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

Dietary supplementation of L-arginine and conjugated linoleic acid reduces retroperitoneal fat mass and increases lean body mass in rats

We hypothesized that l-arginine and conjugated linoleic acid (CLA) would have additive effects in decreasing adiposity. Sprague Dawley rats were assigned to the following dietary groups (n = 6/group; 5 wk total): 1) control (2.55% l-alanine plus 1.5% canola oil); 2) arginine (1.25% l-arginine plus 1.5% canola oil); 3) CLA (2.55% l-alanine plus 1.5% CLA); and 4) arginine plus CLA (1.25% l-arginine plus 1.5% CLA). Supplemental amino acids were provided in drinking water and CLA was incorporated into the food pellets. Daily weight gain, food intake, arginine intake, and final body and eviscerated body weights were greater in rats fed supplemental CLA then in rats fed canola oil. The retroperitoneal adipose tissue:body weight ratio was less in rats fed supplemental CLA than in rats fed canola oil, but epididymal adipose tissue, liver, and soleus and extensor digitorum longus muscle weights were unaffected by arginine or CLA. CLA decreased epididymal adipose tissue concentrations of palmitoleic, oleic, and cis-vaccenic acid. CLA and arginine increased palmitate oxidation to CO(2) in epididymal adipose tissue in vitro relative to control rats. Glucose and palmitate incorporation into total lipids in epididymal adipose tissue was lower in rats fed supplemental arginine than in alanine-fed rats. Arginine increased plasma glycerol relative to alanine-fed rats and CLA and arginine independently decreased most serum essential amino acids and alanine, glutamate, glutamine, and ornithine. We conclude that CLA and arginine modulated adipose tissue metabolism by separate, but not additive, effects. Also, CLA and arginine may have depressed muscle protein turnover.

Board-invited review: the biology and regulation of preadipocytes and adipocytes in meat animals

The quality and value of the carcass in domestic meat animals are reflected in its protein and fat content. Preadipocytes and adipocytes are important in establishing the overall fatness of a carcass, as well as being the main contributors to the marbling component needed for consumer preference of meat products. Although some fat accumulation is essential, any excess fat that is deposited into adipose depots other than the marbling fraction is energetically unfavorable and reduces efficiency of production. Hence, this review is focused on current knowledge about the biology and regulation of the important cells of adipose tissue: preadipocytes and adipocytes.

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.

Trans-10, cis-12 conjugated linoleic acid antagonizes ligand-dependent PPARgamma activity in primary cultures of human adipocytes

We previously demonstrated that trans-10, cis-12 (10,12) conjugated linoleic acid (CLA) causes human adipocyte delipidation, insulin resistance, and inflammation in part by attenuating PPARgamma target gene expression. We hypothesized that CLA antagonizes the activity of PPARgamma in an isomer-specific manner. 10,12 CLA, but not cis-9, trans-11 (9,11) CLA, suppressed ligand-stimulated activation of a peroxisome proliferator response element-luciferase reporter. This decreased activation of PPARgamma by 10,12 CLA was accompanied by an increase in PPARgamma and extracellular signal-related kinase (ERK)1/2 phosphorylation, followed by decreased PPARgamma protein levels. To investigate if 10,12 CLA-mediated delipidation was preventable with a PPARgamma ligand (BRL), cultures were treated for 1 wk with 10,12 CLA or 10,12 CLA + BRL and adipogenic gene and protein expression, glucose uptake, and triglyceride (TG) were measured. BRL cosupplementation completely prevented 10,12 CLA suppression of adipocyte fatty acid-binding protein, lipoprotein lipase, and perilipin mRNA levels without preventing reductions in PPARgamma or insulin-dependent glucose transporter 4 (GLUT4) expression, glucose uptake, or TG. Lastly, we investigated the impact of CLA withdrawal in the absence or presence of BRL for 2 wk. CLA withdrawal did not rescue CLA-mediated reductions in adipogenic gene and protein expression. In contrast, BRL supplementation for 2 wk following CLA withdrawal rescued mRNA levels of PPARgamma target genes. However, the levels of PPARgamma and GLUT4 protein and TG were only partially rescued by BRL. Collectively, we demonstrate for the first time, to our knowledge, that 10,12 CLA antagonizes ligand-dependent PPARgamma activity, possibly via PPARgamma phosphorylation by ERK.

