Trans-10,cis-12 CLA increases liver and decreases adipose tissue lipids in mice: possible roles of specific lipid metabolism genes

Effects of forage species and feeding systems on rumen fermentation, microbiota and conjugated linoleic acid content in dairy goats

The objective of this experiment was to investigate the effects of forage species and feeding systems on ruminal fermentation, microbiota (Butyrivibrio fibrisolvens, Fibrobacter succinogenes and total bacteria) and conjugated linoleic acid (CLA) concentration of milk in dairy goats. Twenty female crossbred Saanen lactating goats (~35 ± 3.0 kg bodyweight) in early to mid-lactation stage were assigned to a 45-day completely randomised-design feeding experiment, with the following four forage (roughage) treatments: cut-and-carry grass (CG), grazing of grass (GG), cut-and-carry leucaena (CL) and grazing of leucaena (GL; n = 5). All animals were given concentrate equivalent to 1.5% of their bodyweight. The grass used in the study was napier Pak Chong 1 grass (Pennisetum purpureum × Pennisetum americanum hybrid). The results showed that irrespective of the type of forage, grazing goats (GG and GL) had a higher (P < 0.05) forage intake and, thus, total dry-matter and crude-protein intakes than did those fed indoors (CG and CL). However, the intake of C18:2n6 and particularly of C18:3n3 was generally higher for grass-fed goats than for leucaena-fed goats. Treatments did not exert significant differences on rumen fermentation characteristics. However, the populations of B. fibrisolvens, F. succinogenes and total bacteria were significantly (P < 0.05) higher in grazing goats (GG and GL) than in their counterparts fed with the cut-and-carry system (CG and CL). Goats in the grazing system also had a higher (P < 0.05) milk yield, and milk fat, c9, t11 CLA and omega-3 fatty acid concentrations than did those in the cut-and-carry system and only grazing goats produced detectable levels of t10, c12 CLA in milk. Putting the above together, it can be concluded that allowing dairy goats to outdoor grazing stimulates a higher forage intake, including that of C18:2n6 and C18:3n3, as well as enhancing population of B. fibrisolvens (involved in the synthesis of milk CLA), resulting in a higher milk yield, and enhances c9, t11 and t10, c12 CLA in goat milk.

Advances in research on cis-9, trans-11 conjugated linoleic acid: a major functional conjugated linoleic acid isomer

Conjugated linoleic acid (CLA) consists of a group of positional and geometric conjugated isomers of linoleic acid. Since the identification of CLA as a factor that can inhibit mutagenesis and carcinogenesis, thousands of studies have been conducted in the last several decades. Among the many isomers discovered, cis-9, trans-11 CLA is the most intensively studied because of its multiple, isomer-specific effects in humans and animals. This paper provides an overview of the available data on cis-9, trans-11 CLA, including its isomer-specific effects, biosynthesis, in vivo/in vitro research models, quantification, and the factors influencing its content in ruminant products.

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.

A dietary phytochemical blend prevents liver damage associated with adipose tissue mobilization in ovariectomized rats

OBJECTIVE

Menopausal reduction in estrogen causes increased adipose accumulation, leading many to turn to dietary supplements to prevent and treat such changes. Enhanced adipose mobilization stimulated by some supplements can increase the risk of non-alcoholic fatty liver disease (NAFLD). Cytoprotective and anti-obesity compounds may prevent the lipotoxicity associated with mobilization.

METHODS

A phytochemical blend was tested in aged, ovariectomized rats. Rats were given the AIN-93M basal diet or a diet containing varying doses of phytochemicals with 2.4 IU/g vitamin D [diet 1: 1000 mg/kg genistein (G); diet 2: 500 mg/kg (G), 200 mg/kg resveratrol (R), and 1000 mg/kg quercetin (Q); diet 3: 1000 mg/kg (G), 400 mg/kg (R), and 2000 mg/kg (Q)].

RESULTS

Serum free fatty acids and hepatic triglycerides were elevated with diets 2 and 3. Despite this increase, the phytochemical blends did not increase apoptotic, cell repair, or remodeling gene expression. The highest phytochemical dose prevented increases in serum alanine aminotransferase.

CONCLUSIONS

Adverse hepatic effects secondary to ovariectomy were mitigated through the inclusion of a dietary phytochemical blend in aged ovariectomized rats. The use of such compounds may not only help with weight management and disease risk in menopausal women, but may also prevent the lipotoxicity in NAFLD.

