Trans-10, cis-12 conjugated linoleic acid increases fatty acid oxidation in 3T3-L1 preadipocytes

The purpose of this study was to examine the effect of 0-50 micromol/L trans-10, cis-12 conjugated linoleic acid (CLA) and cis-9, trans-11 CLA isomers on lipid and glucose metabolism in cultures of differentiating 3T3-L1 preadipocytes. Specifically, we investigated the effects of 6 d of CLA treatment on the following: 1) (14)C-glucose and (14)C-oleic acid incorporation and esterification into lipid; 2) (14)C-glucose and (14)C-fatty acid oxidation; and 3) basal and isoproterenol-stimulated lipolysis. Trans-10, cis-12 CLA supplementation (25 and 50 micromol/L) increased both (14)C-glucose and (14)C-oleic acid incorporation into the cellular lipid fraction, which was primarily triglyceride (TG), compared with bovine serum albumin (BSA) controls. Although glucose oxidation ((14)C-glucose to (14)C-CO(2)) was unaffected by CLA supplementation, oleic acid oxidation ((14)C-oleic acid to (14)C-CO(2)) was increased by approximately 55% in the presence of 50 micromol/L trans-10, cis-12 CLA compared with BSA controls. In contrast, 50 micromol/L linoleic acid (LA) and cis-9, trans-11 CLA-treated cultures had approximately 50% lower CO(2) production from (14)C-oleic acid compared with control cultures after 6 d of fatty acid exposure. Finally, 50 micromol/L trans-10, cis-12 CLA modestly increased basal, but not isoproterenol-stimulated lipolysis compared with control cultures. Thus, the TG-lowering actions of trans-10, cis-12 CLA in cultures of 3T3-L1 preadipocytes may be via increased fatty acid oxidation, which exceeded its stimulatory effects on glucose and oleic acid incorporation into lipid.     

The trans-10,cis-12 isomer of conjugated linoleic acid reduces hepatic triacylglycerol content without affecting lipogenic enzymes in hamsters

Conjugated linoleic acid (CLA) refers to the positional and geometric dienoic isomers of linoleic acid. The dietary intake of CLA has been associated with changes in lipid metabolism. The aim of the present work was to assess the effects of the two main isomers of CLA on sterol regulatory element binding protein (SREBP)-1a and SREBP-1c mRNA levels, as well as on mRNA levels and the activities of several lipogenic enzymes in liver. For this purpose hamsters were fed an atherogenic diet supplemented with 5 g linoleic acid, cis-9,trans-11 or trans-10,cis-12 CLA/kg diet for 6 weeks. The trans-10,cis-12 isomer intake produced significantly greater liver weight, but also significantly decreased liver fat accumulation. No changes in mRNA levels of SREBP-1a, SREBP-1c and lipogenic enzymes, or in the activities of these enzymes, were observed. There was no effect of feeding cis-9,trans-11 CLA. These results suggest that increased fat accumulation in liver does not occur on the basis of liver enlargement produced by feeding the trans-10,cis-12 isomer of CLA in hamsters. The reduction in hepatic triacylglycerol content induced by this isomer was not attributable to changes in lipogenesis.     

Opposing effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on blood lipids in healthy humans