Expression and nutritional regulation of lipogenic genes in the ruminant lactating mammary gland

The effect of nutrition on milk fat yield and composition has largely been investigated in cows and goats, with some differences for fatty acid (FA) composition responses and marked species differences in milk fat yield response. Recently, the characterization of lipogenic genes in ruminant species allowed in vivo studies focused on the effect of nutrition on mammary expression of these genes, in cows (mainly fed milk fat-depressing diets) and goats (fed lipid-supplemented diets). These few studies demonstrated some similarities in the regulation of gene expression between the two species, although the responses were not always in agreement with milk FA secretion responses. A central role for trans-10 C18:1 and trans-10, cis-12 CLA as regulators of milk fat synthesis has been proposed. However, trans-10 C18:1 does not directly control milk fat synthesis in cows, despite the fact that it largely responds to dietary factors, with its concentration being negatively correlated with milk fat yield response in cows and, to a lesser extent, in goats. Milk trans-10, cis-12 CLA is often correlated with milk fat depression in cows but not in goats and, when postruminally infused, acts as an inhibitor of the expression of key lipogenic genes in cows. Recent evidence has also proven the inhibitory effect of the trans-9, cis-11 CLA isomer. The molecular mechanisms by which nutrients regulate lipogenic gene expression have yet to be well identified, but a central role for SREBP-1 has been outlined as mediator of FA effects, whereas the roles of PPARs and STAT5 need to be determined. It is expected that the development of in vitro functional systems for lipid synthesis and secretion will allow future progress toward (1) the identification of the inhibitors and activators of fat synthesis, (2) the knowledge of cellular mechanisms, and (3) the understanding of differences between ruminant species.

Human SGBS cells - a unique tool for studies of human fat cell biology

The human Simpson-Golabi-Behmel syndrome (SGBS) preadipocyte cell strain provides a unique and useful tool for studies of human adipocyte biology. The cells originate from an adipose tissue specimen of a patient with SGBS. They are neither transformed nor immortalized, and provide an almost unlimited source due to their ability to proliferate for up to 50 generations with retained capacity for adipogenic differentiation. So far, the cells have been used for a number of studies on adipose differentiation, adipocyte glucose uptake, lipolysis, apoptosis, regulation of expression of adipokines, and protein translocation. The cells are efficiently differentiated in the presence of PPARgammaagonists and in the absence of serum and albumin. SGBS adipocytes respond to insulin stimulation by increasing glucose uptake several-fold (EC50 approximately 100 pmol/l), and by very effectively inhibiting (IC50 approximately 10 pmol/l) catecholamine-stimulated lipolysis.

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.

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.

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.

Upregulation of tumor necrosis factor-alpha expression by trans10-cis12 conjugated linoleic acid enhances phagocytosis of RAW macrophages via a peroxisome proliferator-activated receptor gamma-dependent pathway

The aim of this study was to examine whether tumor necrosis factor (TNF)-alpha expression in the phagocytic activity of RAW macrophages by trans10-cis12 (10t-12c) conjugated linoleic acid (CLA) is associated with peroxisome proliferator-activated receptor gamma (PPARgamma) activation. 10t-12c CLA induced the TNF-alpha expression in RAW macrophages. Phagocytic activity of naive RAW macrophages was increased either by recombinant mouse (rm) TNF-alpha or by culture supernatant from 10t-12c CLA-treated RAW macrophages. This phagocytic activity was inhibited by addition of anti-rmTNF-alpha polyclonal antibody (pAb). 10t-12c CLA also increased the level of PPARgamma protein and mRNA in RAW macrophages. When naive RAW macrophages were incubated with the culture supernatant from RAW macrophages treated with 10t-12c CLA plus GW 9662, a PPARgamma antagonist, their phagocytic activity was significantly inhibited. In addition, GW 9662 antagonized the effect of 10t-12c CLA in stimulating TNF-alpha expression. These results suggest that 10t-12c CLA modulates the phagocytic activity of RAW macrophages by upregulating TNF-alpha expression via a PPARgamma-dependent pathway.

Six months supplementation with conjugated linoleic acid induces regional-specific fat mass decreases in overweight and obese

Long-term supplementation with conjugated linoleic acid (CLA) reduces body fat mass (BFM) and increases or maintains lean body mass (LBM). However, the regional effect of CLA was not studied. The study aimed to evaluate the effect of CLA per region and safety in healthy, overweight and obese adults. A total of 118 subjects (BMI: 28-32 kg/m2) were included in a double blind, placebo-controlled trial. Subjects were randomised into two groups supplemented with either 3 x 4 g/d CLA or placebo for 6 months. CLA significantly decreased BFM at month 3 (Delta=- 0 x 9 %, P=0 x 016) and at month 6 (Delta=- 3 x 4 %, P=0 x 043) compared with placebo. The reduction in fat mass was located mostly in the legs (Delta=- 0 x 8 kg, P<0 x 001), and in women (Delta=-1 x 3 kg, P=0 x 046) with BMI >30 kg/m2 (Delta=-1 x 9 kg, P=0 x 011), compared with placebo. The waist-hip ratio decreased significantly (P=0 x 043) compared with placebo. LBM increased (Delta=+0 x 5 kg, P=0 x 049) within the CLA group. Bone mineral content was not affected (P=0 x 70). All changes were independent of diet and physical exercise. Safety parameters including blood lipids, inflammatory and diabetogenic markers remained within the normal range. Adverse events did not differ between the groups. It is concluded that supplementation with CLA in healthy, overweight and obese adults decreases BFM in specific regions and is well tolerated.

