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

Body compositional changes and growth alteration in chicks from hens fed conjugated linoleic acid

Effects of feeding conjugated linoleic acid (CLA) to hens on progeny chick development and composition at hatch (NHC) and three weeks of age (TWC) were assessed. CLA (0 or 0.5%, composed of mixed isomers of cis-9,trans-11 or trans-10,cis-12-CLA) was fed to hens with either safflower (SO) or olive oil (OO) (3 or 3.5%) to assure successful hatch for 2 weeks prior to collection for incubation. Maternal CLA feeding had no effect on hatchability, but improved egg fertility (p < 0.05). Maternal feeding of CLA with SO increased 21 day-old progeny growth, while CLA with OO decreased growth (oil*CLA, p < 0.05). In 25 day-old chicks (TWC), but not NHC, maternal CLA decreased the proportion of total body water (p < 0.05) and increased body ash (p < 0.05). While monounsaturated fatty acids were decreased and saturated fatty acids increased in eggs and NHC from hens fed CLA, no differences in fatty acid composition were observed in chicks at 25 days of age from hens fed CLA. Maternal CLA feeding resulted in the presence of c9,t11 and t10,c12-CLA in NHC, but only c9,t11 in the TWC. In conclusion, hens fed CLA led to improved fertility and altered body composition at 3 weeks of age.

Dietary supplementation with conjugated linoleic acid plus n-3 polyunsaturated fatty acid increases food intake and brown adipose tissue in rats

The effect of supplementation with 1% conjugated linoleic acid and 1% n-3 long chain polyunsaturated fatty acids (CLA/n-3) was assessed in rats. Food intake increased with no difference in body weights. White adipose tissue weights were reduced whereas brown adipose tissue and uncoupling protein-1 expression were increased. Plasma adiponectin, triglyceride and cholesterol levels were reduced while leptin, ghrelin and liver weight and lipid content were unchanged. Hypothalamic gene expression measurements revealed increased expression of orexigenic and decreased expression of anorexigenic signals. Thus, CLA/n-3 increases food intake without affecting body weight potentially through increasing BAT size and up-regulating UCP-1 in rats.

Dietary fat concentration influences the effects of trans-10, cis-12 conjugated linoleic acid on temporal patterns of energy intake and hypothalamic expression of appetite-controlling genes in mice

This study tested the hypothesis that the effect of trans-10, cis-12 conjugated linoleic acid (t10, c12 CLA) on energy intake (EI) and body weight (BW)/composition is confounded by dietary fat concentration and involves hypothalamic appetite-controlling mechanisms. ICR mice received low-fat (LF; 5 g/100 g) or high-fat (HF; 30 g/100 g) diets, with or without 0.5 g/100 g t10, c12 CLA (>98% pure) for 27 d. By d 13, BW and cumulative EI of the mice fed CLA supplemented LF diet (LF/CLA) were 6.6 and 23.6% lower, respectively, than the LF mice. In the subsequent 14 d, their EI rebounded and did not differ from the LF group. BW and EI did not differ between the HF and CLA supplemented HF (HF/CLA) groups. Hypothalamic pro-opiomelanocortin (POMC) mRNA expression was elevated (P = 0.031) on d 13 but suppressed (P < 0.001) on d 27 due to CLA treatment. CLA also suppressed AMP-activated protein kinase alpha2 expression. Mice in Expt. 2 received the LF diet, the LF/CLA, or were pair-fed the LF diet to the EI of the CLA group (LF/PF). LF/CLA and LF/PF mice did not differ in the hypothalamic POMC:neuropeptide Y expression ratio on d 13, but it was significantly lower in the LF/PF group on d 27. We conclude that the habitual dietary fat concentration influences the magnitude of weight loss induced by dietary t10, c12 CLA. The effect is in part independent of EI. Hypothalamic neuropeptides and nutrient sensing mechanisms may play a role.

Effects of dietary conjugated linoleic acid at high-fat levels on triacylglycerol regulation in mice

OBJECTIVE

Our aim was to investigate the effects of dietary conjugated linoleic acid (CLA) at high-fat (HF) levels on parameters related to triacylglycerol (TG) regulation and some potential impacts on liver damage.

METHODS

Growing mice were fed a control diet (7% corn oil), an HF diet containing 20% corn oil, or an HF diet containing 3% CLA (HF + CLA) for 30 d. Tissue and organ weights, plasma and tissue TG levels, and parameters related to their regulation were evaluated. Liver oxidative status was also assessed.

RESULTS

Dietary CLA showed detrimental and beneficial effects. CLA added to the HF diet caused hepatomegaly (+32%) and exacerbated the hepatic TG accumulation (+168%) observed with the HF diet without inducing liver damage; however, it significantly reduced plasma TG concentrations (-37%) and normalized muscular TG content. An increase in glutathione was associated with total normalization of liver lipid peroxidation. In addition, HF + CLA caused dystrophy of epididymal fat pads, even when the HF diet had increased the adipose tissue mass (30%). The biochemical mechanisms involved in the regulation of lipid levels were related to reduced (-20%) hepatic very low-density lipoprotein-TG secretion and decreased muscle (-35%) and adipose (-49%) tissue contributions to the removal of plasma TG by lipoprotein lipase enzymes.

CONCLUSION

Examination of CLA at HF levels showed hepatomegaly and exacerbation of lipid accretion as a negative impact; however, some positive aspects such as hypotriglyceridemia and protection against oxidative stress were also induced. Even the fat reduction is nutritionally important for weight control; the biochemical mechanisms whereby CLA mediates the potential effects could produce undesirable metabolic alterations.

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.

Conjugated linoleic acid-induced fat loss dependence on Delta6-desaturase or cyclooxygenase

OBJECTIVE

To determine whether conjugated linoleic acid (CLA)-induced body fat loss is dependent upon metabolism of CLA by Delta6-desaturase, cyclooxygenase, or lipoxygenase.

