Inhibition of phospholipase A2 activity by conjugated linoleic acids in human macrophages

Effect of CLA supplementation on factors related to vascular dysfunction in arteries of orchidectomized rats

The vascular endothelium is a monolayer of flat epithelial cells located between the circulating blood and the underlying connective tissue. It conveys key functions that when impaired, lead to endothelial dysfunction. This condition is responsible for the pathogenesis of vascular diseases. The cardioprotective effect of sex hormones is widely known; hence, a murine orchidectomized model has been employed to study the effects caused by their deficiency. In the search for approaches to maintain vascular health, the effect of dietary fatty acids as CLA on cardiovascular diseases has been studied. Some proven beneficial properties of CLA are antioxidant, antiatherogenic and anti-inflammatory. Our objective was to evaluate the effect of a diet supplemented with 1.8 % (w/w) of CLA, administered during eight weeks, on the amount of cholesterol oxidation products (COPs) produced by orchidectomy and on factors related to vascular dysfunction in the aorta and the mesenteric arteries. The diet with CLA prevented the increase in prostanoids formation and maintained the normal physiological conditions of NO and antioxidant activity. In addition, it prevented the increase in cholesterol and COPs at the vascular wall. CLA-supplemented diet prevented the orchidectomy-induced alterations on prostanoids, NO and COPs and also improved the antioxidant activity. These findings could contribute to understand the mechanisms of actions of CLA involved in the prevention of cardiovascular diseases.

Conjugated Linoleic Acid and Brain Metabolism: A Possible Anti-Neuroinflammatory Role Mediated by PPARα Activation

Fatty acids play a crucial role in the brain as specific receptor ligands and as precursors of bioactive metabolites. Conjugated linoleic acid (CLA), a group of positional and geometric isomers of linoleic acid (LA, 18:2 n-6) present in meat and dairy products of ruminants and synthesized endogenously in non-ruminants and humans, has been shown to possess different nutritional properties associated with health benefits. Its ability to bind to peroxisome proliferator-activated receptor (PPAR) α, a nuclear receptor key regulator of fatty acid metabolism and inflammatory responses, partly mediates these beneficial effects. CLA is incorporated and metabolized into brain tissue where induces the biosynthesis of endogenous PPARα ligands palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), likely through a positive feedback mechanism where PPARα activation sustains its own cellular effects through ligand biosynthesis. In addition to PPARα, PEA and OEA may as well bind to other receptors such as TRPV1, further extending CLA own anti-neuroinflammatory actions. Future studies are needed to investigate whether dietary CLA may exert anti-inflammatory activity, particularly in the setting of neurodegenerative diseases and neuropsychiatric disorders with a neuroinflammatory basis.

A Comparison of the Anti-Inflammatory Effects of Cis-9, Trans-11 Conjugated Linoleic Acid to Celecoxib in the Collagen-Induced Arthritis Model

Cyclooxygenase (COX)-2 inhibitors, such as celecoxib, for chronic inflammatory disease are associated with adverse health events, while cis-9, trans-11 (c9t11) conjugated linoleic acid (CLA) is anti-inflammatory without adverse events attributed to pure intake. Mechanistically, celecoxib and c9t11 disrupt the arachidonic acid cascade; however, the equivalency of anti-inflammatory effects between these compounds is unknown. Therefore, to test the hypothesis that 0.5% dietary c9t11 reduces inflammation equivalently to a celecoxib dose intended to treat rheumatoid arthritis (RA; 5 mg/kg bw), arthritic mice received diets containing one of the following supplements: 1% corn oil (CO, w/w), 0.5% c9t11 (>91% purity) +0.5% CO, or 1% CO + 0.5, 5, or 50 mg/kg bw celecoxib, and were assessed for changes in arthritic severity over 6 weeks. Overall, arthritic severity in mice fed c9t11 was reduced (34%, P < 0.01) while celecoxib doses (0.5, 5, 50 mg/kg) reduced arthritic severity (16, 56, 48%, respectively) compared to CO-fed arthritic mice. Linear regression of the celecoxib dose-response showed 0.5% c9t11 (570 mg/kg bw) reduced arthritic severity equivalently to 1.5 mg/kg celecoxib. Interleukin-6 (IL-6) was increased in paws of arthritic mice fed CO compared to shams, but was decreased in arthritic groups fed 0.5% c9t11 and 5 mg/kg celecoxib, compared to arthritic mice fed CO (Ps ≤ 0.05). Additionally, paw and plasma IL-10 levels in arthritic mice were decreased by 5 mg/kg celecoxib, but were unaffected by c9t11 compared to CO. Results suggest dietary c9t11 may be an effective adjunct to COX-2 inhibition for treating chronic inflammation.