Non-fat milk solids attenuate hypercholesterolemic effect of conjugated linoleic acid

The present study instigates the notion that non-fat milk has a beneficial effect on hypercholesterolemia caused by dietary conjugated linoleic acid (CLA). Two groups of mice (6 per group) were fed synthetic CLA (predominantly a mixture of t10, c12 and c9, t11 isomers) at 1 % level in the diet with or without skim milk powder (SMP). Another group (control) was fed a similar diet without CLA and SMP. The study was conducted for 60 days (d). Daily feed intake and weekly body weight were recorded. Plasma lipid profile was determined monthly. At the conclusion of experiment, animals were sacrificed and liver tissue was removed to assay cholesterol and triacylglycerols (TAG). Following 60 day feeding, the plasma total cholesterol content increased significantly in CLA group (218 mg/dl) than in control group (167 mg/dl), while in CLA + SMP group (fed non-fat milk solids along with CLA), it was similar to that in control group. The fractions of high density lipoproteins (HDL) and low density lipoprotein + very low density lipoprotein (LDL + VLDL) cholesterol as well as triacylglycerols (TAG) in plasma increased in CLA group, but in CLA + SMP group it remained similar to the control levels. Thus, it is concluded that dietary CLA increases plasma cholesterol and TAG contents in mice on normocholesterolemic diet and the inclusion of non-fat milk solids reverses this effect.

A commonly used rumen-protected conjugated linoleic acid supplement marginally affects fatty acid distribution of body tissues and gene expression of mammary gland in heifers during early lactation

Background

Conjugated linoleic acids (CLA) in general, and in particular the trans-10,cis-12 (t10,c12-CLA) isomer are potent modulators of milk fat synthesis in dairy cows. Studies in rodents, such as mice, have revealed that t10,c12-CLA is responsible for hepatic lipodystrophy and decreased adipose tissue with subsequent changes in the fatty acid distribution. The present study aimed to investigate the fatty acid distribution of lipids in several body tissues compared to their distribution in milk fat in early lactating cows in response to CLA treatment. Effects in mammary gland are further analyzed at gene expression level.

Methods

Twenty-five Holstein heifers were fed a diet supplemented with (CLA groups) or without (CON groups) a rumen-protected CLA supplement that provided 6 g/d of c9,t11- and t10,c12-CLA. Five groups of randomly assigned cows were analyzed according to experimental design based on feeding and time of slaughter. Cows in the first group received no CLA supplement and were slaughtered one day postpartum (CON0). Milk samples were taken from the remaining cows in CON and CLA groups until slaughter at 42 (period 1) and 105 (period 2) days in milk (DIM). Immediately after slaughter, tissue samples from liver, retroperitoneal fat, mammary gland and M. longissimus (13th rib) were obtained and analyzed for fatty acid distribution. Relevant genes involved in lipid metabolism of the mammary gland were analyzed using a custom-made microarray platform.

Results

Both supplemented CLA isomers increased significantly in milk fat. Furthermore, preformed fatty acids increased at the expense of de novo-synthesized fatty acids. Total and single trans-octadecenoic acids (e.g., t10-18:1 and t11-18:1) also significantly increased. Fatty acid distribution of the mammary gland showed similar changes to those in milk fat, due mainly to residual milk but without affecting gene expression. Liver fatty acids were not altered except for trans-octadecenoic acids, which were increased. Adipose tissue and M. longissimus were only marginally affected by CLA supplementation.

Conclusions

Daily supplementation with CLA led to typical alterations usually observed in milk fat depression (reduction of de novo-synthesized fatty acids) but only marginally affected tissue lipids. Gene expression of the mammary gland was not influenced by CLA supplementation.

Male mice that lack the G-protein-coupled receptor GPR41 have low energy expenditure and increased body fat content

SCFA are produced in the gut by bacterial fermentation of undigested carbohydrates. Activation of the Gαi-protein-coupled receptor GPR41 by SCFA in β-cells and sympathetic ganglia inhibits insulin secretion and increases sympathetic outflow, respectively. A possible role in stimulating leptin secretion by adipocytes is disputed. In the present study, we investigated energy balance and glucose homoeostasis in GPR41 knockout mice fed on a standard low-fat or a high-fat diet. When fed on the low-fat diet, body fat mass was raised and glucose tolerance was impaired in male but not female knockout mice compared to wild-type mice. Soleus muscle and heart weights were reduced in the male mice, but total body lean mass was unchanged. When fed on the high-fat diet, body fat mass was raised in male but not female GPR41 knockout mice, but by no more in the males than when they were fed on the low-fat diet. Body lean mass and energy expenditure were reduced in male mice but not in female knockout mice. These results suggest that the absence of GPR41 increases body fat content in male mice. Gut-derived SCFA may raise energy expenditure and help to protect against obesity by activating GPR41.

Hepatic Metabolic, Inflammatory, and Stress-Related Gene Expression in Growing Mice Consuming a Low Dose of Trans-10, cis-12-Conjugated Linoleic Acid

Dietary trans-10, cis-12-conjugated linoleic acid (trans-10, cis-12-CLA) fed to obese and nonobese rodents reduces body fat but leads to greater liver mass due to steatosis. The molecular mechanisms accompanying such responses remain largely unknown. Our study investigated the effects of chronic low trans-10, cis-12-CLA supplementation on hepatic expression of 39 genes related to metabolism, inflammation, and stress in growing mice. Feeding a diet supplemented with 0.3% trans-10, cis-12-CLA (wt/wt basis) for 6 weeks increased liver mass and concentration of long-chain fatty acids (LCFAs) in liver, while adipose tissue mass decreased markedly. These changes were accompanied by greater expression of genes involved in LCFA uptake (Cd36), lipogenesis, and triacylglycerol synthesis (Acaca, Gpam, Scd, Pck1, Plin2). Expression of these genes was in line with upregulation of the lipogenic transcription factor Srebf1. Unlike previous studies where higher >0.50% of the diet) doses of trans-10, cis-12-CLA were fed, we found greater expression of genes associated with VLDL assembly/secretion (Mttp, Cideb), ketogenesis (Hmgcs2, Bdh1), and LCFA oxidation (Acox1, Pdk4) in response to trans-10, cis-12-CLA. Dietary CLA, however, did not affect inflammation- and stress-related genes. Results suggested that a chronic low dose of dietary CLA increases liver mass and lipid accumulation due to activation of lipogenesis and insufficient induction of LCFA oxidation and VLDL assembly/secretion.