METHODS AND PROCEDURES

Mice were fed diets with or without CLA and inhibitors to either Delta6-desaturase (SC-26196), cyclooxygenase (aspirin), or lipoxygenase (nordihydroguaiaretic acid (NDGA)) for 2 weeks. Body fat percent, lean mass, fat pad weights, liver weight, and fatty acid concentrations were determined. A Delta6-desaturase index was calculated, and adipose tissue prostaglandin E(2) (PGE(2)) and leukotriene B(4) (LTB(4)) concentrations were determined to confirm enzyme inhibition.

RESULTS

Inhibition of Delta6-desaturase and cyclooxygenase were confirmed. CLA caused a loss of body fat (P < 0.001). The body fat loss was blocked (P = 0.08) by the Delta6-desaturase inhibitor at a dose that decreased (P < 0.05) the calculated index. Aspirin and NDGA had no effect on body fat and did not interact with CLA.

DISCUSSION

Inhibition of Delta6-desaturase prevented CLA from being able to cause a body fat loss. Therefore, a desaturated metabolite of CLA appears to be involved in the CLA antiobesity effect. This effect of CLA does not seem dependent upon cyclooxygenase. Because lipoxygenase activity was not blocked by NDGA, we cannot draw conclusions about its importance in mediating the antiobesity effect of CLA.

Dietary combination of conjugated linoleic acid (CLA) and pine nut oil prevents CLA-induced fatty liver in mice

Conjugated linoleic acid (CLA) strongly prevents fat accumulation in adipose tissue of mice, even if hepatic fat deposition and insulin resistance are concomitantly observed. This study investigated the possibility of maintaining the antiadiposity properties of CLA while preventing adverse effects such as liver steatosis and hyperinsulinemia. To this end, mice were divided into three groups and fed a standard diet (control) or a diet supplemented with 1% CLA (CLA) or a mixture of 1% CLA plus 7.5% pine nut oil (CLA + P). The combination of CLA + P preserved the CLA-mediated antiadiposity properties (70% fat reduction), preventing hepatic steatosis and a sharp increase in plasmatic insulin starting from the eighth week of CLA treatment. The assay of both fatty acid synthesis and oxidation in the CLA + P mice revealed a time-dependent biphasic behavior of the corresponding enzymatic activities. A sudden change in these metabolic events was indeed found at the eighth week. A strong correlation between the changes in key enzymes of lipid metabolism and in insulin levels apparently exists in CLA-fed mice. Furthermore, lower levels of lipids, in comparison to values found in CLA-fed mice, were observed in the liver and plasma of CLA + P-fed animals.

Adiposity and serum parameters in hamsters fed energy restricted diets supplemented or not with trans-10,cis-12 conjugated linoleic acid

Numerous studies have demonstrated that conjugated linoleic acid (CLA) modulates body composition, reducing body fat accumulation in various mammalian species. However, very few studies have been carried out to assess the effect of CLA on previously stored body fat. The aim of the present work was to analyse the effectiveness of trans-10,cis-12 CLA in improving alterations produced by high-fat feeding in body fat and serum parameters when it was included in an energy-restricted diet. For this purpose male Syrian Golden hamsters were fed on high-fat diet for 7 weeks in order to increase their body fat content, and a further 25% energy-restricted diet supplemented or not with 0.5% trans-10,cis-12 CLA for 3 weeks. Adipose tissues, liver and gastrocnemious muscles were dissected and weighed. Adipocyte diameter and number were assessed in epididymal adipose tissue. Total cholesterol, triacylglycerols, non-esterified fatty acids and glucose were measured in serum. Three weeks of energy restriction resulted in a reduction in body weight and white adipose tissue size in all anatomical locations, without changes in liver and gastrocnemious muscle weights. Epididymal adipocyte size was reduced, but total adipocyte number remained unchanged. Serum cholesterol, triacylglycerols and glucose were significantly reduced. No differences were observed between the restricted groups (control and CLA supplemented). In conclusion, under our experimental conditions, the addition of trans-10,cis-12 CLA to the diet does not increase the benefits produced by energy restriction.

Conjugated linoleic acid-mediated inflammation and insulin resistance in human adipocytes are attenuated by resveratrol

Inflammation plays a role in trans-10, cis-12 (10,12)-conjugated linoleic acid (CLA)-mediated delipidation and insulin resistance in adipocytes. Given the anti-inflammatory role of resveratrol (RSV), we hypothesized that RSV would attenuate inflammation and insulin resistance caused by 10,12 CLA in human adipocytes. RSV blocked 10,12 CLA induction of the inflammatory response by preventing activation of extracellular signal-related kinase and induction of inflammatory gene expression (i.e., IL-6, IL-8, IL-1beta) within 12 h. Similarly, RSV suppressed 10,12 CLA-mediated activation of the inflammatory prostaglandin pathway involving phospholipase A(2), cyclooxygenase-2, and PGF(2alpha). In addition, RSV attenuated 10,12 CLA increase of intracellular calcium and reactive oxygen species associated with cellular stress, and activation of stress-related proteins (i.e., activating transcription factor 3, JNK) within 12 h. 10,12 CLA-mediated insulin resistance and suppression of fatty acid uptake and triglyceride content were attenuated by RSV. Finally, 10,12 CLA-mediated decrease of peroxisome proliferator-activated receptor gamma (PPARgamma) protein levels and activation of a peroxisome proliferator response element (PPRE) reporter were prevented by RSV. RSV increased the basal activity of PPRE, suggesting that RSV increases PPARgamma activity. Collectively, these data demonstrate for the first time that RSV prevents 10,12 CLA-mediated insulin resistance and delipidation in human adipocytes by attenuating inflammation and cellular stress and increasing PPARgamma activity.

