Chronic but not acute treatment with conjugated linoleic acid (CLA) isomers (trans-10, cis-12 CLA and cis-9, trans-11 CLA) affects lipid metabolism in Caco-2 cells

Molecular targets of omega 3 and conjugated linoleic Fatty acids - "micromanaging" cellular response

Essential fatty acids cannot be synthesized de novo by mammals and need to be ingested either with the diet or through the use of supplements/functional foods to ameliorate cardiovascular prognosis. This review focus on the molecular targets of omega 3 fatty acids and conjugated linoleic acid, as paradigmatic molecules that can be exploited both as nutrients and as pharmacological agents, especially as related to cardioprotection. In addition, we indicate novel molecular targets, namely microRNAs that might contribute to the observed biological activities of such essential fatty acids.

Antineoplastic effects of melatonin on a rare malignancy of mesenchymal origin: melatonin receptor-mediated inhibition of signal transduction, linoleic acid metabolism and growth in tissue-isolated human leiomyosarcoma xenografts

Melatonin provides a circadian signal that regulates linoleic acid (LA)-dependent tumor growth. In rodent and human cancer xenografts of epithelial origin in vivo, melatonin suppresses the growth-stimulatory effects of linoleic acid (LA) by blocking its uptake and metabolism to the mitogenic agent, 13-hydroxyoctadecadienoic acid (13-HODE). This study tested the hypothesis that both acute and long-term inhibitory effects of melatonin are exerted on LA transport and metabolism, and growth activity in tissue-isolated human leiomyosarcoma (LMS), a rare, mesenchymally-derived smooth muscle tissue sarcoma, via melatonin receptor-mediated inhibition of signal transduction activity. Melatonin added to the drinking water of female nude rats bearing tissue-isolated LMS xenografts and fed a 5% corn oil (CO) diet caused the rapid regression of these tumors (0.17 +/- 0.02 g/day) versus control xenografts that continued to grow at 0.22 +/- 0.03 g/day over a 10-day period. LMS perfused in situ for 150 min with arterial donor blood augmented with physiological nocturnal levels of melatonin showed a dose-dependent suppression of tumor cAMP production, LA uptake, 13-HODE release, extracellular signal-regulated kinase (ERK 1/2), mitogen activated protein kinase (MEK), Akt activation, and [(3)H]thymidine incorporation into DNA and DNA content. The inhibitory effects of melatonin were reversible and preventable with either melatonin receptor antagonist S20928, pertussis toxin, forskolin, or 8-Br-cAMP. These results demonstrate that, as observed in epithelially-derived cancers, a nocturnal physiological melatonin concentration acutely suppress the proliferative activity of mesenchymal human LMS xenografts while long-term treatment of established tumors with a pharmacological dose of melatonin induced tumor regression via a melatonin receptor-mediated signal transduction mechanism involving the inhibition of tumor LA uptake and metabolism.

The effect of trans-10, cis-12 conjugated linoleic acid on gene expression profiles related to lipid metabolism in human intestinal-like Caco-2 cells

We conducted an in-depth investigation of the effects of conjugated linoleic acid (CLA) on the expression of key metabolic genes and genes of known importance in intestinal lipid metabolism using the Caco-2 cell model. Cells were treated with 80 mumol/L of linoleic acid (control), trans-10, cis-12 CLA or cis-9, trans-11 CLA. RNA was isolated from the cells, labelled and hybridized to the Affymetrix U133 2.0 Plus arrays (n = 3). Data and functional analysis were preformed using Bioconductor. Gene ontology analysis (GO) revealed a significant enrichment (P < 0.0001) for the GO term lipid metabolism with genes up-regulated by trans-10, cis-12 CLA. Trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, altered the expression of a number of genes involved in lipid transport, fatty acid metabolism, lipolysis, beta-oxidation, steroid metabolism, cholesterol biosynthesis, membrane lipid metabolism, gluconeogenesis and the citrate cycle. These observations warrant further investigation to understand their potential role in the metabolic syndrome.

Conjugated linoleic acid alters global gene expression in human intestinal-like Caco-2 cells in an isomer-specific manner

Conjugated linoleic acid (CLA) exhibits isomer-specific effects on transepithelial calcium (Ca) transport as well as on cell growth in human intestinal-like Caco-2 cells. However, the molecular mechanisms of action are still unclear. Therefore, this study used a transcriptomic approach to help elucidate the molecular mechanisms underlying such isomer-specific effects. Caco-2 cells were treated with 80 micromol/L linoleic acid (control), 80 micromol/L trans-10, cis-12 CLA, or 80 micromol/L cis-9, trans-11 CLA for 12 d. Ca transport was measured radio-isotopically. RNA was isolated from the cells, labeled, and hybridized to the Affymetrix U133 2.0 Plus arrays (n = 3). Data and functional analysis was preformed using Bioconductor. Using a minimum fold-change criterion of 1.6 and a false discovery rate criterion of P-value <or= 0.05, trans-10, cis-12 CLA altered the expression of 918 genes, whereas, cis-9, trans-11 CLA had no effect on gene expression. Gene ontology analysis revealed that trans-10, cis-12 CLA strongly modulated a number of processes inherently related to carcinogenesis, such as cell cycle, cell proliferation, and DNA metabolism. Trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, increased transepithelial Ca transport in Caco-2 cells, which corresponded to changes in molecular mediators of paracellular (including claudin 2 and 4) and transcellular (calbindin D(9)k and vitamin D receptor) Ca transport. This microarray-based study highlighted a number of gene expression patterns of relevance to 2 important intestinal processes (carcinogenesis and Ca transport), which were modulated by trans-10, cis-12 CLA. These may help our mechanistic understanding of the role of CLA in promoting gut function and health.