BACKGROUND: Conjugated linoleic acid (CLA) is reported to have weight-reducing and antiatherogenic properties when fed to laboratory animals. However, the effects of CLA on human health and, in particular, the effects of individual CLA isomers are unclear. OBJECTIVE: This study investigated the effects of 3 doses of highly enriched cis-9,trans-11 (0.59, 1.19, and 2.38 g/d) or trans-10,cis-12 (0.63, 1.26, and 2.52 g/d) CLA preparations on body composition, blood lipid profile, and markers of insulin resistance in healthy men. DESIGN: Healthy men consumed 1, 2, and 4 capsules sequentially, containing either 80% cis-9,trans-11 CLA or 80% trans-10,cis-12 CLA for consecutive 8-wk periods. This phase was followed by a 6-wk washout and a crossover to the other isomer. RESULTS: Body composition was not significantly affected by either isomer of CLA. Mean plasma triacylglycerol concentration was higher during supplementation with trans-10,cis-12 CLA than during that with cis-9,trans-11 CLA, although there was no influence of dose. There were significant effects of both isomer and dose on plasma total cholesterol and LDL-cholesterol concentrations but not on HDL-cholesterol concentration. The ratios of LDL to HDL cholesterol and of total to HDL cholesterol were higher during supplementation with trans-10,cis-12 CLA than during that with cis-9,trans-11 CLA. CLA supplementation had no significant effect on plasma insulin concentration, homeostasis model for insulin resistance, or revised quantitative insulin sensitivity check index. CONCLUSION: Divergent effects of cis-9,trans-11 CLA and trans-10,cis-12 CLA appear on the blood lipid profile in healthy humans: trans-10,cis-12 CLA increases LDL:HDL cholesterol and total:HDL cholesterol, whereas cis-9,trans-11 CLA decreases them.     

Effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on immune cell function in healthy humans

BACKGROUND: Animal studies have suggested that conjugated linoleic acid (CLA), a natural component of ruminant meat and dairy products, may confer beneficial effects on health. However, little information on the effects of CLA on immune function is available, especially in humans. Furthermore, the effects of individual isomers of CLA have not been adequately investigated. OBJECTIVE: This study investigated the effects of supplementing the diet with 3 doses of highly enriched cis-9,trans-11 CLA (0.59, 1.19, and 2.38 g/d) or trans-10,cis-12 CLA (0.63, 1.26, and 2.52 g/d) on immune outcomes in healthy humans. DESIGN: The study had a randomized, double-blind, crossover design. Healthy men consumed 1, 2, and 4 capsules sequentially that contained 80% of either cis-9,trans-11 CLA or trans-10,cis-12 CLA for consecutive 8-wk periods. This regimen was followed by a 6-wk washout and a crossover to the other isomer. RESULTS: Both CLA isomers decreased mitogen-induced T lymphocyte activation in a dose-dependent manner. There was a significant negative correlation between mitogen-induced T lymphocyte activation and the proportions of both cis-9,trans-11 CLA and trans-10,cis-12 CLA in peripheral blood mononuclear cell lipids. However, CLA did not affect lymphocyte subpopulations or serum concentrations of C-reactive protein and did not have any consistent effects on ex vivo cytokine production. CONCLUSION: CLA supplementation results in a dose-dependent reduction in the mitogen-induced activation of T lymphocytes. The effects of cis-9,trans-11 CLA and trans-10,cis-12 CLA were similar, and there was a negative correlation between mitogen-induced T lymphocyte activation and the cis-9,trans-11 CLA and trans-10,cis-12 CLA contents of mononuclear cells.     

Trans-10, cis-12 conjugated linoleic acid antagonizes ligand-dependent PPARgamma activity in primary cultures of human adipocytes

We previously demonstrated that trans-10, cis-12 (10,12) conjugated linoleic acid (CLA) causes human adipocyte delipidation, insulin resistance, and inflammation in part by attenuating PPARgamma target gene expression. We hypothesized that CLA antagonizes the activity of PPARgamma in an isomer-specific manner. 10,12 CLA, but not cis-9, trans-11 (9,11) CLA, suppressed ligand-stimulated activation of a peroxisome proliferator response element-luciferase reporter. This decreased activation of PPARgamma by 10,12 CLA was accompanied by an increase in PPARgamma and extracellular signal-related kinase (ERK)1/2 phosphorylation, followed by decreased PPARgamma protein levels. To investigate if 10,12 CLA-mediated delipidation was preventable with a PPARgamma ligand (BRL), cultures were treated for 1 wk with 10,12 CLA or 10,12 CLA + BRL and adipogenic gene and protein expression, glucose uptake, and triglyceride (TG) were measured. BRL cosupplementation completely prevented 10,12 CLA suppression of adipocyte fatty acid-binding protein, lipoprotein lipase, and perilipin mRNA levels without preventing reductions in PPARgamma or insulin-dependent glucose transporter 4 (GLUT4) expression, glucose uptake, or TG. Lastly, we investigated the impact of CLA withdrawal in the absence or presence of BRL for 2 wk. CLA withdrawal did not rescue CLA-mediated reductions in adipogenic gene and protein expression. In contrast, BRL supplementation for 2 wk following CLA withdrawal rescued mRNA levels of PPARgamma target genes. However, the levels of PPARgamma and GLUT4 protein and TG were only partially rescued by BRL. Collectively, we demonstrate for the first time, to our knowledge, that 10,12 CLA antagonizes ligand-dependent PPARgamma activity, possibly via PPARgamma phosphorylation by ERK.     

