in several animal models, including hamsters, but the mechanism of action of the main food-derived CLA isomer is unknown in this species. This study thus focused on cis-9,trans-11-CLA (rumenic acid), and its effect was compared with that of fish oil, which is known to influence several aspects of atherogenesis. Syrian hamsters were fed (for 12 wk) diets containing 20% (wt/wt) butter fat (B diet) or the same diet augmented with either 1% (wt/wt) of a cis-9,trans-11-CLArich oil (BR diet) or 1% (wt/wt) fish oil (BF diet). The BR diet induced the lowest aortic lipid deposition (from Ϫ30% to Ϫ45%) among the butter oil-fed hamsters. In this group, plasma also displayed a reduced non-HDL-to-HDL-cholesterol ratio (21% less than in the butter oil group) and inflammatory serum amyloid A levels (70 -80%) and an improvement of anti-oxidized LDL paraoxonase activity (all P Ͻ 0.05). Compared with the B group, the beneficial effects of the BR diet could be further explained in part by preventing the high VCAM-1 expression rate, increasing (30%) ATP-binding cassette subfamily A1 expression in the aorta, and downregulating expression of inflammatory-related genes (TNF-␣, IL-1␤, and cyclooxygenase 2, 2-to 2.8-fold, P Ͻ 0.05). This effect was partly associated with an activation of peroxisome proliferator-activating receptor (PPAR)/liver X receptor (LXR)-␣ signaling cascade. Interestingly, activation of PPAR/LXR-␣ signaling was not observed in hamsters fed the BF diet, in which the early signs of atherogenesis were increased. In conclusion, this study demonstrated that milk fat-rich cis-9,trans-11-CLA reduces the atherogenic process in hyperlipidemic hamsters.

Milk fat is usually considered to be proatherogenic, although its fatty acid composition can vary, due mainly to farming conditions. No study has evaluated whether such variation can modify the atherogenic properties of dairy fat. Aortic lipid deposition and related risk factors were examined in Syrian hamsters fed diets for 12 wk containing 200 g/kg of 2 commercial milk fats [high content of saturated fatty acids (HSF) and low content of saturated fatty acids (LSF)] contrasting, respectively, in total saturated fatty acids (72 vs. 67 g/100 g), 18:1, trans (4.24 vs. 7.26 g/100g), and conjugated linoleic acid (mainly cis-9,trans-11 or rumenic acid; 0.39 vs. 2.59 g/100 g). Hamsters fed the LSF-diet had 25% less aortic cholesteryl-ester deposition than those fed the HSF-diet; this was accompanied by an improved plasma cholesterol profile (lower LDL cholesterol and LDL:HDL cholesterol ratio), a lower local inflammatory status (aortic gene expression of cyclooxygenase-2), and lower aortic gene expression of vascular cell adhesion molecule-1 (all P < 0.05). Supplementation of the LSF-diet with rumenic acid (up to 9 g/kg) amplified the antiatherogenic effect of the original LSF-diet compared with the HSF-diet, i.e., less aortic cholesterol loading, increased reverse cholesterol transport potential (higher plasma HDL cholesterol concentration and ATP-binding cassette, subfamily A, transporter 1 gene expression in aorta), and decreased LDL-peroxidability index and gene expression of proinflammatory IL-1beta in the aorta (all P < 0.05). In conclusion, our results suggest that the atherogenic potential of milk fat can be greatly reduced in products with a naturally high abundance of rumenic acid, and argue for increasing this fatty acid in milk.

Gender and dietary fatty acids are involved in the regulation of lipid metabolism, disturbances of which can lead to pathologies such as metabolic syndrome or CVD. Possible interactions between these factors were investigated in male and female hamsters fed diets rich in either saturated fatty acids ('butter' diet) or in a-linolenic acid ('linseed oil' diet). Gender effect predominated over the diet effect on cholesterol (CH) metabolism; compared to males, females exhibited lower concentrations of plasma total CH (220 %, P,0·001), LDL-CH (240 %, P,0·001) and HDL-CH (2 16 %, P, 0·001), together with higher LDL receptor (þ 40 %) and lower HDL receptor (260 %) hepatic content. Triacylglycerol (TG) metabolism was affected by diet above all: compared to animals fed the 'butter' diet, those fed the 'linseed oil' diet exhibited lower plasma (223 %, P¼0·046) and liver TG (220 %, P¼ 0·026) concentration which may result from both an increased b-oxidation (P,0·001), without any change in PPARa mRNA, and a decreased hepatic lipogenesis (P¼ 0·023), without increased sterol response element binding protein 1c (SREBP1c) mRNA. The response to diet was much more pronounced in males than in females, without gender effect on the transcription level of PPARa and SREBP1c. Finally, the 'linseed oil' diet decreased the insulin resistance index (2 80 %, P,0·001) with a more marked effect in males, in relation to their higher hepatic PPARg expression (þ 90 %, P¼ 0·012). In conclusion, in our model, the response of either TG or CH to dietary fatty acids is modulated differently by gender. The possible relevance of these interactions to dietary practice should be taken into account in man.a-Linolenic acid: Gender: Lipid metabolism: Dietary fatty acids

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