Influence of conjugated linoleic acid (CLA) on establishment and progression of atherosclerosis in rabbits

Effects of trans-10, cis-12 conjugated linoleic acid on the expression of uncoupling proteins in hamsters fed an atherogenic diet

It is known that conjugated linoleic acid (CLA) feeding decreases body adiposity but the mechanisms involved are not clear. The aim of this study was to analyse whether alterations in uncoupling protein (UCP) expression in white and brown adipose tissues (WAT and BAT, respectively) and in skeletal muscle may be responsible for the effect of trans-10, cis-12 CLA on the size of body fat depots in hamsters. Animals were divided into three groups and fed an atherogenic diet with different amounts of trans-10, cis-12 CLA (0 control, 0.5, or 1 g/100 g diet) for 6 weeks. CLA feeding reduced adipose depot weights, but had no effect on body weight. Leptin mRNA expression decreased in both subcutaneous and perirenal WAT depots, in accordance with lower adiposity, whereas resistin mRNA expression was not changed. Animals fed CLA had lower UCP1 mRNA levels in BAT (both doses of CLA) and in perirenal WAT (the low dose), and lower UCP3 mRNA levels in subcutaneous WAT (the high dose). UCP2 mRNA expression in WAT was not significantly affected by CLA feeding. Animals fed the high dose of CLA showed increased UCP3 and carnitine palmitoyl transferase-I (CPT-I) mRNA expression levels in skeletal muscle. In summary, induction of UCP1 or UCP2 in WAT and BAT is not likely to be responsible for the fat-reduction action of CLA, but the increased expression of UCP3 in skeletal muscle, together with a higher expression of CPT-I, may explain the previously reported effects of dietary CLA in lowering adiposity and increasing fatty acid oxidation by skeletal muscle.

Gender differences in the modulation of cardiac gene expression by dietary conjugated linoleic acid isomersThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

In an earlier study, we showed that dietary conjugated linoleic acid (CLA) isomers can exert differential effects on heart function in male and female rats, but the underlying mechanisms for these actions are not known. Cardiomyocyte Ca2+ cycling is a key event in normal cardiac contractile function and defects in Ca2+ cycling are associated with cardiac dysfunction and heart disease. We therefore hypothesized that abnormalities in the sarcolemmal (SL) and sarcoplasmic reticulum (SR)-mediated regulation of intracellular Ca2+ contribute to altered cardiac contractile function of male and female rats owing to dietary CLA isomers. Healthy male and female Sprague–Dawley rats were fed different CLA isomers, (cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12)) individually and in combination (50:50 mix as triglyceride or fatty acids) from 4 to 20 weeks of age. We determined the mRNA levels of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) 2a, ryanodine receptor, phospholamban, calsequestrin, Na+–Ca2+-exchanger (NCX), and L-type Ca2+ channel in the left ventricle (LV) by RT-PCR. The SR function was assessed by measurement of Ca2+-uptake and -release. Significant gender differences were seen in the LV NCX, L-type Ca2+ channel, and ryanodine receptor mRNA expression levels in control male and female rats. Dietary CLA isomers in the various forms induced changes in the mRNA levels of SERCA 2a, NCX, and L-type Ca2+ channel in the LV of both male and female hearts. Whereas protein contents of the Ca2+ cycling proteins were altered, changes in SR Ca2+-uptake and -release were also detected in both male and female rats in response to dietary CLA. The results of this study demonstrate that long-term dietary supplementation can modulate cardiac gene expression and SR function in a gender-related manner and may, in part, contribute to altered cardiac contractility.

Butters Varying in trans 18:1 and cis-9,trans-11 Conjugated Linoleic Acid Modify Plasma Lipoproteins in the Hypercholesterolemic Rabbit

The experiment was designed to study the effects of butters differing in conjugated linoleic acid (CLA) and trans 18:1 contents on lipoproteins associated with the risk of atherogenesis. New Zealand White male rabbits (9.6 weeks; 2.1 kg) were assigned for 6 or 12 weeks to three diets (n = 6 per diet) made of conventional pellets with 0.2% cholesterol and with 12% fat provided from a butter poor in trans-10 and trans-11 18:1 and in CLA (standard group), or rich in trans-10 18:1 (trans-10 18:1 group) or rich in trans-11 18:1 and in cis-9,trans-11 CLA (trans-11 18:1/CLA group). Blood samples were collected at the end of dietary treatments. Lipoproteins were separated by gradient-density ultracentrifugation. Lipid classes were determined enzymatically and apolipoproteins A-I and B by radial immunodiffusion. Mainly in the 12-week rabbits, higher plasma triglycerides and apolipoprotein B levels shown in the standard and trans-10 18:1 groups compared with those in the trans-11 18:1/CLA group are associated with higher plasma levels of very low density lipoproteins (VLDL) and low density lipoproteins (LDL) also shown in these two groups. In the 12-week rabbits, a shift towards denser LDL, considered as more atherogenic, was shown only in the trans-10 18:1 group. In these animals, the VLDL + LDL to HDL ratio was 1.7-2.3 times higher in the trans-10 18:1 group than in the other groups (P = 0.076). These results suggest a rather neutral effect of trans-11 18:1/CLA butter towards the risk of atherogenesis, whereas trans-10 18:1 butter would tend to be detrimental.

Safety of Dietary Conjugated Linoleic Acid (CLA) in a 12-weeks Trial in Healthy Overweight Japanese Male Volunteers

A study was conducted to investigate the short-term safety of dietary conjugated linoleic acid (CLA) in overweight Japanese male volunteers. The study design was a randomized, double-blind placebo-controlled trial including 60 healthy overweight volunteers (body mass index (BMI), 25 approximately 35 kg/m(2)). The subjects were randomly assigned to three groups: 5.4 g CLA-triacylglycerol (3.4 g as CLA), 10.8 g CLA-triacylglycerol (6.8 g as CLA) and placebo (10.8 g safflower oil) daily for 12 weeks. The CLA-triaclyglycerol contained 9c,11t- and 10t,12c-isomers at an equal proportion. The safety was evaluated by analyses of blood parameters and by clinical examinations at the baseline, and at 6 and 12 weeks, including vital signs and adverse effects. All subjects completed the study. The occurrence of adverse events tended to be higher in the CLA groups than in the placebo group, but all of the adverse events were mild to moderate, within normal ranges, and temporary. Serum aspartate aminotransferase (AST) activity did not differ significantly between the groups at 12 weeks, but in the high CLA group it was slightly increased from the baseline. Serum alanine aminotransferase (ALT) activity was higher in the high CLA group than in the placebo group after 12 weeks and was higher than at the baseline in both CLA groups. However, statistical analysis of the population of apparently healthy volunteers who had normal blood parameters at the baseline revealed that AST and ALT levels did not differ significantly among the 3 groups at 12 weeks. Moreover, no clinically significant changes in vital signs were observed in any of the groups. These results indicate that CLA at a dose of 3.4 g/day is a safe dietary level in healthy Japanese populations in terms of the parameters examined.

