Expression of adipose microRNAs is sensitive to dietary conjugated linoleic acid treatment in mice

Background

Investigation of microRNAs (miRNAs) in obesity, their genetic targets and influence by dietary modulators is of great interest because it may potentially identify novel pathways involved in this complex metabolic disorder and influence future therapeutic approaches. This study aimed to determine whether miRNAs expression may be influenced by conjugated linoleic acid (CLA), currently used to induce fat loss.

Methodology/Principal Findings

We determined retroperitoneal adipose tissue (rWAT) expression of five miRNAs related to adipocyte differentiation (miRNA-143) and lipid metabolism (miRNA-103 and -107) and altered in obesity (miRNA-221 and -222), using the TaqMan®MicroRNA Assay (Applied-Biosystems). In the first experiment, mice were fed with a standard fat diet and orally treated with sunflower oil (control group) and 3 or 10 mg CLA/day for 37 days. In the second experiment, mice were fed with a high fat diet for 65 days. For the first 30 days, mice received the same doses of CLA described above and, from that time onwards, animals received a double dose. Results showed that expression of selected miRNAs was modified in response to CLA treatment and metabolic status. Interestingly, a strong correlation was observed between miR-103 and -107 expression, as well as miR-221 and -222 in both experiments. Moreover, changes in miRNAs expression correlated with several adipocyte gene expressions: miR-103 and -107 correlated with genes involved in fatty acid metabolism whereas miR-221 and miR-222 correlated with the expression of adipocytokines. Regarding the minor changes observed in miR-143 expression, no differences in expression of adipogenic markers were observed.

Conclusions/Significance

Although elucidating the functional implications of miRNAs is beyond the scope of this study, these findings provide the first evidence that miRNAs expression may be influenced by dietary manipulation, reflecting or even contributing to the new metabolic state originated by CLA treatment.     

Increased energy metabolism and suppressed body fat accumulation in mice by a low concentration of conjugated linoleic acid.

We investigated the dose-effect of the long-term intake of conjugated linoleic acid (CLA) on the energy metabolism and fat accumulation in mice. Five-week-old male Std ddY mice were fed on a diet containing none (control), 0.25%, 0.5% or 1.0% CLA for 4 or 8 weeks. The body weight was lower in the CLA groups than in the control group, and significant differences were detected between the 1.0% CLA group and the control group at both 4 and 8 weeks. The epididymal and perirenal adipose tissue weights were significantly lower in the CLA groups than in the control group. The liver weight and hepatic triglyceride values were higher in the 1.0% CLA group than in the other groups. The metabolic rate was measured after 8 weeks by using a gas analyzer. The oxygen consumption of the mice in the CLA groups was significantly higher than that of the control mice. Since there was a significant effect on the mice supplemented with 0.25% CLA, low concentration of CLA is suggested to suppress the body fat accumulation and increase the energy metabolism.     

Fatty acid composition and conjugated linoleic acid content of different tissues in rats fed individual conjugated linoleic acid isomers given as triacylglycerols small star,filled

HEAT TREATMENT OF VEGETABLE OILS GAVE RISE TO FOUR MAIN CONJUGATED LINOLEIC ACID (CLA) ISOMERS : the 9c,11t, 9t,11t, 10t,12c and 10t,12t. The diet of male Wistar rats was supplemented with 150 mg/day either 9c,11t-, 9t,11t-, 10t,12c- or 10t,12t CLA isomers for 6 days and their effects on lipid composition were investigated in liver, heart, skeletal muscle Gastrocnemius, kidneys, brain and adipose tissue. The incorporation of all isomers was low (< 1.4%) and the level was as follows : adipose tissue > Gastrocnemius > liver, kidneys > brain. The main changes in the overall lipid composition were observed in skeletal muscle (Gastrocnemius) and in heart and were associated with feeding the 10t,12c and 10t,12t isomers. The diet enriched in 10t,12t CLA decreased the total long chain polyunsaturated fatty acid proportion in Gastrocnemius (from 18.4% to 14.4%) and increased that of 20:4 n-6 in heart (from 16.9 to 19.3%). The diet enriched in 10t,12c CLA decreased the monounsaturated fatty acid proportion in Gastrocnemius (from 32.0 to 26.1%) and produced an effect similar to the 10t,12t in heart. By contrast, the 9c,11t and 9t,11t isomers did not affect fatty acid composition in all tissues and organs. We concluded that ingestion of 10t,12c and 10t,12t CLA present in oils and in CLA mixtures could change muscle lipid composition.     

