Conjugated linoleic acid deteriorates insulin resistance in obese/diabetic mice in association with decreased production of adiponectin and leptin

Anti-obesity effects of Spirulina platensis protein hydrolysate by modulating brain-liver axis in high-fat diet fed mice

Spirulina platensis is a blue-green algae with potential anti-obesity effects. In this study, the anti-obesity effects of whole Spirulina platensis (WSP), Spirulina platensis protein (SPP) and Spirulina platensis protein hydrolysate (SPPH) were compared in high-fat diet fed mice, and the potential acting mechanism of SPPH was also investigated. Totally, SPPH exhibited good anti-obesity effects (reducing 39.8%±9.7% of body weight), lowering 23.8%±1.6% of serum glucose, decreasing 20.8%±1.4% of total cholesterol, while positive drug Simvastatin had the corresponding values: 8.3%±4.6%, 24.8%±1.9% and -2.1%±0.2%, respectively. Subsequently, PCR array was used to conduct gene expression analysis in brain and liver tissues of SPPH-treated mice, which displayed distinctly different expression pattern. The most markedly changed genes included: Acadm (-34.7 fold), Gcg (2.5 fold), Adra2b (2 fold) and Ghsr (2 fold) in brain; Retn (39 fold), Fabp4 (15.5 fold), Ppard (6 fold) and Slc27a1 (5.4 fold) in liver. Further network analysis demonstrated that the significantly expressed genes in brain and liver tissues were mapped into an interacting network, suggesting a modulatory effect on brain-liver axis, major pathways were involved in the axis: PPAR, adipocytokine, AMPK, non-alcoholic fatty liver disease and MAPK. This study showed that Spirulina platensis protein hydrolysate possessed anti-obesity effect in mice.

Anti-diabetic effect of S-adenosylmethionine and α-glycerophosphocholine in KK-Ay mice

Six-week-old male KK-A^y mice received drinking water with S-adenosylmethionine (SAM), α-glycerophosphocholine (GPC), or SAM+GPC for 10 weeks. The serum glucose of SAM+GPC at 15 weeks old, total cholesterol of GPC at 12 weeks old, and triglyceride of GPC at 15 weeks old and of SAM at 16 weeks old were reduced. SAM+GPC reduced serum leptin and food intake. Abbreviations: SAM: S-adenosylmethionine; GPC: α-glycerophosphocholine.

Salivary gland hypofunction in KK-Ay type 2 diabetic mice

BACKGROUND

Hypofunction of different organs in the body is associated with diabetes, including in the oral cavity. Diabetes is often associated with xerostomia, but the underlying mechanism is not well characterized. Thus, the mechanisms underlying diabetes-induced xerostomia were investigated in this study in KK-A ^y mice as an experimental model of type 2 diabetes.

METHODS

The mechanisms involved in diabetes-induced xerostomia were investigated using the ex vivo glandular perfusion technique, histological analysis, and immunohistochemical and intracellular signaling analyses.

RESULTS

Ex vivo submandibular gland secretions from KK-A^y mice decreased by 30% following stimulation with 0.3 μmol/L carbachol (CCh), a cholinergic agonist. Acinar cell weight was comparable between KK-A^y and control mice, whereas duct cell weight was significantly greater in KK-A^y mice. Concentrations of Na⁺ and Cl^- in the secreted saliva decreased significantly in KK-A^y mice, supporting the finding of increased ductal tissue in KK-A^y mice. Immunohistochemistry revealed no significant differences between KK-A^y and control mice in terms of the expression of Cl^- and water channels, Na⁺ -K⁺ -2Cl^- cotransporters, and membrane proteins critical for fluid secretion. Cellular signaling analysis revealed that the increase in [Ca²⁺ ]_i in response to 0.3 μmol/L CCh was reduced by 30% in KK-A^y mice, although there was no significant difference in the thapsigargin (1.0 μmol/L)-induced increase in store-depleted calcium between KK-A^y and control mice.