Intestinal bifidobacteria that produce trans-9, trans-11 conjugated linoleic acid: a fatty acid with antiproliferative activity against human colon SW480 and HT-29 cancer cells

Bifidobacterium breve species of human intestinal origin have the ability to synthesize cis-9, trans-11 (c9, t11) conjugated linoleic acid (CLA) from free linoleic acid. In this study, the ability of Bifidobacterium species to isomerize C(18) polyunsaturated fatty acids was investigated, and the antiproliferative activities of the two main microbially produced CLA isomers were assessed. Linoleic acid was converted principally to c9, t11 CLA and lesser amounts of t9, t11 CLA, whereas c9, t11 CLA was converted mainly to t9, t11 CLA. Likewise, t10, c12 CLA was converted principally to t9, t11 CLA, which was incorporated into the bacterial cell membranes. To examine the antiproliferative effect of the two main CLA isomers formed, SW480 and HT-29 human colon cancer cells were cultured in the presence of c9, t11 CLA and t9, t11 CLA. The t9, t11 CLA had a more potent antiproliferative effect than c9, t11 CLA. It is tempting to suggest that the ability of Bifidobacterium to produce such bioactive metabolites may be associated with the beneficial effects of bifidobacteria present in the human gastrointestinal tract.

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.

Conjugated linoleic acid: a functional nutrient in the different pathophysiological components of the metabolic syndrome?

PURPOSE OF REVIEW

Much attention has focused on the therapeutic potential of conjugated linoleic acid with the most abundant isomers being cis-9,trans-11 conjugated linoleic acid and trans-10,cis-12 conjugated linoleic acid. Initial animal studies associated conjugated linoleic acid with beneficial health properties, such as reducing the risk of cancer, diabetes, atherosclerosis, inflammation and obesity. This review has appraised the evidence in relation to the effect of conjugated linoleic acid on components of the metabolic syndrome (clinically or experimentally), in particular, obesity, insulin resistance, atherosclerosis and inflammation.

RECENT FINDINGS

More recent human conjugated linoleic acid supplementation studies have often shown conflicting and less convincing health benefits. The marked variation between studies may reflect the isomer-specific effect of the individual conjugated linoleic acid isomers, which can often have opposing effects. Detrimental effects have been observed in some studies, in particular after supplementation with the trans-10,cis-12 conjugated linoleic acid isomer.

SUMMARY

Further studies and long-term clinical trials will be required to determine the efficacy and safety of conjugated linoleic acid isomers before conjugated linoleic acid could be considered as a functional nutrient in humans.

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

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

Conjugated linoleic acid isomers reduce blood cholesterol levels but not aortic cholesterol accumulation in hypercholesterolemic hamsters

The aim of the present study was to characterize plasma lipids and lipoprotein cholesterol and glucose concentrations in hamsters fed either cis-9,trans-11 CLA (9c,11 tCLA); trans-10,cis-12 CLA (10t,12c CLA); or linoleic acid (LA) on the accumulation of aortic cholesterol in hypercholesterolemic hamsters. One hundred male F1B strain Syrian Golden Hamsters (Mesocricetus auratus) (BioBreeders Inc., Watertown, MA) approximately 9 wk of age were housed in individual stainless steel hanging cages at room temperature with a 12-h light/dark cycle. Hamsters were given food and water ad libitum. Following a 1-wk period of acclimation, the hamsters were fed a chow-based (nonpurified) hypercholesterolemic diet (HCD) containing 10% coconut oil (92% saturated fat) and 0.1% cholesterol for 2 wk. After an overnight fast, the hamsters were bled and plasma cholesterol concentrations were measured. The hamsters were then divided into 4 groups of 25 based on similar mean plasma VLDL and LDL cholesterol (nonHDL-C) concentrations. Group 1 remained on the HCD (control). Group 2 was fed the HCD plus 0.5% 9c,11t CLA isomer. Group 3 was fed the HCD plus 0.5% 10t,12c CLA isomer. Group 4 was fed the HCD plus 0.5% LA. Compared with the control, both CLA isomers and LA had significantly lower plasma total cholesterol and HDL cholesterol concentrations (P < 0.001) after 12 but not 8 wk of treatment and were not significantly different from each other. Also, both CLA isomers had significantly lower plasma nonHDL-C concentrations (P < 0.01) compared with the control after 12 but not 8 wk of treatment and were not significantly different from each other or the LA-fed hamsters. Plasma TG concentrations were significantly higher (P < 0.004) with the 10t, 12c CLA isomer compared with the other treatments at 8 but not at 12 wk of treatment. Plasma TG concentrations were also significantly lower (P < 0.03) with the 9c,11t CLA isomer compared with the control at 12 wk of treatment. Also, the 10t,12c CLA isomer and LA had significantly higher plasma glucose concentrations compared with the control and 9c,11t CLA isomer (P < 0.008) at 12 wk of treatment, whereas at 8 wk, only the LA treatment had significantly higher plasma glucose concentrations (P < 0.001) compared with the 9c,11t CLA isomer. Although liver weights were significantly higher in 10t,12c CLA isomer-fed hamsters, liver total cholesterol, free cholesterol, cholesterol ester, and TG concentrations were significantly lower in these hamsters compared with hamsters fed the control, 9c,11t CLA isomer, and LA diets (P< 0.05). The 9c,11t CLA isomer and LA diets tended to reduce cholesterol accumulation in the aortic arch, whereas the 10t,12c CLA isomer diet tended to raise cholesterol accumulation compared with the control diet; however, neither was significant. In summary, no differences were observed between the CLA isomers for changes in plasma lipids or lipoprotein cholesterol concentrations. However, the 9c,11t CLA isomer did appear to lower plasma TG and glucose concentrations compared with the 10t,12c CLA isomer. Such differences may increase the risk of insulin resistance and type 2 diabetes in humans when the 10t,12c CLA isomer is fed separately.

Selective conjugated fatty acids inhibit guinea pig platelet aggregation

Conjugated linoleic acids have been shown to reduce eicosanoid release from select tissues and/or cells. To elucidate effects of conjugated linoleic acid isomers on cyclooxygenase-1 (COX-1) activity and their application as platelet aggregation inhibitors, conjugated linoleic acid isomers and conjugated nonadecadienoic acid were incubated with ovine COX-1 and Raw264.7 macrophage to examine their effects on COX-1 activity. The effects were further examined in collagen and ADP-induced guinea pig whole blood platelet aggregation. Fatty acids tested were shown to inhibit COX-1 enzymatic activity. However, only 10t, 12c-conjugated linoleic acid, 9t, 11t-conjugated linoleic acid and conjugated nonadecadienoic acid inhibited collagen and ADP-induced platelet aggregation with IC(50) 125.9 microM (74.2 microM to 213.4 microM, 95% confidence interval), 99.3 microM (52.8 microM to 187.2 microM, 95% confidence interval) and 124.3 microM (85.1 microM to 181.5 microM, 95% confidence interval) respectively in collagen-induced aggregation. TxB(2) release was also appreciably inhibited by 10t, 12c-conjugated linoleic acid, 9t, 11t-conjugated linoleic acid and conjugated nonadecadienoic acid. Based on these data, we conclude 10t, 12c-conjugated linoleic acid, 9t, 11t-conjugated linoleic acid and conjugated nonadecadienoic acid are platelet aggregation inhibitors while 9c, 11t-conjugated linoleic acid is a moderate inhibitor and linoleic acid, and 9c, 11c-conjugated linoleic acid have no effect on whole blood platelet aggregation.