Anti-obesity effects of conjugated linoleic acid, docosahexaenoic acid, and eicosapentaenoic acid

Obesity has become a prevailing epidemic throughout the globe. Effective therapies for obesity become attracting. Food components with beneficial effects on "weight loss" have caught increasing attentions. Conjugated linoleic acid (CLA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) belong to different families of polyunsaturated fatty acids (PUFA). However, they have similar effects on alleviating obesity and/or preventing from obesity. They influence the balance between energy intake and expenditure; and reduce body weight and/or fat deposition in animal models, but show little effect in healthy human subjects. They inhibit key enzymes responsible for lipid synthesis, such as fatty acid synthase and stearoyl-CoA desaturase-1, enhance lipid oxidation and thermogenesis, and prevent free fatty acids from entering adipocytes for lipogenesis. PUFA also exert suppressive effects on several key factors involved in adipocyte differentiation and fat storage. Despite their similar effects and shared mechanisms, they display differences in the regulation of lipid metabolism. Moreover, DHA and EPA exhibit "anti-obesity" effect as well as improving insulin sensitivity, while CLA induces insulin resistance and fatty liver in most cases. A deeper and more detailed investigation into the complex network of anti-obesity regulatory pathways by different PUFA will improve our understanding of the mechanisms of body weight control and reduce the prevalence of obesity.

Biopsied and vitrified bovine embryos viability is improved by trans10, cis12 conjugated linoleic acid supplementation during in vitro embryo culture

Bovine embryos cultured in serum-containing media abnormally accumulate lipids in the cytoplasm. This is well known to contribute to their higher susceptibility to cryopreservation and biopsied embryos are even further susceptible. We aimed to improve in vitro produced (IVP) embryos resistance to micromanipulation and cryopreservation by supplementing serum-containing media with trans-10, cis-12 conjugated linoleic acid (t10, c12 CLA). The effect of t10, c12 CLA on lipid deposition and embryonic development was also tested. After in vitro maturation and fertilization (IVF day=D0), zygotes were cultured on granulosa cells+M199+10% serum+100microM GSH supplemented with 100microM of t10, c12 CLA (CLA group, n=1394) or without supplementation (control group, n=1431). Samples of D7/D8 embryos were observed under Nomarsky microscopy for lipid droplets evaluation while others were biopsied and vitrified (group B-Control, n=24; group B-CLA, n=23). Non-biopsied embryos were also frozen (group NB-Control, n=49; group NB-CLA, n=45). Biopsied cells were used for embryo sex determination. Postwarming embryo survival and viability were determined at 0 and 24h of culture, respectively. Supplementation of t10, c12 CLA did not influence cleavage, embryo sex ratio, D7/D8 embryo rate or morphological quality. CLA embryos had higher number of small lipid droplets (P<or=0.003) and a smaller (P<0.001) fat embryo index being leaner (P=0.008) than control embryos. Embryo postwarming survival was higher in B-CLA than in B-control group (95.0+/-7.0% versus 62.5+/-7.9%; P<0.001). After 24h of culture, the viability (expansion rate) of biopsied embryos and nonbiopsied embryos, cultured with t10, c12 CLA was higher than control embryos (B-CLA=64.6+/-4.4% and B-control=27.5+/-2.5%, P=0.01; NB-CLA=86.0+/-3.5% and NB-Control=68.6+/-7.0%, P=0.05). Results showed that supplying t10, c12 CLA to serum-containing media decreases embryo cytoplasmic lipid deposition during in vitro culture and significantly improves resistance of IVP embryos to micromanipulation and cryopreservation.

Fish oil increases the duodenal flow of long chain polyunsaturated fatty acids and trans-11 18:1 and decreases 18:0 in steers via changes in the rumen bacterial community

Ruminant fat is rich in SFA, partly due to the biohydrogenation of dietary PUFA to SFA in the rumen. This process can be inhibited by the dietary inclusion of fish oil. The only bacteria isolated from the rumen capable of converting PUFA to SFA are closely related to Clostridium proteoclasticum. The aim of this study was to investigate if a correlation could be found in vivo between dietary fish oil inclusions and the composition of the ruminal bacterial community and specifically of C. proteoclasticum. Six Hereford x Friesian steers, prepared with ruminal and duodenal cannulae, received grass silage plus 1 of 3 concentrates resulting in total dietary fish oil contents of 0, 1, or 3% of dry matter. A dual flow marker technique was employed to estimate the relative flow of fatty acids. Steers fed the 3% fish oil diet had 100% increases in trans 18:1 flow, whereas 18:0 flow declined to 39% of steers fed the control diet. 16S ribosomal RNA-based denaturing gradient gel electrophoresis profiles obtained from ruminal digesta showed major changes in the bacterial community within steers fed the 3% fish oil diet. Quantitative PCR indicated only a weak relation between numbers of C. proteoclasticum and 18:0 flow between treatments and in individual steers (P < 0.05, but the percentage variance accounted for only 22.8) and did not provide unambiguous evidence that numbers of C. proteoclasticum in the rumen dictate the ratios of SFA:PUFA available for absorption by the animal. Understanding which microbes biohydrogenate PUFA in the rumen is key to developing novel strategies to improve the quality of ruminant products.

Antiobesity effect of trans-10,cis-12-conjugated linoleic acid-producing Lactobacillus plantarum PL62 on diet-induced obese mice

AIMS

To observe the antiobesity activity of trans-10,cis-12-conjugated linoleic acid (CLA)-producing lactobacillus in mice.

METHODS AND RESULTS

Lactobacillus plantarum PL62, which can grow in the presence of linoleic acid, was selected and studied. The culture supernatant of Lact. plantarum PL62 contained trans-10,cis-12-conjugated linoleic acid (6.4 microg ml(-1)), and the crude enzyme prepared from washed cells produced trans-10,cis-12 CLA (1395 microg mg(-1) protein). Lact. plantarum PL62 reduced the weights of epididymal, inguinal, mesenteric, and perirenal white adipose tissues and significantly reduced the blood levels of total glucose and body weights of mice (P<0.01).

CONCLUSIONS

trans-10,cis-12-CLA-producing Lact. plantarum PL62 can exert the same antiobesity activity as trans-10,cis-12-CLA in mice.

SIGNIFICANCE AND IMPACT OF THE STUDY

trans-10,cis-12-CLA-producing Lactobacillus can be a replacement for CLA for obesity treatment via the continuous production of trans-10,cis-12-CLA. The results provide a novel opportunity to develop foods with antiobesity activity.

