Abstract
A series of experiments was conducted using 3T3-L1 preadipocytes as the cell model to determine: (i) whether the triglyceride (TG)-lowering effects of a crude mixture of conjugated linoleic acid (CLA) isomers were due to a specific isomer of CLA and the timing of treatment, (ii) if CLA reduced TG content by inhibiting a key regulator of adipogenesis, (iii) if CLA incorporated into either neutral lipid or phospholipid cell fractions, and (iv) whether the effects of CLA treatment were reversible. Trans-10,cis-12 CLA reduced TG content, whereas the cis-9,trans-11 isomer increased TG content compared to vehicle [bovine serum albumin (BSA)] controls. Treatment with 50 μM trans-10,cis-12 CLA during the entire 6 d of differentiation reduced TG content to a greater extent than treatment during either the first 3 d or last 3 d of differentiation. Trans-10,cis-12 CLA treatment of preadipocyte cultures for 48 h increased peroxisome proliferator activated receptor γ2 (PPARγ2) protein expression compared to cultures treated with linoleic acid (LA) or the BSA controls. CLA had no effect on adipose P2 (aP2), a fatty acid-binding protein regulated by PPARγ2. Both the cis-9,trans-11 and the trans-10,cis-12 isomers of CLA were incorporated into neutral lipids and phospholipids. However, cis-9,trans-11 CLA levels were one- to twofold higher than trans-10,cis-12 CLA levels. Moreover, trans-10,cis-12 CLA treatment reduced cis-11 18∶1 concentrations in both neutral lipids and phospholipids while increasing cis-9 18∶1 and 18∶2 concentrations. Palmitoleic acid (16∶1) levels were also lower in the neutral lipid fraction of cultures treated with trans-10,cis-12 CLA. Supplementing trans-10,cis-12 CLA-treated cultures (50 μM) with increasing levels of LA resulted in a dose-dependent increase in TG content compared to cultures treated with 50 μM CLA alone. LA supplementation also prevented some of the morphological changes associated with trans-10,cis-12 CLA treatment as seen with scanning electron microscopy. Treatment with 50μM trans-10,cis-12 CLA for 6 d decreased PPARγ2 levels, and supplementation of CLA-treated cultures with LA increased PPARγ2 levels compared with cultures treated with CLA alone. Taken together, these data indicate that in cultures of 3T3-L1 preadipocytes: (i) trans-10,cis-12 CLA is the TG-lowering isomer of CLA, and its effects are dependent on dose, duration of treatment, and the amount of LA in the cultures; (ii) trans-10,cis-12 CLA treatment alters the monounsaturated fatty acid profile of neutral- and phospholipids of the cultures; and (iii) although acute (2−d) trans-10,cis-12 CLA treatment increased PPARγ2 protein levels, chronic (6−d) treatment decreased PPARγ2 levels.
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Abbreviations
- AA:
-
arachidonic acid
- ANOVA:
-
analysis of variance
- BCA:
-
bicinchoninic acid
- BSA:
-
bovine serum albumin
- CLA:
-
conjugated linoleic acid
- DMEM:
-
Dulbecco’s modified Eagle’s medium
- FBS:
-
fetal bovine serum
- HMDS:
-
hexamethyldisilazane
- IBMX:
-
isobutylmethylxanthine
- LA:
-
linoleic acid
- LPL:
-
lipoprotein lipase
- PBS:
-
phosphate buffered saline
- PPARγ2:
-
peroxisome proliferator activated receptor γ2
- SCD-1:
-
stearoyl-CoA desaturase-1
- SEM:
-
scanning electron microscopy
- TBP:
-
TFII basal transcription factor
- TBS-T:
-
medium containing Tris HCl+NaCl+Tween 20
- TG:
-
triglyceride
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Evans, M., Park, Y., Pariza, M. et al. Trans-10,Cis-12 conjugated linoleic acid reduces triglyceride content while differentially affecting peroxisome proliferator activated receptor γ2 and aP2 expression in 3T3-L1 preadipocytes. Lipids 36, 1223–1232 (2001). https://doi.org/10.1007/s11745-001-0836-z
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DOI: https://doi.org/10.1007/s11745-001-0836-z