Impact of dietary betaine and conjugated linoleic acid on insulin sensitivity,protein and fat metabolism of obese pigs

To determine possible mechanisms of action that might explain the nutrient partitioning effect of betaine and conjugated linoleic acid (CLA) in Iberian pigs and to address potential adverse effects, twenty gilts were restrictively fed from 20 to 50 kg BW Control, 0.5% betaine, 1% CLA or 0.5% betaine + 1% CLA diets. Serum hormones and metabolites profile were determined at 30 kg BW and an oral glucose test was performed before slaughter. Pigs were slaughtered at 50 kg BW and livers were obtained for chemical and histological analysis. Decreased serum urea in pigs fed betaine and betaine + CLA diets (11%; P = 0.0001) indicated a more efficient N utilization. The increase in serum triacylglycerol (58% and 28%, respectively; P = 0.0098) indicated that CLA and betaine + CLA could have reduced adipose tissue triacylglycerol synthesis from preformed fatty acids. Serum glucose, low-density lipoprotein (LDL) cholesterol and non-esterified fatty acids were unaffected. CLA and betaine + CLA altered serum lipids profile, although liver of pigs fed CLA diet presented no histopathological changes and triglyceride content was not different from Control pigs. Compared with controls, serum growth hormone decreased (20% to 23%; P = 0.0209) for all treatments. Although serum insulin increased in CLA, and especially in betaine + CLA pigs (28% and 83%; P = 0.0001), indices of insulin resistance were unaffected. In conclusion, CLA, and especially betaine + CLA, induced changes in biochemical parameters and hormones that may partially explain a nutrient partitioning effect in young pigs. Nevertheless, they exhibited weak, although detrimental, effects on blood lipids. Moreover, although livers were chemically and histologically normal, pigs fed CLA diet challenged with a glucose load had higher serum glucose than controls.     

Dietary coconut oil increases conjugated linoleic acid-induced body fat loss in mice independent of essential fatty acid deficiency

Conjugated linoleic acid (CLA) induces a body fat loss that is enhanced in mice fed coconut oil (CO), which lacks essential fatty acids (EFA). Our objective was to determine if CO enhancement of CLA-induced body fat loss is due to the lack of EFA. The CLA-EFA interaction was tested by feeding CO and fat free (FF) diets for varying times with and without replenishment of individual EFA. Mice fed CO during only the 2-week CLA-feeding period did not differ from control mice in their adipose EFA content but still tended (P=0.06) to be leaner than mice fed soy oil (SO). Mice raised on CO or FF diets and fed CLA were leaner than the SO+CLA-fed mice (P<0.01). Mice raised on CO and then replenished with linoleic, linolenic, or arachidonic acid were leaner when fed CLA than mice raised on SO (P<0.001). Body fat of CO+CLA-fed mice was not affected by EFA addition. In summary, CO-fed mice not lacking in tissue EFA responded more to CLA than SO-fed mice. Also, EFA addition to CO diets did not alter the enhanced response to CLA. Therefore, the increased response to CLA in mice raised on CO or FF diets appears to be independent of a dietary EFA deficiency.     

Dietary conjugated linoleic acid reduces body fat mass and affects gene expression of proteins regulating energy metabolism in mice

ICR and C57BL/6J mice were fed experimental diets containing either a 2% fatty acid preparation rich in conjugated linoleic acid (CLA) or a preparation rich in linoleic acid and free of CLA for 21 days. CLA greatly decreased weights of white adipose tissue and interscapular brown adipose tissue in the two strains. CLA reduced mRNA levels of glucose transporter 4 (Glut 4) in white and brown adipose tissue of both strains. A CLA-dependent decrease in mRNA levels of peroxisome proliferator activated receptor (PPAR) gamma was seen in interscapular brown adipose tissue of both strains and in white adipose tissue of C57BL/6J but not ICR mice. Dietary CLA was found to cause a decrease in the mRNA levels of uncoupling protein (UCP) 1 in brown adipose tissue when the value was corrected for the expression of a house-keeping gene (beta-actin) in the two strains. Uncorrected values were, however, indistinguishable between the animals fed the CLA diet and CLA-free diet. UCP 3 expression in brown adipose tissue was much lower in mice fed the CLA diet than in those fed the control diet in both strains. In contrast, CLA greatly up-regulated the gene expression of UCP 2 in brown adipose tissue. Dietary CLA also increased UCP 2 mRNA level in skeletal muscle. It is apparent that dietary CLA decreases white and brown adipose tissue mass, accompanying changes in the gene expression of proteins regulating energy metabolism in white and brown adipose tissues, and skeletal muscle of mice.     