Effects of margarine supplemented with t10c12 and C9T11 CLA on atherosclerosis and steatosis in apoE/LDLR -/- mice

OBJECTIVES

The objective of this study was to evaluate functional effects of margarine supplemented with individual CLA isomers trans-10, cis-12 and cis-9, trans-11 in apoE/LDLR -/- mice.

DESIGN

In LONG experiment (LONG), two-month old mice with no atherosclerosis were assigned to experimental groups and fed for the next 4 months. In SHORT experiment (SHORT), four-month old mice, with pre-established atherosclerosis, were assigned to experimental groups and fed for the next 2 months. The experimental diets were: AIN-93G (margarine), AIN-93G + 0.5% trans-10, cis-12 CLA (t10c12), and AIN-93G + 0.5% cis-9, trans-11 CLA (c9t11).

RESULTS

In both experiments (LONG and SHORT), liver weight was significantly (P<0.05) increased in mice fed t10c12 CLA. Hepatic steatosis was found in animals fed t10c12 diet and no signs of the steatosis was observed in mice fed c9t11 CLA. Dietary treatments with t10c12 CLA significantly increased total plasma cholesterol and plasma triacylglycerols. There were no isomer-specific effects of CLA isomers on area of atherosclerotic plaque in aortic root.

CONCLUSION

In conclusion, t10c12 CLA significantly increased liver weight in mice in LONG and SHORT experiments. Our results do not support the notion that CLA isomer supplementation to the margarine possess anti-atheroclerotic effect. Therefore, no isomer-specific effects of CLA on development of atherosclerosis were observed.

Effects of trans-10,cis-12 CLA on liver size and fatty acid oxidation under energy restriction conditions in hamsters

OBJECTIVE

Little evidence exists concerning the effects of trans-10,cis-12 conjugated linoleic acid (CLA) under energy restriction. Thus, the effects of this CLA isomer on adipose tissue size, liver composition, as well as on expression and activity of carnitine-palmitoyl transferase I (CPT-I) and acyl CoA oxidase (ACO), in hamsters fed an energy-restricted diet were analyzed.

METHODS

Hamsters were fed a high-fat diet for 7 wk and then subjected to 25% energy-restricted diets supplemented with 0.5% linoleic acid or 0.5% trans-10,cis-12 CLA for 3 wk. Serum insulin, free-triiodothyronine and non-esterified fatty acid levels, liver triacylglycerol, protein and water contents, and CPT-I, ACO, and Peroxisome proliferator-activated receptor alpha (PPARα) expressions and enzyme activities were assessed.

RESULTS

Energy restriction reduced liver size, serum levels of insulin, free-triiodothyronine, and non-esterified fatty acid and increased CPT-I activity. Liver composition was not modified. No differences were found between both restricted groups, with the exception of CPT-I and ACO oxidative enzyme activities, which were greater in hamsters fed the CLA diet.

CONCLUSIONS

Energy restriction does not cause trans-10,cis-12 CLA to induce liver hyperplasia. Although this CLA isomer increases liver CPT-I and ACO activities, this effect does not result in reduced hepatic triacylglyerol content or decreased adipose tissue size. Consequently, this CLA isomer seems not to be a useful tool for inclusion in body weight loss strategies followed during obesity treatment.

Combination of conjugated linoleic acid with fish oil prevents age-associated bone marrow adiposity in C57Bl/6J mice

The inverse relationship between fat in bone marrow and bone mass in the skeleton of aging subjects is well known. However, there is no precise therapy for the treatment of bone marrow adiposity. We investigated the ability of conjugated linoleic acid (CLA) and fish oil (FO), alone or in combination, to modulate bone loss using 12 months old C57Bl/6J mice fed 10% corn oil diet as control or supplemented with 0.5% CLA or 5% FO or 0.5% CLA+5% FO for 6 months. We found, CLA-fed mice exhibited reduced body weight, body fat mass (BFM) and enhanced hind leg lean mass (HLLM) and bone mineral density (BMD) in different regions measured by dual energy x-ray absorptiometry (DXA); however, associated with fatty liver and increased insulin resistance; whereas, FO fed mice exhibited enhanced BMD, improved insulin sensitivity, with no changes in BFM and HLLM. Interestingly, CLA+FO fed mice exhibited reduced body weight, BFM, peroxisome proliferator-activated receptor gamma and cathepsin K expression in bone marrow with enhanced BMD and HLLM. Moreover, CLA+FO supplementation reduced liver hypertrophy and improved insulin sensitivity with remarkable attenuation of bone marrow adiposity, inflammation and oxidative stress in aging mice. Therefore, CLA with FO combination might be a novel dietary supplement to reduce fat mass and improve BMD.

