Isomer-specific effects of conjugated linoleic acid on gene expression in RAW 264.7

Conjugated linoleic acid (CLA) is a mixture of dietary fatty acids that has various beneficial effects including decreasing cancer, atherosclerosis, diabetes and inflammation in animal models. Some controversy exists on the specific isomers of CLA that are responsible for the benefits observed. This study was conducted to examine how different CLA isomers regulate gene expression in RAW 264.7. A mouse macrophage cell line, RAW 264.7, was treated with five different CLA isomers (9E,11E-, 9Z,11E-, 9Z,11Z-, 10E,12Z- and 11Z,13E-CLA). Gene expression microarrays were performed, and several significantly regulated genes of interest were verified by a real-time polymerase chain reaction (PCR). Examination of the biological functions of various significantly regulated genes by the five CLA isomers showed distinct properties. Isomers 9E,11E-, 9Z,11Z-, 10E,12Z- and 11Z,13E-CLA decreased production of proinflammatory cytokines such as interleukin (IL)-1α, IL-1β and IL-6. Many of CLA's effects are believed to be mediated by the fatty acid receptors such as the peroxisome proliferator-activated receptors (PPAR) and retinoid-X-receptors (RXR). Using PPAR and RXR specific antagonists and coactivator recruitment assays, it was evident that multiple mechanisms were responsible for gene regulation by CLA isomers. Coactivator recruitment by CLA isomers showed their distinct properties as selective receptor modulators for PPARγ and RXRα. These studies demonstrate distinct isomer differences in gene expression by CLA and will have important ramifications for determining the potential therapeutic benefit of these dietary fatty acids in prevention of inflammation-related diseases.     

Conjugated linoleic acids mediate insulin release through islet G protein-coupled receptor FFA1/GPR40

Among dietary components, conjugated linoleic acids (CLAs) have attracted considerable attention as weight loss supplements in the Western world because they reduce fat stores and increase muscle mass. However, a number of adverse effects are also ascribed to the intake of CLAs such as aggravation of insulin resistance and the risk of developing diabetes. However, the mechanisms accounting for the effects of CLAs on glucose homeostasis are incompletely understood. Herein we provide evidence that CLAs specifically activate the cell surface receptor FFA1, an emerging therapeutic target to treat type 2 diabetes. Using different recombinant cellular systems engineered to stably express FFA1 and a set of diverse functional assays including the novel, label-free non-invasive dynamic mass redistribution technology (Corning® Epic® biosensor), both CLA isomers cis-9, trans-11-CLA and trans-10, cis-12-CLA were found to activate FFA1 in vitro at concentrations sufficient to also account for FFA1 activation in vivo. Each CLA isomer markedly increased glucose-stimulated insulin secretion in insulin-producing INS-1E cells that endogenously express FFA1 and in primary pancreatic β-cells of wild type but not FFA1^−/− knock-out mice. Our findings establish a clear mechanistic link between CLAs and insulin production and identify the cell surface receptor FFA1 as a molecular target for CLAs, explaining their acute stimulatory effects on insulin secretion in vivo. CLAs are also revealed as insulinotropic components in widely used nutraceuticals, a finding with significant implication for development of FFA1 modulators to treat type 2 diabetes.     

CLA isomers inhibit TNFα-induced eicosanoid release from human vascular smooth muscle cells via a PPARγ ligand-like action

