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.     

Dietary Intake of c9,t11-Conjugated Linoleic Acid Correlates with Its Concentration in Plasma Lipid Fractions of Men but Not Women

The c9,t11-18:2 isomer of conjugated linoleic acid (c9,t11-CLA) represents the main dietary CLA form with putative health benefits. Whereas CLA intake influences the tissue CLA concentration, little is known about the association between dietary CLA and the CLA content of plasma lipid fractions. This study was designed to document fasting and nonfasting plasma c9,t11-CLA concentrations in a population of free-living adults (n = 94) and relate these concentrations to c9,t11-CLA intake. We also determined the c9,t11-CLA content of the primary plasma lipid fractions in a subset (n = 50) of our participants, related these to c9,t11-CLA intake, and determined whether c9,t11-CLA intake or plasma c9,t11-CLA was correlated with plasma cholesterol. Mean fasting plasma c9,t11-CLA concentrations were 0.46 ± 0.01 and 0.54 ± 0.01% (wt:wt) of total fatty acids for men and women, respectively (P < 0.05); nonfasting concentrations were 0.28 ± 0.01 and 0.38 ± 0.01% of total fatty acids, respectively (P < 0.001). All major esterified plasma lipid fractions contained c9,t11-CLA; TG had the highest percentages. In men, c9,t11-CLA intake correlated (r = 0.47; P < 0.05) with TG c9,t11-CLA content, suggesting that TG c9,t11-CLA may serve as a biomarker for c9,t11-CLA intake. In females, there were no correlations between c9,t11-CLA intake and the c9,t11-CLA content of any esterified plasma lipid fraction. In neither sex was there a relation between dietary c9,t11-CLA or plasma c9,t11-CLA concentration and circulating lipoprotein cholesterol concentration. The influence of sex on circulating c9,t11-CLA content and further validation of biomarkers of c9,t11-CLA intake warrant further investigation.     

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.     

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.     

共轭亚油酸对肿瘤细胞亚油酸代谢途径中限速酶的影响

目的采用体外细胞培养方法,研究不同浓度c9,t11-共轭亚油酸(c9,t11-CLA)对人胃腺癌细胞(SGC-7901)中亚油酸代谢途径的限速酶的影响。方法用200、100、50和25μmol／L浓度的c9,t11-CLA处理SGC-7901细胞24h,四甲基偶氮唑盐实验检测c9,t11-CLA对SGC-7901细胞增殖的抑制作用,采用逆转录聚合酶链反应检测c9,t11-CLA对SGC-7901细胞中亚油酸代谢途径的Δ6-脱氢酶、△5-脱氢酶、环氧合酶(COX)-1、COX-2和5-脂氧合酶(5-LOX)mRNA表达的影响。结果在200、100、50和25μmol／L浓度时,c9,t11-CLA对SGC-7901增殖的抑制率分别为54．3％、20．5％、10．5％、2．93％;均可下调COX-2mRNA的表达,上调Δ6-脱氢酶、COX-1mRNA的表达,但对Δ5-脱氢酶和5-LOXmRNA表达的影响不显著。结论c9,t11-CLA可通过调节Δ6-脱氢酶和COX的表达抑制肿瘤细胞的增殖,说明c9,t11-CLA通过影响亚油酸代谢途径中限速酶的基因表达而改变类二十碳烷酸的形成,推测c9,t11-CLA影响肿瘤细胞中亚油酸代谢途径的限速酶是其发挥抗癌活性的另一作用机制。     

环氧合酶-2在c9,t11-共轭亚油酸抑制胃腺癌细胞增殖中的作用

目的　采用体外细胞培养方法,研究不同浓度c9,t11 共轭亚油酸对人胃腺癌细胞(SGC- 790 1)的亚油酸代谢途径中限速酶———环氧合酶(COX -2 )及其产物前列腺素E2 (PGE2 )的影响。方法　采用逆转录聚合酶链反应(RT- PCR)和Westernblot方法检测不同浓度c9,t11 CLA处理后的SGC 790 1细胞中COX- 2mRNA和蛋白的表达,放射免疫方法检测细胞分泌的PGE2 浓度。结果　在2 5、5 0、10 0和2 0 0 μmol L浓度时,c9,t11 CLA均可下调COX 2mRNA和蛋白的表达,同时降低细胞中PGE2 的分泌。结论　环氧合酶2是c9,t11 CLA抑制肿瘤细胞增殖的作用靶点。     

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.     

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.     

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.     

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.     

环氧合酶-2在c9,t11-共轭亚油酸抑制肿瘤细胞转移中的作用

目的 研究c9,t11-共轭亚油酸（c9,t11-CLA）抑制人胃腺癌细胞（SGC-7901）转移作用与亚油酸代谢途径中限速酶环氧合酶-2（COX-2）的关系。方法采用体外细胞培养方法,用COX-2的选择性抑制剂NS．398抑制SGC-7901细胞中COX-2的活性,再加入200、100、50和25μmol／L浓度的c9,t11-CLA,利用重组基底膜侵袭实验、黏附实验、趋向运动实验检测c9,t11-CLA抑制肿瘤细胞转移的作用与COX-2的关系。结果与NS-398组比较,NS-398＋100Ixmol／Lc9,t11-CLA和NS-398＋200μmol／L c9,t11-CLA对SGC-7901细胞的侵袭有明显的抑制作用,穿过膜的细胞数分别为48．7±1．5（F=14．309,P=0．000）和43．7±4．0（F=19．005,P=0．000）;NS-398＋200μmol／L c9,t11-CLA组能显著降低SGC-7901细胞对基质成分层粘连蛋白、纤维粘连蛋白和基质胶的黏附作用,所测吸光度值（A值）分别为0．052±0．011,0．058±0．008（F=3．063,P=0．021）和0．042±0．004（F=6．692,P=0．001;F=11．999,P=0．000）;NS-398＋200ixmol／L c9,t11-CLA对SGC-7901细胞的趋向运动能力无明显的抑制作用（F=1．380,P=0．276）,其中NS-398＋2001xmol／L c9,t11-CLA组细胞数为26．6±3．4。结论 c9,t11-CLA具有抑制SGC-7901细胞体外侵袭能力、黏附能力和趋向运动能力,这种抑制作用可能与COX-2途径有关。     

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.     

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.     

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。