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

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

Conjugated linoleic acids reduce body fat in healthy postmenopausal women

Isomers of conjugated linoleic acids (CLA) reduce fat mass (FM) and increase insulin sensitivity in some, but not all, murine studies. In humans, this effect is still debatable. In this study, we compared the effect of 2 CLA supplements on total and regional FM assessed by dual energy X-ray absorptiometry, changes in serum insulin and glucose concentrations, and adipose tissue (AT) gene expression in humans. In a double-blind, parallel, 16-wk intervention, we randomized 81 healthy postmenopausal women to 1) 5.5 g/d of 40/40% of cis9,trans11-CLA (c9,t11-CLA) and trans10,cis12-CLA (t10,c12-CLA) (CLA-mix); 2) cis9, trans11-CLA (c9,t11-CLA); or 3) control (olive oil). We assessed all variables before and after the intervention. The CLA-mix group had less total FM (4%) and lower-body FM (7%) than the control (P = 0.02 and < 0.001, respectively). Post hoc analyses showed that serum insulin concentrations were greater in the CLA-mix group (34%) than the control group (P = 0.02) in the highest waist circumference tertile only. AT mRNA expression of glucose transporter 4, leptin, and lipoprotein lipase was lower, whereas expression of tumor necrosis factor-alpha was higher in the CLA-mix group than in the control group (P < 0.04). In conclusion, a 50:50 mixture of c9,t11- and t10,c12-CLA isomers resulted in less total and lower-body FM in postmenopausal women and greater serum insulin concentrations in the highest waist circumference tertile. Future research is needed to confirm the insulin desensitizing effect of the CLA mixture and the effect on the mRNA expression of adipocyte-specific genes in humans.

Trans-10, cis-12-conjugated linoleic acid reduces the hepatic triacylglycerol content and the leptin mRNA level in adipose tissue in obese Zucker fa/fa rats

Conjugated linoleic acid (CLA) isomers have been reported to reduce body weight and beneficially affect glucose metabolism in animals, but the results are inconsistent and seem to depend on animal model and type of CLA isomer. In the present study, feeding male Zucker fa/fa rats diets supplemented with 1% trans-10, cis-12-CLA for 10 d reduced the liver TAG content without improving the overall adiposity, and enhanced hepatic mitochondrial and peroxisomal beta-oxidation. The increased carnitine palmitoyltransferase (CPT)-I activity and mRNA level as well as the increased n-3:n-6 PUFA ratio in liver suggest that trans-10, cis-12-CLA increased the hepatic beta-oxidation by stimulation of PPARalpha. The reduced hepatic TAG content may be partly due to lower activity of stearoyl-CoA desaturase, as the ratios of 18 : 1n-9:18 : 0 and 16 : 1n-7:16 : 0 were reduced in liver. Trans-10, cis-12-CLA increased the CPT-I mRNA in retroperitoneal white adipose tissue (WAT), and increased uncoupling protein-2 mRNA in epididymal and inguinal WAT depots. Leptin mRNA level was decreased in all examined WAT depots, implying reduced insulin sensitivity. The resistin mRNA level was increased in all WAT depots, whereas adiponectin mRNA was reduced in inguinal and retroperitoneal WAT. The present results suggest that dietary supplementation with trans-10, cis-12-CLA may increase the catabolism of lipids in liver and adipose tissue. Moreover, we provide new data suggesting that trans-10, cis-12-CLA modulates the expression of resistin and adiponectin inversely in adipose tissue. Hence, the present results suggest that trans-10, cis-12-CLA may have some beneficial effects on lipid metabolism and adiposity but possibly reduces insulin sensitivity.

Effects of dietary conjugated linoleic acid at high-fat levels on triacylglycerol regulation in mice

OBJECTIVE

Our aim was to investigate the effects of dietary conjugated linoleic acid (CLA) at high-fat (HF) levels on parameters related to triacylglycerol (TG) regulation and some potential impacts on liver damage.

METHODS

Growing mice were fed a control diet (7% corn oil), an HF diet containing 20% corn oil, or an HF diet containing 3% CLA (HF + CLA) for 30 d. Tissue and organ weights, plasma and tissue TG levels, and parameters related to their regulation were evaluated. Liver oxidative status was also assessed.

RESULTS

Dietary CLA showed detrimental and beneficial effects. CLA added to the HF diet caused hepatomegaly (+32%) and exacerbated the hepatic TG accumulation (+168%) observed with the HF diet without inducing liver damage; however, it significantly reduced plasma TG concentrations (-37%) and normalized muscular TG content. An increase in glutathione was associated with total normalization of liver lipid peroxidation. In addition, HF + CLA caused dystrophy of epididymal fat pads, even when the HF diet had increased the adipose tissue mass (30%). The biochemical mechanisms involved in the regulation of lipid levels were related to reduced (-20%) hepatic very low-density lipoprotein-TG secretion and decreased muscle (-35%) and adipose (-49%) tissue contributions to the removal of plasma TG by lipoprotein lipase enzymes.