Conjugated linoleic acids (CLAs) were reported to have anti-atherogenic properties in animal feeding experiments. In an attempt to elucidate the molecular mechanisms of these anti-atherogenic effects, the modulatory potential of CLA on cytokine-induced eicosanoid production from smooth muscle cells (SMCs), which contributes to the chronic inflammatory response associated with atherosclerosis, has been investigated in the present study. cis-9, trans-11 CLA and trans-10, cis-12 CLA were shown to reduce proportions of the eicosanoid precursor arachidonic acid in SMC total lipids and to inhibit cytokine-induced NF-κB DNA-binding activity, mRNA levels of inducible enzymes involved in eicosanoid formation (cPLA₂, COX-2, mPGES), and the production of the prostaglandins PGE₂ and PGI₂ by TNFα-stimulated SMCs in a dose-dependent manner. The effect of 50 μmol/L of either CLA isomer was as effective as 10 μmol/L of the PPARγ agonist troglitazone in terms of inhibiting the TNFα-stimulated eicosanoid production by SMCs. PPARγ DNA-binding activity was increased by both CLA isomers compared to control cells. Moreover, it was shown that the PPARγ antagonist T0070907 partially abrogated the inhibitory action of CLA isomers on cytokine-induced eicosanoid production and NF-κB DNA-binding activity by vascular SMCs suggesting that PPARγ signalling is at least partially involved in the action of CLA in human vascular SMCs. With respect to the effects of CLA on experimental atherosclerosis, our findings suggest that the anti-inflammatory effect of CLA is at least partially responsible for the anti-atherogenic effects of CLA observed in vivo.     

Antioxidant activity of conjugated linoleic acid isomers, linoleic acid and its methyl ester determined by photoemission and DPPH techniques

The chemiluminescent response of conjugated linoleic acid isomers (CLAs), linoleic acid (LA) and methyl linoleate (LAME) against the prooxidant t-butyl hydroperoxide (tBHP) was analyzed. The c9, t11-CLA and t10, c12-CLA isomers showed significant photoemission at the highest concentration used, while photoemission was not detected at any concentration of LA and LAME analyzed. These results show that CLAs are more susceptible to peroxidation than LA and LAME. Likewise, the effect of CLA, LA and LAME on lipid peroxidation of triglycerides rich in C20:5 omega3 and C22:6 omega3 (Tg omega3-PUFAs) was investigated. For that, chemiluminescence produced by triglycerides in the presence of tBHP, previously incubated with different concentrations of CLAs, LA and LAME (from 1 to 200 mM) was registered for 60 min. Triglycerides in the presence of t-BHP produced a peak of light emission (3151+/-134 RLUs) 5 min after addition. CLAs produced significant inhibition on photoemission, t10, c12-CLA being more effective than the c9, t11-CLA isomer. LA and LAME did not have an effect on lipid peroxidation of Tg omega3-PUFAs. CLA isomers, LA and LAME were also investigated for free radical scavenging properties against the stable radical (DPPH()). Both CLA isomers reacted and quenched DPPH() at all tested levels (from 5 to 25 mM), while LA and LAME did not show radical quenching activity even at the highest concentration tested. These data indicate that CLAs would provide protection against free radicals, but LA and LAME cannot.     

cis-9,trans-11 conjugated linoleic acid stimulates expression of angiopoietin like-4 in the placental extravillous trophoblast cells

A number of studies have been carried out to examine the biological function of conjugated linoleic acid (CLA) and its potential health benefits. However, not much is known about how CLA isomers mediate their effect on angiogenesis and vascularization during early placentation. In this paper we demonstrate that cis-9,trans-11(c9,t11)-CLA stimulated the expression of angiopoietin like-4 (ANGPTL4) mRNA and protein accompanied by tube formation in first trimester placental trophoblast cells, HTR8/SVneo whereas the other CLA isomer, trans-10,cis-12 (t10,c12)-CLA had no such effects. c9,t11-CLA however did not stimulate expression of the most potent angiogenic factor, vascular endothelial growth factor (VEGF) in these cells. Silencing ANGPTL4 in these cells significantly reduced the stimulatory effect of c9,t11-CLA on tube formation, indicating the involvement of ANGPTL4. In addition, c9,t11-CLA increased the mRNA expression of several pro-angiogenic factors such as fatty acid binding protein-4 (FABP4), cyclooxygenase-2 (COX-2) and adipose differentiation-related protein (ADRP) in HTR8/SVneo cells. c9,t11-CLA also induced the uptake of docosahexaenoic acid, 22:6n − 3 (DHA), a stimulator of tube formation in these cells. Triacsin C, an acylCoA synthetase inhibitor, attenuated c9,t11-CLA induced DHA uptake, tube formation and cellular proliferation in HTR8/SVneo cells.     

