Alfredo Fernández-Quintela

Conjugated linoleic acid isomers: Differences in metabolism and biological effects

The term conjugated linoleic acid (CLA) refers to a mixture of linoleic acid positional and geometric isomers, characterized by having conjugated double bonds, not separated by a methylene group as in linoleic acid. CLA isomers appear as a minor component of the lipid fraction, found mainly in meat and dairy products from cows and sheep. The most abundant isomer is cis‐9,trans‐11, which represents up to 80% of total CLA in food. These isomers are metabolized in the body through different metabolic pathways, but important differences, that can have physiological consequences, are observed between the two main isomers. The trans‐10,cis‐12 isomer is more efficiently oxidized than the cis‐9,trans‐11 isomer, due to the position of its double bounds. Interest in CLA arose in its anticarcinogenic action but there is an increasing amount of specific scientific literature concerning the biological effects and properties of CLA. Numerous biological effects of CLA are due to the separate action of the most studied isomers, cis‐9,trans‐11 and trans‐10,cis‐12. It is also likely that some effects are induced and/or enhanced by these isomers acting synergistically. Although the cis‐9,trans‐11 isomer is mainly responsible for the anticarcinogenic effect, the trans‐10,cis‐12 isomer reduces body fat and it is referred as the most effective isomer affecting blood lipids. As far as insulin function is concerned, both isomers seem to be responsible for insulin resistance in humans. Finally, with regard to the immune system it is not clear whether individual isomers of CLA could act similarly or differently.

Composition and functional properties of protein isolates obtained from commercial legumes grown in northern Spain

Pea (Pisum sativum), faba bean (Vicia faba) and soybean (Glycine max) seeds were characterized, and protein isolates were prepared following an isoelectric point precipitation procedure. Soybean seeds showed the highest protein content (36.7%) and carbohydrate was the major constituent in the pea (59.4%) and the faba bean seeds (52.1%). Protein contents were higher than 80% in all the protein isolates. The amino acid contents in the protein isolates were, in general, higher than those in their own starting seeds. The antinutritional factor contents were reduced after the protein isolate preparation. The highest reductions achieved for tannins were 95% in the faba bean protein isolate, and for phytates (45%) and trypsin inhibitor activity (46%) in the pea protein isolate. Haemagglutinating activity was not detected in any of the protein isolates. Minimum solubility values were observed at a pH range between 4.0 and 6.0, and maximal solubilities were obtained at basic pH values. The faba bean protein isolate showed the highest water and oil absorption capacities, and the best gelling properties. The soybean protein isolate had the best foam expansion capacity. Thus, the protein isolates had an improvement in some of the characteristics compared to their original seeds with lower contents in tannins, phytates and haemagglutinating activity, but had weak functional properties.

Resveratrol: Anti-Obesity Mechanisms of Action

Resveratrol is a non-flavonoid polyphenol which belongs to the stilbenes group and is produced naturally in several plants in response to injury or fungal attack. Resveratrol has been recently reported as preventing obesity. The present review aims to compile the evidence concerning the potential mechanisms of action which underlie the anti-obesity effects of resveratrol, obtained either in cultured cells lines and animal models. Published studies demonstrate that resveratrol has an anti-adipogenic effect. A good consensus concerning the involvement of a down-regulation of C/EBPα and PPARγ in this effect has been reached. Also, in vitro studies have demonstrated that resveratrol can increase apoptosis in mature adipocytes. Furthermore, different metabolic pathways involved in triacylglycerol metabolism in white adipose tissue have been shown to be targets for resveratrol. Both the inhibition of de novo lipogenesis and adipose tissue fatty acid uptake mediated by lipoprotein lipase play a role in explaining the reduction in body fat which resveratrol induces. As far as lipolysis is concerned, although this compound per se seems to be unable to induce lipolysis, it increases lipid mobilization stimulated by β-adrenergic agents. The increase in brown adipose tissue thermogenesis, and consequently the associated energy dissipation, can contribute to explaining the body-fat lowering effect of resveratrol. In addition to its effects on adipose tissue, resveratrol can also acts on other organs and tissues. Thus, it increases mitochondriogenesis and consequently fatty acid oxidation in skeletal muscle and liver. This effect can also contribute to the body-fat lowering effect of this molecule.