CONCLUSION

Examination of CLA at HF levels showed hepatomegaly and exacerbation of lipid accretion as a negative impact; however, some positive aspects such as hypotriglyceridemia and protection against oxidative stress were also induced. Even the fat reduction is nutritionally important for weight control; the biochemical mechanisms whereby CLA mediates the potential effects could produce undesirable metabolic alterations.

Effect of conjugated linoleic acid on bone formation and rheumatoid arthritis

Conjugated linoleic acid (CLA) has shown a variety of biologically beneficial effects. Dietary CLA inhibits eddosteal bone resorption, increases endocortical bone formation, and modulates the action and expression of cyclooxygenase (COX) enzyme, thereby decreasing prostaglandin-dependent bone resorption. CLA also enhances calcium absorption and may improve bone formation in animals, although results are not consistent. Since CLA can also affect inflammatory cytokines, it is hypothesized that CLA may be a good tool for prevention or reduction of rheumatoid arthritis symptoms. The possible mechanisms by which CLA prevents rheumatoid arthritis as well as other inflammatory diseases is discussed.

Thetrans-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 ortrans-10,cis-12 CLA/kg diet for 6 weeks. Thetrans-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 feedingcis-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 thetrans-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.

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

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

Dietary trans 10, cis 12-conjugated linoleic acid reduces the expression of fatty acid oxidation and drug detoxification enzymes in mouse liver

Mice fed diets containing trans 10, cis 12 (t10, c12)-conjugated linoleic acid (CLA) develop fatty livers and the role of the hepatic fatty acid oxidation enzymes in this development is not well defined. We examined the effects of dietary cis 9, trans 11-CLA (c9, t11-CLA) and t10, c12-CLA on the expression of hepatic genes for fatty acid metabolism. Female mice, 8 weeks old, (six animals per group) were fed either a control diet or diets supplemented with 0.5% c9, t11- or c12-CLA for 8 weeks. DNA microarray analysis showed that t10, c12-CLA increased the expression of 278 hepatic genes and decreased those of 121 genes (>2 fold); c9, t11-CLA increased expression of twenty-two genes and decreased those of nine. Real-time PCR confirmed that t10, c12-CLA reduced by the expression of fatty acid oxidation genes including flavin monooxygenase (FMO)-3 95%, cytochrome P450 (cyt p450) 69%, carnitine palmitoyl transferase 1a 77%, acetyl CoA oxidase (ACOX) 50% and PPARalpha 65%: it increased the expression of fatty acid synthase by 3.5-fold (P<0.05 for all genes, except ACOX P=0.08). It also reduced the enzymatic activity of hepatic microsomal FMO by 40% and the FMO3 specific protein by 67%. c9, t11-CLA reduced FMO3 and cyt P450 expression by 61% (P=0.001) and 38% (P=0.06) and increased steoryl CoA desaturase transcription by 5.9-fold (P=0.07). Both decreased fatty acid oxidation and increased fatty acid synthesis seem to contribute to the CLA-induced fatty liver. Since FMO and cyt P450 are also involved in drug detoxification, suppression of the transcription of these genes by CLA may have other health consequences besides development of fatty liver.

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

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

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.

Effects of cis-9, trans-11, CLA in rats at intake levels reported for breast-fed infants

CLA intake in exclusively breast-fed infants is close to levels found to have physiological effects in animals. However, in the majority of studies mixtures of CLA isomers have been used and the independent effects of the major CLA isomer in human milk, cis-9,trans-11 CLA, at the intake level in exclusively breast-fed infants have hardly been studied. We therefore studied the effects of cis-9,trans-11 CLA on plasma lipids and glucose, immune function, and bone metabolism in growing rats. Thirty male Sprague-Dawley rats (n = 10/group) were fed either 20 mg/kg/d cis-9,trans-11 CLA and 20 mg/kg/d sunflower oil (CLA20), 40 mg/kg/d cis-9,trans-11 CLA (CLA40), or 40 mg/kg/d sunflower oil (placebo) for 8 wk. No significant differences between groups were found in plasma lipids, glucose, insulin, C-reactive protein, or lipid peroxidation. Liver fat content was lowest in the CLA20 group. In vitro interleukin 2 (IL-2) production increased, and tumor necrosis factor alpha, IL-1beta, prostaglandin E2, and leukotriene B4 production decreased in the CLA20 group. No differences between groups were detected in IL-4, IL-6, or interferon gamma production, plasma osteocalcin, insulin-like growth factor, or urinary deoxypyridinoline crosslinks. Plasma tartrate-resistant acid phosphatase 5b activity was significantly increased in the CLA40 group. The results indicate anti-inflammatory effects and enhanced T-cell function for the CLA20 group. No adverse effects were seen in the CLA20 group, whereas indications of increased bone resorption rate were observed in the CLA40 group.