Conjugated linoleic acid regulates phosphorylation of PPARγ by modulation of ERK 1/2 and p38 signaling in human macrophages/fatty acid-laden macrophages

Stimulation of macrophages by a variety fatty acids causes activation of MAP kinases (MAPKs). The consequences arising from down-regulation of MAPKs may be a limitation in the activity of PPARγ, which is modulated by a modification catalyzed by these kinases. Phosphorylation of MAP kinases-ERK1/2 and p38 as well as PPARγ was determined by real-time polymerase chain reaction and Western blotting in human macrophages cultured with conjugated linoleic acids (CLAs). We demonstrated that CLA isomers alter MAP kinase phosphorylation and PPARγ activation. Phosphorylation of ERK1/2 was diminished in cells cultivated with cis-9,trans-11 CLA, whereas phosphorylation of p38 was reduced by trans-10,cis-12 CLA. PPARγ was phosphorylated mainly by ERK1/2, and consequently, PPARγ phosphorylation was suppressed mainly by cis-9,trans-11 isomer. In human adipocytes, cis-9,trans-11 C 18:2 raised the activation of PPAR and several of its downstream target genes. We suggest that a similar process may also occur in human macrophages.

Metabolism and actions of conjugated linoleic acids on atherosclerosis-related events in vascular endothelial cells and smooth muscle cells

Conjugated linoleic acids (CLAs) are biologically highly active lipid compounds that have attracted great scientific interest due to their ability to cause either inhibition of atherosclerotic plaque development or even regression of pre-established atherosclerotic plaques in mice, hamsters and rabbits. The underlying mechanisms of action, however, are only poorly understood. Since cell culture experiments are appropriate to gain insight into the mechanisms of action of a compound, the present review summarizes data from cell culture studies about the metabolism and the actions of CLAs on atherosclerosis-related events in endothelial cells (ECs) and smooth muscle cells (SMCs), which are important cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLAs exert several beneficial actions including inhibition of inflammatory and vasoactive mediator release from ECs and SMCs, which may help explain the anti-atherogenic effect of CLAs observed in vivo. The observation that significant levels of CLA metabolites, which have been reported to have significant biological activities, are well detectable in ECs and SMCs indicates that the anti-atherogenic effects observed with CLAs are presumably mediated not only by CLAs themselves but also by their metabolites.

Fatty acids and signalling in endothelial cells

The endothelium is critical for the maintenance of a proper vessel function. Disturbances of endothelial function, called endothelial dysfunction, have serious implications, and lead to the development of atherosclerosis. It is well established that the risk for atherosclerosis development is influenced by nutritional factors such as the intake of certain fatty acids. Due to the fundamental role of the endothelium for atherosclerosis development, it is, therefore, likely that fatty acids directly influence the function of endothelial cells. The present review aims to explain the divergent effects of different types of fatty acids on cardiovascular disease risk by summarizing in vitro-data on the effects of fatty acids on (1) important signalling pathways involved in the modulation of endothelial cell function, and (2) endothelial cell functional properties, namely vasoactive mediator release and mononuclear cell recruitment, both of which are typically dysregulated during endothelial dysfunction.

Influence of conjugated linoleic acids on functional properties of vascular cells

Conjugated linoleic acids (CLA) are biologically highly active lipid compounds that inhibit the development of atherosclerotic plaques in experimental animals. The underlying mechanisms of action, however, are only poorly understood. Since cell-culture experiments are appropriate to provide a detailed view into the mechanisms of action of a compound, the present review summarises results fromin vitrostudies dealing with the effects of CLA isomers and CLA mixtures on functional properties of cells of the vascular wall, such as endothelial cells, smooth muscle cells and monocyte-derived macrophages, which are amongst the major cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLA exert several beneficial actions in cells of the vascular wall through the activation of nuclear PPAR. These actions of CLA, which may, at least partially, explain the inhibition of atherogenesis by dietary CLA, include modulation of vasoactive mediator release from endothelial cells, inhibition of inflammatory and fibrotic processes in activated smooth muscle cells, abrogation of inflammatory responses in activated macrophages, and reduction of cholesterol accumulation in macrophage-derived foam cells.

