| Conjugated linoleic acid (CLA), a group of positional and geometric fatty acid isomers derived from linoleic acid [18:2 (n-6)] that occur naturally in ruminant meats, pasteurized cheeses and dairy products, has been shown to decrease body fat when fed to animals. However, the mechanism by which one or more of CLA's isomers reduces adiposity remains unknown. Thus, the purpose of this study was to determine the effect of a crude mixture of CLA isomers as well as its two primary isomers, trans-10, cis-12 and cis-9, trans-11 CLA, on triglyceride (TG) content, differentiation, and metabolism of preadipocytes using 3T3-L1 preadipocytes as the cell model.; 3T3-L1 preadipocytes supplemented with a crude mixture of CLA isomers were found to have less TG and to be smaller in size than cultures supplemented with linoleic acid (LA). Moreover, trans-10, cis-12 CLA was determined to be the isomer responsible for the reduction in TG content. In addition, cultures treated with mixed CLA and trans-10, cis-12 CLA for 24-96 h had more cells exhibiting apoptosis compared to BSA or LA-treated cultures. Interestingly, trans-10, cis-12 CLA treatment of preadipocyte cultures for 2 d increased PPARγ2 protein expression whereas 6 d of CLA treatment reduced PPARγ2 expression. CLA had no effect on adipose P2 (aP2), a fatty acid binding protein regulated by PPARγ2.; Gas chromatography analysis of the fatty acid profile determined that cis-9, trans-11 and trans-10, cis-12 CLA were incorporated into the neutral lipids and phospholipids of the cultures. Moreover, trans-10, cis-12 CLA treatment altered the levels of saturated:monounsaturated fatty acids. Finally, supplementing trans-10, cis-12 CLA-treated cultures with increasing levels of linoleic acid prevented the TG-lowering effects of CLA.; Trans-10, cis-12 CLA also increased both 14C-glucose and 14C-oleic acid incorporation into the lipid fraction of the cultures compared to BSA controls. Moreover, 90% of the radiolabeled carbon was recovered in the TG component of the lipid fraction. CO2 production from 14C-oleic acid also increased while glucose oxidation was unaffected by trans-10, cis-12 CLA supplementation. Finally, basal lipolysis increased modestly following trans-10, cis-12 CLA treatment compared to controls. In conclusion, these data suggest that trans-10, cis-12 CLA, the TG-lowering isomer of CLA, reduces adipocyte TG and cellularity primarily by increasing fatty acid oxidation and inducing apoptosis, respectively. |