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

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

Fatty acid composition of liver, adipose tissue, spleen, and heart of mice fed diets containing t10, c12-, and c9, t11-conjugated linoleic acid

Conjugated linoleic acid (CLA) isomers have unique effects on tissue lipids. Here we investigated the influence of individual CLA isomers on the lipid weight and fatty acid composition of lipid metabolizing (i.e. liver and retroperitoneal adipose) and lipid sensitive (i.e. spleen and heart) tissues. Female mice (8 week old; n=6/group) were fed either a control or one of the two CLA isomer supplemented (0.5%) diets for 8 weeks. The cis-9, trans-11-CLA diet reduced the 18:1n-9 wt% by 20-50% in liver, adipose tissue, and spleen, reduced the spleen n-3 polyunsaturated fatty acid (PUFA) by 90%, and increased the n-6 PUFA wt% by 20-50% in all tissues except heart. The trans-10, cis-12-CLA reduced both the n-6 and n-3 PUFA wt% in liver (>50%), reduced the heart n-3 PUFA wt% by 25%, and increased the wt% of spleen n-3 PUFA by 700%. The functional consequences of such changes in tissue fatty acid composition need to be investigated.

Effects of conjugated linoleic acid on skeletal muscle triacylglycerol metabolism in hamsters

OBJECTIVE

The present work evaluated the effects of conjugated linoleic acid (CLA) on various aspects of triacylglycerol metabolism in skeletal muscle to determine the potential involvement of this tissue in the effect of CLA to decrease body fat.

METHODS

Animals were randomized to three groups that were fed atherogenic diets that provided different amounts of trans-10,cis-12 CLA (0%, 0.5%, or 1%) for 6 wk. Muscle triacylglycerol, protein, water, glycogen, and DNA contents and fatty acid profile in triacylglycerols were analyzed. Lipoprotein lipase and carnitine palmitoyltransferase-I (CPT-I) activities were assessed. Triacylglycerol, glucose, and insulin concentrations were evaluated in serum.

RESULTS

The high dose of CLA increased food efficiency and gastrocnemius muscle weight. CLA feeding resulted in decreased muscle triacylglycerol content without changes in protein, water, glycogen, and DNA contents or in cell size (protein/DNA ratio) and produced decreased lipoprotein lipase activity and increased CPT-I activity. No differences were found between CLA doses. CLA feeding led to the saturation of stored triacylglycerols.

CONCLUSIONS

Decreased fatty acid uptake and increased fatty acid oxidation can contribute to the decreased muscle triacylglycerol content observed in hamsters fed the CLA diets. The increase in muscle fatty acid beta-oxidation might ultimately prevent storage of triacylglycerols in adipose tissue. Nevertheless, the lack of matching of lipoprotein lipase and CPT-I modifications makes it difficult to ensure that skeletal muscle is responsible, at least in part, for the effect of CLA on decreasing body fat; thus, further research is needed.

Conjugated linoleic acid reduces hepatic steatosis, improves liver function, and favorably modifies lipid metabolism in obese insulin-resistant rats

CLA has been shown to induce or suppress excess liver lipid accumulation in various animal models. Interestingly, the state of insulin resistance may be an important modulator of this effect. The objective of the current study was to determine how feeding a dietary CLA mixture would affect liver lipid accumulation in insulin-resistant/obese and lean rats in relation to liver function, lipidemia, liver TAG and phospholipid FA composition, and expression of hepatic markers of FA transport, oxidation, and synthesis. Six-week-old fa/fa and lean Zucker rats (n = 20/genotype) were fed either a 1.5% CLA mixture or a control diet for 8 wk. CLA supplementation reduced liver lipid concentration of fa/fa rats by 62% in concurrence with improved liver function (lower serum alanine aminotransferase and alkaline phosphatase) and favorable modification of the serum lipoprotein profile (reduced VLDL and LDL and elevated HDL) compared with controlfed fa/fa rats. The fa/fa genotype had two-thirds the amount of CLA (as % total FA) incorporated into liver TAG and phospholipids compared with the lean genotype. In both genotypes, CLA altered the hepatic FA profile (TAG greater than phospholipids) and these changes were explained by a desaturase enzyme index. Liver-FA-binding protein and acyl CoA oxidase, markers of FA transport and oxidation, respectively, were expressed at higher levels in CLA-fed fa/fa rats. In summary, these results illustrate a strong relationship between the state of insulin resistance and liver lipid metabolism and suggest that CLA acts to favorably modify lipid metabolism in fa/fa Zucker rats.