Activation of phosphatidylinositol-3 kinase,AMP-activated kinase and Akt substrate-160 kDa by trans-10, cis-12 conjugated linoleic acid mediates skeletal muscle glucose uptake

Conjugated linoleic acid (CLA), a dietary lipid, has been proposed as an antidiabetic agent. However, studies specifically addressing the molecular dynamics of CLA on skeletal muscle glucose transport and differences between the key isomers are limited. We demonstrate that acute exposure of L6 myotubes to cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12) CLA isomers mimics insulin action by stimulating glucose uptake and glucose transporter-4 (GLUT4) trafficking. Both c9,t10-CLA and t10,c12-CLA stimulate the phosphorylation of phosphatidylinositol 3-kinase (PI3-kinase) p85 subunit and Akt substrate-160 kDa (AS160), while showing isomer-specific effects on AMP-activated protein kinase (AMPK). CLA isomers showed synergistic effects with the AMPK activator, 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR). Blocking PI3-kinase and AMPK prevented the stimulatory effects of t10,c12-CLA on AS160 phosphorylation and glucose uptake, indicating that this isomer acts via a PI3-kinase and AMPK-dependent mechanism, whereas the mechanism of c9,t11-CLA remains unclear. Intriguingly, CLA isomers sensitized insulin-Akt-responsive glucose uptake and prevented high insulin-induced Akt desensitisation. Together, these results establish that CLA exhibits isomer-specific effects on GLUT4 trafficking and the increase in glucose uptake induced by CLA treatment of L6 myotubes occurs via pathways that are distinctive from those utilised by insulin.     

Conjugated linoleic acid exhibits stimulatory and inhibitory effects on prostanoid production in human endothelial cells and platelets

In addition to their reported antitumorigenic properties, various conjugated linoleic acid (CLA) isomers have also been shown to decrease prostanoid synthesis as a result of inhibiting the cyclooxygenase (COX) enzyme. We have previously reported that several CLA isomers inhibited both platelet aggregation and formation of thromboxane A(2) (TXA(2)), a proaggregatory and vasoconstrictive agent. Since the interaction between platelets and vascular endothelial cells is essential to maintaining vascular homeostasis, we decided to investigate the effects of various CLA isomers on the production of endothelial prostacyclin (PGI(2)), a potent vasodilator and inhibitor of platelet function. Using interleukin 1-beta (IL1-beta)-stimulated human umbilical vein endothelial cells (HUVECs), we initially established that HUVECs of passage #2 should be used since these cells were most responsive to thrombin-induced conversion of endogenous arachidonic acid to PGI(2), as monitored by the formation of its stable, inactive metabolite, 6-ketoPGF(1alpha). In the first part of the study, the effects of CLA isomers in the free fatty acid form were tested. The 10(E), 12(Z)- and 9(Z), 11(E)-CLA isomers inhibited thrombin-induced 6-ketoPGF(1alpha) formation with I(50)'s of 2.6 and 5.5 microM, whereas the 9(Z), 11(Z)- and 9(E), 11(E)-CLA were ineffective at concentrations up to 60 microM. The inhibitory effect of the 10(E), 12(Z)-CLA was irreversible. Next, the effects of CLA incorporation into HUVECs on PGI(2) generation was determined. An average 8-fold stimulation of 6-ketoPGF(1alpha) formation was obtained with quiescent IL1-beta-exposed HUVECs pretreated for 18 h with 25 microM 9(Z), 11(Z)-CLA, whereas cells preincubated with the 10(E), 12(Z) isomer enhanced this eicosanoid 3-fold. Such IL1-beta-treated HUVECs prelabeled with 25 microM 9(Z), 11(Z)-CLA became refractory to thrombin stimulation, as measured by 6-ketoPGF(1alpha) production, whereas a small, statistically insignificant, inhibition was observed upon thrombin treatment of HUVECs prelabeled with the 10(E), 12(Z) isomer. Qualitative similar results were obtained with resting or thrombin-stimulated platelets containing these esterified CLA isomers indicating that these effects occur with cells that contain either the COX-1 or COX-2 isozymes. The results of this in vitro study indicate that the effects of CLA on cellular prostanoid formation in endothelial cells and platelets can be either inhibitory or stimulatory, and this seems to depend not only on the specific CLA isomer and whether or not the CLA is in the free fatty acid form or esterified into cellular lipids, but also whether cells are in the resting or stimulated state. These findings suggest that in vivo, CLA might have multiple, complex effects on vascular homeostasis.     