Eicosapentaenoic acid and 3,10 dithia stearic acid inhibit the desaturation oftrans-vaccenic acid intocis-9,trans-11-conjugated linoleic acid through different pathways in Caco-2 and T84 cells

Stearoyl-CoA desaturase (SCD) is a key enzyme that determines the composition and metabolic fate of ingested fatty acids, in particular the conversion oftrans-vaccenic acid (TVA) to conjugated linoleic acid (CLA). The present study addressed the hypothesis that intestinal TVA absorption and biotransformation into CLA can be modulated by EPA and 3,10-dithia stearic acid (DSA) via altered SCD mRNA levels and desaturation indices (cis-9,trans-11-CLA:TVA and oleic acid:stearic acid ratios) in Caco-2 and T84 cells, two well-establishedin vitromodels of the human intestinal epithelium. The study determined the effect of acute (3h with 0·3mm-EPA or 0·3mm-DSA) and acute-on-chronic (1 week with 0·03mm-EPA or -DSA, followed by respectively, 0·3mm-EPA or -DSA for 3h) treatments. In both cell lines, acute EPA treatment did not alter SCD desaturation indices, whereas the acute-on-chronic treatment affected these surrogate markers of SCD activity. This was associated with reduced sterol regulatory-element binding protein-1c and SCD mRNA levels. In contrast, acute and acute-on-chronic DSA treatments significantly reduced SCD desaturation indices without affecting SCD mRNA levels in Caco-2 cells. The present study on intestinal cells shows that the conversion rate of TVA to c9, t11-CLA is affected by other fatty acids present in the diet such as EPA, confirming previous observations in hepatic and mammary cell models.

The effects of conjugated linoleic acid supplementation on immune function in healthy volunteers

OBJECTIVE

To assess the effects of dietary supplementation using two isomeric blends of conjugated linoleic acid (CLA) on immune function in healthy human volunteers.

DESIGN

Double-blind, randomised, placebo-controlled intervention trial.

SUBJECTS AND INTERVENTION

A total of 55 healthy volunteers (n=20 males, n=35 females) were randomised into one of three study groups who received 3 g/day of a fatty acid blend containing a 50:50 cis-9, trans-11: trans-10, cis-12 CLA isomer blend (2 g CLA), and 80:20 cis-9, trans-11: trans-10, cis-12 (80:20) CLA isomer blend (1.76 g CLA) or linoleic acid (control, 2 g linoleic acid) for 8 weeks.

RESULTS

Supplementation with the 80:20 CLA isomer blend significantly (P< or =0.05) enhanced PHA-induced lymphocyte proliferation. CLA decreased basal interleukin (IL)-2 secretion (P< or =0.01) and increased PHA-induced IL-2 and tumor necrosis factor alpha (TNF(alpha)) production (P< or =0.01). However, these effects were not solely attributable to CLA as similar results were observed with linoleic acid. CLA supplementation had no significant effect on peripheral blood mononuclear cells IL-4 production, or on serum-soluble intercellular adhesion molecule-1 (sICAM-1) or plasma prostaglandin E2 (PGE2) or leukotreine B4 (LTB4) concentrations.

CONCLUSIONS

This study shows that CLA supplementation had a minimal effect on the markers of human immune function. Furthermore, supplementation with CLA had no immunological benefit compared with linoleic acid.

Conjugated linoleic acid and atherosclerosis: no effect on molecular markers of cholesterol homeostasis in THP-1 macrophages