Lower thigh subcutaneous and higher visceral abdominal adipose tissue content both contribute to insulin resistance

It is well known that visceral adipose tissue (VAT) is associated with insulin resistance (IR). Considerable debate remains concerning the potential positive effect of thigh subcutaneous adipose tissue (TSAT). Our objective was to observe whether VAT and TSAT are opposite, synergistic or additive for both peripheral and hepatic IR. Fifty-two volunteers (21 male/31 female) between 30 and 75 years old were recruited from the general population. All subjects were sedentary overweight or obese (mean BMI 33.0 ± 3.4 kg/m(2)). Insulin sensitivity was determined by a 4-h hyperinsulinemic-euglycemic clamp with stable isotope tracer dilution. Total body fat and lean body mass were determined by dual X-ray absorptiometry. Abdominal and mid-thigh adiposity was determined by computed tomography. VAT was negatively associated with peripheral insulin sensitivity, while TSAT, in contrast, was positively associated with peripheral insulin sensitivity. Subjects with a combination of low VAT and high TSAT had the highest insulin sensitivity, subjects with a combination of high VAT and low TSAT were the most insulin resistant. These associations remained significant after adjusting for age and gender. These data confirm that visceral excess abdominal adiposity is associated with IR across a range of middle-age to older men and women, and further suggest that higher thigh subcutaneous fat is favorably associated with better insulin sensitivity. This strongly suggests that these two distinct fat distribution phenotypes should both be considered in IR as important determinants of cardiometabolic risk.     

Effect of supplementation with conjugated linoleic acid on human serum lipids and body fat

Conjugated linoleic acid (CLA) is a natural component of meat and dairy products with anticarcinogenic, fat lowering, antiatherogenic and anticatabolic activity in animals. The purpose of this study was to examine the effect of CLA supplementation to humans on body fat, certain biochemical parameters of serum, and the CLA content of serum lipids. Twenty-two volunteers were divided into a study group and a control group in a doubly blind design. The study group received 0.7 g of CLA for four weeks and 1.4 g of CLA for the next four weeks, while the control group received placebo. Diet was controlled and no significant differences in energy or macronutrient intake were found between the two groups. Measurements were taken at baseline, four weeks, and eight weeks. The sum of the thickness of ten skinfolds, percentage body fat calculated from it and fat mass was significantly reduced in the CLA group during the second period (P < 0.004) but not overall during the study. Serum HDL-cholesterol decreased significantly (P < 0.001) and triacylglycerols as well as total cholesterol tended to decrease in the CLA group during the first period. The CLA content of serum non-esterified fatty acids, triacylglycerols, phospholipids, and cholesteryl esters increased gradually with supplementation; the CLA content of total serum lipids doubled at the end of the study compared to baseline. Phospholipids had the highest CLA content regardless of supplementation. These data indicate that supplementation with 0.7-1.4 g CLA daily for 4-8 weeks may modulate body fat and serum lipids, as well as increase the CLA content of serum lipids in humans.     

Combined effects of rosiglitazone and conjugated linoleic acid on adiposity, insulin sensitivity, and hepatic steatosis in high-fat-fed mice