Conjugated linoleic acid inhibits glucose metabolism, leptin and adiponectin secretion in primary cultured rat adipocytes

Conjugated linoleic acid (CLA) supplementation has been reported to induce insulin resistance in animals and humans, however, the underlying mechanisms remain unclear. The aim of this study was to examine the direct effects of CLA on leptin and adiponectin secretion, two hormones with actions known to influence insulin sensitivity. Isolated rat adipocytes were incubated with CLA (1-200microM) in the absence and presence of insulin (1.6nM). CLA inhibited both basal and insulin-stimulated leptin gene expression and secretion (-30 to -40%, P<0.05-0.01). CLA also inhibited basal adiponectin production (-20 to -40%, P<0.05-0.01), but not in the presence of insulin. CLA (50-200muM) decreased basal glucose uptake (P<0.05-0.01) and significantly increased the proportion of glucose metabolized to lactate (P<0.01). Insulin treatment partially prevented the inhibitory effects of CLA on glucose uptake and induced a significant increase (P<0.05-0.01) in the percentage of glucose metabolized to lactate. A strong inverse relationship was observed between the increase in the anaerobic utilization of glucose and the decreases of both leptin and adiponectin secretion. In addition, lipolysis and the expression of the adipogenic transcription factor PPARgamma were decreased by CLA. These results indicate that CLA inhibits leptin and adiponectin secretion and suggest that increased anaerobic metabolism of glucose may be involved in these effects. The inhibition of PPARgamma could also mediate the inhibition of adiponectin induced by CLA. Furthermore, the inhibition of leptin and adiponectin production induced by CLA may contribute to insulin resistance observed in CLA-treated animals and humans.

Effect of conjugated linoleic acid type, treatment period, and dosage on differentiation of 3T3 cells

This study was conducted to determine effect of CLA and linoleic acid (LA) on cell differentiation, cellular glycerol-3-phosphate dehydrogenase (GPDH) activity, and FA accumulation in differentiating 3T3-L1 cells (3 isomers x 3 treatment periods x 4 doses). The cells were cultured in 24-well plates for proliferation until confluence. Then they were treated with media containing 0, 10, 35, or 70 mg/L (0, 35, 125, or 250 mmol/L, respectively) of LA, cis9,trans11- or trans10,cis12-CLA during early (day 0-2), intermediate and late (day 3-8), or overall (day 0-8) differentiation periods. Dexamethasone, methyl-isobutylxanthine, and insulin were supplemented to the media only for the early period to induce the differentiation. On day 8 of postconfluence the cells were harvested for Oil Red O staining, analysis of GPDH activity, and determination of the FA Concentration. Cellular LA or CLA was found to accumulate in a dose-response manner, mainly during the intermediate/late period. Treatment with trans10,cis12-CLA lowered (P < 0.05) GPDH activity and the concentration of FA including palmitic acid (16:0) and palmitoleic acid (16:1), especially during the intermediate/late and overall periods, or whenever a high dose of 70 mg/L was applied. This also resulted in a higher (P < 0.05) ratio of saturated FA to monounsaturated FA. Treatment with LA or cis9,trans11-CLA lowered cellular FA only when they applied during the early period at a dose of 70 mg/L. The results demonstrated that the inhibitory effects of CLA on differentiation, GPDH activity, and FA accumulation of 3T3-L1 cells are dependent on the isomer type, treatment period, and dose.

Trans-10,cis-12-conjugated linoleic acid increases phagocytosis of porcine peripheral blood polymorphonuclear cellsin vitro

Trans-10,cis-12-conjugated linoleic acid (t10c12-CLA) has been shown to alter immune function. PPARγ has been shown to potentially play an important role in regulating inflammatory and immune responses by modulating the activity of monocytes and macrophages. Previous studies have indicated that the phagocytic capacity of porcine peripheral blood polymorphonuclear cells (PMN) was enhanced by the culture supernatant fraction from t10c12-CLA-stimulated porcine peripheral blood mononuclear cells (PBMC) but not by t10c12-CLA itself. In the present study, we examined the effects of t10c12-CLA on PPARγ and TNF-α expression of porcine PBMC and the phagocytic capacity of PMN. t10c12-CLA increased TNF-α mRNA expression and production by PBMC. The phagocytic capacity of porcine PMN was enhanced by either culture supernatant fraction from PBMC treated with t10c12-CLA or recombinant porcine (rp) TNF-α. Anti-rpTNF-α polyclonal antibody inhibited the enhancement of PMN phagocytic capacity. t10c12-CLA also up regulated PPARγ mRNA expression in porcine PBMC. Bisphenol A diglycidyl ether, a PPARγ antagonist, not only completely negated the t10c12-CLA-stimulating effects on TNF-α expression and production by porcine PBMC, but also decreased the enhancement of PMN phagocytic capacity by the t10c12-CLA-stimulated porcine PBMC culture supernatant fraction. These results suggest that t10c12-CLA has an immunostimulating effect on porcine PMN phagocytic capacity, which is mediated by TNF-α from PBMC via a PPARγ-dependent pathway.