Os efeitos do ácido linoléico conjugado no metabolismo animal: avanço das pesquisas e perspectivas para o futuro

Realizou-se uma revisão sistemática, sem restrição de data, sobre os efeitos fisiológicos do ácido linoléico conjugado sobre a regressão da carcinogênese, o estresse oxidativo, o metabolismo de lípides e glicose e a alteração da composição corporal. Objetivando estabelecer o aspecto histórico do avanço da pesquisa em ácido linoléico conjugado, consideraram-se artigos originais resultantes de trabalhos realizados com animais, com cultura de células e com humanos. Quanto às pesquisas sobre o efeito anticarcinogênico do ácido linoléico conjugado foram encontradas inúmeras evidências a esse respeito, especialmente na regressão dos tumores mamários e de cólon, induzida por ambos os isômeros os quais agem de maneiras distintas. Os pesquisadores se empenham em reinvestigar as propriedades antioxidantes do ácido linoléico conjugado. Embora tenham sido investigadas as propriedades antioxidantes, tem-se identificado efeito pró-oxidante, levando ao estresse oxidativo em humanos. Foram poucos os estudos que demonstraram efeito positivo significativo do ácido linoléico conjugado sobre o metabolismo dos lípides e da glicose e sobre a redução da gordura corporal, especialmente em humanos. Estudos sobre efeitos adversos foram também identificados. Há fortes indícios de que a ação deste ácido graxo conjugado sobre uma classe de fatores de transcrição - os receptores ativados por proliferadores de peroxissomo - e sobre a conseqüente modulação da expressão gênica, possa ser a explicação fundamental dos efeitos fisiológicos. Embora incipientes, os mais recentes estudos reforçam o conceito da nutrigenômica, ou seja, a modulação da expressão gênica induzida por compostos presentes na alimentação humana. O cenário atual estimula a comunidade científica a buscar um consenso sobre os efeitos do ácido linoléico conjugado em humanos, já que este está presente naturalmente em alguns alimentos, que, quando consumidos em quantidades adequadas e de forma freqüente, poderiam atuar como coadjuvantes na prevenção e no controle de inúmeras doenças crônicas.

Ácido linoléico conjugado e perfil de ácidos graxos no músculo e na capa de gordura de novilhos bubalinos alimentados com diferentes fontes de lipídios

Avaliaram-se o teor de ácido linoléico conjugado (CLA) e o perfil de ácidos graxos no músculo e na capa de gordura de novilhos bubalinos alimentados com diferentes fontes de lipídios. Utilizaram-se 12 animais castrados, da raça Murrah, com peso vivo de 306±8kg, submetidos aos tratamentos sem lipídeo adicional, grão de soja e óleo de soja, confinados durante 84 dias. Após o abate a carcaça foi resfriada a 5ºC, durante 24 horas. Foi feita secção entre a nona e a 11ª costelas da meia carcaça direita, de onde se separou músculo e capa de gordura, analisadas as concentrações de CLA e de ácidos graxos, por cromatografia gasosa. O fornecimento de óleo de soja resultou em maior concentração de CLA no músculo e na capa de gordura, e a adição de óleo de soja menores concentrações de ácidos graxos saturados, principalmente os ácidos mirístico e palmítico. Os animais que receberam a dieta com grão de soja integral também apresentaram menor teor de CLA e redução nas concentrações de mirístico e palmítico. Esses efeitos foram observados somente na capa de gordura e em menor intensidade.

Regulation of fat synthesis by conjugated linoleic acid: lactation and the ruminant model

Conjugated linoleic acid (CLA) isomers effect an impressive range of biological processes including the ability to inhibit milk fatty acid synthesis. Although this has been demonstrated in several mammals, research has been most extensive with dairy cows. The first isomer shown to affect milk fat synthesis during lactation was trans-10, cis-12 CLA, and its effects have been well characterized including dose-response relationships. Recent studies have tentatively identified 2 additional CLA isomers that regulate milk fat synthesis. Regulation by CLA occurs naturally in dairy cows when specific CLA isomers produced as intermediates in rumen biohydrogenation act to inhibit milk fat synthesis; this physiological example of nutritional genomics is referred to as diet-induced milk fat depression. Molecular mechanisms for the reduction in mammary lipid synthesis involve a coordinated down-regulation of mRNA expression for key lipogenic enzymes associated with the complementary pathways of milk fat synthesis. Results provide strong evidence of a role for sterol response element-binding protein 1 and Spot 14 in this translational regulation. Effects of CLA on body fat accretion have also been investigated in nonlactating animals, but CLA effects on mammary fatty acid synthesis occur at an order-of-magnitude lower dose and appear to involve very different mechanisms than those proposed for the antiobesity effects of CLA. Overall, results demonstrate the unique value of cows as a model to investigate the role of CLA in the regulation of milk fat synthesis during lactation.

Isomer-specific regulation of differentiating pig preadipocytes by conjugated linoleic acids

Conjugated linoleic acids are a group of geometric and positional isomers of linoleic acid that decrease body fat in growing animals by a poorly understood mechanism. The objective of this study was to investigate the isomer-specific effect of CLA on the proliferation and differentiation of pig preadipocytes in primary culture. The effect of CLA on preadipocyte proliferation was determined using cleavage of the tetrazolium salt, WST-1, as a marker for proliferation. Preadipocyte number was decreased in a dose-dependent fashion by trans-12,cis-10 CLA (P < 0.05). No other fatty acid affected preadipocyte number. Differentiation was monitored on d 10 after induction morphologically, enzymatically, and by measuring the mRNA abundance of key adipogenic transcription factors. Both a crude CLA preparation containing a mixture of CLA isomers (CLA-mix) and the pure trans-10,cis-12 CLA isomer inhibited glycerol-3-phosphate dehydrogenase (GPDH) activity in a dose-dependent fashion, with trans-10,cis-12 CLA being more potent (P < 0.01) than the CLA-mix. Cis-9,trans-11 CLA failed to decrease GPDH activity; however, increasing concentrations of cis-9,trans-11 CLA tended to blunt the inhibitory effect of trans-10,cis-12 CLA on GPDH activity (P < 0.09), suggesting that cis-9,trans-11 CLA may antagonize the action of trans-10,cis-12 CLA in porcine adipocytes. Finally, the isomer-specific effect of CLA on adipogenic transcription factor gene expression was investigated. Trans-10,cis-12 CLA decreased expression of peroxisome proliferator-activated receptor gamma (PPAR gamma; P < 0.01) and sterol regulatory element-binding protein-1c (SREBP-1c; P < 0.05) mRNA, while failing to alter the expression of CCAAT/enhancer binding protein alpha (C/EBPalpha) mRNA. Interestingly, both the CLA-mix and the trans-10,cis-12 CLA isomer increased the mRNA abundance of chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF; P < 0.002). No other fatty acid affected COUP-TF mRNA levels. Collectively these data support the concept that CLA decreases fat accretion in pigs, in part by inhibiting preadipocyte proliferation and differentiation, with trans-10,cis-12 CLA being an active isomer eliciting these effects. Furthermore, trans-10,cis-12 CLA inhibits porcine preadipocyte differentiation by a mechanism that involves the down-regulation of PPARgamma and SREBP-1c mRNA. This mechanism is independent of changes in C/EBPalpha mRNA abundance and may involve COUP-TF.