Conjugated linoleic acids have no effect on TNFα-induced adhesion molecule expression, U937 monocyte adhesion, and chemokine release in human aortic endothelial cells

Leukocyte recruitment and adhesion to the endothelium are critical steps in the early phase of atherosclerosis. Synthetic ligands of peroxisome proliferator-activated receptors (PPARs) were shown to reduce cytokine-stimulated leukocyte-endothelial cell interactions by inhibiting the NF-kappaB mediated inflammatory response. Conjugated linoleic acids (CLA), which are natural ligands of PPARs, were demonstrated to have anti-inflammatory and anti-atherogenic properties in vivo. With a view to elucidating the anti-atherogenic mechanisms of CLA, the present study aimed to explore the effects of cis-9, trans-11 CLA and trans-10, cis-12 CLA on cytokine-induced chemokine release, surface expression of adhesion molecules (ICAM-1, VCAM-1, and E-selectin) and U937 monocyte adhesion in human aortic endothelial cells (HAEC). Treatment of HAECs with 2 ng/mL of TNFalpha markedly increased expression of adhesion molecules, U937 monocyte adhesion, and release of the monocyte chemoattractant protein (MCP)-1. However, treatment of HAECs with either CLA isomer or linoleic acid did not modulate the cytokine-induced expression of ICAM-1, VCAM-1, and E-selectin, U937 cell adhesion and MCP-1 release. In addition, both CLA isomers and linoleic acid slightly increased PPARgamma DNA-binding activity, but did not alter DNA-binding activity of NF-kappaB. In conclusion, CLA isomers showed no effect on cytokine-induced monocyte-endothelial cell interactions and on the molecular mechanisms regulating these processes in HAEC. This study suggests that anti-atherogenic effects of CLA observed in vivo are probably not mediated by reduced monocyte-endothelial cell interactions.

The ancestral human diet: what was it and should it be a paradigm for contemporary nutrition?

Awareness of the ancestral human diet might advance traditional nutrition science. The human genome has hardly changed since the emergence of behaviourally-modern humans in East Africa 100-50 x 10(3) years ago; genetically, man remains adapted for the foods consumed then. The best available estimates suggest that those ancestors obtained about 35% of their dietary energy from fats, 35% from carbohydrates and 30% from protein. Saturated fats contributed approximately 7.5% total energy and harmful trans-fatty acids contributed negligible amounts. Polyunsaturated fat intake was high, with n-6:n-3 approaching 2:1 (v. 10:1 today). Cholesterol consumption was substantial, perhaps 480 mg/d. Carbohydrate came from uncultivated fruits and vegetables, approximately 50% energy intake as compared with the present level of 16% energy intake for Americans. High fruit and vegetable intake and minimal grain and dairy consumption made ancestral diets base-yielding, unlike today's acid-producing pattern. Honey comprised 2-3% energy intake as compared with the 15% added sugars contribute currently. Fibre consumption was high, perhaps 100 g/d, but phytate content was minimal. Vitamin, mineral and (probably) phytochemical intake was typically 1.5 to eight times that of today except for that of Na, generally <1000 mg/d, i.e. much less than that of K. The field of nutrition science suffers from the absence of a unifying hypothesis on which to build a dietary strategy for prevention; there is no Kuhnian paradigm, which some researchers believe to be a prerequisite for progress in any scientific discipline. An understanding of human evolutionary experience and its relevance to contemporary nutritional requirements may address this critical deficiency.

Biological effects of conjugated linoleic acids in health and disease

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

Characterization and regulation of the bovine stearoyl-CoA desaturase gene promoter

The bovine stearoyl-CoA desaturase (Scd) gene plays an important role in the bovine mammary gland where substrates such as stearic and vaccenic acids are converted to oleic acid and conjugated linoleic acid (CLA), respectively. Up to 90% of the CLA in bovine milk is formed due to the action of this enzyme in the mammary gland. The areas of the bovine promoter of importance in regulating this key enzyme were examined and an area of 36bp in length was identified as having a critical role in transcriptional activation and is designated the Scd transcriptional enhancer element (STE). Electrophoretic mobility shift assay detected three binding complexes on this area in Mac-T cell nuclear extracts. Treatment of cells with CLA caused a significant reduction in transcriptional activity, with this effect being mediated through the STE region. The bovine Scd gene promoter was up-regulated by insulin and down-regulated by oleic acid.

Diets rich in conjugated linoleic acid and vaccenic acid have no effect on blood pressure and isobaric arterial elasticity in healthy young men

The objective of this study was to examine the effect on blood pressure (BP) and isobaric arterial elasticity (AE), as a measure of arterial health, of a commercial mixture of conjugated linoleic acids (CLA) and of milk fat produced through livestock feeding to have a high content of vaccenic acid (VA). Healthy young men (n = 60) with a BMI of 22.5 +/- 2 kg/m2 (mean +/- SD) participated in this double-blind, randomized, 5-wk, parallel intervention study. The participants substituted 115 g of their daily fat intake with fat from 1 of 3 test diets: 1) CLA-diet rich in CLA (4.7 g/d of c9,t11- and t10,c12-CLA isomers in equal amounts); 2) VA-diet rich in VA (3.6 g/d); or 3) C-diet, a control diet with a low content of VA and CLA. All test diets were based on milk fat. BP and AE (measured by an oscillometric method) were measured before and after the intervention period. The effects of the test diets did not differ on any outcome variable: e.g., systolic- and diastolic blood pressure (SBP and DBP), pulse pressure (PP), isobaric arterial compliance (AC), distensibility (AD), or volume (AV). In conclusion, diets rich in milk fat and either CLA or VA have no effect on BP or AE indices in healthy young men compared with a control diet.

Conjugated linoleic acid supplementation for 1 y does not prevent weight or body fat regain

BACKGROUND

Conjugated linoleic acid (CLA) is marketed as a safe, simple, and effective dietary supplement to promote the loss of body fat and weight. However, most previous studies have been of short duration and inconclusive, and some recent studies have questioned the safety of long-term supplementation with CLA.

OBJECTIVE

Our aim was to assess the effect of 1-y supplementation with CLA (3.4 g/d) on body weight and body fat regain in moderately obese people.