Selective effect of conjugated linoleic acid isomers on atherosclerotic lesion development in apolipoprotein E knockout mice

Research suggests that conjugated linoleic acid (CLA) may inhibit atherosclerosis, but there are contradictory results in different animal models fed heterogeneous mixtures of CLA isomers. This study addressed the hypothesis that the individual CLA isomers may exert different atherogenic properties. ApoE(-/-) mice were fed isocaloric, isonitrogenous westernized diets containing 0.15% cholesterol and enriched with 1% (w/w) cis-9,trans-11-CLA (c9,t11-CLA), trans-10,cis-12-CLA (t10,c12-CLA) or linoleic acid (control diet) for 12 weeks. At the end of the dietary intervention, the effects of CLA isomers on the development of atherosclerotic vascular lesions, lipid metabolism, inflammation and oxidative stress were assessed. The t10,c12-CLA diet had a profound pro-atherogenic effect, whereas c9,t11-CLA impeded the development of atherosclerosis. En face aortic lesion assessment showed more dorsal and lumbar extensions presenting atherosclerotic foci after the t10,c12-CLA diet. Furthermore, animals fed t10,c12-CLA had pronounced hyperlipidemia, higher 8-iso-prostaglandin F(2alpha) levels, higher vulnerable atherosclerotic plaque with a lower smooth muscle and fibre contents and higher macrophage content and activation, assayed as plasma chitotriosidase compared to the control or c9,t11-CLA dietary groups. Plasma chitotriosidase activity was more closely associated with the extent of the plaque than with MOMA staining or than monocyte chemoattractant protein-1 levels. Our results demonstrate that CLA isomers differentially modulate the development of atherosclerosis, c9,t11-CLA impedes, whereas t10,c12-CLA promotes atherosclerosis. These opposing effects may be ascribed to divergent effects on lipid, oxidative, inflammatory and fibro muscular components of this pathology. Plasma chitotriosidase is a better indicator of dietary fat interventions that alter plaque monocyte activity in this murine model.

The cis-9,trans-11 isomer of conjugated linoleic acid (CLA) lowers plasma triglyceride and raises HDL cholesterol concentrations but does not suppress aortic atherosclerosis in diabetic apoE-deficient mice

OBJECTIVE

Reduction in atherosclerosis has been reported in experimental animals fed mixtures of conjugated linoleic acid (CLA). In this study, the major naturally occurring CLA isomer (cis-9,trans-11) was tested in an atherosclerosis-prone mouse model.

METHODS

In a model of insulin deficient apoE deficient mice, 16 animals were fed for 20 weeks with supplemental CLA (09.%, w/w) and compared with a similar number of mice of this phenotype. A control comparison was made of metabolic changes in non-diabetic apoE deficient mice that develop little atherosclerosis over 20 weeks. At 20 weeks, plasma lipids were measured and aortic atherosclerosis quantified by Sudan staining in the arch, thoracic and abdominal segments.

RESULTS

The diabetic apoE deficient mice developed marked dyslipidemia, primarily as cholesterol-enriched chylomicron and VLDL-sized lipoproteins and atherosclerosis in the aortic arch. However, there were no significant differences between CLA fed and non-CLA fed mice in either phenotype in plasma cholesterol concentration (in diabetic: 29.4+/-7.7 and 29.5+/-5.9 mmol/L, respectively) or in the area of aortic arch atherosclerosis (in diabetic: 24.8+/-10.3 and 27.6+/-7.7%, respectively). However, among diabetic mice the triglyceride concentration in triglyceride-rich lipoproteins was significantly lower in those fed CLA (for plasma 2.2+/-0.8 to 1.1+/-0.3 mmol/L; P<0.001), a significant difference that was seen also in the non-diabetic mice in which HDL cholesterol increased significantly with CLA (0.35+/-0.12-0.56+/-0.15 mmol/L).

CONCLUSION

In this atherosclerosis-prone model, the diabetic apoE deficient mouse, supplemental 0.9% CLA (cis-9,trans-11) failed to reduce the severity of aortic atherosclerosis, although plasma triglyceride concentration was substantially lowered and HDL cholesterol raised.

Influence of dietary oil content and conjugated linoleic acid (CLA) on lipid metabolism enzyme activities and gene expression in tissues of Atlantic salmon (Salmo salar L.)