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 ofc-9,t-11 andt-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 ort-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 oft-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 thatt-10,c-12 CLA is the biologically active agent when anti-obesity and hypocholesterolaemic properties of CLA are considered. In contrast, the isomerc-9,t-11 has no effect on lipid metabolism in hamsters.ResumenEl término ácido linoleico conjugado (ALC) se utiliza para designar una serie de isómeros del ácido linoleico, presentes en los lácteos y la carne, que presentan los dobles enlaces en posición conjugada. El objetivo del presente trabajo consistió en estudiar el efecto de los isómerosc-9,t-11 yt-10,c-12 del ALC sobre la acumulación de grasa corporal y los lípidos séricos, en hámsters alimentados con una dieta aterogénica. Los hámsters se distribuyeron en cuatro grupos: un grupo recibió pienso de laboratorio (control) y los otros tres grupos, dietas aterogénicas con 0,5% de ácido linoleico, ALCc-9,t-11 ó ALCt-10,c-12. Se midió diariamente la ingesta de alimento y el peso corporal. Tras 6 semanas, se diseccionaron y pesaron los tejidos adiposos de diferentes localizaciones anatómicas y el hígado. Se midieron las concentraciones séricas de glucosa, colesterol total, c-HDL, c-LDL y triglicéridos, y el contenido hepático de colesterol total y libre, triglicéridos y fosfolípidos, por métodos enzimáticos. No se encontraron diferencias significativas ni en la ingesta de energía ni en el peso corporal final. El isómerot-10,c-12 redujo la acumulación de grasa y disminuyó el colesterol total sérico; no obstante, su nivel se mantuvo por encima del de los animales control. La reducción del colesterol sérico se produjo a expensas del c-LDL. Este isómero también disminuyó el contenido hepático de triglicéridos pero no modificó los triglicéridos séricos. El presente estudio demuestra que el isómerot-10,c-12 del ALC es el biológicamente activo como agente anti-obesidad e hipocolesterolemiante. Por el contrario, el isómeroc-9,t-11 no afectó al metabolismo lipídico en hámsters.

Effects of resveratrol on obesity-related inflammation markers in adipose tissue of genetically obese rats

OBJECTIVE The aim of this study was to examine whether resveratrol might represent a promising therapeutic tool with which to combat adipose tissue chronic inflammation in a model of genetic obesity and to link its anti-inflammatory activity with its effect on body fat reduction. METHODS Twenty 6-wk-old male Zucker (fa/fa) rats were randomly distributed into two experimental groups. Resveratrol (RSV) was given orally (15 mg/kg body weight/d in RSV group) by means of an orogastric catheter for 6 wk. Enzyme activities were measured spectrophotometrically or fluorimetrically. Gene and protein expressions were analyzed by reverse transcriptase polymerase chain reaction and Western blot respectively. Cytokine concentrations and the activity of nuclear factor κ-light-chain-enhancer of activated β cells (NF-κB) were measured by using commercial kits. RESULTS RSV reduced the weight of internal adipose tissues. In epididymal depot glucose-6P-dehydrogenase, acetyl-CoA carboxylase activities, as well as lipoprotein lipase expression and activity were reduced by RSV. The expression of hormone-sensitive lipase was increased, and that of the cluster of differentiation 36 was reduced. Serum concentrations of tumor necrosis factor-α, monocyte chemoattractant protein 1, and C-reactive protein were lower in the RSV-treated group than in the control group. Protein expression of interleukin-6 and the activity of NF-κB, were decreased by RSV. CONCLUSION The present results provide evidence that fatty acid uptake and lipolysis are metabolic pathways involved in the response of adipose tissue to RSV. This polyphenol modulates plasma cytokine levels partially by reducing macrophage infiltration in adipose tissue and inhibiting NF-κB activity.