DESIGN

One hundred twenty-two obese healthy subjects with a body mass index (in kg/m2) > 28 underwent an 8-wk dietary run-in with energy restriction (3300-4200 kJ/d). One hundred one subjects who lost >8% of their initial body weight were subsequently randomly assigned to a 1-y double-blind CLA (3.4 g/d; n = 51) or placebo (olive oil; n = 50) supplementation regime in combination with a modest hypocaloric diet of -1250 kJ/d. The effects of treatment on body composition and safety were assessed with the use of dual-energy X-ray absorptiometry and with blood samples and the incidence of adverse events, respectively.

RESULTS

After 1 y, no significant difference in body weight or body fat regain was observed between the treatments. The CLA group (n = 40) regained a mean (+/-SD) 4.0 +/- 5.6 kg body weight and 2.1 +/- 5.0 kg fat mass compared with a regain of 4.0 +/- 5.0 kg body weight and 2.7 +/- 4.9 kg fat mass in the placebo group (n = 43). No significant differences in reported adverse effects or indexes of insulin resistance were observed, but a significant increase in the number of leukocytes was observed with CLA supplementation.

CONCLUSION

A 3.4-g daily CLA supplementation for 1 y does not prevent weight or fat mass regain in a healthy obese population.

Factors affecting conjugated linoleic acid content in milk and meat

Conjugated linoleic acid (CLA) has been recently studied mainly because of its potential in protecting against cancer, atherogenesis, and diabetes. Conjugated linoleic acid (CLA) is a collective term for a series of conjugated dienoic positional and geometrical isomers of linoleic acid, which are found in relative abundance in milk and tissue fat of ruminants compared with other foods. The cis-9, trans-11 isomer is the principle dietary form of CLA found in ruminant products and is produced by partial ruminal biohydrogenation of linoleic acid or by endogenous synthesis in the tissues themselves. The CLA content in milk and meat is affected by several factors, such as animal's breed, age, diet, and management factors related to feed supplements affecting the diet. Conjugated linoleic acid in milk or meat has been shown to be a stable compound under normal cooking and storage conditions. Total CLA content in milk or dairy products ranges from 0.34 to 1.07% of total fat. Total CLA content in raw or processed beef ranges from 0.12 to 0.68% of total fat. It is currently estimated that the average adult consumes only one third to one half of the amount of CLA that has been shown to reduce cancer in animal studies. For this reason, increasing the CLA contents of milk and meat has the potential to raise the nutritive and therapeutic values of dairy products and meat.

Gender differences in the cardiac response to dietary conjugated linoleic acid isomers

The present study was undertaken to assess the heart function, by the in vivo catheterization technique, of healthy male and female Sprague–Dawley rats fed different conjugated linoleic acid (CLA) isomers, (cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12)) individually and in combination (50:50 mix as triglyceride or fatty acids) from 4 to 20 weeks of age. Whereas the triglyceride form of the CLA isomer mix lowered the heart rate, the rate of contraction (+dP/dt) and rate of relaxation (–dP/dt), systolic and diastolic pressures, mean arterial pressure, and the left ventricular systolic pressure were higher in male rats as compared with all the other dietary groups. In contrast, there were no significant effects in the cardiac function of the female rats in response to the CLA isomer mix in triglyceride form. Whereas the heart rate, +dP/dt, and left ventricular systolic pressure were lower in male rats fed the t10,c12 CLA isomer alone, the heart rate of the female rats was higher, but the systolic pressure, +dP/dt, and mean arterial pressure were lower compared with the control group. Also, the left ventricular end-diastolic pressure was specifically higher in the female rats in response to free fatty acids-containing CLA mix. Furthermore, an additive effect of the free fatty acids-containing CLA mix was seen in the +dP/dt and –dP/dt of female rats compared with the control group. These results indicate that CLA isomers exert differential effects on heart function and suggest the need for a complete evaluation of the benefits, interactions, and potential side effects of each isomer.

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.

CLA isomers inhibit TNFalpha-induced eicosanoid release from human vascular smooth muscle cells via a PPARgamma ligand-like action

Conjugated linoleic acids (CLAs) were reported to have anti-atherogenic properties in animal feeding experiments. In an attempt to elucidate the molecular mechanisms of these anti-atherogenic effects, the modulatory potential of CLA on cytokine-induced eicosanoid production from smooth muscle cells (SMCs), which contributes to the chronic inflammatory response associated with atherosclerosis, has been investigated in the present study. cis-9, trans-11 CLA and trans-10, cis-12 CLA were shown to reduce proportions of the eicosanoid precursor arachidonic acid in SMC total lipids and to inhibit cytokine-induced NF-kappaB DNA-binding activity, mRNA levels of inducible enzymes involved in eicosanoid formation (cPLA2, COX-2, mPGES), and the production of the prostaglandins PGE2 and PGI2 by TNFalpha-stimulated SMCs in a dose-dependent manner. The effect of 50 micromol/L of either CLA isomer was as effective as 10 micromol/L of the PPARgamma agonist troglitazone in terms of inhibiting the TNFalpha-stimulated eicosanoid production by SMCs. PPARgamma DNA-binding activity was increased by both CLA isomers compared to control cells. Moreover, it was shown that the PPARgamma antagonist T0070907 partially abrogated the inhibitory action of CLA isomers on cytokine-induced eicosanoid production and NF-kappaB DNA-binding activity by vascular SMCs suggesting that PPARgamma signalling is at least partially involved in the action of CLA in human vascular SMCs. With respect to the effects of CLA on experimental atherosclerosis, our findings suggest that the anti-inflammatory effect of CLA is at least partially responsible for the anti-atherogenic effects of CLA observed in vivo.

Detection of conjugated dienoic fatty acids in human vascular smooth muscle cells treated with conjugated linoleic acid

Conjugated linoleic acids (CLA) have attracted scientific interest due to their potential beneficial effects on atherosclerosis. Recent studies demonstrated that conjugated metabolites of CLA are found in tissues of CLA-fed animals and cultured cells treated with CLA. This observation has gained in importance since it has recently been shown that these metabolites of CLA exert specific biological activities. Therefore, the present study aimed to explore the potential formation of metabolites of cis-9, trans-11 CLA, trans-10, cis-12 CLA and trans-9, trans-11 CLA in cells of the vascular wall, which has not yet been shown. Examination of fatty acid composition of total cell lipids using Ag+-HPLC, GC-FID and GC-MS analysis revealed a significant isomer-specific formation of conjugated metabolites of CLA such as CD16:2, CD20:2 and CD22:2 in human coronary artery smooth muscle cells treated with various CLA isomers. Different CD16:2/CLA ratios between various CLA isomers as observed in the present study indicate that fatty acid metabolism is differently affected by the configuration of the double bonds. In conclusion, the observation from the present study suggests that the effects of CLA in vascular cells might not only be mediated by CLA itself but also by its conjugated metabolites. Future studies using highly purified conjugated metabolites of CLA are necessary to study their role in mediating biological effects of CLA in cell culture systems.