The overall objective is to test the hypothesis that conjugated linoleic acid (CLA) has beneficial effects in Atlantic salmon as a result of affecting lipid and FA metabolism. The specific aims of the present study were to determine the effects of CLA on some key pathways of FA metabolism, including FA oxidation and highly unsaturated FA (HUFA) synthesis. Salmon smolts were fed diets containing two levels of fish oil (low, approximately 17%, and high, approximately 34%) containing three levels of CLA (a 1:1 mixture of cis-9,trans-11 and trans-10,cis-12 at 0, 1, and 2% of diet) for 3 mon. The effects of dietary CLA on HUFA synthesis and beta-oxidation were measured, and the expression of key genes in the FA oxidation and HUFA synthesis pathways, and the potentially important transcription factors peroxisome proliferators activated receptors (PPAR), were determined in selected tissues. Liver HUFA synthesis and desaturase gene expression was increased by dietary CLA and decreased by high dietary oil content. Carnitine palmitoyltransferase-I (CPT-I) activity and gene expression were generally increased by CLA in muscle tissues although they were relatively unaffected by dietary oil content. In general CPT-I activity or gene expression was not correlated with P-oxidation. Dietary CLA tended to increase PPARalpha and beta gene expression in both liver and muscle tissues, and PPARgamma in liver. In summary, gene expression and activity of the FA pathways were altered in response to dietary CLA and/or oil content, with data suggesting that PPAR are also regulated in response to CLA. Correlations were observed between dietary CLA, liver HUFA synthesis and desaturase gene expression, and liver PPARalpha expression, and also between dietary CLA, CPT-I expression and activity, and PPARalpha expression in muscle tissues. In conclusion, this study suggests that dietary CLA has effects on FA metabolism in Atlantic salmon and on PPAR transcription factors. However, further work is required to assess the potential of CLA as a dietary supplement, and the role of PPAR in the regulation of lipid metabolism in fish.

Action of epoxyeicosatrienoic acids on cellular function

Epoxyeicosatrienoic acids (EETs), which function primarily as autocrine and paracrine mediators in the cardiovascular and renal systems, are synthesized from arachidonic acid by cytochrome P-450 epoxygenases. They activate smooth muscle large-conductance Ca(2+)-activated K(+) channels, producing hyperpolarization and vasorelaxation. EETs also have anti-inflammatory effects in the vasculature and kidney, stimulate angiogenesis, and have mitogenic effects in the kidney. Many of the functional effects of EETs occur through activation of signal transduction pathways and modulation of gene expression, events probably initiated by binding to a putative cell surface EET receptor. However, EETs are rapidly taken up by cells and are incorporated into and released from phospholipids, suggesting that some functional effects may occur through a direct interaction between the EET and an intracellular effector system. In this regard, EETs and several of their metabolites activate peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARgamma, suggesting that some functional effects may result from PPAR activation. EETs are metabolized primarily by conversion to dihydroxyeicosatrienoic acids (DHETs), a reaction catalyzed by soluble epoxide hydrolase (sEH). Many potentially beneficial actions of EETs are attenuated upon conversion to DHETs, which do not appear to be essential under routine conditions. Therefore, sEH is considered a potential therapeutic target for enhancing the beneficial functions of EETs.

trans-10,cis-12 Conjugated linoleic acid inhibits lipoprotein lipase but increases the activity of lipogenic enzymes in adipose tissue from hamsters fed an atherogenic diet

The aim of the present work was to investigate the effects of trans-10,cis-12 conjugated linoleic acid (CLA) on the activity and expression of lipogenic enzymes and lipoprotein lipase (LPL), as well as on the expression of transcriptional factors controlling these enzymes, in adipose tissue from hamsters, and to evaluate the involvement of these changes in the body fat-reducing effect of this CLA isomer. Thirty male hamsters were divided into three groups and fed atherogenic diets supplemented with 0 (linoleic group), 5 or 10 g trans-10,cis-12 CLA/kg diet, for 6 weeks. Body and adipose tissue weights, food intake and serum insulin were measured. Total and heparin-releasable LPL and lipogenic enzyme activities (acetyl-CoA carboxylase (ACC); fatty acid synthase (FAS); glucose-6-phosphate dehydrogenase (G6PDH); and malic enzyme (ME)) were assessed. ACC, FAS, LPL, sterol regulatory element-binding proteins (SREBP-1a), SREBP-1c and PPARgamma mRNA levels were also determined by real-time PCR. CLA did not modify food intake, body weight and serum insulin level. CLA feeding reduced adipose tissue weight, LPL activity and expression, and increased lipogenic enzyme activities, despite a significant reduction in ACC and FAS mRNA levels. The expression of the three transcriptional factors analysed (SREBP-1a, SREBP-1c and PPARgamma) was also reduced. These results appear to provide a framework for partially understanding the reduction in body fat induced by CLA. Inhibition of LPL activity seems to be an important mechanism underlying body fat reduction in hamsters. Further research is needed to better characterize the effects of CLA on lipogenesis and the role of these effects in CLA action.

Functional genomic characterization of delipidation elicited by trans-10, cis-12-conjugated linoleic acid (t10c12-CLA) in a polygenic obese line of mice