Conjugated linoleic acid fails to worsen insulin resistance but induces hepatic steatosis in the presence of leptin in ob/ob mice

Conjugated linoleic acid (CLA) induces insulin resistance preceded by rapid depletion of the adipokines leptin and adiponectin, increased inflammation, and hepatic steatosis in mice. To determine the role of leptin in CLA-mediated insulin resistance and hepatic steatosis, recombinant leptin was coadministered with dietary CLA in ob/ob mice to control leptin levels and to, in effect, negate the leptin depletion effect of CLA. In a 2 x 2 factorial design, 6 week old male ob/ob mice were fed either a control diet or a diet supplemented with CLA and received daily intraperitoneal injections of either leptin or vehicle for 4 weeks. In the absence of leptin, CLA significantly depleted adiponectin and induced insulin resistance, but it did not increase hepatic triglyceride concentrations or adipose inflammation, marked by interleukin-6 and tumor necrosis factor-alpha mRNA expression. Insulin resistance, however, was accompanied by increased macrophage infiltration (F4/80 mRNA) in adipose tissue. In the presence of leptin, CLA depleted adiponectin but did not induce insulin resistance or macrophage infiltration. Despite this, CLA induced hepatic steatosis. In summary, CLA worsened insulin resistance without evidence of inflammation or hepatic steatosis in mice after 4 weeks. In the presence of leptin, CLA failed to worsen insulin resistance but induced hepatic steatosis in ob/ob mice.

Lipolysis is stimulated by PEGylated conjugated linoleic acid through the cyclic adenosine monophosphate-independent signaling pathway in 3T3-L1 cells: activation of MEK/ERK MAPK signaling pathway and hyper-secretion of adipo-cytokines

We previously reported that PEGylated conjugated linoleic acid (PCLA) as a pro-drug treatment of cultures of 3T3-L1 cells containing differentiated adipocytes caused de-differentiation by downregulation of PPARgamma2-induced adipogenesis, and cell apoptosis induced by PCLA was lower than that induced by conjugated linoleic acid (CLA) owing to the biocompatible and hydrophilic properties of poly(ethylene glycol) (PEG). To further investigate our previous observations, the present study is designed to evaluate the lipolytic action of PCLA and its role in biochemical signaling pathways of 3T3-L1 cells when compared to the CLA itself. Although both CLA and PCLA stimulated lipolysis, our results indicated a sensitivity difference between CLA and PCLA treatment: a time-dependent effect on lipolysis and p-extracellular signal-related kinases (ERK) expression was observed for PCLA-treated, but not for CLA-treated cultures. Also, the induction by PCLA of mitogen-activated protein kinase kinase (MEK)/ERK mitogen-activated protein kinase (MAPK) activation was linked to secretion of adipo-cytokines, interleukin-6 (IL-6), and interleukin-8 (IL-8), in time-dependent manners. Interestingly, adenylyl cyclase inhibitor, 2', 5'-dideoxyadenosine (DDA), pre-treatment did not prevent PCLA-stimulated lipolysis. In fact, isoproterenol, but not PCLA, caused a significant increase in cyclic adenosine monophosphate (cAMP) levels, suggesting that the PCLA-induced lipolysis was not mediated in the conventional cAMP-dependent pathway and the cAMP was the intracellular mediator for isoproterenol-induced lipolysis. Overall, our findings provide support for a role for PCLA as a pro-drug in the regulation of metabolism in adipose tissue.

The trans-10, cis-12 isomer of conjugated linoleic acid decreases adiponectin assembly by PPARgamma-dependent and PPARgamma-independent mechanisms

The adipocyte-derived secretory protein adiponectin functions as an insulin-sensitizing agent. In plasma, adiponectin exists as low, medium, and high molecular weight oligomers. Treatment with trans-10, cis-12 conjugated linoleic acid (t-10, c-12 CLA) reduces levels of adiponectin as well as triglyceride (TG) in mice and adipocyte cell culture models. The aim of this study was to determine whether the effects of t-10, c-12 CLA on adiponectin and TG are mediated through modulation of the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma). 3T3-L1 cells were treated either during or after differentiation into adipocytes with 100 microM t-10, c-12 CLA with or without 10 microM troglitazone, a PPARgamma agonist, or 1 microM GW9662, a PPARgamma antagonist, and adiponectin and TG levels were analyzed. Treatment with t-10, c-12 CLA reduced TG as well as cellular and secreted adiponectin levels and impaired the assembly of adiponectin oligomers. These changes were accompanied by decreases in PPARgamma mass. Troglitazone was able to reverse the t-10, c-12 CLA-mediated decrease in TG levels and restore the assembly of adiponectin oligomers but was unable to restore adiponectin synthesis. Conversely, treatment with GW9662 decreased TG mass and impaired adiponectin oligomer assembly but did not decrease total adiponectin mass. In a reporter assay, t-10, c-12 CLA appeared to be a partial PPARgamma agonist and prevented the stimulation of reporter activity by troglitazone. Therefore, the t-10, c-12 CLA isomer appears to alter adipocyte adiponectin metabolism through PPARgamma-dependent and PPARgamma-independent mechanisms.

