction of the latter. This milk fat also decreased (P<0.05) [14C]AA conversion to prostaglandin (PG) E2 while increasing conversion to PGF2alpha in both cell lines. All milk-fat samples increased (P<0.05) lipid peroxidation as measured by 8-epi-PGF2alpha in both cell lines. In SW480 cells the milk-fat samples decreased (P<0.05) bcl-2 and cytosolic glutathione levels while increasing (P<0.05) membrane-associated annexin V levels. All milk-fat samples decreased (P<0.05) the expression of ras in SW480 cells. These data suggest that milk-fat CLA was effective at modulating synthetic CLA-responsive biomarkers.     

Dietary conjugated linoleic acids alter adipose tissue and milk lipids of pregnant and lactating sows

Conjugated linoleic acids (CLA) have been shown to affect fatty acid synthesis in various tissues. The objective of the study was to compare the effect of a commercial source of CLA with a linoleic acid-enriched oil (LA), supplied to 12 multiparous sows during gestation and lactation, on adipose tissue and milk fatty acid composition. The CLA isomers detected in the CLA oil were (in order of magnitude) c9,t11; t10,c12; c9,c11; t9,t11/t10,t12 and c10,c12 and amounted to 58.9 g/100 g fat. Biopsies were taken from the backfat on d 7 and 97 of gestation and milk samples were collected on d 2, 9, 16 and 23 after farrowing. Collection of colostrum and mature milk samples took place at 1100 h for sows who farrowed in the morning or at 1500 h for those who farrowed in the afternoon. All major CLA isomers in the supplement were transferred to the tissue and milk fat and, compared with the LA group, significantly increased saturated fatty acid and decreased monounsaturated fatty acid levels in the tissue and milk. These findings suggest a distinct involvement of CLA in the de novo fatty acid synthesis and desaturation process in the adipose tissue and mammary gland. Estimated transfer efficiency of dietary CLA isomers was 41-52% for the backfat and 55-69% for the mature milk. The incorporation and uptake efficiency seemed to be selective with the highest values found for c9,t11-CLA. Overall, dietary CLA supplementation of sows during gestation and lactation markedly altered backfat and milk fatty acid composition.     

Effect of conjugated linoleic acid isomers on insulin resistance and mRNA levels of genes regulating energy metabolism in high-fat-fed rats

OBJECTIVE: We investigated the effects of specific conjugated linoleic acid (CLA) isomers on glucose metabolism and insulin resistance and on mRNA levels of genes important in glucose and lipid metabolism. METHODS: Sprague-Dawley rats were fed for 8 wk on a high-fat diet (45% kcal from fat) or one of three CLA-supplemented diets (1% CLA) containing differing isomers of CLA, including a mixture of CLAs (CLA mix), cis-9, trans-11-CLA (C9,T11-CLA), or trans-10, cis-12-CLA (T10,C12-CLA). RESULTS: Compared with the high-fat group, all the CLA groups had enhanced glucose tolerance. Insulin resistance index was significantly lower in the CLA-treated groups. No significant difference could be observed in the level of serum lipids between groups and in the activities of phosphoenolpyruvate carboxylase, glucose-6-phosphatase, and glucokinase. However, C9,T11-CLA and T10,C12-CLA significantly increased acyl coenzyme A oxidase mRNA in skeletal muscle. In addition, C9,T11-CLA increased hepatic acyl coenzyme A oxidase mRNA and skeletal muscle uncoupling protein-2 mRNA. The CLA mix showed intermediate effects on the levels of these genes. CONCLUSIONS: The addition of all types of CLA to Sprague-Dawley rats fed a high-fat diet can decrease insulin resistance. Possible mechanisms are increased fat oxidation and energy expenditure by increasing acyl coenzyme A oxidase and uncoupling protein-2 mRNA in the liver and/or skeletal muscle.     

Control of rat mammary epithelium proliferation by conjugated linoleic acid.

Past research showed that mammary gland morphogenesis in the pubescent rat was retarded by the feeding of conjugated linoleic acid (CLA). A major objective of the present study was to examine the proliferative activity and the expression of cell cycle regulatory proteins in the developing mammary epithelium of rats fed a mixture of CLA isomers (primarily as free fatty acid c9, t11-CLA and t10,c12-CLA) or a highly enriched natural source of c9,t11-CLA (as triacylglycerol in butterfat). In both experiments, the diets, with or without CLA, were started at weaning and continued for four weeks. The two CLA preparations were equally effective in suppressing bromodeoxyuridine labeling and the expression of cyclin D1 and cyclin A (determined by immunohistochemistry) in the terminal end buds and alveolar clusters of the mammary epithelium while it undergoes extensive ductal branching during pubescence. There was a trend of an increase, although not statistically significant, in the proportion of cells expressing the p16 and p27 cdk inhibitors. A separate experiment was designed to evaluate the effect of c9,t11-CLA (as a free fatty acid of > 90% purity) treatment on the rate of proliferation of the mammary epithelium as the animal matured from weanling to adult. The bromodeoxyuridine labeling data indicated that the mammary epithelium appeared to lose its sensitivity to CLA control of proliferation as it completely filled the fat pad and became quiescent. These observations suggest that the responsiveness of mammary epithelial cells to CLA intervention may be dependent on their proliferative status.     