Dysfunctional cross talk between adipose tissue and liver tissue results in metabolic and inflammatory disorders. As an insulin sensitizer, rosiglitazone (Rosi) improves insulin resistance yet causes increased adipose mass and weight gain in mice and humans. Conjugated linoleic acid (CLA) reduces adipose mass and body weight gain but induces hepatic steatosis in mice. We examined the combined effects of Rosi and CLA on adiposity, insulin sensitivity, and hepatic steatosis in high-fat-fed male C57Bl/6 mice. CLA alone suppressed weight gain and adipose mass but caused hepatic steatosis. Addition of Rosi attenuated CLA-induced insulin resistance and dysregulation of adipocytokines. In adipose, CLA significantly suppressed lipoprotein lipase and fatty acid translocase (FAT/CD36) mRNA, suggesting inhibition of fatty acid uptake into adipose; addition of Rosi completely rescued this effect. In addition, CLA alone increased markers of macrophage infiltration, F4/80, and CD68 mRNA levels, without inducing TNF-alpha in epididymal adipose tissue. The ratio of Bax to Bcl2, a marker of apoptosis, was significantly increased in adipose of the CLA-alone group and was partially prevented by treatment of Rosi. Immunohistochemistry of F4/80 demonstrates a proinflammatory response induced by CLA in epididymal adipose. In the liver, CLA alone induced microsteatotic liver but surprisingly increased the rate of very-low-density lipoprotein-triglyceride production without inducing inflammatory mediator-TNF-alpha and markers of macrophage infiltration. These changes were accompanied by significantly increased mRNA levels of stearoyl-CoA desaturase, FAT/CD36, and fatty acid synthase. The combined administration of CLA and Rosi reduced hepatic liver triglyceride content as well as lipogenic gene expression compared with CLA alone. In summary, dietary CLA prevented weight gain in Rosi-treated mice without attenuating the beneficial effects of Rosi on insulin sensitivity. Rosi ameliorated CLA-induced lipodystrophic disorders that occurred in parallel with rescued expression of adipocytokine and adipocytes-abundant genes.     

The lowering of hepatic fatty acid uptake improves liver function and insulin sensitivity without affecting hepatic fat content in humans

Lipolysis may regulate liver free fatty acid (FFA) uptake and triglyceride accumulation; both are potential causes of insulin resistance and liver damage. We evaluated whether 1) systemic FFA release is the major determinant of liver FFA uptake in fasting humans in vivo and 2) the beneficial metabolic effects of FFA lowering can be explained by a reduction in liver triglyceride content. Sixteen healthy subjects were subdivided in two groups of similar characteristics to undergo positron emission tomography with [(11)C]acetate and [(11)C]palmitate to quantify liver FFA metabolism (n = 8), or magnetic resonance spectroscopy (MRS) to measure hepatic fat content (n = 8), before and after the acute lowering of circulating FFAs by using the antilipolytic agent acipimox. MRS was again repeated after a 1-wk treatment period. Acipimox suppressed FFA levels while stimulating hepatic fractional extraction of FFAs (P < 0.05). As a result, fasting liver FFA uptake was decreased by 79% (P = 0.0002) in tight association with lipolysis (r = 0.996, P < 0.0001). The 1-wk treatment induced a significant improvement in systemic (+30%) and liver (+70%) insulin sensitivity (P < 0.05) and decreased circulating triglycerides (-20%, P = 0.06) and liver enzymes (ALT -20%, P = 0.03). No change in liver fat content was observed after either acute or sustained FFA suppression. We conclude that acute and sustained inhibitions of lipolysis and liver FFA uptake fail to deplete liver fat in healthy human subjects. Liver FFA uptake was decreased in proportion to FFA delivery. As a consequence, liver and systemic insulin sensitivity were improved, together with liver function, independently of changes in hepatic triglyceride accumulation.     

Maintenance of adiponectin attenuates insulin resistance induced by dietary conjugated linoleic acid in mice

Conjugated linoleic acid (CLA) causes insulin resistance and hepatic steatosis in conjunction with depletion of adipokines in some rodent models. Our objective was to determine whether the maintenance of adipokines, mainly leptin and adiponectin, by either removing CLA from diets or using an adiponectin enhancer, rosiglitazone (ROSI), could attenuate CLA-induced insulin resistance. Male C57BL/6 mice were consecutively fed two experimental diets containing 1.5% CLA mixed isomer for 4 weeks followed by a diet without CLA for 4 weeks. CLA significantly depleted adiponectin but not leptin and was accompanied by hepatic steatosis and insulin resistance. These effects were attenuated after switching mice to the diet without CLA along with restoration of adiponectin. To further elucidate the role of adiponectin in CLA-mediated insulin resistance, ROSI was used in a subsequent study in male ob/ob mice fed either control (CON) or CLA diet. ROSI maintained significantly higher adiponectin levels in CON- and CLA-fed mice and prevented the depletion of epididymal adipose tissue and the development of insulin resistance. In conclusion, we show that insulin resistance induced by CLA may be related more to adiponectin depletion than to leptin and that maintaining adiponectin levels alone either by removing CLA or using ROSI can attenuate these effects.     