t10c12-CLA maintains higher bone mineral density during aging by modulating osteoclastogenesis and bone marrow adiposity

Conjugated linoleic acid (CLA) has been shown to positively influence calcium and bone metabolism. Earlier, we showed that CLA (equal mixture of c9t11-CLA and t10c12-CLA) could protect age-associated bone loss by modulating inflammatory markers and osteoclastogenesis. Since, c9t11-CLA and t10c12-CLA isomers differentially regulate functional parameters and gene expression in different cell types, we examined the efficacy of individual CLA isomers against age-associated bone loss using 12 months old C57BL/6 female mice fed for 6 months with 10% corn oil (CO), 9.5% CO + 0.5% c9t11-CLA, 9.5% CO + 0.5% t10c12-CLA or 9.5% CO + 0.25% c9t11-CLA + 0.25% t10c12-CLA. Mice fed a t10c12-CLA diet maintained a significantly higher bone mineral density (BMD) in femoral, tibial and lumbar regions than those fed CO and c9t11-CLA diets as measured by dual-energy-X-ray absorptiometry (DXA). The increased BMD was accompanied by a decreased production of osteoclastogenic factors, that is, RANKL, TRAP5b, TNF-alpha and IL-6 in serum. Moreover, a significant reduction of high fat diet-induced bone marrow adiposity was observed in t10c12-CLA fed mice as compared to that of CO and c9t11-CLA fed mice, as measured by Oil-Red-O staining of bone marrow sections. In addition, a significant reduction of osteoclast differentiation and bone resorbing pit formation was observed in t10c12-CLA treated RAW 264.7 cell culture stimulated with RANKL as compared to that of c9t11-CLA and linoleic acid treated cultures. In conclusion, these findings suggest that t10c12-CLA is the most potent CLA isomer and it exerts its anti-osteoporotic effect by modulating osteoclastogenesis and bone marrow adiposity.     

Differential effects of conjugated linoleic acid isomers in insulin-resistant female C57Bl/6J mice

Obesity is associated with a high risk of developing diabetes and cardiovascular disease. Therefore, management of body weight to prevent obesity remains as an important priority. The present investigation addresses the effects of conjugated linoleic acid (CLA) isomers on body weight and composition of body fat in female C57Bl/6J mice. To investigate the differential effects of individual CLA isomers and their mixture on changes in lean mass, fat mass, glucose and insulin, 6-month-old female C57BL/6J mice were fed with 10% corn oil (CO) as a dietary fat source and either supplemented with purified cis 9,trans 11 (c9t11) CLA (0.5%) or trans 10,cis 12 (t10c12) CLA (0.5%) and/or their mixture (50:50) for 6 months. As a result of 6 months' dietary intervention, both the t10c12-CLA and CLA mix showed increased lean mass and reduced fat mass compared to the CO and c9t11-CLA groups. Insulin resistance was, however, increased in t10c12-CLA and CLA mix-fed groups based on the results of homeostasis model assessment (HOMA), the revised quantitative insulin-sensitivity check index (R-QUICKI) and also with intravenous glucose tolerance test (IVGTT). In conclusion, long-term feeding of the major CLA isomers in 12-month-old C57Bl/6J mice revealed a contrasting effect on fat mass, glucose and insulin metabolism. The t10c12 isomer is found to reduce the fat mass and increase the lean mass but significantly contributed to increase insulin resistance and liver steatosis, whereas c9t11 isomer prevented the insulin resistance.     