Conjugated linoleic acid in humans: regulation of adiposity and insulin sensitivity

Conjugated linoleic acid (CLA) isomers, a group of positional and geometric isomers of linoleic acid [18:2(n-6)], have been studied extensively due to their ability to modulate cancer, atherosclerosis, obesity, immune function and diabetes in a variety of experimental models. The purpose of this review was to examine CLA's isomer-specific regulation of adiposity and insulin sensitivity in humans and in cultures of human adipocytes. It has been clearly demonstrated that specific CLA isomers or a crude mixture of CLA isomers prevent the development of obesity in certain rodent and pig models. This has been attributed mainly to trans-10, cis-12 CLA, both in vivo and in vitro. However, CLA's ability to modulate human obesity remains controversial because data from clinical trials using mixed isomers are conflicting. In support of some studies in humans, our group demonstrated that trans-10, cis-12 CLA prevents triglyceride (TG) accumulation in primary cultures of differentiating human preadipocytes. In contrast, cis-9, trans-11 CLA increases TG content. Closer examination has revealed that CLA's antiadipogenic actions are due, at least in part, to regulation of glucose and fatty acid uptake and metabolism. This review presents our current understanding of potential isomer-specific mechanisms by which CLA reduces human adiposity and insulin sensitivity.     

Trans-10,cis-12 conjugated linoleic acid suppresses the desaturation of linoleic and alpha-linolenic acids in HepG2 cells

The objective of this study was to determine the effects of cis-9,trans-11 and trans-10,cis-12 CLA on the fatty acid desaturation in a human hepatoma cell line, HepG2. Therefore, experiments were conducted in which HepG2 cells were incubated with various concentrations of those fatty acids and the concentrations of fatty acids in various lipid fractions of HepG2 cells were determined. In the presence of linoleic acid as substrate, cells treated with 25 micromol/L of trans-10,cis-12 CLA had lower ratios of dihomo-gamma-linoleic acid to linoleic acid and of arachidonic acid to linoleic acid in phospholipids than control cells; with alpha-linolenic acid as substrate, they had a lower ratio of eicosapentaenoic acid to alpha-linolenic acid in phospholipids than control cells. Cells treated with cis-9,trans-11 CLA did not differ in these ratios from control cells. Cells treated with trans-10,cis-12 CLA had also a markedly lower ratio of monounsaturated fatty acids (MUFA) to saturated fatty acids (SFA) in lipids than control cells; cells treated with cis-9,trans-11 CLA had a slightly lower MUFA:SFA ratio than control cells. These findings suggest that trans-10,cis-12 CLA suppresses Delta9-, Delta6- and Delta5-desaturation in HepG2 cells; cis-9,trans-11 CLA slightly reduces Delta9-desaturation but does not inhibit Delta6- and Delta5-desaturation. Moreover, HepG2 cells treated with 100 micromol/L of trans-10,cis-12 CLA released larger amounts of 6-keto-prostaglandin F(1alpha) and prostaglandin F(2alpha) than control cells. Treatment of cells with cis-9,trans-11 CLA did not alter the release of these eicosanoids compared with control cells. In conclusion, this study suggests that trans-10,cis-12 CLA has significant effects on the metabolism of essential fatty acids in HepG2 cells, whereas cis-9, trans-11 CLA does not have any effect in this respect.     

