Karen J. Albright

Effect of conjugated linoleic acid on body composition in mice.

The effects of conjugated linoleic acid (CLA) on body composition were investigated. ICR mice were fed a control diet containing 5.5% corn oil or a CLA-supplemented diet (5.0% corn oil plus 0.5% CLA). Mice fed CLA-supplemented diet exhibited 57% and 60% lower body fat and 5% and 14% increased lean body mass relative to controls (P<0.05). Total carnitine palmitoyltransferase activity was increased by dietary CLA supplementation in both fat pad and skeletal muscle; the differences were significant for fat pad of fed mice and skeletal muscle of fasted mice. In cultured 3T3-L1 adipocytes CLA treatment (1×10−4 M) significantly reduced heparin-releasable lipoprotein lipase activity (−66%) and the intracellular concentrations of triacylglyceride (−8%) and glycerol (−15%), but significantly increased free glycerol in the culture medium (+22%) compared to control (P<0.05). The effects of CLA on body composition appear to be due in part to reduced fat deposition and increased lipolysis in adipocytes, possibly coupled with enhanced fatty acid oxidation in both muscle cells and adipocytes.

Evidence that the trans-10,cis-12 isomer of conjugated linoleic acid induces body composition changes in mice

We investigated the effects of conjugated linoleic acid (CLA) preparations, which were enriched for the cis-9,trans-11 CLA isomer or the trans-10,cis-12 CLA isomer, on body composition in mice. Body composition changes (reduced body fat, enhanced body water, enhanced body protein, and enhanced body ash) were associated with feeding the trans-10,cis-12 CLA isomer. In cultured 3T3-L1 adipocytes, the trans-10,cis-12 isomer reduced lipoprotein lipase activity, intracellular triacylglycerol and glycerol, and enhanced glycerol release into the medium. By contrast, the cis-9,trans-11 and trans-9,trans-11 CLA isomers did not affect these biochemical activities. We conclude that CLA-associated body composition change results from feeding the trans-10,cis-12 isomer.

Changes in Body Composition in Mice During Feeding and Withdrawal of Conjugated Linoleic Acid

Two experiments were conducted. In Experiment 1, 8-wk-old mice were fed control diet or diet supplemented with 0.5% conjugated linoleic acid (CLA) to study the effect of CLA on body composition (CLA: 40.8–41.1% c-9,t-11 isomer, 43.5–44.9% t-10,c-12 isomer). The data for CLA-fed mice vs. controls described parallel but significantly distinct responses for both absolute and relative changes in body fat mass (reduced in CLA-fed mice) and for relative changes in whole body protein and whole body water (both of which were increased in CLA-fed mice). In the CLA-fed mice, the effect on whole body protein appeared to precede the reduction in body fat mass. In Experiment 2, weanling mice were fed control diet or diet supplemented with 0.5% CLA for 4 wk (test group), at which time all mice were fed control diet devoid of added CLA. The test group exhibited significantly reduced body fat and significantly enhanced whole body water relative to controls at the time of diet change. Time trends for changes in relative body composition were described by parallel lines where the test group exhibited significantly less body fat but significantly more whole body protein, whole body water, and whole body ash than controls. Tissue CLA levels declined following the withdrawal of CLA from the diet. In skeletal muscle of mice fed CLA-supplemented diet, the t-10,c-12 isomer was cleared significantly faster than the c-9,t-11 CLA isomer.

Trans-10, cis-12 CLA Inhibits Differentiation of 3T3-L1 Adipocytes and Decreases PPARγ Expression

The trans-10,cis-12 isomer of conjugated linoleic acid (CLA) has been shown to reduce body fat gain in mice. However, the underlying molecular mechanism is not well characterized. Here we report evidence that trans-10,cis-12 (t10c12) CLA inhibits preadipocyte differentiation. Treating differentiating 3T3-L1 preadipocytes with t10c12 CLA and conjugated nonadecadienoic acid (CNA, a 19-carbon CLA cognate) resulted in decreased intracellular triglyceride accumulation and mRNA levels of the adipogenic gene fatty acid synthase and adipocyte lipid binding protein. T10c12 CLA and CNA also reduced protein levels of adipocyte transcription factors, peroxisome proliferator-activated receptor gamma and CCAAT/enhancer binding protein alpha. Similarly, CLA reduced body fat gain and significantly inhibited the expression of PPAR gamma and its downstream target lipoprotein lipase in mouse adipose tissue. These observations indicate that CLA decreases body fat gain in part by inhibiting the differentiation of preadipocytes.

