Abstract
We have previously shown that both a commercially available mixture of conjugated linoleic acid (CLA) isomers and the trans-10, cis-12 isomer of CLA reduced the triglyceride (TG) content and induced apoptosis in differentiating cultures of murine 3T3-L1 preadipocytes. However, the influence of CLA isomers on differentiating human (pre)adipocytes is unknown. Therefore, we conducted a series of studies using primary cultures of stromal vascular cells isolated from human adipose tissue to determine: 1) the influence of seeding density and thiazolidinedione (TZD) concentration on TG content; 2) the chronic dose response of cis-9, trans-11 CLA vs. trans-10, cis-12 CLA on TG content; 3) whether chronic linoleic acid supplementation could rescue the TG content of CLA-treated cultures; and 4) whether trans-10, cis-12-mediated reduction in cellular TG was due to decreased lipogenesis and/or increased lipolysis. In expt. 1, the TG content [micromol/(L x 10(6) cells)] increased as both seeding density and TZD concentration increased. For example, cultures seeded at 4 x 10(4) cells/cm(2) and supplemented with 10 micromol/L BRL 49653 had 10-fold more TG than similarly seeded cultures without BRL 49653. In expt. 2, TG content decreased as the level of trans-10, cis-12 CLA increased from 1 to 10 micromol/L, whereas the TG content increased with increasing concentrations of either linoleic acid or cis-9, trans-11 CLA. In expt. 3, linoleic acid supplementation restored the TG content of cultures treated with trans-10, cis-12 CLA compared with cultures treated with CLA alone, suggesting that attenuation of TG content by CLA is reversible. In expt. 4, glucose incorporation into total lipid decreased with increasing levels of trans-10, cis-12 CLA, whereas neither CLA isomer acutely affected lipolysis. These data suggest that the reported antiobesity actions of a supplement containing a crude mixture of CLA isomers given to humans may be due to inhibition of lipogenesis by the trans-10, cis-12 isomer.
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