The role of dietary fat in adipose tissue metabolism

Energy intake and expenditure tend on average to remain adjusted to each other in order to maintain a stable body weight, which is only likely to be sustained if the fuel mix oxidised is equivalent to the nutrient content of the diet. Whereas protein and carbohydrate degradation and oxidation are closely adjusted to their intakes, fat balance regulation is less precise and that fat is more likely to be stored than oxidised. It has been demonstrated that dietary fatty acids have an influence not only on the fatty acid composition of membrane phospholipids, thus modulating several metabolic processes that take place in the adipocyte, but also on the composition and the quantity of different fatty acids in adipose tissue. Moreover, dietary fatty acids also modulate eicosanoid presence, which have hormone-like activities in lipid metabolism regulation in adipose tissue. Until recently, the adipocyte has been considered to be no more than a passive tissue for storage of excess energy. However, there is now compelling evidence that adipocytes have a role as endocrine secretory cells. Some of the adipokines produced by adipose tissue, such as leptin and adiponectin, act on adipose tissue in an autocrine/paracrine manner to regulate adipocyte metabolism. Furthermore, dietary fatty acids may influence the expression of adipokines. The nutrients are among the most influential of the environmental factors that determine the way adipose tissue genes are expressed by functioning as regulators of gene transcription. Therefore, not only dietary fat amount but also dietary fat composition influence adipose tissue metabolism.

High-throughput sequencing of microRNAs in peripheral blood mononuclear cells: identification of potential weight loss biomarkers.

Introduction MicroRNAs (miRNAs) are being increasingly studied in relation to energy metabolism and body composition homeostasis. Indeed, the quantitative analysis of miRNAs expression in different adiposity conditions may contribute to understand the intimate mechanisms participating in body weight control and to find new biomarkers with diagnostic or prognostic value in obesity management. Objective The aim of this study was the search for miRNAs in blood cells whose expression could be used as prognostic biomarkers of weight loss. Methods Ten Caucasian obese women were selected among the participants in a weight-loss trial that consisted in following an energy-restricted treatment. Weight loss was considered unsuccessful when <5% of initial body weight (non-responders) and successful when >5% (responders). At baseline, total miRNA isolated from peripheral blood mononuclear cells (PBMC) was sequenced with SOLiD v4. The miRNA sequencing data were validated by RT-PCR. Results Differential baseline expression of several miRNAs was found between responders and non-responders. Two miRNAs were up-regulated in the non-responder group (mir-935 and mir-4772) and three others were down-regulated (mir-223, mir-224 and mir-376b). Both mir-935 and mir-4772 showed relevant associations with the magnitude of weight loss, although the expression of other transcripts (mir-874, mir-199b, mir-766, mir-589 and mir-148b) also correlated with weight loss. Conclusions This research addresses the use of high-throughput sequencing technologies in the search for miRNA expression biomarkers in obesity, by determining the miRNA transcriptome of PBMC. Basal expression of different miRNAs, particularly mir-935 and mir-4772, could be prognostic biomarkers and may forecast the response to a hypocaloric diet.

The body fat-lowering effect of conjugated linoleic acid: a comparison between animal and human studies