10t,12c-conjugated linoleic acid inhibits lipopolysaccharide-induced cyclooxygenase expression in vitro and in vivo

Previous data demonstrated that conjugated linoleic acid (CLA) reduced eicosanoid release from select organs. We hypothesized that one active CLA isomer was responsible for the reduced prostaglandin release and that the mechanism was through the inhibition of inducible cyclooxygenase-2 (COX-2). Here, we examined the effects of 10t,12c-CLA and 9c,11t-CLA on COX-2 protein/mRNA expression, prostaglandin E(2) (PGE(2)) production, and the mechanism by which CLA affects COX-2 expression and prostaglandin release. The COX-2 protein expression level was inhibited 80% by 10t, 12c-CLA and 26% by 9c,11t-CLA at 100 microM in vitro. PGE(2) production was decreased from 5.39 to 1.12 ng/2 x 10(6) cells by 10t,12c-CLA and from 5.7 to 4.5 ng/2 x 10(6) cells by 9c,11t-CLA at 100 microM. Mice fed 10t,12c-CLA but not 9c,11t-CLA were found to have a 34% decrease in COX-2 protein and a 43% reduction of PGE(2) release in the lung. 10t,12c-CLA reduced COX-2 mRNA expression level by 30% at 100 microM in vitro and by 30% in mouse lung in vivo. Reduced COX-2 mRNA was attributable to an inhibition of the nuclear factor kappaB (NF-kappaB) pathway by 10t,12c-CLA. These data suggested that the inhibition of NF-kappaB was one of the mechanisms for the reduced COX-2 expression and PGE(2) release by 10t,12c-CLA.

Lack of effect of dietary conjugated linoleic acids naturally incorporated into butter on the lipid profile and body composition of overweight and obese men

BACKGROUND

Dietary conjugated linoleic acid (CLA) is known to reduce atherosclerosis, plasma total and LDL-cholesterol concentrations, and body fat accumulation in several animal species. Of the few studies that investigated the effects of CLA supplementation in humans, all used commercially formulated oral supplements made from a mixture of CLA isomers.

OBJECTIVE

We compared the effects on plasma lipoproteins and body composition of the consumption of a modified butter naturally enriched with CLA (CLA-B: 4.22 g CLA/100 g butter fat) by the addition of sunflower oil to the diet of dairy cows with the consumption of a control butter (CON-B) that was low in CLA (0.38 g CLA/100 g butter fat).

DESIGN

In a crossover design study including an 8-wk washout period, 16 men [x +/- SD age: 36.6 +/- 12.4 y; body mass index (in kg/m2): 31.2 +/- 4.4] were fed each of the 2 experimental isoenergetic diets, providing 15% of energy as protein, 45% as carbohydrates, and 40% as lipids, of which >60% was derived from experimental fats, for 4 wk.

RESULTS

Consumption of the CLA-B diet induced a significantly (P < 0.05) smaller reduction in plasma total cholesterol and in the ratio of total to HDL cholesterol (-0.02 mmol/L and -0.00, respectively) than did consumption of the CON-B diet (-0.26 mmol/L and-0.34, respectively). Abdominal adipose tissue area measured by computed tomography showed no difference in accumulation of either visceral or subcutaneous adipose tissue after the 2 experimental diets.

CONCLUSION

These results suggest that a 10-fold CLA enrichment of butter fat does not induce beneficial metabolic effects in overweight or obese men.

Acis-9,trans-11-conjugated linoleic acid-rich oil reduces the outcome of atherogenic process in hyperlipidemic hamster

Conjugated linoleic acid (CLA) mixtures demonstrated antiatherogenic properties in several animal models, including hamsters, but the mechanism of action of the main food-derived CLA isomer is unknown in this species. This study thus focused on cis-9, trans-11-CLA (rumenic acid), and its effect was compared with that of fish oil, which is known to influence several aspects of atherogenesis. Syrian hamsters were fed (for 12 wk) diets containing 20% (wt/wt) butter fat (B diet) or the same diet augmented with either 1% (wt/wt) of a cis-9, trans-11-CLA-rich oil (BR diet) or 1% (wt/wt) fish oil (BF diet). The BR diet induced the lowest aortic lipid deposition (from −30% to −45%) among the butter oil-fed hamsters. In this group, plasma also displayed a reduced non-HDL-to-HDL-cholesterol ratio (21% less than in the butter oil group) and inflammatory serum amyloid A levels (70–80%) and an improvement of anti-oxidized LDL paraoxonase activity (all P < 0.05). Compared with the B group, the beneficial effects of the BR diet could be further explained in part by preventing the high VCAM-1 expression rate, increasing (30%) ATP-binding cassette subfamily A1 expression in the aorta, and downregulating expression of inflammatory-related genes (TNF-α, IL-1β, and cyclooxygenase 2, 2- to 2.8-fold, P < 0.05). This effect was partly associated with an activation of peroxisome proliferator-activating receptor (PPAR)/liver X receptor (LXR)-α signaling cascade. Interestingly, activation of PPAR/LXR-α signaling was not observed in hamsters fed the BF diet, in which the early signs of atherogenesis were increased. In conclusion, this study demonstrated that milk fat-rich cis-9, trans-11-CLA reduces the atherogenic process in hyperlipidemic hamsters.

Butter naturally enriched in conjugated linoleic acid and vaccenic acid alters tissue fatty acids and improves the plasma lipoprotein profile in cholesterol-fed hamsters

Butter, which is naturally enriched in cis-9, trans-11 conjugated linoleic acid (rumenic acid; RA) and vaccenic acid (VA), has been shown to be an effective anticarcinogen in studies with animal models; however, there has been no examination of the effects of a naturally derived source of VA and RA on atherosclerosis-related biomarkers. The current study was designed to determine the effect of a diet containing VA/RA-enriched butter on plasma lipoproteins and tissue fatty acid profiles in cholesterol-fed hamsters. Male Golden Syrian hamsters were fed diets containing 0.2% cholesterol and 20% added fat as: 1) Control, 20% standard butter (CT); 2) 5% standard butter + 15% VA/RA-enriched butter (EB); 3) 15% standard butter + 5% partially-hydrogenated vegetable oil (VO). After 4 wk, plasma lipoproteins were isolated, cholesterol quantified, and tissue fatty acid profiles determined. Tissue concentrations of VA and RA were increased by consumption of the EB diet compared with both the CT and VO diets, whereas the VO diet increased their concentration compared with the CT diet only. Total and LDL cholesterol concentrations were significantly reduced in hamsters fed EB and VO compared with CT, whereas VLDL cholesterol concentrations were reduced in hamsters fed EB compared with those fed CT and VO. HDL cholesterol concentrations did not differ among treatments. The ratio of potentially atherogenic lipoproteins [VLDL + intermediate density lipoproteins (IDL) + LDL] to antiatherogenic HDL was significantly lower in hamsters fed VA/RA-enriched butter (0.60) than in those fed either control diet (1.70) or the diet containing partially hydrogenated vegetable oil (1.04). Thus, increasing the VA/RA concentration of butter results in a plasma lipoprotein cholesterol profile that is associated with a reduced risk of atherosclerosis.