Gene expression was measured during t10c12-CLA-induced body fat reduction in a polygenic obese line of mice. Adult mice (n = 185) were allotted to a 2 x 2 factorial experiment consisting of either nonobese (ICR-control) or obese (M16-selected) mice fed a 7% fat, purified diet containing either 1% linoleic acid (LA) or 1% t10c12-CLA. Body weight (BW) by day 14 was 12% lower in CLA- compared with LA-fed mice (P < 0.0001). By day 14, t10c12-CLA reduced weights of epididymal, mesenteric, and brown adipose tissues, as a percentage of BW, in both lines by 30, 27, and 58%, respectively, and increased liver weight/BW by 34% (P < 0.0001). Total RNA was isolated and pooled (4 pools per tissue per day) from epididymal adipose (days 5 and 14) of the obese mice to analyze gene expression profiles using Agilent mouse oligo microarray slides representing > 20,000 genes. Numbers of genes differentially expressed by greater than or equal to twofold in epididymal adipose (days 5 and 14) were 29 and 125, respectively. It was concluded that, in adipose tissue, CLA increased expression of uncoupling proteins (1 and 2), carnitine palmitoyltransferase system, tumor necrosis factor-alpha (P < 0.05), and caspase-3 but decreased expression of peroxisome proliferator-activated receptor-gamma, glucose transporter-4, perilipin, caveolin-1, adiponectin, resistin, and Bcl-2 (P < 0.01). In conclusion, this experiment has revealed candidate genes that will be useful in elucidating mechanisms of adipose delipidation.

Conjugated Linoleic Acid Impairs Endothelial Function

OBJECTIVE

To determine the effect of dietary supplementation with conjugated linoleic acid (CLA) on body mass index (BMI), body fat distribution, endothelial function, and markers of cardiovascular risk.

METHODS AND RESULTS

Forty healthy volunteers with BMI >27 kg/m2 were randomized to receive a CLA isomeric mixture or olive oil in a 12-week double-blind study. Subcutaneous body fat and abdominal/hepatic fat content were assessed using skin-fold thicknesses and computed tomography scanning, respectively. Endothelial function was assessed by brachial artery flow-mediated dilatation (FMD). Plasma isoprostanes were measured as an index of oxidative stress. CLA supplementation did not result in a significant change in BMI index or total body fat. There was a significant decrease in limb (-7.8 mm, P<0.001), but not torso skin-fold thicknesses or abdominal or liver fat content. Brachial artery FMD declined (-1.3%, P=0.013), and plasma F2-isoprostanes increased (+91 pg/mL, P=0.042).

CONCLUSIONS

A CLA isomeric mixture had at most modest effects on adiposity and worsened endothelial function. On the basis of these results, the use of the isomeric mixture of CLA as an aid to weight loss cannot be recommended.

Sulfur-substituted and alpha-methylated fatty acids as peroxisome proliferator-activated receptor activators

FA with varying chain lengths and an alpha-methyl group and/or a sulfur in the beta-position were tested as peroxisome proliferator-activated receptor (PPAR)alpha, -delta(beta), and -gamma ligands by transient transfection in COS-1 cells using chimeric receptor expression plasmids, containing cDNAs encoding the ligand-binding domain of PPARalpha, -delta, and -gamma. For PPARalpha, an increasing activation was found with increasing chain length of the sulfur-substituted FA up to C14-S acetic acid (tetradecylthioacetic acid = TTA). The derivatives were poor, and nonsignificant, activators of PPARdelta. For PPARgamma, activation increased with increasing chain length up to C16-S acetic acid. A methyl group was introduced in the alpha-position of palmitic acid, TTA, EPA, DHA, cis9,trans11 CLA, and trans10,cis12 CLA. An increased activation of PPARalpha was obtained for the alpha-methyl derivatives compared with the unmethylated FA. This increase also resulted in increased expression of the two PPARalpha target genes acyl-CoA oxidase and liver FA-binding protein for alpha-methyl TTA, alpha-methyl EPA, and alpha-methyl DHA. Decreased or altered metabolism of these derivatives in the cells cannot be excluded. In conclusion, saturated FA with sulfur in the beta-position and increasing carbon chain length from C9-S acetic acid to C14-S acetic acid have increasing effects as activators of PPARalpha and -gamma in transfection assays. Furthermore, alpha-methyl FA derivatives of a saturated natural FA (palmitic acid), a sulfur-substituted FA (TTA), and PUFA (EPA, DHA, c9,t11 CLA, and t10,c12 CLA) are stronger PPARalpha activators than the unmethylated compounds.

A suplementação com ácido linoléico conjugado reduziu a gordura corporal em ratos Wistar

O ácido linoléico conjugado, um conjunto de isômeros geométricos e de posição do ácido linoléico, vem sendo muito estudado devido ao seu efeito sobre a composição corporal, promovendo redução da massa gorda. O objetivo deste trabalho foi avaliar o efeito da suplementação com ácido linoléico conjugado sobre a composição corporal de ratos Wistar saudáveis em crescimento. Um total de 40 ratos, divididos em quatro grupos, foram suplementados diariamente durante três semanas com AdvantEdge® ácido linoléico conjugado (EAS TM) nas concentrações 1,0%, 2,0% e 4,0% sobre o consumo diário de dieta, constituindo, respectivamente, os grupos AE1, AE2 e AE4, e com ácido linoléico na concentração de 2% sobre o consumo diário de dieta, constituindo o grupo-controle. Os animais foram suplementados por meio de entubação orogástrica. Para a avaliação da composição corporal centesimal foi removido o conteúdo intestinal para obtenção da carcaça vazia. Em seguida, a carcaça foi congelada em nitrogênio líquido, fatiada, liofilizada, moída e armazenada a -25°C, até o momento das determinações de umidade, cinzas, proteína bruta e gordura. O grupo AE1 apresentou maior consumo de dieta e ganho de peso, mas não diferiu quanto à eficiência alimentar dos demais grupos (p< 0,05). Em relação à composição corporal, constatou-se redução dos teores de gordura corporal dos grupos AE2 (11,2%) e AE4 (11,6%), quando comparados ao teor do grupo-controle (13,9%). A suplementação com ácido linoléico conjugado nas concentrações de 2,0% e 4,0% sobre o consumo diário de dieta promoveu redução de gordura corporal de 18,0% nos ratos Wistar.