Conjugated linoleic acid isomers reduce cholesterol accumulation in acetylated LDL-induced mouse RAW264.7 macrophage-derived foam cells

Synthetic activators of peroxisome proliferator-activated receptors (PPAR)-alpha and -gamma are capable of reducing macrophage foam cell cholesterol accumulation through the activation of genes involved in cholesterol homeostasis. Since conjugated linoleic acids (CLA) were also demonstrated to activate PPARalpha and PPARgamma in vivo and in vitro, we tested the hypothesis that CLA are also capable of reducing macrophage foam cell cholesterol accumulation. Thus, mouse RAW264.7 macrophage-derived foam cells were treated with CLA isomers, c9t11-CLA and t10c12-CLA, and linoleic acid (LA), as reference fatty acid, and analyzed for the concentrations of free and esterified cholesterol, cholesterol efflux and expression of genes involved in cholesterol homeostasis (CD36, ABCA1, LXRalpha, NPC-1, and NPC-2). Treatment with c9t11-CLA and t10c12-CLA, but not LA, lowered cholesterol accumulation, stimulated acceptor-dependent cholesterol efflux, and increased relative mRNA concentrations of CD36, ABCA1, LXRalpha, NPC-1, and NPC-2 (P < 0.05). In conclusion, the present study showed that CLA isomers reduce cholesterol accumulation in RAW264.7 macrophage-derived foam cells presumably by enhancing lipid acceptor-dependent cholesterol efflux.

Troglitazone but not conjugated linoleic acid reduces gene expression and activity of matrix-metalloproteinases-2 and -9 in PMA-differentiated THP-1 macrophages

Gene expression and activity of matrix-metalloproteinases (MMP)-2 and -9 in macrophages are reduced through peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent inhibition of NF-kappaB. Since conjugated linoleic acids (CLAs) are PPARgamma ligands and known to inhibit NF-kappaB via PPARgamma, we studied whether CLA isomers are capable of reducing gene expression and gelatinolytic activity of MMP-2 and -9 in PMA-differentiated THP-1 macrophages, which has not yet been investigated. Incubation of PMA-differentiated THP-1 cells with either c9t11-CLA, t10c12-CLA or linoleic acid (LA), as a reference fatty acid, resulted in a significant incorporation of the respective fatty acids into total cell lipids relative to control cells (P<.05). Treatment of PMA-differentiated THP-1 cells with 10 and 20 micromol/L troglitazone but not with 10 or 100 micromol/L c9t11-CLA, t10c12-CLA or LA reduced relative mRNA concentrations and activity of MMP-2 and MMP-9 compared to control cells (P<.05). DNA-binding activity of NF-kappaB and PPARgamma and mRNA expression of the NF-kappaB target gene cPLA2 were not influenced by treatment with CLA. In contrast, treatment of PMA-differentiated THP-1 cells with troglitazone significantly increased transactivation of PPARgamma and decreased DNA-binding activity of NF-kappaB and relative mRNA concentration of cPLA2 relative to control cells (P<.05). In conclusion, the present study revealed that CLA isomers, in contrast to troglitazone, did not reduce gene expression and activity of MMP-2 and -9 in PMA-differentiated THP-1 macrophages, which is probably explained by the observation that CLA isomers neither activated PPARgamma nor reduced DNA-binding activity of NF-kappaB. This suggests that CLA isomers are ineffective in MMP-associated extracellular matrix degradation which is thought to contribute to the progression and rupture of advanced atherosclerotic plaques.

Effect of conjugated linoleic acids on the activity and mRNA expression of 5- and 15-lipoxygenases in human macrophages

Lipoxygenases are a family of non-heme enzyme dioxygenases. The role of lipoxygenases is synthesis of hydroperoxides of fatty acids, which perform signaling functions in the body. Studies on conjugated linoleic acids (CLAs) as fatty acids with a potential anti-atherosclerotic function have recently been initiated. The aim of the study was to test the effect of CLAs and linoleic acid on 5- and 15-lipoxygenase (5-LO, 15-LO-1) enzyme activity, their mRNA expression, and concentration in the cells. It was also desired to determine whether the CLAs are substrates for the enzymes. For the experiments monocytic cell line (THP-1) and monocytes obtained from human venous blood were used. Monocytes were differentiated to macrophages: THP-1 (CD14+) by PMA administration (100 nM for 24 h) and monocytes from blood (CD14+) by 7-day cultivation with the autologous serum (10%). After differentiation, macrophages were cultured with 30 microM CLAs or linoleic acid for 48 h. The 15- and 5-lipoxygenase products were measured by HPLC method. mRNA expression and protein content were analyzed by real-time PCR and Western blot analysis. The in vitro studies proved that both CLA isomers are not substrates for 15-LO-1; in ex vivo studies hydroxydecadienoic acid (HODE) concentration was significantly reduced (p = 0.019). The trans-10,cis-12 CLA isomer reduced HODE concentration by 28% (p = 0.046) and the cis-9,trans-11 CLA isomer by 35% (p = 0.028). In macrophages obtained from THP-1 fatty acids did not change significantly mRNA expression of the majority of the investigated genes. CLAs did not change the content of 5-LO and 15-LO-1 proteins in macrophages obtained from peripheral blood. Linoleic acid induced 15-LO-1 expression (2.6 times, p < 0.05). CLAs may perform the function of an inhibitor of lipoxygenase 15-LO-1 activity in macrophages.