Divergent mechanisms of cis 9, trans 11 ‐ and trans 10 , cis 12 ‐ conjugated linoleic acid affecting insulin resistance and inflammation in apolipoprotein E knockout mice: a proteomics approach

Conjugated linoleic acids (CLA) affect atherogenesis, but mechanisms are not well understood. We explored how two isomers of CLA, cis9, trans11-CLA and trans10, cis12-CLA, affected lipid and glucose metabolism, as well as hepatic protein expression, in apolipoprotein E knockout mice. After 12 wk of intervention, plasma triglyceride, NEFA, and glucose concentrations were significantly higher in the trans10, cis12-CLA group, whereas plasma triglyceride, NEFA, glucose, and insulin concentrations were significantly lower in the cis9, trans11-CLA group, compared with control mice consuming linoleic acid. Proteomics identified significant up- or down-regulation of 113 liver cytosolic proteins by either CLA isomer. Principal component analysis revealed that the treatment effect of cis9, trans11-CLA was mainly explained by the up-regulation of different posttranslational forms of heat shock protein 70 kD. In contrast, the treatment effect of trans10, cis12-CLA was mainly explained by up-regulation of key enzymes in the gluconeogenic, beta-oxidation, and ketogenesic pathways. Correlation analysis again emphasized the divergent effects of both CLA isomers on different pathways, but also revealed a linkage between insulin resistance and increased levels of hepatic serotransferrin. Thus, our systems biology approach provided novel insights into the mechanisms by which individual CLA isomers differentially affect pathways related to atherogenesis, such as insulin resistance and inflammation.

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

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

Effects of conjugated linoleic acid supplementation on blood lipids and adiposity of rats fed diets rich in saturated versus unsaturated fat

Conjugated linoleic acid (CLA) may decrease adiposity and improve blood lipid profiles under some conditions. The goal of this study was to determine the effects of CLA supplementation on blood lipid profiles and adiposity of rats fed a diet containing a primarily saturated fat versus a diet containing a primarily unsaturated fat. Twenty-eight male Sprague-Dawley rats were randomly assigned to one of four diets containing coconut oil, coconut oil with CLA, corn oil or corn oil with CLA. After 28 days, blood was collected and serum concentrations of total cholesterol (TC), HDL-cholesterol (HDL-C), and triacylglycerols (TG) were assessed. Food intake, body weights, and epididymal fat pads were measured. No significant differences (p>0.05) were noted among groups for amount of food consumed, weight gained, food efficiency ratio or serum TG concentrations. TC concentrations were lower (p<0.05) in the CLA-supplemented rats that were fed coconut oil but not those consuming corn oil. Serum HDL-C was lower (p<0.05) in rats consuming corn oil but was not significantly different (p>0.05) for CLA supplemented groups. Epididymal fat pads weighed significantly more (p<0.05) in the coconut oil fed group compared to the corn oil fed group, but there was no significant difference (p>0.05) between the corn oil and coconut oil + CLA group. Overall, this study suggests that CLA is more beneficial for control of blood lipids and adiposity when supplemented to a diet rich in saturated versus unsaturated fat.

Supplementation with conjugated linoleic acid for 24 months is well tolerated by and reduces body fat mass in healthy, overweight humans

After 12 mo in a randomized, double-blind, placebo-controlled trial of conjugated linoleic acid (CLA) supplementation (2 groups received CLA as part of a triglyceride or as the free fatty acid, and 1 group received olive oil as placebo), 134 of the 157 participants who concluded the study were included in an open study for another 12 mo. The goals of the extension study were to evaluate the safety [with clinical chemistry analyses and reported adverse events (AEs)] and assess the effects of CLA on body composition [body fat mass (BFM), lean body mass (LBM), bone mineral mass (BMM)], body weight, and BMI. All subjects were supplemented with 3.4g CLA/d in the triglyceride form. Circulating lipoprotein(a) and thrombocytes increased in all groups. There was no change in fasting blood glucose. Aspartate amino transferase, but not alanine amino transferase, increased significantly. Plasma total cholesterol and LDL cholesterol were reduced, whereas HDL cholesterol and triglycerides were unchanged. The AE rate decreased compared with the first 12 mo of the study. Body weight and BFM were reduced in the subjects administered the placebo during the initial 12 mo study (-1.6 +/- 3.2 and -1.7 +/- 2.8 kg, respectively). No fat or body weight changes occurred in the 2 groups given CLA during the initial 12 mo. LBM and BMM were not affected in any of the groups. Changes in body composition were not related to diet and/or training. In conclusion, this study shows that CLA supplementation for 24 mo in healthy, overweight adults was well tolerated. It confirms also that CLA decreases BFM in overweight humans, and may help maintain initial reductions in BFM and weight in the long term.

Consumption of conjugated linoleic acid (CLA) from CLA-enriched cheese does not alter milk fat or immunity in lactating women

Isomers of conjugated linoleic acid (CLA) decreased milk fat, altered immunity, and reduced the risk for cardiovascular disease (CVD) in some animals. The major form of CLA in the human diet is c9,t11-18:2 (rumenic acid; RA). We studied the effects of high RA consumption on plasma and milk RA concentration, milk composition, immunity, and CVD risk factors in lactating women (n = 36) assigned to 1 of 3 treatments: control, low CLA cheese (LCLA; 160 mg RA/d), or high CLA cheese (HCLA; 346 mg RA/d). The increase in plasma RA concentration between baseline and 8 wk in women consuming HCLA cheese was significantly greater than that of controls. At study completion (8 wk), milk RA concentration among women consuming HCLA cheese was greater (P < 0.05) than that of controls (0.37 vs. 0.26% of fatty acids). Treatment did not affect milk fat, protein, or lactose concentrations, immune indices (e.g., plasma T-helper cells and interleukin-2), or measured risk factors for CVD (e.g., plasma triacylglyceride and cholesterol). In summary, consumption of a RA-enriched cheese modestly increased plasma and milk RA concentrations without affecting total milk fat, plasma and milk indices of immunity, or selected risk factors for CVD.