Conjugated linoleic acid evokes de-lipidation through the regulation of genes controlling lipid metabolism in adipose and liver tissue

Conjugated linoleic acid (CLA) is a unique lipid that elicits dramatic reductions in adiposity in several animal models when included at < or = 1% of the diet. Despite a flurry of investigations, the precise mechanisms by which conjugated linoleic acid elicits its dramatic effects in adipose tissue and liver are still largely unknown. In vivo and in vitro analyses of physiological modifications imparted by conjugated linoleic acid on protein and gene expression suggest that conjugated linoleic acid exerts its de-lipidating effects by modulating energy expenditure, apoptosis, fatty acid oxidation, lipolysis, stromal vascular cell differentiation and lipogenesis. The purpose of this review shall be to examine the recent advances and insights into conjugated linoleic acid's effects on obesity and lipid metabolism, specifically focused on changes in gene expression and physiology of liver and adipose tissue.

Effects of structural changes of fatty acids on lipid accumulation in adipocytes and primary hepatocytes

Conjugated linoleic acids (CLAs), tetradecylthioacetic acid (TTA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are all shown to differently affect lipid homeostasis. Additionally, previous studies have shown that introducing a methyl group in the molecule potentiates the hypolipidemic effect of EPA. The objective of this study was to determine how cis9,trans11 CLA, trans10,cis12 CLA, TTA, EPA and DHA affect lipid accumulation in 3T3-L1 adipocytes and in cultured primary rat hepatocytes, and to what extent changes in cis/trans configuration or introducing a methyl group in the molecules influence their way of affecting lipid accumulation in these cells. Our results show that trans10,cis12 CLA is highly specific in preventing lipid accumulation in adipocytes, and that small structural changes in the molecule (changing to trans/trans or introducing an alpha-methyl group) totally abolish this effect and up-regulate the expression levels of adipogenic marker genes towards control levels. Furthermore, all the fatty acids increased hepatic lipid accumulation, whereas the lipid content was normalized after adding an alpha-methyl group into the molecules. Taken together, our data demonstrate that the various fatty acids are highly specialized molecules, and that small structural changes markedly alter their way of affecting lipid accumulation in adipocytes and hepatocytes.

Impaired lipid accumulation by trans10, cis12 CLA during adipocyte differentiation is dependent on timing and length of treatment

Conjugated linoleic acids (CLAs) are a group of polyunsaturated fatty acids found in ruminant products, where the predominant isomers are cis9, trans11 (c9,t11) and trans10, cis12 (t10,c12) CLA. We have previously shown that t10,c12 CLA prevents lipid accumulation in mature adipocytes in part by acting as a peroxisome proliferator-activated receptor gamma (PPAR gamma) modulator. The objective of this study was to further establish the molecular mechanisms underlying the attenuating effect on lipid accumulation by t10,c12 CLA, with focus on time point and duration of treatment during adipogenesis. We have shown that t10,c12 CLA treatment has its most attenuating effect early (day (D) 0-6) during differentiation. Treatment during this period is sufficient to prevent lipid accumulation in mature adipocytes. The adipogenic marker genes PPAR gamma and CCAAT/enhancer binding protein alpha (C/EBP alpha) are both down-regulated after treatment within the period from D0-6, while additional treatment also down-regulates the expression of sterol regulatory element binding protein-1c (SREBP-1c), liver X receptor alpha (LXR alpha), fatty acid binding protein (aP2), fatty acid translocase (CD36) and insulin-sensitive glucose transporter 4 (GLUT4). These effects of t10,c12 CLA reflect the subsequent attenuation of lipid accumulation observed in mature adipocytes. Interestingly, the early B-cell factor (O/E-1), which is known to promote adipogenesis and to be involved in control of genes important for terminal adipocyte differentiation, is unaffected by treatment of t10,c12 CLA. Taken together, our data indicate that inhibition of lipid accumulation induced by t10,c12 CLA treatment during adipocyte differentiation is associated with a tight regulatory cross-talk between early (PPAR gamma and C/EBP alpha) and late (LXR alpha, aP2 and CD36) adipogenic marker genes.