Body fat-lowering effect of conjugated linoleic acid is not due to increased lipolysis

The ability of conjugated linoleic acid (CLA) to reduce adiposity may be due to changes in energy expenditure and/or direct effects on adipocyte lipid metabolism. The aim of the present work was to analyse if CLA supplementation modifies lipolytic activity in adipose tissue from hamsters fed on high-fat diet. Hamsters were divided into two groups and fed on diets supplemented with either 0.5% linoleic acid (control) or 0.5% trans-10,cis-12 CLA. After 6 weeks, animals were fasted overnight and adipose tissues were dissected and weighed. Adipocytes were isolated by collagenase digestion and incubated in Krebs-Ringer bicarbonate buffer with or without several agents acting at different levels of the lipolytic cascade. Adipocyte diameters were measured by microscopy. Adipose tissue DNA content was assessed by spectrophotometry. Animals fed on CLA diet showed significantly reduced adipose tissue mass. No differences between both groups was found for basal lipolysis, lipolytic effects of isoproterenol, forskolin, dibutyryl-cAMP and isobutylmethylxanthine, and pD2 for isoproterenol. A similar total DNA amount was found in adipose tissue of both groups, showing that CLA diet had no effect on total cell number per fat pad. Although DNA content per gram tissue, an indirect reverse index of cell size, was significantly increased in CLA fed hamsters, microscopy did not reveal differences in medium mature adipocyte diameter, nor in cell size distribution between both groups. These results suggest that adipose tissue size reduction induced by trans-10,cis-12 CLA intake is not due to changes in lipolysis. Reduced preadipocyte differentiation into mature adipocytes may account for this fat-lowering effect.

Effects of conjugated linoleic acid on liver composition and fatty acid oxidation are isomer-dependent in hamster

OBJECTIVE

The present work was designed to study the effects of the two main isomers of conjugated linoleic acid (CLA), cis-9,trans-11 and trans-10,cis-12, on liver composition and hepatic fatty acid oxidation in hamsters.

METHODS

Animals were divided into three groups that were fed atherogenic diets supplemented with 0.5% linoleic acid, cis-9,trans-11 CLA, or trans-10,cis-12 CLA for 6 wk. Liver lipids, protein, water and DNA contents, and histologic structure were analyzed. Hepatic carnitine palmitoyltransferase-I and acyl coenzyme A oxidase activities were assessed. Triacylglycerol concentration, and aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase, and alkaline phosphatase activities were evaluated in serum. CLA isomer contents were analyzed by gas chromatography in hepatic triacylglycerols. Peroxisome proliferator-activated receptor-alpha mRNA was determined by reverse transcriptase polymerase chain reaction.

RESULTS

Trans-10,cis-12 CLA led to significantly greater weight, lower levels of triacylglycerol, cholesterol, and phospholipid, and larger total cell number in liver. Carnitine palmitoyltransferase-I and acyl coenzyme A oxidase activities were significantly increased by this isomer. No changes were induced by cis-9,trans-11 CLA. Trans-10,cis-12 CLA was recovered in significantly lower proportions than cis-9,trans-11 in liver triacylglycerols. Histopathologic analysis showed no abnormalities. No significant differences in serum aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase, and alkaline phosphatase activities or in hepatic mRNA peroxisome proliferator-activated receptor-alpha expression were found among the three experimental groups.

CONCLUSIONS

These results suggest that the addition of 0.5% of these CLA isomers to the diet do not induce toxic effects in liver after 6 wk of feeding. Intake of trans-10,cis-12 isomer but not of cis-9,trans-11 CLA increases liver fatty acid oxidation. This effect leads to decreased hepatic and serum triacylglycerols.

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

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

Interaction of fish oil and conjugated linoleic acid in affecting hepatic activity of lipogenic enzymes and gene expression in liver and adipose tissue

The interaction of dietary fish oil and conjugated linoleic acid (CLA) in affecting the activity of hepatic lipogenic enzymes and gene expression in liver and adipose tissue was examined in mice. A diet containing 1.0% CLA, mainly composed of 9cis,11trans- and 10trans,12cis-octadecadienoic acids at equivalent amounts, greatly decreased adipose tissue weight and serum concentrations of leptin and adiponectin and was accompanied by a downregulation of the expression of various adipocyte-abundant genes in epididymal adipose tissue. However, CLA increased the serum insulin concentration fourfold, and it caused hepatomegaly, with huge increases in the triacylglycerol level and the activity and mRNA levels of hepatic lipogenic enzymes. Different amounts (1.5, 3, and 6%) of fish oil added to CLA-containing diets dose-dependently downregulated parameters of lipogenesis and were accompanied by a parallel decrease in the triacylglycerol level in the liver. The supplementation of CLA-containing diets with fish oil was also associated with an increase in fat pad mass and mRNA levels of many adipocyte-abundant genes in epididymal adipose tissue along with a normalization of serum concentrations of leptin and adiponectin in a dose-dependent manner. However, in mice fed a diet containing 1.5% fish oil and CLA in whom fat pad mass was still low and comparable to that in the animals fed CLA alone, the serum insulin concentration greatly exceeded (twofold) the value observed in mice fed CLA alone, indicating an aggravation of insulin resistance. This hyperinsulinemia was ameliorated with increasing amounts of fish oil in the diets. Apparently, many of the physiological effects of CLA can be reversed by fish oil.

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

Background

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

Results

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

Conclusions

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

Development of conjugated linoleic acid (CLA)-mediated lipoatrophic syndrome in the mouse

Conjugated linoleic acids (CLA) are positional and geometric dienoic isomers of linoleic acid. Dietary CLA supplementation leads to a drop in fat mass in various species, including in humans. The t10,c12-CLA isomer is responsible for this anti-obesity effect. The reduction of fat mass is especially dramatic in the mouse, in which it is associated with severe hyperinsulinemia, insulin resistance and massive liver steatosis. The origin of these adverse side effects and putative chronology of events leading to CLA-mediated lipoatrophic syndrome are presented and discussed in this review.