Modulation of nitric oxide and 6-keto-prostaglandin F(1alpha) production in bovine aortic endothelial cells by conjugated linoleic acid

Conjugated linoleic acid (CLA) refers to a group of polyunsaturated fatty acids that exist as positional (18:2) and stereo (cis/trans) isomers of conjugated dienoic octadecadienoate. Reports consistently indicate that CLA may inhibit both the onset and progression of atherosclerosis, via an as yet unknown mechanism(s). In an effort to identify the putative biochemical effects of CLA on bovine aortic endothelial cells (BAECs), the authors examined both the temporal and dose-dependent effects of a commercial CLA isomeric mixture on the expression and enzymatic function of endothelial nitric oxide synthase (eNOS) and cyclooxygenase-I/II (COX-I/II) in these cells. Initial investigations indicated that CLA mix (0 to 10 microg/mL, 0 to 24 h) failed to regulate either the expression or activity of eNOS in BAECs under basal conditions. Pretreatment of BAECs with CLA mix (10 microg/mL) for either 3 or 24 h, followed by incubation with 5 microM bradykinin (BK) for 3 h, however, increased BK-stimulated nitrite release by 2.4 +/- 0.6- and 3.0 +/- 0.4-fold, respectively, more than control cells (BK-stimulation without CLA pretreatment). Under basal conditions, CLA mix (10 microg/mL, 0 to 24 h) had no significant effect on either COX-I or COX-II expression, genes that could be readily induced in response to hemodynamic stimuli. CLA could, however, significantly attenuate BAEC release of 6-keto-prostaglandin F(1alpha) (6k-PGF(1alpha)), a stable breakdown product of prostaglandin I2 (PGI2) within the cyclooxygenase pathway, in a dose- and time-dependent manner. In conclusion, therefore, the results suggest that CLA may potentiate agonist-stimulated eNOS activation whilst attenuating COX-dependent PGI2 synthesis in BAECs. This ability to increase agonist-stimulated nitric oxide (NO) levels, whilst reducing production of inflammatory mediators within vascular ECs, supports a putative atheroprotective role for CLA and provides an important biochemical insight into its purported ability to modulate endothelium-mediated vascular homeostasis.

Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus

BACKGROUND

Some animal studies have suggested that conjugated linoleic acid (CLA) supplementation may have therapeutic potential with respect to insulin sensitivity and lipid metabolism, which are important cardiovascular disease (CVD) risk factors associated with type 2 diabetes mellitus.

OBJECTIVE

We investigated the effect of CLA supplementation on markers of glucose and insulin metabolism, lipoprotein metabolism, and inflammatory markers of CVD in subjects with type 2 diabetes.

DESIGN

The study was a randomized, double-blind, placebo-controlled trial. Thirty-two subjects with stable, diet-controlled type 2 diabetes received CLA (3.0 g/d; 50:50 blend of cis-9,trans-11 CLA and trans-10,cis-12 CLA) or control for 8 wk. A 3-h 75-g oral-glucose-tolerance test was performed, and fasting plasma lipid concentrations and inflammatory markers were measured before and after the intervention.

RESULTS

CLA supplementation significantly increased fasting glucose concentrations (6.3%; P < 0.05) and reduced insulin sensitivity as measured by homeostasis model assessment, oral glucose insulin sensitivity, and the insulin sensitivity index (composite) (P = 0.05). Total HDL-cholesterol concentrations increased by 8% (P < 0.05), which was due to a significant increase in HDL(2)-cholesterol concentrations (P < 0.05). The ratio of LDL to HDL cholesterol was significantly reduced (P < 0.01). CLA supplementation reduced fibrinogen concentrations (P < 0.01) but had no effect on the inflammatory markers of CVD (C-reactive protein and interleukin 6).

CONCLUSIONS

CLA supplementation had an adverse effect on insulin and glucose metabolism. Whereas CLA had positive effects on HDL metabolism and fibrinogen, a therapeutic nutrient should not be associated with potentially adverse effects on other clinical markers of type 2 diabetes.

Conjugated linoleic acid and atherosclerosis: no effect on molecular markers of cholesterol homeostasis in THP-1 macrophages

Macrophage cholesterol homeostasis is a key process involved in the initiation and progression of atherosclerosis. Peroxisome proliferator-activated receptors (PPARs) regulate the transcription of the genes involved in cholesterol homeostasis and thus represent an important therapeutic target in terms of reducing atherosclerosis. Conjugated linoleic acid (CLA) is a potent anti-atherogenic dietary fatty acid in animal models of atherosclerosis and is capable of activating PPARs in vitro and in vivo. Therefore, this study examined whether the anti-atherogenic effects of CLA in vivo could be ascribed to altered cholesterol homeostasis in macrophages and macrophage derived foam cells. Of several genes that regulate cholesterol homeostasis investigated, CLA had most effect on the class B scavenger receptor CD36. The cis-9,trans-11 CLA (c9,t11-CLA) and trans-10,cis-12 CLA (t10,c12-CLA) isomers augmented CD36 mRNA expression (P<0.001). Confocal laser microscopy characterised the three-dimensional expression patterns of CD36 in THP-1 macrophages. Linoleic acid, CLA and the PPARgamma ligand rosiglitazone increased discrete cell surface CD36 localisation, with a heterogeneous punctate pattern of expression. In agreement with the observed increases in CD36 mRNA and cell surface expression, intracellular cholesterol concentrations were greater in macrophages exposed to linoleic acid and CLA. Further analysis of cholesterol metabolism showed that CLA had no effect on THP-1 derived foam cell cholesterol efflux to apo AI. Thus, altered cholesterol homeostasis in the macrophage may not explain the anti-atherogenic effects of CLA observed in vivo.

Opposing effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on blood lipids in healthy humans

BACKGROUND

Conjugated linoleic acid (CLA) is reported to have weight-reducing and antiatherogenic properties when fed to laboratory animals. However, the effects of CLA on human health and, in particular, the effects of individual CLA isomers are unclear.

OBJECTIVE

This study investigated the effects of 3 doses of highly enriched cis-9,trans-11 (0.59, 1.19, and 2.38 g/d) or trans-10,cis-12 (0.63, 1.26, and 2.52 g/d) CLA preparations on body composition, blood lipid profile, and markers of insulin resistance in healthy men.

DESIGN

Healthy men consumed 1, 2, and 4 capsules sequentially, containing either 80% cis-9,trans-11 CLA or 80% trans-10,cis-12 CLA for consecutive 8-wk periods. This phase was followed by a 6-wk washout and a crossover to the other isomer.

RESULTS

Body composition was not significantly affected by either isomer of CLA. Mean plasma triacylglycerol concentration was higher during supplementation with trans-10,cis-12 CLA than during that with cis-9,trans-11 CLA, although there was no influence of dose. There were significant effects of both isomer and dose on plasma total cholesterol and LDL-cholesterol concentrations but not on HDL-cholesterol concentration. The ratios of LDL to HDL cholesterol and of total to HDL cholesterol were higher during supplementation with trans-10,cis-12 CLA than during that with cis-9,trans-11 CLA. CLA supplementation had no significant effect on plasma insulin concentration, homeostasis model for insulin resistance, or revised quantitative insulin sensitivity check index.

CONCLUSION

Divergent effects of cis-9,trans-11 CLA and trans-10,cis-12 CLA appear on the blood lipid profile in healthy humans: trans-10,cis-12 CLA increases LDL:HDL cholesterol and total:HDL cholesterol, whereas cis-9,trans-11 CLA decreases them.