Effects of three different conjugated linoleic acid preparations on insulin signalling, fat oxidation and mitochondrial function in rats fed a high-fat diet

To investigate the effects of three different conjugated linoleic acid (CLA) preparations containing different ratios of CLA isomers on insulin signalling, fatty acid oxidation and mitochondrial function, Sprague-Dawley rats were fed a high-fat diet either unsupplemented or supplemented with one of three CLA preparations at 1 % of the diet for 8 weeks. The first CLA preparation contained approximately 30 % cis-9, trans-11 (c9, t11)-CLA isomer and 40 % trans-10, cis-12 (t10, c12)-CLA isomer (CLA-mix). The other two preparations were an 80:20 mix (c9, t11-CLA-mix) or a 10:90 mix of two CLA isomers (t10, c12-CLA-mix). Insulin resistance was decreased in all three supplemented groups based on the results of homeostasis model assessment and the revised quantitative insulin-sensitivity check index. The phosphorylation of insulin receptor substrate-1 on serine decreased in the livers of all three supplemented groups, while subsequent Akt phosphorylation increased only in the t10, c12-CLA-mix group. Both the c9, t11-CLA-mix and the t10, c12-CLA-mix increased the expression of hepatic adiponectin receptors R1 and 2, which are thought to enhance insulin sensitivity and fat oxidation. The c9, t11-CLA-mix increased protein and mRNA levels of PPAR alpha, acyl-CoA oxidase and uncoupling protein, which are involved in fatty acid oxidation and energy dissipation. The c9, t11-CLA-mix enhanced mitochondrial function and protection against oxidative stress by increasing the activities of cytochrome c oxidase, manganese-superoxide dismutase, glutathione peroxidase, and glutathione reductase and the level of GSH. In conclusion, all three CLA preparations reduced insulin resistance. Among them, the c9, t11-CLA-mix was the most effective based on the parameters reflecting insulin resistance and fat oxidation, and mitochondrial antioxidative enzyme activity in the liver.     

CLA-enriched diet containing t10,c12-CLA alters bile acid homeostasis and increases the risk of cholelithiasis in mice

Mice fed a mixture of CLA containing t10,c12-CLA lose fat mass and develop hyperinsulinemia and hepatic steatosis due to an accumulation of TG and cholesterol. Because cholesterol is the precursor in bile acid (BA) synthesis, we investigated whether t10,c12-CLA alters BA metabolism. In Expt. 1, female C57Bl/6J mice were fed a standard diet for 28 d supplemented with a CLA mixture (1 g/100 g) or not (controls). In Expt. 2, the feeding period was reduced to 4, 6, and 10 d. In Expt. 3, mice were fed a diet supplemented with linoleic acid, c9,t11-CLA, or t10,c12-CLA (0.4 g/100 g) for 28 d. In Expt. 1, the BA pool size was greater in CLA-fed mice than in controls and the entero-hepatic circulation of BA was altered due to greater BA synthesis and ileal reclamation. This resulted from higher hepatic cholesterol 7α-hydroxylase (CYP7A1) and ileal apical sodium BA transporter expressions in CLA-fed mice. Furthermore, hepatic Na(+)/taurocholate co-transporting polypeptide (NTCP) (-52%) and bile salt export pump (BSEP) (-77%) protein levels were lower in CLA-fed mice than in controls, leading to a greater accumulation of BA in the plasma (+500%); also, the cholesterol saturation index and the concentration of hydrophobic BA in the bile were greater in CLA-fed mice, changes associated with the presence of cholesterol crystals. Expt. 2 suggests that CLA-mediated changes were caused by hyperinsulinemia, which occurred after 6 d of the CLA diet before NTCP and BSEP mRNA downregulation (10 d). Expt. 3 demonstrated that only t10,c12-CLA altered NTCP and BSEP mRNA levels. In conclusion, t10,c12-CLA alters BA homeostasis and increases the risk of cholelithiasis in mice.