Conjugated linoleic acids: are they beneficial or detrimental to health?

Conjugated linoleic acids (CLAs) comprise a family of positional and geometric isomers of linoleic acid (18:2n-6; LA) that are formed by biohydrogenation and oxidation processes in nature. The major dietary sources of these unusual fatty acids are foods derived from ruminant animals, in particular dairy products. The main form of CLA, cis-9, trans-11-18:2, can be produced directly by bacterial hydrogenation in the rumen or by delta-9 desaturation of the co-product vaccenic acid (trans-11-18:1) in most mammalian tissues including man. The second most abundant isomer of CLA is the trans-10, cis-12-18:2 form. Initially identified in grilled beef as a potential anti-carcinogen a surprising number of health benefits have subsequently been attributed to CLA mixtures and more recently to the main individual isoforms. It is also clear from recent studies that the two main isoforms can have different effects on metabolism and cell functions and can act through different cell signalling pathways. The majority of studies on body compositional effects (i.e. fat loss, lean gain), on cancer and cardiovascular disease attenuation, on insulin sensitivity and diabetes and on immune function have been conducted with a variety of animal models. Observations clearly emphasise that differences exist between mammalian species in their response to CLAs with mice being the most sensitive. Recent studies indicate that some but not all of the effects observed in animals also pertain to human volunteers. Reports of detrimental effects of CLA intake appear to be largely in mice and due mainly to the trans-10, cis-12 isomer. Suggestions of possible deleterious effects in man due to an increase in oxidative lipid products (isoprostanes) with trans-10, cis-12 CLA ingestion require substantiation. Unresponsiveness to antioxidants of these non-enzymatic oxidation products casts some doubt on their physiological relevance. Recent reports, albeit in the minority, that CLAs, particularly the trans-10, cis-12 isomer, can elicit pro-carcinogenic effects in animal models of colon and prostate cancer and can increase prostaglandin production in cells also warrant further investigation and critical evaluation in relation to the many published anti-cancer and anti-prostaglandin effects of CLAs.

Effects of specific conjugated linoleic acid isomers on growth characteristics in obese Zucker rats

Growing female obese Zucker (fa/fa) rats were treated (via intragastric gavage) for 21 d with either a (i) vehicle [corn oil; 0.9 g/kg body weight (BW)], (ii) CLA mixture [50:50; trans-10, cis-12 and cis-9, trans-11 CLA], (iii) cis-9,trans-11 CLA, or (iv) trans- 10, cis-12 CLA (CLA treatments at 1.5 g CLA/kg BW). Compared with controls, average daily gain (g/d) was reduced 24 and 44% by the CLA mixture and trans-10, cis-12 CLA, respectively. There was no treatment effect on average whole-body (minus heart and liver) composition (dry matter basis): fat (70.2%), protein (21.0%), and ash (4.3%). Compared with animals treated with cis-9,trans-11 CLA, obese Zucker rats treated with trans-10, cis-12 and the CLA mixture had 7.8% more carcass water. Treatment had no effect on heart or liver weights or on heart or liver weights as a percentage of body weight, but compared with the other treatments trans-10, cis-12 CLA increased liver lipid content by 33%. Hepatic lipid ratios of 16:1/16:0 and 18:1/18:0 (a proxy for delta9-desaturase capability) were not affected by treatment (0.1 and 0.6, respectively). Similar to previous reports, CLA increased hepatic lipid content and altered both liver and carcass FA composition (i.e., reduced arachidonic acid content), but the ability of CLA to manipulate body composition in obese Zucker rats remains questionable.

A test of Ockham's razor: implications of conjugated linoleic acid in bone biology

The philosopher William of Ockham is recognized for the maxim that an assumption introduced to explain a phenomenon must not be multiplied beyond necessity, or that the simplest explanation is probably the correct explanation. The general truth is that conjugated linoleic acids (CLAs) are nutrients. However, the demonstration that these isomers of octadecadienoic acid protect against cancers in rodents stimulated curiosity that directed significant resources to characterize the biological functions of these fatty acids in cell and animal models. The benefits to human subjects given supplements of CLA were at best modest. The disappointing results in humans should be taken as an opportunity to critically evaluate all findings of CLA use and to consolidate the common actions of this nutrient so that future investigations focus on specific isomers and the most reasonable mechanisms. As such, the principal and consistently reported benefits of CLA have been in improving cancer outcomes, reducing body fat in growing animals, and modulating cell functions. Recognizing where related actions of CLA converge in specific disease conditions and physiologic states is how research efforts should be directed to minimize the pursuit of superfluous theories. Here, we briefly review the current biological effects of CLA and attempt to integrate their potential effect on the physiology and health of the skeletal system. Thus, the purpose of this review is to advance the science of CLA and to identify areas of research in which these nutrients affect bone metabolism and skeletal health.