Conjugated linoleic acid isomer effects in atherosclerosis: Growth and regression of lesions

Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of octadecadienoic acid, has been shown to inhibit experimentally induced atherosclerosis in rabbits and also to cause significant regression of pre-established atheromatous lesions in rabbits. The two major CLA isomers (cis9,trans11 and trans10,cis12), now available at 90% purity, have been tested individually for their anti-atherogenic or lesion regression potency. The two major isomers and the mixture were fed for 90 d to rabbits fed 0.2% cholesterol. Atherosclerosis was inhibited significantly by all three preparations. The two CLA isomers and the isomer mix were also fed (1.0%) as part of a cholesterol-free diet for 90 d to rabbits bearing atheromatous lesions produced by feeding an atherogenic diet. A fourth group was maintained on a cholesterol-free diet. On the CLA-free diet atherosclerosis was exacerbated by 35%. Reduction of severity of atheromatous lesions was observed to the same extent in all three CLA-fed groups. The average reduction of severity in the three CLA-fed groups was 26 +/- 2% compared with the first control (atherogenic diet) and 46 +/- 1% compared with the regression diet. Insofar as individual effects on atherosclerosis were concerned, there was no difference between the CLA mix and the cis9,trans11 and trans10,cis12 isomers. They inhibit atherogenesis by 50% when fed as a component of a semipurified diet containing 0.2% cholesterol; and when fed as part of a cholesterol-free diet, they reduce established lesions by 26%. Reduction of atheromata to the observed extent by dietary means alone is noteworthy.

Conjugated linoleic acids, atherosclerosis, and hepatic very-low-density lipoprotein metabolism

Conjugated linoleic acids (CLAs) are isomeric forms of the 18:2 fatty acid that contain conjugated sites of unsaturation. Although CLAs are minor components of the diet, they have many reported biological activities. For nearly a decade, the potential for CLA to modify the atherosclerotic process has been examined in animal models, and studies of supplementation of the human diet with CLA were started with the anticipation that such an intervention could also reduce the risk of cardiovascular disease. Central to the hypothesis is the expectation that dietary modification could alter plasma lipid and lipoprotein metabolism toward a more cardioprotective profile. This review examines the evidence in support of the hypothesis and the mechanistic studies that lend support for a role of CLA in hepatic lipid and lipoprotein metabolism. Although there are still limited studies in strong support of a role for CLA in the reduction of early atherosclerotic lesions, there has been considerable progress in defining the mechanisms of CLA action. CLA could primarily modulate the metabolism of fatty acids in the liver. The tools are now available to examine isomer-specific effects of CLA on hepatic lipid and lipoprotein metabolism and the potential of CLA to modify hepatic gene expression patterns. Additional animal and cell culture studies will increase our understanding of these unusual fatty acids and their potential for health benefits in humans.

Conjugated linoleic acid-enriched beef production

Canadian beef consumption is approximately 31 kg per annum, or a third of all meats consumed. Beef is a nutrient-rich food, providing good quality protein, vitamins B-6 and B-12, niacin, iron, and zinc. However, animal fats have gained the reputation of being less healthy. The identification of the anticarcinogenic effects of beef extracts due to the presence of conjugated linoleic acid (CLA) has heightened interest in increasing the amount of CLA deposited in beef. Beef cattle produce CLA and deposit these compounds in the meat; thus, beef consumers can receive bioformed CLA. Beef contains both of the bioactive CLA isomers, namely, cis-9, trans-11 and trans-10, cis-12. The relative content of these CLA isomers in beef depends on the feeds consumed by the animals during production. Feeding cattle linoleic acid-rich oils for extended periods of time increases the CLA content of beef. Depending on the type and relative maturity of the pasture, beef from pasture-fed cattle may have a higher CLA content than beef from grain- or silage-fed cattle. In feedlot animals fed high-grain diets, inclusion of dietary oil along with hay during both the growth and finishing phases led to an increase in CLA content from 2.8 to 14 mg/g beef fat, which would provide 77 mg CLA in an 85-g serving of beef. The CLAs appear to be concentrated in intramuscular and subcutaneous fat of beef cattle, with the CLA trans-10, cis-12 isomer being greater in the subcutaneous fat.

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.

Detection of conjugated C16 PUFAs in rat tissues as possible partial beta-oxidation products of naturally occurring conjugated linoleic acid and its metabolites

In a previous paper, we showed that naturally occurring conjugated linoleic acid (CLA) from butter fat is metabolized in vivo to higher metabolites such as conjugated diene (CD) 18:3, CD 20:3 and CD 20:4, all the while retaining the conjugated diene structure. In this paper, we describe the detection of two more metabolites with characteristic conjugated diene UV spectra. HPLC retention times, UV and MS spectra identified the CLA metabolites as CD 16:2 and CD 16:3. The accumulation of CD 16:2 was significantly higher than that of CD 16:3 in all tissues examined. Tissue distributions of CD 16:2 and CD 16:3 were similar, with plasma and adipose tissue showing the highest levels, while kidney had the lowest and the liver an intermediate level. CD 16 fatty acids accounted for about 20% of the total CLA metabolites. The kidney, however, was an exception where CD 16 fatty acids accounted for only 11% of total metabolites. Analyses of liver lipid classes showed that CD 16:2 and CD 16:3 were preferentially incorporated into neutral lipids. This preferential incorporation was very similar to CLA as shown previously. We hypothesize that CD 16:2 and CD 16:3 may be derived from partial beta-oxidation of CLA and CD 20:4, respectively, even though we cannot rule out that CD 16:3 may also be derived from CD 18:3 and CD 20:3. Incubation of skin human fibroblasts from X-linked adrenoleukodystrophy (ALD) patients with c9,t11 CLA showed that CD 16:2 formation in ALD cells was about 50% lower than control cells. This result may tempt to hypothesize that, at least in part, CD 16:2 is beta-oxidized in peroxisomes.

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.

Effects of conjugated linoleic acid on body fat accumulation and serum lipids in hamsters fed an atherogenic diet

Conjugated linoleic acid (CLA) refers to a mixture of naturally occurring positional and geometric isomers of linoleic acid that exist in dairy products and meat. The aim of the present work was to study the effects of c-9,t-11 and t-10,c-12 CLA isomers on body fat accumulation and serum lipids in hamsters fed an atherogenic diet. Hamsters were divided in four groups: one group was fed a chow diet (control) and the other three groups were given semi-purified atherogenic diets with 0.5% linoleic acid (LA), c-9,t-11 or t-10,c-12 CLA. Body weight and food intake were measured daily. After 6 weeks, adipose tissues from different anatomical locations and liver were dissected and weighed. Serum glucose, total cholesterol, HDL-c, LDL-c and triacylglycerol levels, as well as total and free cholesterol, triacylglycerol and phospholipid content in liver were determined by enzymatic methods. No differences in either energy intake or final body weight were found. The addition of t-10,c-12 CLA reduced fat accumulation and led to lower serum cholesterol, as compared with LA group. Nevertheless the level remained higher than in the control animals. The reduction in serum cholesterol was limited to LDL-c. This isomer also reduced triacylglycerol content in liver but did not modify serum triacylglycerol level. In summary, the present study demonstrates that t-10,c-12 CLA is the biologically active agent when anti-obesity and hypocholesterolaemic properties of CLA are considered. In contrast, the isomer c-9,t-11 has no effect on lipid metabolism in hamsters.