Slow Absorption of Conjugated Linoleic Acid in Rat Intestines,and Similar Absorption Rates of 9c,11t-Conjugated Linoleic Acid and 10t,12c-Conjugated Linoleic Acid

We have previously shown that the 9c,11t-conjugated linoleic acid (CLA) concentration was always significantly higher than the 10t,12c-CLA concentration following the administration of these compounds to mice and rats, and considered that structural differences between the conjugated double bonds in these isomers affected absorption in the small intestine. This study investigates the absorption of CLA in the rat intestine by a lipid absorption assay of lymph from the thoracic duct. In Study 1, we used safflower oil and a triacylglycerol form of CLA (CLA-TG), while in Study 2, we used 9c,11t-CLA and 10t,12c-CLA. The cumulative recovery of CLA was lower than that of linoleic acid until two hours after sample administration. There was no difference in the extent of lymphatic recovery of 9c,11t-CLA and 10t,12c-CLA after the administration of CLA-TG, 9c,11t-CLA, and 10t,12c-CLA to the rats, suggesting that geometrical and positional isomerism of the conjugated double bonds did not influence the absorption.     

Potent inhibitory effect of trans9, trans11 isomer of conjugated linoleic acid on the growth of human colon cancer cells

This study compared the growth inhibitory effects of pure conjugated linoleic acid (CLA) isomers [cis(c)9,c11-CLA, c9,trans(t)11-CLA, t9,t11-CLA, and t10,c12-CLA] on human colon cancer cell lines (Caco-2, HT-29 and DLD-1). When Caco-2 cells were incubated up to 72 h with 200 μM, each isomer, even in the presence of 10% fetal bovine serum (FBS), cell proliferation was inhibited by all CLA isomers in a time-dependent manner. The strongest inhibitory effect was shown by t9,t11-CLA, followed by t10,c12-CLA, c9,c11-CLA and c9,t11-CLA, respectively. The strongest effect of t9,t11-CLA was also observed in other colon cancer cell lines (HT-29 and DLD-1). The order of the inhibitory effect of CLA isomer was confirmed in the presence of 1% FBS. CLA isomers supplemented in the culture medium were readily incorporated into the cellular lipids of Caco-2 and changed their fatty acid composition. The CLA contents in cellular lipids were 26.2±2.7% for t9,t11-CLA, 35.9±0.3% for c9,t11-CLA and 46.3±0.8% for t10,c12-CLA, respectively. DNA fragmentation was clearly recognized in Caco-2 cells treated with t9,t11-CLA. This apoptotic effect of t9,t11-CLA was dose- and time-dependent. DNA fragmentation was also induced by 9c,11t-CLA and t10,c12-CLA. However, fragmentation levels with both isomers were much lower than that with t9,t11-CLA. t9t11-CLA treatment of Caco-2 cells decreased Bcl-2 levels in association with apoptosis, whereas Bax levels remained unchanged. These results suggest that decreased expression of Bcl-2 by t9t11-CLA might increase the sensitivity of cells to lipid peroxidation and to programmed cell death, apoptosis.     

Conjugated linoleic acids promote human fat cell apoptosis.

Conjugated linoleic acids (CLAs) are conjugated dienoic isomers of linoleic acid. Some isomers have been shown to reduce fat mass in animal and cell culture models. However, controversial results were obtained in studies of supplementation of CLAs in human subjects. In order to get more insights into the direct effects of CLAs on human fat cells, we have studied the influence of cis-9, trans-11 CLA and trans-10, cis-12 CLA on the biology of human SGBS preadipocytes and adipocytes. Both CLA isomers equally inhibited the proliferation of preadipocytes in a dose-dependent manner. Continuous treatment with 1-10 microM trans-10, cis-12 CLA, and to a weaker extent cis-9, trans-11 CLA, inhibited accumulation of lipids during adipogenic differentiation. Treatment with higher doses of CLA induced apoptosis in preadipocytes, in differentiating cells, and adipocytes. The trans-10, cis-12 isomer had a higher apoptotic potency in adipocytes than cis-9, trans-11 CLA. Taken together, the treatment of human preadipocytes and adipocytes with physiological relevant concentrations of CLAs resulted in an impairment of proliferation and differentiation and induction of apoptosis. The trans-10, cis-12 isomer was more potent than the cis-9, trans-11 isomer. Further clinical studies are needed to evaluate the effects of CLAs on human fat mass and metabolism in vivo.     