CONCLUSIONS

These results demonstrate that submandibular fluid secretion is diminished in KK-A^y mice because of a diminished increase in [Ca²⁺ ]_i . Duct cell weight increased in KK-A^y mice, possibly leading to increased ion reabsorption and thus decreased Na⁺ and Cl^- concentrations in the secreted saliva.

Soy Protein Isolate Suppresses Lipodystrophy-induced Hepatic Lipid Accumulation in Model Mice

Lipodystrophies are acquired and genetic disorders characterized by the complete or partial absence of body fat with a line of metabolic disorders, including hepatic steatosis. Because soy protein isolate (SPI) has been reported to reduce cholesterol and triglyceride levels in animals and humans, we explored the effect of SPI on the pathophysiology of hepatic lipid accumutaion in a diet-induced lipodystrophy model mice. Four weeks of the lipodystrophy model diet induced hepatic lipid accumulation concomitant with marked deficiencies of adipose tissue and serum adipocytokines in mice. However, supplementing the lipodystrophy model diet with SPI could alleviate the hepatic lipid acculation without affecting the lipoatrophic effect of the diet. Enhanced lipogenesis is the principal mechanism of hepatic steatosis in this model, but SPI supplementation significantly attenuated the increase in enzyme activity and/or mRNA expression. Additionally, SPI supplementation upregulated the hepatic mRNA expression of an enzyme involved in cholesterol catabolism. In conclusion, our results indicate the possibility of dietary SPI to attenuate lipodystorophy-induced hepatic steatosis through the direct reduction of hepatic lipogenesis without affecting adipocytokine production.

Two opposite extremes of adiposity similarly reduce inflammatory response of antigen-induced acute joint inflammation

OBJECTIVE

Acute inflammation is a normal response of tissue to an injury. During this process, inflammatory mediators are produced and metabolic alterations occur. Adipose tissue is metabolically activated, and upon food consumption, it disrupts the inflammatory response. However, little is known about the acute inflammatory response in joints that results from diet-induced adipose tissue remodeling. The objective of this study was to determine whether alterations in adipose tissue mass arising from food consumption modify the inflammatory response of antigen-induced joint inflammation in mice.

METHODS

Male BALB/c mice were fed a chow diet, a highly refined carbohydrate-containing (HC) diet for 8 wk. They were then immunized and, after 2 wk, received a knee injection of methylated bovine serum albumin (mBSA). They were sacrificed at 6, 24, and 48 h after injection. The effect of the cafeteria diet for 8 wk, which also increases adipose tissue, or conjugated linoleic acid (CLA) supplementation for 4 wk, a model of lipodystrophy, was evaluated 24 h after knee challenge with mBSA.

RESULTS

Cellular influx, predominantly neutrophils, in synovial fluid was attenuated in the HC diet group, as were levels of myeloperoxidase and IL-1β in periarticular tissue and histopathological analysis. These responses were associated with reduced adiponectin and increased leptin in serum, which was pronounced in mice fed the HC diet. Cafeteria diet and CLA supplementation induced a profile similar to that seen with the HC diet in terms of inflammation, disease response, and metabolic alteration. Interestingly, after the injection of mBSA, the area of adipocytes in the infrapatellar fat pad increased in mice fed with chow diet similar to those fed the HC and cafeteria diet.

CONCLUSIONS

We demonstrated that attenuation of joint response induced by diet was independent of adipose tissue remodeling but could be associated with metabolic alterations.

Impact of Conjugated Linoleic Acid (CLA) on Skeletal Muscle Metabolism

Conjugated linoleic acid (CLA) has garnered special attention as a food bioactive compound that prevents and attenuates obesity. Although most studies on the effects of CLA on obesity have focused on the reduction of body fat, a number of studies have demonstrated that CLA also increases lean body mass and enhances physical performances. It has been suggested that these effects may be due in part to physiological changes in the skeletal muscle, such as changes in the muscle fiber type transformation, alteration of the intracellular signaling pathways in muscle metabolism, or energy metabolism. However, the mode of action for CLA in muscle metabolism is not completely understood. The purpose of this review is to summarize the current knowledge of the effects of CLA on skeletal muscle metabolism. Given that CLA not only reduces body fat, but also improves lean mass, there is great potential for the use of CLA to improve muscle metabolism, which would have a significant health impact.