Macrophage cholesterol homeostasis is a key process involved in the initiation and progression of atherosclerosis. Peroxisome proliferator-activated receptors (PPARs) regulate the transcription of the genes involved in cholesterol homeostasis and thus represent an important therapeutic target in terms of reducing atherosclerosis. Conjugated linoleic acid (CLA) is a potent anti-atherogenic dietary fatty acid in animal models of atherosclerosis and is capable of activating PPARs in vitro and in vivo. Therefore, this study examined whether the anti-atherogenic effects of CLA in vivo could be ascribed to altered cholesterol homeostasis in macrophages and macrophage derived foam cells. Of several genes that regulate cholesterol homeostasis investigated, CLA had most effect on the class B scavenger receptor CD36. The cis-9,trans-11 CLA (c9,t11-CLA) and trans-10,cis-12 CLA (t10,c12-CLA) isomers augmented CD36 mRNA expression (P<0.001). Confocal laser microscopy characterised the three-dimensional expression patterns of CD36 in THP-1 macrophages. Linoleic acid, CLA and the PPARgamma ligand rosiglitazone increased discrete cell surface CD36 localisation, with a heterogeneous punctate pattern of expression. In agreement with the observed increases in CD36 mRNA and cell surface expression, intracellular cholesterol concentrations were greater in macrophages exposed to linoleic acid and CLA. Further analysis of cholesterol metabolism showed that CLA had no effect on THP-1 derived foam cell cholesterol efflux to apo AI. Thus, altered cholesterol homeostasis in the macrophage may not explain the anti-atherogenic effects of CLA observed in vivo.

Differential inhibition of fatty acid transport in tissue-isolated steroid receptor negative human breast cancer xenografts perfused in situ with isomers of conjugated linoleic acid

In established rodent tumors and human cancer cell lines, conjugated dienoic isomers of linoleic acid (CLA) suppress the growth-stimulating effects of linoleic acid (LA) and its metabolism to the mitogenic agent, 13-hydroxyoctadecadienoic acid (13-HODE). Here, we compared the effects of three CLA isomers on LA uptake and metabolism, and growth in human breast xenografts perfused in situ in female nude rats. The results demonstrated that two CLA isomers [10t, 12c-CLA>9t, 11t-CLA] caused a dose-dependent inhibition of LA uptake, cAMP content, 13-HODE formation, Erk 1/2 activity, and [(3)H]thymidine incorporation into tumor DNA; 9c, 11t-CLA showed no effect. The inhibitory effect is reversible with either pertussis toxin (PTX) or 8-Br-cAMP suggesting that CLA isomers differentially inhibit LA uptake and metabolism and cell proliferation in human breast cancer in vivo via a receptor-mediated, PTX-sensitive pathway.

Conjugated linoleic acids, atherosclerosis, and hepatic very-low-density lipoprotein metabolism

Conjugated linoleic acids (CLAs) are isomeric forms of the 18:2 fatty acid that contain conjugated sites of unsaturation. Although CLAs are minor components of the diet, they have many reported biological activities. For nearly a decade, the potential for CLA to modify the atherosclerotic process has been examined in animal models, and studies of supplementation of the human diet with CLA were started with the anticipation that such an intervention could also reduce the risk of cardiovascular disease. Central to the hypothesis is the expectation that dietary modification could alter plasma lipid and lipoprotein metabolism toward a more cardioprotective profile. This review examines the evidence in support of the hypothesis and the mechanistic studies that lend support for a role of CLA in hepatic lipid and lipoprotein metabolism. Although there are still limited studies in strong support of a role for CLA in the reduction of early atherosclerotic lesions, there has been considerable progress in defining the mechanisms of CLA action. CLA could primarily modulate the metabolism of fatty acids in the liver. The tools are now available to examine isomer-specific effects of CLA on hepatic lipid and lipoprotein metabolism and the potential of CLA to modify hepatic gene expression patterns. Additional animal and cell culture studies will increase our understanding of these unusual fatty acids and their potential for health benefits in humans.

cis-9,trans-11 and trans-10,cis-12 CLA affect lipid metabolism differently in primary white and brown adipocytes of djungarian hamsters

We explored whether CLA isomers and other C18 FA affect (i) lipid content and FA concentrations in total adipocyte lipids, (ii) FA synthesis from glucose in TAG and phospholipids of primary brown (BAT) and white adipocytes (WAT), and (iii) mRNA expression of uncoupling protein 1 (UCP1) in primary brown adipocytes of Djungarian hamsters (Phodopus sungorus). c9,t11-CLA, oleic, linoleic, and alpha-linolenic acid increased whereas t10,c12-CLA decreased lipid accumulation in both adipocyte types. t10,c12-CLA treatment affected FA composition mainly in BAT cells. CLA incorporation into lipids, in particular c9,t11-CLA, was higher in BAT. In both cell types, t10,c12-CLA treatment reduced the incorporation of glucose 13C carbon into FA of TAG and phospholipids, whereas c9,t11-CLA, linoleic, and alpha-linolenic acid either did not influence or dose-dependently increased glucose carbon incorporation into FA. UCP1 mRNA expression was inhibited by t10,c12-CLA but increased by c9,t11-CLA, linoleic, and alpha-linolenic acid. It is concluded that c9,t11-CLA and t10,c12-CLA have distinctly different effects on lipid metabolism in primary adipocytes. The effects of c9,t11-CLA are similar to those of other unsaturated C18 FA. The opposite effects of c9,t11-CLA and t10,c12-CLA are evident in both WAT and BAT cultures; however, brown adipocytes seem to be more susceptible to CLA treatment.