Prolonged treatment of genetically obese mice with conjugated linoleic acid improves glucose tolerance and lowers plasma insulin concentration: possible involvement of PPAR activation

Background

Studies in rodents and some studies in humans have shown that conjugated linoleic acid (CLA), especially its trans-10, cis-12 isomer, reduces body fat content. However, some but not all studies in mice and humans (though none in rats) have found that CLA promotes insulin resistance. The molecular mechanisms responsible for these effects are unclear, and there are conflicting reports on the effects of CLA on peroxisomal proliferator-activated receptor-γ (PPARγ) activation and expression. We have conducted three experiments with CLA in obese mice over three weeks, and one over eleven weeks. We have also investigated the effects of CLA isomers in PPARγ and PPARα reporter gene assays.

Results

Inclusion of CLA or CLA enriched with its trans-10, cis-12 isomer in the diet of female genetically obese (lep^ob/lep^ob) mice for up to eleven weeks reduced body weight gain and white fat pad weight. After two weeks, in contrast to beneficial effects obtained with the PPARγ agonist rosiglitazone, CLA or CLA enriched with its trans-10, cis-12 isomer raised fasting blood glucose and plasma insulin concentrations, and exacerbated glucose tolerance. After 10 weeks, however, CLA had beneficial effects on glucose and insulin concentrations. At this time, CLA had no effect on the plasma TNFα concentration, but it markedly reduced the plasma adiponectin concentration. CLA and CLA enriched with either isomer raised the plasma triglyceride concentration during the first three weeks, but not subsequently. CLA enriched with its trans-10, cis-12 isomer, but not with its cis-9, trans-11 isomer, stimulated PPARγ-mediated reporter gene activity; both isomers stimulated PPARα-mediated reporter gene activity.

Conclusions

CLA initially decreased but subsequently increased insulin sensitivity in lep^ob/lep^ob mice. Activation of both PPARγ and PPARα may contribute to the improvement in insulin sensitivity. In the short term, however, another mechanism, activated primarily by trans-10, cis-12-CLA, which probably leads to reduced adipocyte number and consequently reduced plasma adiponectin concentration, may decrease insulin sensitivity.

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.

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.

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

BACKGROUND

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSION

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

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

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

Conjugated linoleic acid in humans: regulation of adiposity and insulin sensitivity

Conjugated linoleic acid (CLA) isomers, a group of positional and geometric isomers of linoleic acid [18:2(n-6)], have been studied extensively due to their ability to modulate cancer, atherosclerosis, obesity, immune function and diabetes in a variety of experimental models. The purpose of this review was to examine CLA's isomer-specific regulation of adiposity and insulin sensitivity in humans and in cultures of human adipocytes. It has been clearly demonstrated that specific CLA isomers or a crude mixture of CLA isomers prevent the development of obesity in certain rodent and pig models. This has been attributed mainly to trans-10, cis-12 CLA, both in vivo and in vitro. However, CLA's ability to modulate human obesity remains controversial because data from clinical trials using mixed isomers are conflicting. In support of some studies in humans, our group demonstrated that trans-10, cis-12 CLA prevents triglyceride (TG) accumulation in primary cultures of differentiating human preadipocytes. In contrast, cis-9, trans-11 CLA increases TG content. Closer examination has revealed that CLA's antiadipogenic actions are due, at least in part, to regulation of glucose and fatty acid uptake and metabolism. This review presents our current understanding of potential isomer-specific mechanisms by which CLA reduces human adiposity and insulin sensitivity.

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

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

ISOMERS OF CONJUGATED LINOLEIC ACID MODULATE HUMAN PREADIPOCYTE DIFFERENTIATION

Conjugated linoleic acids (CLAs) reduce fat deposition in several mammalian species. Among the proposed mechanisms for this effect are reduced preadipocyte proliferation and differentiation. We measured proliferation and differentiation of cultured human preadipocytes treated with CLAs. Preadipocytes were differentiated with insulin, hydrocortisone, transferrin, and 10% fetal bovine serum, with isobutyl-methylxanthine included for the first 2 d. The differentiation medium contained 200 microM oleic acid (C18:1), 50 microM cis-9,trans-11-CLA (9,11-CLA), or 50 microM trans-10,cis-12-CLA (10,12-CLA); the negative control medium contained no added fatty acid, and the cells did not differentiate. Cell number increased three to four times during the 17 d of differentiation, but was 30-35% lower in the CLA-treated cells than in the negative control cells. Compared with the negative control cells, differentiation was increased in the cells treated with C18:1 (increased Oil Red O-stained material [OROSM], triacylglycerol, glycerol 3-phosphate dehydrogenase activity [GPDH], peroxisome proliferator-activated receptor-gamma [PPAR gamma] messenger ribonucleic acid [mRNA], and lipoprotein lipase [LPL] mRNA). In effect, the C18:1-treated cells act as a positive control to demonstrate the differentiation capacity of each cell lot. Both 9,11-CLA- and 10,12-CLA-treated cells had increased differentiation (increased OROSM, triacylglycerol, GPDH, PPAR gamma, and LPL) compared with the negative control cells. The data suggest that early in differentiation when de novo fatty acid (FA) synthesis is limited and competition for FAs by membrane and triacylglycerol synthetic pathways is great, human preadipocytes do not differentiate unless a PPAR gamma ligand is added. Either CLA isomer or C18:1 can provide such a ligand.