Conjugated linoleic acid alters global gene expression in human intestinal-like Caco-2 cells in an isomer-specific manner

Conjugated linoleic acid (CLA) exhibits isomer-specific effects on transepithelial calcium (Ca) transport as well as on cell growth in human intestinal-like Caco-2 cells. However, the molecular mechanisms of action are still unclear. Therefore, this study used a transcriptomic approach to help elucidate the molecular mechanisms underlying such isomer-specific effects. Caco-2 cells were treated with 80 micromol/L linoleic acid (control), 80 micromol/L trans-10, cis-12 CLA, or 80 micromol/L cis-9, trans-11 CLA for 12 d. Ca transport was measured radio-isotopically. RNA was isolated from the cells, labeled, and hybridized to the Affymetrix U133 2.0 Plus arrays (n = 3). Data and functional analysis was preformed using Bioconductor. Using a minimum fold-change criterion of 1.6 and a false discovery rate criterion of P-value <or= 0.05, trans-10, cis-12 CLA altered the expression of 918 genes, whereas, cis-9, trans-11 CLA had no effect on gene expression. Gene ontology analysis revealed that trans-10, cis-12 CLA strongly modulated a number of processes inherently related to carcinogenesis, such as cell cycle, cell proliferation, and DNA metabolism. Trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, increased transepithelial Ca transport in Caco-2 cells, which corresponded to changes in molecular mediators of paracellular (including claudin 2 and 4) and transcellular (calbindin D(9)k and vitamin D receptor) Ca transport. This microarray-based study highlighted a number of gene expression patterns of relevance to 2 important intestinal processes (carcinogenesis and Ca transport), which were modulated by trans-10, cis-12 CLA. These may help our mechanistic understanding of the role of CLA in promoting gut function and health.

Conjugated linoleic acid (CLA) and obesity

Background

The term conjugated linoleic acid (CLA) refers to several positional and geometric conjugated dienoic isomers of linoleic acid (LA), of which the trans-10,cis-12 isomer has been reported to reduce adiposity and increase lean mass in mice and other animals when included at ≤1% of the diet. However, most dietary CLA in humans is obtained from dairy products, accounting for the cis-9,trans-11 CLA isomer, also known as rumenic acid, for more than 90% of the total CLA intake. Commercial CLA preparations industrially produced, containing trans-10,cis-12 and cis-9,trans-11 CLA isomers in diverse proportions, are attracting consumers’ interest because of the purported body fat-lowering effects of CLA, coupled to the perception of a ‘natural’ compound devoid of harmful effects. Nevertheless, despite numerous studies on CLA effects on body composition for nearly a decade, the mechanisms by which CLA isomers elicit their effects remain largely unknown. The purpose of this paper is to provide an updated review of the studies performed on animals and humans, as well as to describe the potential mechanisms involved in CLA effects on body weight and composition and metabolism.

Method

Literature review.

Results

Experiments in humans have not been able to show a significant effect on body weight, body composition or weight regain related to either of the CLA isomers. In fact, some studies suggest a tendency towards a decrease in body fat mass and an increase in body lean mass, while some others raise concern about the possibility of deleterious effects of trans-10,cis-12 CLA on lipid profile, glucose metabolism and insulin sensitivity.

Conclusions

Evidence regarding effectiveness of CLA in humans is not concluding.

Conjugated linoleic acid supplementation alters the 6-mo change in fat oxidation during sleep

BACKGROUND

Conjugated linoleic acid (CLA) is a family of positional and geometric isomers with 2 conjugated double bonds formed from linoleic acid and linolenic acid. CLA has a wide range of biological effects, including body fat reduction.

OBJECTIVE

The aim of our study was to determine CLA's effects on energy expenditure, macronutrient utilization, and dietary fat oxidation in overweight adults after 6 mo of supplementation.

DESIGN

We recruited 23 subjects from our main CLA efficacy study who were receiving either 4 g/d of 78% active CLA isomers (3.2 g/d: 39.2% cis-9,trans-11 and 38.5% trans-10,cis-12) or 4 g/d of safflower oil. Energy expenditure and substrate utilization were measured before and after 6 mo of CLA supplementation by using whole-room indirect calorimetry. Dietary fat oxidation was measured by using stable isotope-labeled oleate and palmitate.

RESULTS

Our substudy detected a difference in the change in fat utilization between the CLA (4 +/- 8 g) and placebo (-7 +/- 11 g) groups during sleep after 6 mo of supplementation. In addition, the percentage of energy from protein was reduced during sleep in the CLA group (CLA: -3.3 +/- 2.6%; placebo: 0.3 +/- 5.7%). We also detected a difference in the change in energy expenditure during sleep (CLA: 0 +/- 38 kcal; placebo: -43 +/- 90 kcal). We did not detect a change in labeled dietary fat oxidation after 6 mo of CLA supplementation given with a breakfast meal.

CONCLUSION

Mixed isomer CLA supplementation, but not placebo, positively altered fat oxidation and energy expenditure during sleep.

Conjugated linoleic acid increases skeletal muscle ceramide content and decreases insulin sensitivity in overweight, non-diabetic humans

The effect of conjugated linoleic acid (CLA), a popular weight-loss supplement, on insulin sensitivity in humans is controversial and has not been extensively studied. To date no studies have examined the effects of CLA supplementation on human skeletal muscle metabolism or lipid content. It is also unknown whether CLA accumulates in human skeletal muscle with supplementation. In the present study, 9 overweight, non-diabetic individuals received 4 g/d of mixed CLA isomers in the form of 1 g supplements, for 12 weeks. CLA isomers significantly increased in both plasma and skeletal muscle following supplementation. Skeletal muscle ceramide content was also significantly increased, although there was no consistent change in muscle diacylglycerol or triacylglycerol content. Insulin sensitivity was significantly decreased (p<or=0.05) following CLA supplementation, with a significant increase in glucose and insulin area under the curve during an oral glucose tolerance test (p<or=0.005). The protein content of PPARalpha, for which CLA is a potent ligand, was unchanged following supplementation. Accordingly, there was no change in markers of muscle oxidative capacity. In conclusion, mixed-isomer CLA supplementation in overweight non-diabetic humans results in the accumulation of CLA and ceramide in skeletal muscle, and decreases insulin sensitivity.