Differential responses of hamsters and rats fed high-fat or low-fat diets supplemented with conjugated linoleic acid

We compared the effects of dietary conjugated linoleic acid (CLA) on body composition in weanling hamsters and rats fed 20% fat (HF) or 5% fat (LF) diets for 9 weeks. In both species the HF groups appeared to gain more body weight and fat relative to the LF groups but the differences were not significant. In hamsters fed LF or HF, total body fat gain was significantly reduced by CLA-supplementation (0.5% or 1% of diet). Body weight gain was also reduced, but the differences were significant only in the HF group. Feed intake appeared not to be affected for any group. In rats fed HF or LF diet, total body fat was not reduced by CLA supplementation (1% of diet) but the lipid stored in specific fat pads was significantly reduced (for the LF-CLA group the retroperitoneal and omentum fat pads were significantly reduced; for the HF-CLA group the peritoneal fat pad was significantly reduced). Body weight gain and feed intake were not affected except for the LF-CLA group where feed intake was significantly reduced. These results indicate that body fat gain in both hamsters and rats is reduced by CLA feeding, and that hamsters are more responsive than rats in this regard. It is important now to determine the biochemical basis for these differences.

Inhibition of benzo[a]pyrene-induced mouse forestomach neoplasia and reduction of H2O2 concentration in human polymorphonuclear leucocytes by flavour components of Japanese-style fermented soy sauce.

Previously it was reported that 4-hydroxy-2 (or 5)-ethyl-5 (or 2)-methyl-3(2H)-furanone (HEMF), a characteristic flavour component of Japanese-style fermented soy sauce that exhibits antioxidant activity, inhibits benzo[a]pyrene-induced forestomach neoplasia in mice. The antioxidant and anticarcinogenic activities of other structurally similar soy sauce flavour components are now reported. 4-Hydroxy-5-methyl-3(2H)-furanone (HMF) and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) were found to be antioxidants. In particular, HMF and HDMF (as well as HEMF) reduced hydrogen peroxide concentration in human polymorphonuclear leucocytes stimulated by arachidonic acid or 12-O-tetradecanoylphorbol-13-acetate. HMF and HDMF were administered individually in semipurified diet to female ICR mice previously treated with benzo[a]pyrene (1.5 mg/wk, orally for 4 wk) to initiate forestomach neoplasia. The mice were killed at 30 wk of age. Both furanones reduced forestomach neoplasms, with HDMF exhibiting more potency. The data indicate that HDMF and HMF, like HEMF, inhibit carcinogenesis in this system by acting at the post-initiation stage.

Formation and Action of Anticarcinogenic Fatty Acids

Conjugated dienoic derivatives of linoleic acid (referred to by the acronym CLA) constitute a newly recognized class of anticarcinogenic fatty acids. Of the eight major CLA isomers, the cis-9, trans-11 isomer alone is incorporated into phospholipid and may be the most biologically relevant isomer. CLA exhibits potent antioxidant activity; evidence is presented indicating that CLA acts both as an in vitro and in vivo antioxidant. The formation of CLA in foods, and its possible biological significance in cell membranes, is discussed.

Controlling acrylamide in French fry and potato chip models and a mathematical model of acrylamide formation: acrylamide: acidulants, phytate and calcium.

We previously reported that in potato chip and French fry models, the formation of acrylamide can be reduced by controlling pH during processing steps, either by organic (acidulants) or inorganic acids. Use of phytate, a naturally occurring chelator, with or without Ca++ (or divalent ions), can reduce acrylamide formation in both models. However, since phytate itself is acidic, the question remains as to whether the effect of phytate is due to pH alone or to additional effects. In the French fry model, the effects on acrylamide formation of pH, phytate, and/or Ca++ in various combinations were tested in either blanching or soaking (after blanching) steps. All treatments significantly reduced acrylamide levels compared to control. Among variables tested, pH may be the single most important factor for reducing acrylamide levels, while there were independent effects of phytate and/or Ca++ in this French fry model. We also developed a mathematical formula to estimate the final concentration of acrylamide in a potato chip model, using variables that can affect acrylamide formation: glucose and asparagine concentrations, cut potato surface area and shape, cooking temperature and time, and other processing conditions.