Conjugated linoleic acid (CLA) is a naturally occurring group of dienoic derivatives of linoleic acid found in beef and dairy products. CLA has been reported to reduce body fat. To examine the mechanism(s) of CLA reduction of fat mass, female C57BL/6J mice were fed standard semipurified diets (10% fat of total energy) with or without CLA (1% wt/wt). Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick endlabeling (TUNEL) and DNA fragmentation analysis revealed that fat-mass decrease by CLA was mainly due to apoptosis. Tumor necrosis factor (TNF)-␣ and uncoupling protein (UCP)-2 mRNA levels increased 12-and 6-fold, respectively, in isolated adipocytes from CLA-fed mice compared with control mice. Because it is known that TNF-␣ induces apoptosis of adipocytes and upregulates UCP2 mRNA, a marked increase of TNF-␣ mRNA with an increase of UCP2 in adipocytes caused CLA-induced apoptosis. However, with a decrease of fat mass, CLA supplementation resulted in a state resembling lipoatrophic diabetes: ablation of brown adipose tissue, a marked reduction of white adipose tissue, marked hepatomegaly, and marked insulin resistance. CLA supplementation decreased blood leptin levels, but continuous leptin infusion reversed hyperinsulinemia, indicating that leptin depletion contributes to the development of insulin resistance. These results demonstrate that intake of CLA reduces adipose tissue by apoptosis and results in lipodystrophy, but hyperinsulinemia by CLA can be normalized by leptin administration. Diabetes 49:1534-1542, 2000 C onjugated linoleic acid (CLA) is a group of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid. The major dietary sources of CLA for humans are beef and dairy products (1). There is a great interest in CLA because of its anticarcinogenic and antiatherogenic properties and its ability to reduce body fat while enhancing lean body mass (2). Reduction of body fats by CLA was observed in pigs (3), mice (4,5), and hamsters (6).In this study, we investigated the mechanism(s) of CLAmediated reduction of fat mass in mice. Reduction of fat mass by CLA was due to apoptosis. Initially, we expected the beneficial effect of CLA-induced fat mass decrease, such as improvement of insulin resistance and reduction of blood triglyceride concentration. Unexpectedly, however, rapid reduction of fat mass by CLA resulted in marked insulin resistance and hepatomegaly. These metabolic abnormalities are characteristics of lipodystrophy (7,8). During this study, Delany et al. (9) also reported that CLA reduced body fat but resulted in hyperinsulinemia and liver enlargement in AKR/J male mice. To understand the mechanism(s) of CLAinduced lipodystrophy, we examined expression levels of several genes important in energy expenditure and lipid and carbohydrate metabolism in adipose tissues and isolated adipocytes. Furthermore, effects of leptin infusion on CLAinduced insulin resistance were also examined. RESEARCH DESIGN AND METHODSExperimental protocols. Female C57BL/6J mice were obt...

Dietary fish oil induces hepatic peroxisomal and microsomal fatty acid oxidation by peroxisome proliferator-activator receptor ␣ activation, whereas it downregulates lipogenic gene expression by unknown mechanism(s). Because sterol regulatory element-binding proteins (SREBPs) up-regulated lipogenic genes, investigation was made on the effects of fish oil feeding on SREBPs and sterol regulatory element (SRE)-dependent gene expression in C57BL/6J mice. Three forms of SREBPs, SREBP-1a, -1c, and -2, are expressed in liver, and their truncated mature forms activate transcription of sterol-regulated genes. C57BL/6J mice were divided into three groups; the first group was given a high carbohydrate diet, and the other two groups were given a high fat diet (60% of total energy), with the fat in the form of safflower oil or fish oil, for 5 months. Compared with safflower oil feeding, fish oil feeding decreased triglyceride and cholesterol concentrations in liver. There were no differences in amount of SREBP-1 and -2 in both precursor and mature forms between carbohydrate-and safflower oil-fed mice. However, compared with safflower oil feeding, fish oil feeding reduced the amounts of precursor SREBP-1 in membrane fraction by 90% and of mature SREBP-1 in liver nuclei by 57%. Fish oil feeding also reduced precursor SREBP-2 by 65% but did not alter the amount of mature SREBP-2. Compared with safflower oil feeding, fish oil feeding decreased liver SREBP-1c mRNA level by 86% but did not alter SERBP-1a mRNA. Consistent with decrease of mature SREBP-1, compared with safflower oil feeding, fish oil feeding down-regulated the expression of liver SRE-dependent genes, such as low density lipoprotein receptor, 3-hydroxy-3-methylglutaryl-CoA reductase, 3-hydroxy-3-methylglutaryl-CoA synthase, fatty acid synthase, acetyl-CoA carboxylase, and stearoyl-CoA desaturase-1. These data suggested that in liver, fish oil feeding downregulates the mature form of SREBP-1 by decreasing SREBP-1c mRNA expression, with corresponding decreases of mRNAs of cholesterologenic and lipogenic enzymes.

Rodents fed fish oil showed less obesity with a reduction of triglyceride synthesis in liver, relative to other dietary oils, along with a decrease of mature form of sterol regulatory element binding protein-1 (SREBP-1) and activation of peroxisome proliferator-activated receptor ␣ (PPAR ␣ ). Decrease of mature SREBP-1 protein by fish oil feeding was due to either inhibition of SREBP-1 proteolytic cascade or to decrease of its mRNA. To clarify its mechanism and relation to antiobesity effect, mice were fed fish oil in a range from 10 to 60 energy percent (en%). Fish oil feeding decreased body weight and fat mass in a dosedependent manner, in parallel with PPAR ␣ activation and a decrease of SREBP-1 mRNA. However, compared with 0 en% fish oil feeding, 10 en% fish oil feeding decreased mature SREBP-1 protein by 50% with concomitant decreases of lipogenic genes, while precursor SREBP-1 protein rather increased by 1.3-fold. These data suggest that physiological doses of fish oil feeding effectively decrease expression of liver lipogenic enzymes by inhibiting SREBP-1 proteolytic cascade, while substantial decrease of SREBP-1 expression is observed in its pharmacological doses, and that activation of PPAR ␣ rather than SREBP-1 decrease might be related to the antiobesity effect of fish oil feeding. -Nakatani, T., H-J. Kim, Y. Kaburagi, K. Yasuda, and O. Ezaki. A low fish oil feeding inhibits SREBP-1 proteolytic cascade, while a high fish oil feeding decreases SREBP-1 mRNA in mice liver: its relationship to anti-obesity effect. J. Lipid Res.