Synthesis and biological activity of hydroxylated derivatives of linoleic acid and conjugated linoleic acids

Allylic hydroxylated derivatives of the C18 unsaturated fatty acids were prepared from linoleic acid (LA) and conjugated linoleic acids (CLAs). The reaction of LA methyl ester with selenium dioxide (SeO₂) gave mono-hydroxylated derivatives, 13-hydroxy-9Z,11E-octadecadienoic acid, 13-hydroxy-9E,11E-octadecadienoic acid, 9-hydroxy-10E,12Z-octadecadienoic acid and 9-hydroxy-10E,12E-octadecadienoic acid methyl esters. In contrast, the reaction of CLA methyl ester with SeO₂ gave di-hydroxylated derivatives as novel products including, erythro-12,13-dihydroxy-10E-octadecenoic acid, erythro-11,12-dihydroxy-9E-octadecenoic acid, erythro-10,11-dihydroxy-12E-octadecenoic acid and erythro-9,10-dihydroxy-11E-octadecenoic acid methyl esters. These products were purified by normal-phase short column vacuum chromatography followed by high-performance liquid chromatography (HPLC). Their chemical structures were characterized by liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance spectroscopy (NMR). The allylic hydroxylated derivatives of LA and CLA exhibited moderate in vitro cytotoxicity against a panel of human cancer cell lines including chronic myelogenous leukemia K562, myeloma RPMI8226, hepatocellular carcinoma HepG2 and breast adenocarcinoma MCF-7 cells (IC₅₀ 10-75 μM). The allylic hydroxylated derivatives of LA and CLA also showed toxicity to brine shrimp with LD₅₀ values in the range of 2.30-13.8 μM. However these compounds showed insignificant toxicity to honeybee at doses up to 100 μg/bee.     

Influence of different CLA isomers on insulin resistance and adipocytokines in pre-diabetic, middle-aged men with PPARγ2 Pro12Ala polymorphism

Conjugated linoleic acids (CLAs) are natural PPARγ ligands, which showed conflicting effects on metabolism in humans. We examined metabolic effects of different isomers of CLA in subjects with PPARγ2 Pro12Ala polymorphisms. A total of 35 men underwent four intervention periods in a crossover study design: subjects with either genotypes received c9, t11 CLA or t10, c12 CLA, a commercially available 1:1 mix of both isomers or reference oil (linoleic acid (LA)). Adipocytokines, insulin, glucose and triglycerides were assessed in the fasting state and after a standardized mixed meal. Across all genotypes, there was a significant (p = 0.025) CLA treatment effect upon postprandial (pp) HOMA-IR values, with c9, t11 CLA and CLA isomer mix improving, but t10, c12 CLA isomer worsening. In Ala12Ala subjects, the t10, c12 isomer caused weight gain (p = 0.03) and tended to increase postprandial insulin levels (p = 0.05). In Pro12Pro subjects, t10, c12 resulted in reduction in waist circumference (p = 0.03). The comparison of the different genotype groups revealed statistically different changes in fasting and postprandial insulin, HOMA-IR and leptin after intervention. c9, t11 CLA and the commercial CLA mix showed beneficial effects on insulin sensitivity compared with LA, while t10, c12 CLA adversely affects body weight and insulin sensitivity in different PPAR genotypes. CLA isomers have different effects on metabolism in Ala and Pro carriers.     

