Linoleic acid partially restores the triglyceride content of conjugated linoleic acid-treated cultures of 3T3-L1 preadipocytes

We have previously demonstrated that a crude mixture of commercially availa ble conjugated linoleic acid (CLA) isomers suppressed triglyceride (TG) con tent and induced apoptosis in post-confluent cultures of murine 3T3-L1 prea dipocytes. Furthermore, we found that 100 muM of trans-10, cis-12 isomer of CLA had a greater TG-lowering and apoptotic effect than the crude mixture of CLA isomers. Therefore, the purpose of this study was to: 1) compare the potencies of the two main isomers found in the crude mixture of CLA isomer s, e.g. cis-9, trans-ii (41%) and trans-10, cis-12 (44%); and 2) determine if the TG-reducing actions of CLA could be attenuated by the addition of in creasing levels of linoleic acid to the cultures. Preadipocyte differentiat ion was assessed on day 7 of the differentiation protocol by measuring TG c ontent (per 10(6) cells), cell size, and lipid staining. In experiment 1, p ost-confluent cultures of 3T3-L1 preadipocytes treated for the first 6 d of differentiation with 100 muM of a crude mixture of CLA isomers or 44 muM O f trans-10, cis-12 CLA had less TG content than all other cultures. In cont rast, cultures supplemented with 41 muM of the cis-9, trans-ii CLA isomer h ad the same amount of TG as the BSA controls. In experiment 2, post-conflue nt cultures of 3T3-L1 preadipocytes treated for the first 6 d of differenti ation with 50 muM trans-10, cis-12 CLA had less TG content and a greater nu mber of smaller cells (10-12.5 microns) compared to all other treatments. C LA-treated cultures supplemented with increasing levels of linoleic acid (5 0-200 muM) had greater TG contents and greater numbers of larger cells (15- 20 microns) than cultures treated with 50 muM of the trans-10, cis-12 CLA i somer alone. These data demonstrate that: 1) the TG-lowering effects of the crude mixture of CLA isomers is due almost exclusively to the trans-10, ci s-12 isomer; and 2) linoleic acid partially reverses CLA's attenuation of T G content, suggesting that these unsaturated fatty acids may compete for in corporation into TG or phospholipid-derived eicosanoids that regulate pread ipocyte differentiation. (C) 2001 Elsevier Science Inc. All rights reserved .