Docosahexaenoic acid increases cellular adiponectin mRNA and secreted adiponectin protein, as well as PPARγ mRNA, in 3T3-L1 adipocytes

Adiponectin, a protein secreted from adipose tissue, has been shown to have anti-diabetic and anti-inflammatory effects, but its regulation is not completely understood. Long-chain n-3 fatty acids eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) may be involved in adiponectin regulation as they are potential ligands for peroxisome proliferator-activated receptor-γ (PPARγ), a key transcription factor for the adiponectin gene. To examine this, 3T3-L1 adipocytes were incubated with 125 µmol·L–1 EPA, DHA, palmitic, or oleic acids complexed to albumin, or with albumin alone (control) for 24 h. Adipocytes were also incubated for 24 h with EPA and DHA plus bisphenol-A-diglycidyl ether (BADGE), a PPARγ antagonist. Both EPA and DHA increased (p < 0.05) secreted adiponectin concentration compared with the control (44% and 102%, respectively), but did not affect cellular adiponectin protein content. Incubation with BADGE and DHA inhibited increases in secreted adiponectin protein, suggesting that DHA may act through a PPARγ-dependent mechanism. However, BADGE had no effect on EPA-induced increases in secreted adiponectin protein. Only DHA enhanced (p < 0.05) PPARγ and adiponectin mRNA expression compared wtih the control. Our results demonstrate that DHA increases cellular adiponectin mRNA and secreted adiponectin protein in 3T3-L1 adipocytes, possibly by a mechanism involving PPARγ. Moreover, DHA increased adiponectin concentration to a greater extent (40% more, p < 0.05) compared with EPA, emphasizing the need to consider the independent actions of EPA and DHA in adipocytes.

Role of obesity-associated dysfunctional adipose tissue in cancer: a molecular nutrition approach

Obesity is a complex disease caused by the interaction of a myriad of genetic, dietary, lifestyle and environmental factors, which favors a chronic positive energy balance, leading to increased body fat mass. There is emerging evidence of a strong association between obesity and an increased risk of cancer. However, the mechanisms linking both diseases are not fully understood. Here, we analyze the current knowledge about the potential contribution that expanding adipose tissue in obesity could make to the development of cancer via dysregulated secretion of pro-inflammatory cytokines, chemokines and adipokines such as TNF-α, IL-6, leptin, adiponectin, visfatin and PAI-1. Dietary factors play an important role in the risk of suffering obesity and cancer. The identification of bioactive dietary factors or substances that affect some of the components of energy balance to prevent/reduce weight gain as well as cancer is a promising avenue of research. This article reviews the beneficial effects of some bioactive food molecules (n-3 PUFA, CLA, resveratrol and lipoic acid) in energy metabolism and cancer, focusing on the molecular mechanisms involved, which may provide new therapeutic targets in obesity and cancer.

Moderate doses of conjugated linoleic acid reduce fat gain, maintain insulin sensitivity without impairing inflammatory adipose tissue status in mice fed a high-fat diet

BACKGROUND

The enrichment of diet with nutrients with potential benefits on body composition is a strategy to combat obesity. Conjugated linoleic acid (CLA) due its beneficial effects on body composition and inflammatory processes becomes an interesting candidate, since the promotion and impairment of obesity is closely linked to a low-grade inflammation state of adipose tissue. Previously we reported the favourable effects of moderate doses of CLA mixture on body composition and inflammatory status of adipose tissue in mice fed a standard-fat diet. In the present study we assessed the potential beneficial effects of CLA mixture (cis-9, trans-11 and trans-10, cis-12, 50:50) in mice fed a high-fat diet.

METHODS

Two doses were assayed: 0.15 g (CLA1) and 0.5 g CLA/kg body weight (CLA2) for the first 30 days of the study and then animals received a double amount for another 35 days.