Voluntary exercise improves insulin sensitivity and adipose tissue inflammation in diet-induced obese mice

Exercise promotes weight loss and improves insulin sensitivity. However, the molecular mechanisms mediating its beneficial effects are not fully understood. Obesity correlates with increased production of inflammatory cytokines, which in turn, contributes to systemic insulin resistance. To test the hypothesis that exercise mitigates this inflammatory response, thereby improving insulin sensitivity, we developed a model of voluntary exercise in mice made obese by feeding of a high fat/high sucrose diet (HFD). Over four wk, mice fed chow gained 2.3 +/- 0.3 g, while HFD mice gained 6.8 +/- 0.5 g. After 4 wk, mice were subdivided into four groups: chow-no exercise, chow-exercise, HFD-no exercise, HFD-exercise and monitored for an additional 6 wk. Chow-no exercise and HFD-no exercise mice gained an additional 1.2 +/- 0.3 g and 3.3 +/- 0.5 g respectively. Exercising mice had higher food consumption, but did not gain additional weight. As expected, GTT and ITT showed impaired glucose tolerance and insulin resistance in HFD-no exercise mice. However, glucose tolerance improved significantly and insulin sensitivity was completely normalized in HFD-exercise animals. Furthermore, expression of TNF-alpha, MCP-1, PAI-1 and IKKbeta was increased in adipose tissue from HFD mice compared with chow mice, whereas exercise reversed the increased expression of these inflammatory cytokines. In contrast, expression of these cytokines in liver was unchanged among the four groups. These results suggest that exercise partially reduces adiposity, reverses insulin resistance and decreases adipose tissue inflammation in diet-induced obese mice, despite continued consumption of HFD.     

Differential effects of conjugated linoleic acid isomers in insulin-resistant female C57Bl/6J mice

Obesity is associated with a high risk of developing diabetes and cardiovascular disease. Therefore, management of body weight to prevent obesity remains as an important priority. The present investigation addresses the effects of conjugated linoleic acid (CLA) isomers on body weight and composition of body fat in female C57Bl/6J mice. To investigate the differential effects of individual CLA isomers and their mixture on changes in lean mass, fat mass, glucose and insulin, 6-month-old female C57BL/6J mice were fed with 10% corn oil (CO) as a dietary fat source and either supplemented with purified cis 9,trans 11 (c9t11) CLA (0.5%) or trans 10,cis 12 (t10c12) CLA (0.5%) and/or their mixture (50:50) for 6 months. As a result of 6 months' dietary intervention, both the t10c12-CLA and CLA mix showed increased lean mass and reduced fat mass compared to the CO and c9t11-CLA groups. Insulin resistance was, however, increased in t10c12-CLA and CLA mix-fed groups based on the results of homeostasis model assessment (HOMA), the revised quantitative insulin-sensitivity check index (R-QUICKI) and also with intravenous glucose tolerance test (IVGTT). In conclusion, long-term feeding of the major CLA isomers in 12-month-old C57Bl/6J mice revealed a contrasting effect on fat mass, glucose and insulin metabolism. The t10c12 isomer is found to reduce the fat mass and increase the lean mass but significantly contributed to increase insulin resistance and liver steatosis, whereas c9t11 isomer prevented the insulin resistance.     

Dietary effect of conjugated linoleic acid on lipid levels in white adipose tissue of Sprague-Dawley rats.

We examined the effect of dietary conjugated linoleic acid (CLA) on lipid parameters in the liver, white adipose tissue (WAT) and brown adipose tissue (BAT) of Sprague-Dawley rats and found that it reduced the levels of triglycerides and non-esterified fatty acid in the liver and WAT without significant change in the BAT lipid levels. These results suggest that CLA has an obesity-preventing action.     

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.     

Milk fat depression and energy balance in stall-fed dairy goats supplemented with increasing doses of conjugated linoleic acid methyl esters