Adenoma growth stimulation by the trans-10, cis-12 isomer of conjugated linoleic acid (CLA) is associated with changes in mucosal NF-kappaB and cyclin D1 protein levels in the Min mouse

Conjugated linoleic acid (CLA) is a term used to describe the different conjugated isomers of linoleic acid. CLA has been found to be anticarcinogenic in mammary cancer, but its effects on colon carcinogenesis are still inconclusive. In this study, the isomer-specific effects of the cis-9, trans-11 and trans-10, cis-12 CLA isomers were investigated in the Min mouse model for intestinal carcinogenesis. The Min mice (n = 10/group) were fed either an AIN-93G control diet or a diet containing 1 g/100 g cis-9, trans-11 or trans-10, cis-12 CLA for 8 wk. The number and size of adenomas were measured and the proteins from the small intestinal tissues extracted for immunoblotting analysis. The number of adenomas did not differ, but the size of the adenomas was greater in the distal part of the small intestine in mice fed the trans-10, cis-12 isomer than in controls (1.19 +/- 0.16 vs. 0.94 +/- 0.21 mm, mean +/- SD, P < 0.01). The same isomer caused an increase in lipid peroxidation, measured as urinary 8-iso-prostaglandin (PG)F(2alpha). Nuclear p65 protein of the mucosal tissue was not detectable in the trans-10, cis-12 group, which differed (P < 0.05) from the control group. Cyclin D1, a target for the nuclear factor (NF)-kappaB pathway, was elevated in the trans-10, cis-12 group compared with the control group (P < 0.01), but cyclooxygenase-2 levels were not higher. There was no difference in beta-catenin protein levels between the groups. The results indicate that the trans-10, cis-12 isomer of CLA can act as a cancer promoter in colon carcinogenesis possibly through pathways affecting NF-kappaB and cyclin D1.     

Dietary trans-10, cis-12 and cis-9,trans-11 conjugated linoleic acids induce apoptosis in the colonic mucosa of rats treated with 1,2-dimethylhydrazine

We have previously shown that a diet containing a mixture of conjugated linoleic acid (CLA) isomers reduces the incidence of colon tumors in rats treated with 1,2-dimethylhydrazine (DMH). The present study examined which of the two main CLA isomers, trans-10,cis-12 CLA (t10c12) or cis-9,trans-11 CLA (c9t11), decreases colon tumor numbers and the mechanisms for this effect. Six-week-old, male Sprague-Dawley rats were intramuscularly injected with 15 mg/kg of DMH twice per week for 6 weeks and fed a control diet, 1% t10c12, or 1% c9t11 for 30 weeks. The experimental diets were initiated simultaneously with DMH injection. The tumor numbers were decreased and the apoptotic index was significantly increased in the colonic mucosa of the t10c12 and c9t11 groups, when the results were compared with those of the control group. The protein levels of Bcl-2 and cyclooxygenase-2 were significantly decreased, but Bax levels were increased in both of the CLA isomer groups. The thromboxane B(2) levels in colonic mucosa were substantially lower in the two CLA isomer groups than in the control group. However, there was no difference in these parameters between the CLA isomer groups. We have demonstrated that diets containing 1% t10c12 and c9t11 were equally effective in reducing tumor numbers and inducing apoptosis in the colonic mucosa of rats treated with DMH. These results indicate that Bcl-2 family protein levels are associated with CLA-induced apoptosis in the colonic mucosa of DMH-treated rats.     

Trans-10,cis-12, not cis-9,trans-11, conjugated linoleic acid inhibits G1-S progression in HT-29 human colon cancer cells