The Effects of Simultaneous Administration of Dietary Conjugated Linoleic Acid and Telmisartan on Cardiovascular Risks in Rats

Dietary conjugated linoleic acid (CLA) and the antihypertensive drug, telmisartan, have both been shown to modify cardiovascular risks. The effects of a combination of these two agents have, however, not been investigated. This 20 week study sought to assess the therapeutic potential of a CLA/telmisartan co-administration in rats fed a high-fructose high-fat diet. Thirty-three male Sprague-Dawley rats were randomly assigned to five experimental groups, including control, losartan, telmisartan, CLA, and CLA + telmisartan-treated animals. Body weight, blood pressure, and blood levels of lipids, glucose, insulin, and inflammatory markers were measured. Co-administration of CLA and telmisartan resulted in significant (P < 0.05) reductions in body weight, visceral fat, serum total cholesterol, triglycerides, glucose, plasma insulin concentrations, and systolic blood pressure compared with those in the control group. Moreover, plasma levels of IL1-alpha and IFN-gamma were reduced and levels of IL1-beta, IL-4, IL-6, and IL-10, plus TNF-alpha were increased in the co-therapy group, compared with controls. In conclusion, this study suggests that a combination of CLA with telmisartan may modify several risk factors of cardiovascular disease commonly seen in metabolic syndrome. This combination of nutraceuticals and pharmaceuticals may be a safe and cost-effective strategy in a number of high-risk subjects. Future studies will further document clinical benefits of such combination therapy.

CLA differently regulates adipogenesis in stromal vascular cells from porcine subcutaneous adipose and skeletal muscle

Conjugated linoleic acid (CLA), a mixture of isomers of linoleic acid, has previously been shown to be able to decrease porcine subcutaneous (SC) adipose tissue levels while increasing the count of intramuscular (IM) adipose tissue in vivo. However, the underlying mechanisms through which it acts are poorly understood. The objective of this study was to investigate the different effects of CLA on adipogenesis in cultured SC adipose tissue and IM stromal vascular cells obtained from neonatal pigs. As shown here, trans-10, cis-12 CLA decreased the expression of adipocyte-specific genes as well as adipose precursor cell numbers and the accumulation of lipid in cultured SC adipose tissue stromal vascular cells. However, the cis-9, trans-11 CLA did not alter adipogenesis in SC cultures. On the other hand, both CLA isomers increased the expression of adipocyte-specific genes in IM cultures, together with the increasing accumulation of lipid and Oil Red O-stained cells. Collectively, these data show that CLA decreases SC adipose tissue but increases IM adipose tissue by different regulation of adipocyte-specific gene expression. These results suggest that adipogenesis in IM adipocytes differs from that in SC adipocytes.

Supplementation with commercial mixtures of conjugated linoleic acid in association with vitamin E and the process of lipid autoxidation in rats

CLA has been studied for its beneficial effects on health. However, the possibility of adverse effects, such as increased oxidative stress, must also be considered. The present work aims to assess the effect of CLA supplementation on the process of lipid autoxidation, both in the presence and in absence of an antioxidant. The investigation consisted in a biological assay with 60 rats divided into six groups: C (control), CE (control + vitamin E), AE (AdvantEdgeCLA), AEE (AdvantEdgeCLA + Vitamin E), CO (CLA One) and COE (CLA One)+ vitamin E). The CLA amount was 2% of feed consumption. Animals were supplemented for 42 days. As indicators of lipid autoxidation, peroxide (IP), malondialdehyde (MDA), 8-iso-PGF2(alpha) isoprostane and catalase were determined. Hepatic IP results indicated that CLA increased oxidation: values for CLA-supplemented groups, particularly group CO (84.38 +/- 10.97 mequiv/kg), were higher than those of the control group (54.75 +/- 9.70 mequiv/kg). In contrast, serum MDA results showed that CLA reduces oxidation both for group AE (1.8 +/- 0.67 mg of MDA/l) and for group CO (2.43 +/- 0.61 mg of MDA/l) as compared to the control group (3.85 +/- 0.24 mg of MDA/l). Serum catalase indicated a reduction of oxidation: groups AE and CO displayed 4734.23 +/- 1078.93 kU/l and 5916.06 +/- 2490.71 kU/l, respectively. These values are significantly lower than those of the control group. An increase in 8-iso-PGF2(alpha) in urine was observed, particularly in group AE (95.13 +/- 20.26 pg/ml) as compared to the control group (69.46 +/- 16.65 pg/ml). It was concluded that the influence of CLA on lipid autoxidation is dependent on supplement type, supplement dosage and chosen indicator, including its tissue and determination methodology.

Effects of milk supplementation with conjugated linoleic acid (isomers cis-9, trans-11 and trans-10, cis-12) on body composition and metabolic syndrome components

The effects of conjugated linoleic acid (CLA) on body weight and body composition in man are controversial. The aim of this study was to investigate the effects of milk supplementation with CLA on body composition and on the biochemical parameters of the metabolic syndrome. This was a randomised, double-blind, placebo-controlled trial. Subjects were randomised to a daily intake of 500 ml milk supplemented with 3 g CLA (using a mixture of the bioactive isomers cis-9, trans-11 and trans-10, cis-12, marketed as Tonalin, Naturlinea; Central Lechera Asturiana) or placebo for 12 weeks. Sixty healthy men and women (aged 35-65 years) with signs of the metabolic syndrome participated (BMI 25-35 kg/m2). Dual-energy X-ray absorptiometry was used to measure body composition (week 0 baseline and week 12). Total fat mass in the CLA-milk subgroup with a BMI < or = 30 kg/m2 decreased significantly while no changes were detected in the placebo group (approximately 2 %, P = 0.01). Trunk fat mass showed a trend towards reduction (approximately 3 %, P = 0.05). CLA supplementation had no significant effect on the parameters of the metabolic syndrome, nor was it associated with changes in haematological parameters or renal function. The supplementation of milk with 3 g CLA over 12 weeks results in a significant reduction of fat mass in overweight but not in obese subjects. CLA supplementation was not associated with any adverse effects or biological changes.