Feeding dietary supplements containing trans-10, cis-12-conjugated linoleic acid (t10,c12-CLA) has been shown to induce milk fat depression in cows, ewes and goats. However, the magnitude of the response is apparently less pronounced in lactating goats. The objective of this study was to evaluate the effects of increasing doses of CLA methyl esters (CLA-ME) on milk production, composition and fatty-acid profile of dairy goats. Eight Toggenburg goats were separated in two groups (four primiparous and four multiparous) and received the following dietary treatments in a 4×4 Latin Square design: CLA0: 45 g/day of calcium salts of fatty acids (CSFA); CLA15; 30 g/day of CSFA+15 g/day of CLA-ME; CLA30: 15 g/day of CSFA+30 g/day of CLA-ME; and CLA45: 45 g/day of CLA-ME. The CLA-ME supplement (Luta-CLA 60) contained 29.9% of t10,c12-CLA; therefore, the dietary treatments provided 0, 4.48, 8.97 and 13.45 g/day of t10,c12-CLA, respectively. Feed intake, milk production, concentration and secretion of milk protein and lactose, body condition score and body weight were unaffected by the dietary treatments. Milk fat secretion was reduced by 14.9%, 30.8% and 40.5%, whereas milk fat concentration was decreased by 17.2%, 33.1% and 40.7% in response to CLA15, CLA30 and CLA45, respectively. Secretions of both de novo synthesized and preformed fatty acids were progressively reduced as the CLA dose increased, but the magnitude of the inhibition was greater for the former. There was a linear reduction in most milk fat desaturase indexes (14:1/14:0, 16:1/16:0, 17:1/17:0 and 18:1/18:0). Milk fat t10,c12-CLA concentration and secretion increased with the CLA dose, and its apparent transfer efficiency from diet to milk was 1.18%, 1.17% and 1.21% for CLA15, CLA30 and CLA45 treatments, respectively. The estimated energy balance was linearly improved in goats fed CLA.     

Production performance and pattern of milk fat depression of high-yielding dairy cows supplemented with encapsulated conjugated linoleic acid

Several processes have been suggested to protect lipids from bioactivity of the rumen microorganisms. The majority of experiments with conjugated linoleic acid (CLA) were conducted using calcium salts of CLA. The objectives of this study were to determine the effects of encapsulated CLA (E-CLA) that was supplemented during days 21 to 100 post partum (PP), on milk fat depression, recovery rate and performance parameters. Forty-two multiparous Israeli-Holstein cows were divided at day 21 PP into two treatment groups: (i) control - supplemented with 43 g/day per cow of calcium salts of fatty acids (FAs). (ii) E-CLA - supplemented with 50 g/day per cow of encapsulated lipid supplement providing 4.7 g/day per cow of trans-10, cis-12 CLA. Post-treatment cows were followed for recovery rate until 140 days PP. Dry matter intake (DMI) during the treatment period was reduced by 2.5%, and milk yield was enhanced by 4.5% in the E-CLA cows. Milk fat percentage and yield were reduced by 13% and 9%, respectively, in the E-CLA treatment as compared with the control. The energy-corrected milk output was 3.6% higher in the control group than in the E-CLA group. Yields of trans-10, cis-12 CLA isomer in milk was 2.13-fold higher in the E-CLA cows than in the controls. Full recovery to milk fat percentage of the control group occurred 4 to 5 weeks after cessation of the E-CLA supplementation. No differences between groups were observed in any fertility parameter that was tested. In conclusion, the E-CLA supplement decreased DMI, enhanced milk yield, and decreased energy output in milk, and was effective in depressing milk fat. Full recovery to the milk fat content, but not yield, of the control group in the E-CLA group was relatively slow and occurred 4 to 5 weeks after termination of the supplementation.     

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.     

ABCA1 in adipocytes regulates adipose tissue lipid content,glucose tolerance,and insulin sensitivity

Adipose tissue contains one of the largest reservoirs of cholesterol in the body. Adipocyte dysfunction in obesity is associated with intracellular cholesterol accumulation, and alterations in cholesterol homeostasis have been shown to alter glucose metabolism in cultured adipocytes. ABCA1 plays a major role in cholesterol efflux, suggesting a role for ABCA1 in maintaining cholesterol homeostasis in the adipocyte. However, the impact of adipocyte ABCA1 on adipose tissue function and glucose metabolism is unknown. Our aim was to determine the impact of adipocyte ABCA1 on adipocyte lipid metabolism, body weight, and glucose metabolism in vivo. To address this, we used mice lacking ABCA1 specifically in adipocytes (ABCA1^−ad/−ad). When fed a high-fat, high-cholesterol diet, ABCA1^−ad/−ad mice showed increased cholesterol and triglyceride stores in adipose tissue, developed enlarged fat pads, and had increased body weight. Associated with these phenotypic changes, we observed significant changes in the expression of genes involved in cholesterol and glucose homeostasis, including ldlr, abcg1, glut-4, adiponectin, and leptin. ABCA1^−ad/−ad mice also demonstrated impaired glucose tolerance, lower insulin sensitivity, and decreased insulin secretion. We conclude that ABCA1 in adipocytes influences adipocyte lipid metabolism, body weight, and whole-body glucose homeostasis.