RESULTS

The lowest dose (CLA1) had minor effects on body composition, plasma parameters and gene expression. However, a clear reduction in fat accumulation was achieved by CLA2, accompanied by a reduction in leptin, adiponectin and non-esterified fatty acids (NEFA) plasma concentrations. Insulin sensitivity was maintained despite a slight increase in fasting glucose and insulin plasma concentrations. The study of gene expression both in adipocytes and in the stromal vascular fraction (SVF) suggested that CLA may reduce either the infiltration of macrophages in adipose tissue or the induction of expression of pro-inflammatory cytokines.

CONCLUSION

In conclusion, the use of moderate doses of an equimolar mix of the two main CLA isomers reduces body fat content, improves plasma lipid profile, maintains insulin sensitivity (despite a moderate degree of hyperinsulinaemia) without the promotion of inflammatory markers in adipose tissue of mice fed a high-fat diet.

The influence of sex, body composition, and nonesterified fatty acids on serum adipokine concentrations

Serum adiponectin concentrations are higher in women than men. The sexual dimorphism for adiponectin has been attributed to the direct effects of testosterone on adipose tissue adiponectin secretion. However, serum testosterone and adiponectin concentrations are generally lower in obese men than lean men, suggesting that sex steroids may not be the only factor that contributes to sex differences in serum adiponectin. The primary objective of this study was to examine the influence of sex, body composition, and nonesterified fatty acids (NEFAs) on serum adiponectin concentrations. Women and men between the ages of 18 and 35 years were consecutively accrued into the study. Sixty-one participants were partitioned into normal-weight (15 female and 16 male) or obese (14 female and 16 male) groups. Blood samples were obtained after a 12-hour fast. Differences between groups were determined by analysis of variance with Tukey-Kramer post hoc testing. Serum adiponectin was 26% higher in women compared with men. Body mass index was associated with total serum adiponectin in men (r = -0.63, P < .05) but not women. Adiponectin was correlated with the homeostasis model assessment index in women (r = -0.56, P < .05) and men (r = -0.58, P < .05) and with NEFAs (r = -0.68, P < .05) in men only. After partitioning men and women into normal-weight and obese groups, serum adiponectin was lower and NEFAs were higher in obese men only. Homeostasis model assessment was similar between obese women and men despite higher NEFAs in the obese men. Leptin and plasminogen activator inhibitor-1 were higher in obese participants but were not associated with serum NEFAs. These results suggest that serum NEFAs may reduce adiponectin concentrations independent of their effects on insulin sensitivity in obese young men.

Effects of trans-10,cis-12 conjugated linoleic acid on body composition in genetically obese mice

Conjugated linoleic acid (CLA) has shown a number of biologically beneficial effects, including prevention of obesity. The purpose of this study was to test effects of dietary supplementation of 0.5% trans-10,cis-12 CLA in a high fat diet in neuronal basic helix-loop-helix 2 knock-out animals (N2KO), which is a unique animal model representing adult-onset inactivity-related obesity. Eight wild-type (WT) and eight N2KO female mice were fed either 0.5% trans-10,cis-12 CLA-containing diet or control diet (with 20% soybean oil diet) for 12 weeks. Body weights, food intake, adipose tissue weights, body compositions, and blood parameters were analyzed. Overall, N2KO animals had greater body weights, food intake, adipose tissue weights, and body fat compared to WT animals. CLA supplementation decreased overall body weights and total fat, and the effect of dietary CLA on adipose tissue reduction was greater in N2KO than in WT mice. Serum leptin and triglyceride levels were reduced by CLA in both N2KO and WT animals compared to control animals, while there was no effect by CLA on serum cholesterol. The effect of CLA to lower fat mass, increase lean body mass, and lower serum leptin and triglycerides in sedentary mice supports the possibility of using CLA to prevent or alleviate ailments associated with obesity.

Effect of CLA isomers and their mixture on aging C57Bl/6J mice

BACKGROUND

Dietary supplements containing conjugated linoleic acid (CLA) are widely promoted for weight loss management over the counter. Recently, FDA approved the CLA as Generally Recognized as Safe category so that it can be used in various food and beverages. The combined effect of CLA isomers have been studied extensively in animals and humans, however, the role of individual isomers remains unraveled.