Effect of conjugated linoleic acid on bone formation and rheumatoid arthritis

Conjugated linoleic acid (CLA) has shown a variety of biologically beneficial effects. Dietary CLA inhibits eddosteal bone resorption, increases endocortical bone formation, and modulates the action and expression of cyclooxygenase (COX) enzyme, thereby decreasing prostaglandin-dependent bone resorption. CLA also enhances calcium absorption and may improve bone formation in animals, although results are not consistent. Since CLA can also affect inflammatory cytokines, it is hypothesized that CLA may be a good tool for prevention or reduction of rheumatoid arthritis symptoms. The possible mechanisms by which CLA prevents rheumatoid arthritis as well as other inflammatory diseases is discussed.

Daily intake of conjugated linoleic acid-enriched yoghurts: effects on energy metabolism and adipose tissue gene expression in healthy subjects

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid. The present study was designed to determine whether 14-week CLA supplementation as triacylglycerols (3.76 g) with a 50 : 50 combination of the two main isomers (35 % cis-9, trans-11 and 35 % trans-10, cis-12) added to flavoured yoghurt-like products was able to alter body composition in healthy subjects and to alter the expression of several key adipose tissue genes (PPAR gamma, lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and uncoupling protein 2 (UCP-2)). Forty-four healthy subjects were randomly assigned to consume daily either a CLA-supplemented yoghurt-like product or a placebo yoghurt for 98 d. There were no significant effects of CLA supplementation on body weight, fat mass or free fat mass. Basal energy expenditure expressed as kg free fat mass increased significantly in the CLA group (123.3 (SEM 2.5) kJ/kg free fat mass per d on day 98 v. 118.7 (SEM 2.3) kJ/kg free fat mass per d on day 0, P = 0.03). PPAR gamma mRNA gene expression increased significantly with CLA supplementation (53 (SEM 20) %, P < 0.01) and a significant reduction in mRNA levels of HSL was observed ( - 42 (SEM 7) %, P = 0.01). The levels of UCP-2 and LPL mRNA were not affected. The present results suggest that a 98 d supplementation diet with a 50 : 50 mixture of the two CLA isomers cis-9, trans-11 and trans-10, cis-12 in a dairy product was unable to alter body composition, although a significant increase in the RMR has been induced. Moreover, changes in mRNA PPAR gamma and HSL in adipose tissue were recorded.

Conjugated linoleic acid reduces adipose depots without reduction of stearoyl coenzyme A desaturase 1 gene expression

AIMS AND METHODS

This study investigated the effects of conjugated linoleic acid (CLA) on the body weight, fat deposition and the expression of stearoyl coenzyme A desaturase 1 (SCD1) in the livers of male ICR mice that were fed with either beef tallow (BT) or fish oil (FO) supplemented with CLA. Mice weighing 25-30 g were divided into four groups, BT and BT supplemented with 0.5% CLA (BTC), FO and FO supplemented with 0.5% CLA (FOC). Each group consisted of 8 mice, and they were fed the experimental diets for 4 weeks. The experimental diets were composed of 59.18% carbohydrates, 19.73% proteins and 21.09% fat in terms of their contributions to total calories, and other nutrients were identical. CLA was added to the diets of the CLA supplementation groups at 0.5% (w/w). The measurement of triglyceride (TG) was done by using a kit. Fatty acid compositions were analyzed in both the plasma and the liver using a gas chromatograph. The levels of SCD1 expression were analyzed by RT-PCR in the liver.

RESULTS

No significant difference was found in the levels of food intake, body weight and food efficiency among experimental groups. However, the levels of both epididymal and visceral fat weight were significantly lower in the CLA-supplemented groups, BTC and FOC (p < 0.05). The level of the triglyceride concentration was also significantly lower in the CLA-supplemented groups (p < 0.05). The levels of the liver SCD1 gene expression were also higher in the CLA-supplemented groups. However, significant inhibition of conversion from C16:0 to C16:1 was found in both fatty acid compositions of the liver (p < 0.05).

CONCLUSION

Addition of 0.5% CLA did not inhibit the liver SCD1 gene expression; however, it showed decreasing effects on the fat pad weight, the concentration of TG and on fatty acid composition, leading to a decrease in the fat depositions. Such effects were clearer when CLA was supplemented to BT rather than FO.

Intracerebroventricular administration of conjugated linoleic acid (CLA) inhibits food intake by decreasing gene expression of NPY and AgRP

Dietary conjugated linoleic acid (CLA) has been investigated for its beneficial effects on disease prevention and treatment, and now obesity is one of the most perspective researching highlights. In a variety of experimental models, the results of studies on the effects of CLA on food intakes are somewhat inconsistent. Our experiment was conducted to extend these observations to hypothalamus and other regions within the central nervous system so that the mechanism of the actions of CLA might be more easily elucidated. In the experiment, a permanent cannula was inserted into the lateral ventricle of each rat. For the experiment, animals received intracerebroventricular injections of either 150nmol (n=16) CLA, or LA as non-conjugated control, or normal saline as vehicle. Hypothalamus and blood samples were collected at the 2nd, 4th, 8th, and 14th day. The results show that CLA in cerebral ventricle can inhibit food intake of experimented rats and this inhibition is related with the decreased expression of neuropeptides Y (NPY) and agouti-related protein (AgRP). The circulating leptin level was also increased by this tentative treatment (2.94+/-0.71 versus 1.18+/-0.18ng/ml). However, the glucose metabolism was not affected by ICV CLA. It is concluded that CLA in brain can inhibit the appetite of rats through the mechanism of decreasing the expression of NPY and AgRP.