Dietary supplementation with conjugated linoleic acid plus n-3 polyunsaturated fatty acid increases food intake and brown adipose tissue in rats

Abstract

The effect of supplementation with 1% conjugated linoleic acid and 1% n-3 long chain polyunsaturated fatty acids (CLA/n-3) was assessed in rats. Food intake increased with no difference in body weights. White adipose tissue weights were reduced whereas brown adipose tissue and uncoupling protein-1 expression were increased. Plasma adiponectin, triglyceride and cholesterol levels were reduced while leptin, ghrelin and liver weight and lipid content were unchanged. Hypothalamic gene expression measurements revealed increased expression of orexigenic and decreased expression of anorexigenic signals. Thus, CLA/n-3 increases food intake without affecting body weight potentially through increasing BAT size and up-regulating UCP-1 in rats.

Keywords: brain; brown adipose tissue; conjugated linoleic acid; hypothalamus; n-3 long chain polyunsaturated fatty acid; white adipose tissue.

Figure 1

A. Mean food intake of rats receiving rat chow supplemented with either 2% vegetable oil (control) or 2% CLA plus n-3 LC-PUFA. Mean daily intake per rat was calculated for each week to highlight when significant differences in food intake became apparent *P < 0.05 at three weeks. Daily food intake per rat was also calculated over the 12 weeks of the experiment **P < 0.01 B. No significant difference (NS) was found in the body weights of the control supplementation vs. the CLA plus n-3 LC-PUFA at any of the measurement points during the study or in the final body weights.

Figure 2

Effect of CLA plus n-3 LC-PUFA supplementation on tissue weights. A. Retroperitoneal and subcutaneous adipose tissue weights were significantly reduced in the CLA plus n-3 LC- PUFA supplemented rats, *P < 0.05, **P < 0.01. There were no significant (NS) changes in the weights of other adipose tissue depots B. Subscapular BAT weight was increased, ***P < 0.001. C. Weights of gastrocnemius and soleus muscles and D. Liver weight was not significantly (NS) changed by CLA plus n-3 LC-PUFA supplementation.

Figure 3

Effect of CLA plus n-3 LC-PUFA supplementation on circulating lipid and hormone levels. A. CLA plus n-3 LC-PUFA supplementation significantly reduced circulating levels of cholesterol and triglyceride, ***P < 0.001 but had no significant (NS) effect on non esterified fatty acid (NEFA) levels or non-fasted glucose levels. B. Adiponectin levels were significantly reduced, P < 0.001 by CLA plus n-3 LC-PUFA supplementation. There were no significant (NS) changes in plasma ghrelin or plasma leptin levels.

Figure 4

Effect of CLA plus n-3 LC-PUFA supplementation on liver lipid content and circulating levels of liver enzymes. Liver lipid levels and lactate dehydrogenase (LDH) were not significantly (NS) changed by supplementation but aspartate aminotransferase activity (AST) was significantly higher in the CLA plus n-3 LC-PUFA supplemented animals, *P < 0.05.

Figure 5

Effect of CLA plus n-3 LC-PUFA supplementation on WAT, BAT and muscle gene expression. A. There was a significant increase in the expression of SREBP-1c and PPARγ in the BAT of rats receiving the CLA plus n-3 LC-PUFA supplementation, *P < 0.05 and no significant (NS) change in either subcutaneous (Subcut) or the retroperitoneal (Retro) WAT. B. Hormone sensitive lipase (HSL) and lipoprotein lipase (LPL) were significantly decreased in subcutaneous WAT, *P < 0.05 and were not significantly (NS) changed in retroperitoneal WAT compared with control. Adiponectin gene expression was increased by CLA plus n-3 LC-PUFA supplementation in retroperitoneal WAT, * P < 0.05 and not significantly (NS) changed in subcutaneous WAT (P = 0.09). C. UCP-1 expression in BAT was increased by CLA plus n-3 LC-PUFA supplementation, *P < 0.05. D. There was a significant decrease in the expression of both Glut4 and SREBP-1c in the gastrocnemius muscle of rats receiving the CLA plus n-3 LC-PUFA supplementation compared with control animals, **P < 0.01 and *P < 0.05 respectively.

Figure 6

Effect of CLA plus n-3 LC-PUFA supplementation on hypothalamic peptide gene expression including representative autoradiographs of the hypothalamic regions measured. A. There was no significant (NS) change in NPY or B. CART gene expression in either the arcuate nuclei (ARC), ventromedial nuclei (VMH) or paraventricular nuclei (PVN) after supplementation. C. AgRP gene expression was increased in the arcuate nuclei (ARC), ***P < 0.001 after CLA plus n-3 LC-PUFA supplementation while POMC gene expression was reduced, **P < 0.005.

Figure 7

Effect of CLA plus n-3 LC-PUFA supplementation on hypothalamic receptor gene expression and [¹²⁵I]leptin binding. A. GHS-R was increased in the arcuate nuclei (ARC), *P < 0.05 but not significantly (NS) changed in the ventromedial nuclei (VMH). B. Ob-Rb was not significantly (NS) changed in the ARC but significantly decreased in the VMH, *P < 0.05. C. There was no significant change (NS) in Ob-R expression in the choroid plexus (CP). The level of specific [¹²⁵I]leptin binding to the CP was increased significantly after CLA plus n-3 LC-PUFA supplementation in both the CP of the lateral ventricles (not shown) and the dorsal third ventricle, *P < 0.05.