AIM

The present investigation addresses the effects of CLA isomers on body composition and body weight as well as safety using female C57Bl/6J aging mice.

METHODS

Two main CLA isomers and their mixture were fed to 12-months-old female C57Bl/6J mice. Ten percent corn oil (CO) based fat diet supplemented with 0.5% purified cis 9 trans 11 (c9,t11) CLA or trans 10 cis 12 (t10,c12) CLA or their mixture (CLA mix, 50:50) for 6 months. The lean mass, fat mass, glucose, non-esterified fatty acids, and insulin were examined at the end of study.

RESULTS

As a result of 6 months dietary intervention, both t10,c12 CLA and CLA mix groups showed increased lean mass and reduced fat mass compared to that of c9,t11 CLA and CO group. However, insulin resistance and liver hypertrophy were observed in t10,c12 CLA and CLA mix groups based on the results of homeostasis model assessment, revised quantitative insulin-sensitivity check index (R-QUICKI), intravenous glucose tolerance test, and liver histology. Liver histology revealed that increased liver weight was due to hypertrophy.

CONCLUSION

In conclusion, the major CLA isomers have a distinct effect on fat mass, glucose, and insulin metabolism. The t10,c12 isomer was found to reduce the fat mass and to increase the lean mass but significantly contributed to increase insulin resistance and liver hypertrophy, whereas c9,t11 isomer prevented the insulin resistance. Between the two major CLA isomers, the t10,c12 was attributed to reduce fat mass whereas, c9,t11 improves the insulin sensitivity.

Effects of 9cis,11trans and 10trans,12cis CLA on osteoclast formation and activity from human CD14+ monocytes

Background

Mixed CLA isomers variably affect bone resorption in animals and decrease osteoclast formation and activity in murine osteoclasts. These variable effects may be due to the different isomers present in commercial preparations of CLA, and the effects of the predominant individual isomers, 9cis,11trans (9,11) and 10trans,12cis (10,12) CLA are not clear. The objectives of this study were to determine the effects of the individual CLA isomers on osteoclast formation and activity from human CD14⁺ monocytes, and to determine whether any changes are accompanied by changes in cathepsin K, matrix metalloproteinase-9 (MMP-9), receptor activator of NF-κB (RANK) and tumour necrosis factor alpha (TNFα) gene expression. Osteoclasts were identified as TRAP⁺ multinucleated cells. Osteoclast activity was quantified by the amount of TRAP in the cultured media.

Results

At 50 μM, 9,11 CLA inhibited osteoclast formation by ~70%, and both 9,11 and 10,12 CLA decreased osteoclast activity by ~85–90%. Both isomers inhibited cathepsin K (50 μM 9,11 by ~60%; 10,12 by ~50%) and RANK (50 μM 9,11 by ~85%; 50 μM 10,12 by ~65%) expression, but had no effect on MMP-9 or TNFα expression.

Conclusion

9,11 CLA inhibits osteoclast formation and activity from human cells, suggesting that this isomer may prevent bone resorption in humans. Although 10,12 CLA did not significantly reduce osteoclast formation, it reduced osteoclast activity and cathepsin K and RANK expression, suggesting that this isomer may also affect bone resorption.

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

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

Flaxseed oil prevents trans-10, cis-12-conjugated linoleic acid-induced insulin resistance in mice

Insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD) are found in 35 and 30 % of US adults, respectively. Trans-10, cis-12-conjugated linoleic acid (CLA) has been found to cause both these disorders in several animal models. We hypothesised that IR and NAFLD caused by CLA result from n-3 fatty acid deficiency. Pathogen-free C57BL/6N female mice (aged 8 weeks; n 10) were fed either a control diet or diets containing trans-10, cis-12-CLA (0.5 %) or CLA+flaxseed oil (FSO) (0.5 %+0.5 %) for 8 weeks. Weights of livers, concentration of circulating insulin, values of homeostatic model 1 (HOMA1) for IR and HOMA1 for beta cell function were higher by 160, 636, 985 and 968 % in the CLA group compared with those in the control group. FSO decreased fasting glucose by 20 % and liver weights by 37 % compared with those in the CLA group; it maintained circulating insulin, HOMA1-IR and HOMA1 for beta cell function at levels found in the control group. CLA supplementation decreased n-6 and n-3 wt% concentrations of liver lipids by 57 and 73 % and increased the n-6:n-3 ratio by 58 % compared with corresponding values in the control group. FSO increased n-6 and n-3 PUFA in liver lipids by 33 and 342 % and decreased the n-6:n-3 ratio by 70 % compared with corresponding values in the CLA group. The present results suggest that some adverse effects of CLA may be due to n-3 PUFA deficiency and that these can be corrected by a concomitant increase in the intake of alpha-linolenic acid, 18 : 3n-3.

Effect of leptin infusion on insulin sensitivity and lipid metabolism in diet-induced lipodystrophy model mice

BACKGROUND

Lipodystrophies are rare acquired and genetic disorders characterized by the complete or partial absence of body fat with a line of metabolic disorders. Previous studies demonstrated that dietary conjugated linoleic acid (CLA) induces hepatic steatosis and hyperinsulinemia through the drastic reduction of adipocytokine levels due to a paucity of adipose tissue in mice and the pathogenesis of these metabolic abnormalities in CLA-fed mice is similar to that in human lipodystrophy. The present study explores the effect of leptin infusion on the pathogenesis of diet-induced lipodystrophy in mice. C57BL/6N mice were assigned to three groups: (1) mice were fed a semisynthetic diet supplemented with 6% corn oil and infused PBS intraperitoneally (normal group), (2) mice were fed a semisynthetic diet supplemented with 4% corn oil plus 2% CLA and infused PBS intraperitoneally (lipodystrophy-control group), and (3) mice were fed a semisynthetic diet supplemented with 4% corn oil plus 2% CLA and infused recombinant murine leptin intraperitoneally (lipodystrophy-leptin group). All mice were fed normal or lipodystrophy model diets for 4 weeks and were infused intrapeneally 0 or 5 mug of leptin per day from third week of the feeding period for 1 week.

RESULTS

The results indicate that leptin infusion can attenuate hepatic steatosis and hyperinsulinemia through the reduction of hepatic triglyceride synthesis and the improvement of insulin sensitivity in diet-induced lipodystrophy model mice.

CONCLUSION

We expect the use of this model for clarifying the pathophysiology of lipodystrophy-induced metabolic abnormalities and evaluating the efficacy and safety of drug and dietary treatment.

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

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

Dietary conjugated linoleic acid decreases adipocyte size and favorably modifies adipokine status and insulin sensitivity in obese, insulin-resistant rats

Conjugated linoleic acids (CLA) have been shown to alter adiposity in some species with varying effects on insulin resistance. The objective of this 8-week study was to investigate the effects of feeding a CLA mixture (1.5%, wt/wt) on adipocyte size, insulin sensitivity, adipokine status, and adipose lipid composition in fa/fa vs lean Zucker rats. The fa/fa CLA-fed rats had smaller adipocytes and improved insulin sensitivity compared with fa/fa rats fed the control diet. Conjugated linoleic acids did not affect select markers of adipose differentiation, lipid filling, lipid uptake, or oxidation. Dietary CLA, compared with the control diet, reduced circulating leptin and elevated fasting serum adiponectin concentrations in fa/fa rats. Adipose resistin messenger RNA levels were greater in fa/fa CLA-fed rats compared with fa/fa control rats. CLA did not markedly alter adipose phospholipid fatty acid composition, and the changes in the triacylglycerol fatty acid composition reflected a lower delta-9 desaturase index of CLA-fed vs control-fed rats. In conclusion, CLA reduced adipocyte size and favorably modified adipokine status and insulin sensitivity in fa/fa Zucker rats.