Different reasons which justify differences between rodents and humans in body fat reduction produced by conjugated linoleic acid (CLA) could be proposed. The doses used in humans are lower then those used in rodents. Human experiments have been performed with CLA isomer mixtures instead of isolated isomers. The variable dilution of t-10, c-12, the active isomer, among different preparations might explain the reduced responsiveness in humans. Diet composition may modulate CLA effects on body fat accumulation. As far as human studies are concerned, a specific dietary pattern has not been established. As a result differences among studies and also among subjects in the same study are likely. In rodents, the effects of CLA vary with genotype, suggesting that genetic predisposition to fat accumulation can play an important role in the effectiveness of CLA. Human volunteers with different body mass index have participated in the published studies and even in the same experiment. So, differences in lipid metabolism among subjects could help to explain the discrepancies observed in the literature. Age and maturity may also be crucial. Experiments using rodents have been conducted with growing animals and there is little evidence of CLA effectiveness in adult animals. By contrast, human studies have been performed with adults. Inhibition of lipogenesis in white adipose tissue is one of the mechanisms which have been proposed to explain the body-fat lowering effect of CLA, but lipogenesis in this tissue is very low in humans. Another mechanism suggested is increased fatty acid oxidation in the liver associated with peroxisome proliferation, but humans are relatively insensitive to this effect.ResumenSe pueden proponer diferentes razones para justificar las diferencias en el efecto reductor de la grasa corporal inducido por ácido linoleico conjugado (ALC) entre roedores y humanos. Las dosis utilizadas en humanos son menores que las empleadas en roedores. Además, en humanos se suelen utilizar mezclas de isómeros de ALC en lugar de isómeros aislados. La dilución variable del isómero activo, t-10, c-12, en las distintas mezclas podría explicar la baja respuesta observada en los humanos. La composición de la dieta puede modular los efectos del ALC. En los estudios con humanos no se establece un patrón de alimentación concreto y específico, lo que hace probables las diferencias entre estudios, e incluso entre los individuos de un mismo estudio. Los estudios en roedores han puesto de manifiesto que los efectos del ALC varían con el genotipo del animal, lo que sugiere que la eficacia del ALC puede depender de la predisposición del individuo a la acumulación de grasa corporal. En los estudios con humanos han participado individuos con distintos valores de índice de masa corporal, incluso en un mismo estudio. Por tanto, las diferencias en el metabolismo lipídico entre los distintos individuos pueden ayudar a explicar las discrepancias encontradas en la bibliografía. La edad y el estado de maduración pueden ser también cruciales en le efecto del ALC. En roedores, la mayor parte de los estudios se han llevado a cabo en animales jóvenes en crecimiento y hay pocas evidencias de la eficacia del ALC en animales adultos. Por el contrario, todos los estudios con humanos se han realizado en adultos. Uno de los mecanismos propuestos para justificar la reducción de grasa corporal producida por el ALC es la inhibición de la lipogénesis en tejido adiposo, pero dicho proceso metabólico es muy poco relevante en el tejido adiposo humano, a diferencia de lo que ocurre en roedores. Otro de los mecanismos propuestos es el aumento de la oxidación de ácidos grasos en hígado, como consecuencia de la proliferación peroxisomal inducida por el ALC. En el ser humano este efecto sobre los peroxisomas hepáticos es mucho menor que en los roedores.

The trans-10,cis-12 isomer of conjugated linoleic acid reduces hepatic triacylglycerol content without affecting lipogenic enzymes in hamsters

Conjugated linoleic acid (CLA) refers to the positional and geometric dienoic isomers of linoleic acid. The dietary intake of CLA has been associated with changes in lipid metabolism. The aim of the present work was to assess the effects of the two main isomers of CLA on sterol regulatory element binding protein (SREBP)-1a and SREBP-1c mRNA levels, as well as on mRNA levels and the activities of several lipogenic enzymes in liver. For this purpose hamsters were fed an atherogenic diet supplemented with 5 g linoleic acid, cis-9,trans-11 or trans-10,cis-12 CLA/kg diet for 6 weeks. The trans-10,cis-12 isomer intake produced significantly greater liver weight, but also significantly decreased liver fat accumulation. No changes in mRNA levels of SREBP-1a, SREBP-1c and lipogenic enzymes, or in the activities of these enzymes, were observed. There was no effect of feeding cis-9,trans-11 CLA. These results suggest that increased fat accumulation in liver does not occur on the basis of liver enlargement produced by feeding the trans-10,cis-12 isomer of CLA in hamsters. The reduction in hepatic triacylglycerol content induced by this isomer was not attributable to changes in lipogenesis.

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.