Conjugated linoleic acid suppresses dendritic cell activation and subsequent Th17 responses

PUFAs (polyunsaturated fatty acids) can modify immune responses, so they may have potential therapeutic effects in inflammatory disorders. We previously demonstrated that the cis-9, trans-11 isomer of the PUFA conjugated linoleic acid (CLA) can modulate dendritic cell (DC) cytokine production. Since DCs play a central role in initiating inflammation by directing T helper (Th) cell differentiation, here we examined the effects of CLA on DC maturation and migration and the subsequent generation of Th cell responses. We examined the effect of CLA in vitro on the function of lipopolysaccharide (LPS)-activated bone marrow-derived DCs and ex vivo using cells from mice with high levels of CLA in their diet. We report that CLA inhibits DC migration and modulates TLR-induced production of key cytokines involved in Th cell differentiation both in vitro and in vivo. These changes were accompanied by a significant decrease in expression of MHCII, CD80 and CD86 on the DC surface. Exposure of DCs to CLA suppressed their ability to promote differentiation of naïve T cells into Th1 and/or Th17 cells in vitro and following their adoptive transfer in vivo. Furthermore, in a murine model of endotoxic shock, treatment with CLA suppressed LPS-induced induction of circulating IFN-γ, IL-12p40 and IL-1β. This is the first study to demonstrate that exposure of antigen-presenting cells to CLA can modulate the subsequent Th cell response, and the findings may explain some of the beneficial effects of c9, t11-CLA in inflammatory diseases mediated by Th1 and Th17 cells.     

Differential effects of conjugated linoleic acid isomers on macrophage glycerophospholipid metabolism

Conjugated linoleic acids (CLA) are dietary fatty acids. Whereas cis-9,trans-11-(c9,t11)-CLA can be found in meat and dairy products, trans-9,trans-11-(t9,t11)-CLA is a constituent of vegetable oils. Previous studies showed that these two isomers activate different nuclear receptors and, thus, expression of genes related to lipid metabolism. Here we show that these CLA isomers are differentially elongated and desaturated in primary monocyte-derived macrophages isolated from healthy volunteers by using gas chromatography-mass spectrometry (GC-MS). We further demonstrate that c9,t11-CLA incorporates in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species and activates de novo glycerophospholipid synthesis by quantitative electrospray ionization-tandem mass spectrometry (ESI-MS/MS). c9,t11-CLA leads to strong shifts of the species profiles to PC 18:2/18:2 and PE 18:2/18:2, which are due to de novo synthesis and fatty acid remodeling. In contrast, t9,t11-CLA is preferentially bound to neutral lipids, including triglycerides and cholesterol esters. Taken together our results show that c9,t11-CLA and t9,t11-CLA have differential effects on PC and PE metabolism. Moreover, these data demonstrate that the structure of fatty acids not only determines their incorporation into lipid classes but also modulates the kinetics of lipid metabolism, particularly PC synthesis.     

植物乳杆菌ZS2058在磷酸盐缓冲液体系中生物转化共轭亚油酸

植物乳杆菌ZS2058是从泡菜中筛选到一株具有转化共轭亚油酸能力的乳酸菌。该菌株在MRS培养基中经0.5mg/mL的亚油酸诱导培养后,所获得的菌体细胞具有较强的转化能力。文中就植物乳杆菌ZS2058水洗细胞在磷酸盐缓冲液体系中生物转化共轭亚油酸进行了深入研究。在非厌氧条件下,植物乳杆菌ZS2058在亚油酸浓度为1mg/mL,湿细胞质量浓度约为150mg/mL,120r/min、37℃的条件下反应24h后,能将亚油酸转化为共轭亚油酸和羟基脂肪酸,其中c9,t11-CLA占所产生的CLA总量的96.4%,产量可高达312.4μg/mL,说明该菌株有很强的专一性。随着反应进一步进行,反应至36h时,c9,t11-CLA含量逐渐减少,伴随着大量羟基脂肪酸的产生;并且,以CLA(c9,t11-CLA和t10,c12-CLA的混合样品)为底物进行反应时,c9,t11-CLA被转化为羟基脂肪酸。由此可知,c9,t11-CLA可能是该菌株生物转化LA过程中的一个中间产物。