Body composition and selected blood parameters in mice fed a combination of fibre and conjugated linoleic acid

Feeding mice conjugated linoleic acid (CLA) reduces body fat. Soluble fibre decreases apparent lipid digestibility. The objective of the present study was to examine whether a combination of dietary CLA and soluble fibre would further decrease the proportion of body fat than a diet with CLA alone. Therefore, we fed mice diets with CLA and different amounts of Nutrim, containing 10% soluble fibre. CLA was added to the control diet at the expense of high oleic acid sunflower oil (HOSF) component and Nutrim was added at the expense of an isoenergetic combination of starch, dextrose and cellulose. The diets were fed for 28 days. Weight gain after 28 days was less in CLA-fed animals than in HOSF-fed animals. Both CLA and Nutrim increased the body water content. CLA reduced total body fat and epidydymal fat but Nutrim did not. No interaction of CLA and fibre was detected. We, therefore, must conclude that under the present experimental conditions dietary CLA and fibre do not interact to reduce body fat deposition.

Linoleic acid decreases leptin and adiponectin secretion from primary rat adipocytes in the presence of insulin

Obesity rates have dramatically increased over the last few decades and, at the same time, major changes in the type of fatty acid intake have occurred. Linoleic acid, an n-6 polyunsaturated fatty acid, is an essential fatty acid occurring in high amounts in several western diets. A potential role of this fatty acid on obesity has been suggested. Controversial effects of linoleic acid on insulin sensitivity have also been reported. Thus, the aim of this study was to examine the direct effects of linoleic acid on leptin and adiponectin production, two adipokines known to influence weight gain and insulin sensitivity. Because insulin-stimulated glucose metabolism is an important regulator of leptin production, the effects of linoleic acid on adipocyte metabolism were also examined. For this purpose, isolated rat adipocytes were incubated with linoleic acid (1-200 microM) in the absence or presence of insulin. Linoleic acid (1-200 microM) significantly decreased insulin-stimulated leptin secretion and expression (P < 0.05), however, no changes in basal leptin production were observed. Linoleic acid also induced a significant decrease (approximately 20%) in adiponectin secretion (P < 0.05), but only in the presence of insulin and at the highest concentration tested (200 microM). This fatty acid did not modify either glucose uptake or lactate production and the percentage of glucose metabolized to lactate was not changed either. Together, these results suggest that linoleic acid seems to interfere with other insulin signalling pathway different from those controlling glucose uptake and metabolism, but involved in the regulation of leptin and adiponectin production.

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

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

The conjugated linoleic acid ester of estrone induces the mobilisation of fat in male Wistar rats

We investigated whether the substitution of the fatty acid moiety in oleoyl-estrone (OE) by conjugated linoleic acid, i.e. conjugated linoleoyl-estrone (cLE) may help improve the antiobesity effects of OE. Overweight (17% fat) male rats were treated for 10 days with oral OE or cLE (10 nmol/g per day) and compared with controls receiving only the oily vehicle. Rat weight and food intake were measured daily. After killing by decapitation, body composition and main plasma parameters were analysed. cLE induced marked decreases in body weight, energy intake, carcass energy and body lipid, whilst sparing protein; the effects were not significantly different from those obtained with OE. Energy expenditure was unchanged, but energy intake decreased to 46% (OE) or 55% (cLE) of controls; whole body energy decreased by 29% (OE) or 24% (cLE) in the 10-day period studied. Plasma composition showed almost identical decreases in glucose and cholesterol elicited by OE and cLE, with a more marked decrease in triacylglycerols by OE and no effect of either on NEFA. OE decreased leptin and insulin levels, but the effects of cLE were more marked on both, with similar decreases in adiponectin. It can be concluded that cLE is a new drug of the OE family; its overall effects on energy were akin to those of OE, albeit fractionally less effective at the single dose tested. However, this lower potency on lipid mobilisation does not affect other effects, such as powerful hypercholesterolemic effects or the modulation of adiponectin. And last, but not least, cLE seems to produce a more marked decrease in leptin and insulin than OE, which may reflect a coordinate action of the conjugated linoleic acid moiety and the "OE effect" on target tissues. If that were the case, cLE may constitute an improvement over OE in its action on insulin resistance.

Conjugated linoleic acid and chromium lower body weight and visceral fat mass in high-fat-diet-fed mice

More than half of the U.S. population has a body mass index of 25 kg/m2 or more, which classifies them as overweight or obese. Obesity is often associated with comorbidities such as diabetes, cardiovascular diseases, and cancer. CLA and chromium have emerged as major dietary supplements that reduce body weight and fat mass, and increase basal metabolic rate in animal models. However, studies show that CLA induces insulin resistance in mice and in humans, whereas Cr improves insulin sensitivity. Hence, we designed the present study to examine the combined effect of CLA and Cr on body composition and insulin sensitivity in a Balb/c mice (n = 10/group) model of high-fat-diet-induced obesity. CLA alone lowered body weight, total body fat mass, and visceral fat mass, the last of which decreased further with the combination of CLA and Cr. This effect was accompanied by decreased serum leptin levels in CLA-fed and CLA + Cr-fed mice, and by higher energy expenditure (EE) and oxygen consumption (OC) in CLA + Cr-fed mice. Serum levels of glucose, insulin, the pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6), as well as insulin resistance index (IRI), decreased with CLA, whereas CLA and Cr in combination had significant effects on insulin and IL-6 concentrations and IRI. In summary, CLA + Cr decreased body weight and fat mass in high-fat-diet-fed mice, which may be associated with decreased leptin levels and higher EE and OC.

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.

Conjugated linoleic acid intake in humans: a systematic review focusing on its effect on body composition, glucose, and lipid metabolism

Studies performed on different species show that the consumption of conjugated linoleic acid (CLA) leads to a loss of fat and total body weight, reduces the plasma concentrations of total and LDL cholesterol, and has an antiinflammatory effect. This article reviews the clinical trials on human beings that evaluate how mixtures of CLA isomers administered as supplements or CLA-enriched products can affect total body weight, body composition, plasma lipid profile, glycemia, insulinemia, insulin sensitivity, lipid oxidation, and inflammation. After analyzing the few studies published to date in reduced samples of healthy humans or patients with overweight, obesity, metabolic syndrome, or diabetes, we deduce that there is not enough evidence to show that conjugated linoleic acid has an effect on weight and body composition in humans. However, some of these studies have observed that the administration of various CLA isomers has adverse effects on lipid profile (it decreases HDL cholesterol concentration and increases Lp(a) circulating levels), glucose metabolism (glycemia, insulinemia or insulin sensitivity), lipid oxidation, inflammation, or endothelial function. Therefore, long-term randomized clinical trials, controlled with placebo, need to be made in large samples of patients to evaluate the efficacy and safety of CLA isomers before its indiscriminate use in human beings can be recommended.

Conjugated linoleic acid protects against age-associated bone loss in C57BL/6 female mice

Osteoporosis is one of the major causes of morbidity in the elderly. Inflammation exerts a significant influence on bone turnover, inducing the chronic form of osteoporosis. Dietary nutrition has the capacity to modulate inflammatory response. Therefore, nutritional strategies and lifestyle changes may prevent age-related osteoporosis, thereby improving the quality of life of the elderly population. Conjugated linoleic acid (CLA) has been shown to positively influence calcium and bone metabolism. Hence, this study was undertaken to examine the effect of CLA on bone mineral density (BMD) in middle-aged C57BL/6 female mice. After 10 weeks on diet, CLA-fed mice (14 months) maintained a higher BMD in different bone regions than corn oil (CO)-fed mice. The increased BMD was accompanied by a decreased activity of proinflammatory cytokines (such as tumor necrosis factor alpha, interleukin-6 and the receptor activator of NF-kappaB ligand) and decreased osteoclast function. Furthermore, a significant decrease in fat mass and an increase in muscle mass were also observed in CLA-fed mice compared to CO-fed mice. In conclusion, these findings suggest that CLA may prevent the loss of bone and muscle mass by modulating markers of inflammation and osteoclastogenic factors.

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.