Commercial preparations of conjugated linoleic acid (CLA) contain both positional and geometric isomers of octadecadienoic acid, with cis-9,trans-11 CLA (c9t11) and trans-10,cis-12 CLA (t10c12) as the principal isomers. We showed previously that CLA reduced the incidence of colon tumors in rats treated with 1,2-dimethylhydrazine. In addition, our previous in vitro studies showed that t10c12 inhibited the growth of HT-29 and Caco-2 human colon cancer cells, whereas c9t11 had no effect on cell growth. In the present study, to examine the effects of the CLA isomers on cell cycle and cell cycle regulatory proteins, we treated HT-29 cells with various concentrations (0-4 micromol/L) of the individual CLA isomers. A DNA flow cytometric analysis revealed that t10c12 induced a G1 arrest, whereas c9t11 had no effect on the cell cycle. Western blot analysis of total cell lysates revealed no alteration in the protein expression of cyclin A, cyclin D, cyclin E, cyclin-dependent kinase (CDK) 2, or CDK4 due to t10c12 treatment. However, t10c12 substantially increased the protein expression and mRNA accumulation of the CDK inhibitor p21(CIP1/WAF1). The t10c12 isomer increased the association of p21(CIP1/WAF1) with CDK2 and proliferating cell nuclear antigen, but decreased the levels of phosphorylated retinoblastoma protein (Rb), with an increase in the levels of hypophosphorylated Rb protein. An in vitro kinase assay using histone H1 as a substrate showed that the activities of CDK2 were significantly decreased by t10c12. These results indicate that t10c12 exerts its growth inhibitory effects in colon cancer cells through the induction of G1 cell cycle arrest. The induction of p21(CIP1/WAF1) may be one of the mechanisms by which t10c12 inhibits cell cycle progression in HT-29 cells.     

Milk fat synthesis in dairy cows is progressively reduced by increasing supplemental amounts of trans-10, cis-12 conjugated linoleic acid (CLA)

Conjugated linoleic acid (CLA) supplements containing a variety of isomers reduce milk fat yield. We have recently identified trans-10, cis-12 CLA as the isomer responsible for inhibiting milk fat synthesis in dairy cows. Our objectives were to determine milk fat yield and fatty acid composition responses to different doses of trans-10, cis-12 CLA. Multiparous Holstein cows (n = 4) were used in a 4 x 4 Latin square design. Treatments consisted of a 5-d abomasal infusion of four doses of trans-10, cis-12 CLA, i.e., 0.0, 3.5, 7.0 and 14.0 g/d. Milk fat yield was decreased 25, 33, and 50%, and milk fat concentration was reduced 24, 37 and 46% when cows received 3.5, 7.0 and 14.0 g/d of trans-10, cis-12 CLA, respectively. Feed intake, milk yield, and milk protein content and yield were unaffected by treatment. Milk fatty acid composition revealed that de novo synthesized fatty acids (short and medium chain) were extensively reduced when cows received the two highest doses, but at the low dose (3.5 g/d), decreases in de novo synthesized fatty acids and preformed fatty acids were similar. Changes in milk fatty acid composition also demonstrated that (9)-desaturase activity was inhibited at the two high doses of trans-10, cis-12 CLA, but was unaffected by the low dose. Results indicate minimal quantities of trans-10, cis-12 CLA (0.016% of dietary dry matter) markedly inhibited milk fat synthesis (25% reduction) and that a curvilinear reduction in milk fat yield occurred with increasing quantities of trans-10, cis-12 CLA.     

Conjugated linoleic acid in diets for large-size rainbow trout (Oncorhynchus mykiss): effects on growth, chemical composition and sensory attributes

The effects of graded levels (0 %, 0.5 %, 0.75 and 1 %) of dietary conjugated linoleic acid (CLA) were assessed on 97 g rainbow trout. Fish were fed to satiation twice a day for 12 weeks. At the end of the experiment, all groups of fish weighed more than 250 g and no significant differences were detected in growth performance, feed conversion, nutrient or energy utilisation or body composition between treatments. A decrease in liver lipid content resulted from including CLA and was accompanied by a reduction in malic enzyme activity. The muscle saturated acid and PUFA content did not vary between dietary treatments, despite the increasing concentration of stearic acid and CLA. In the liver, however, both fractions increased significantly with dietary CLA. Moreover, the MUFA decreased significantly in both muscle and liver. CLA was incorporated into tissue lipids, with levels in flesh (2.1-4.2 %) being 2-fold higher than in liver (0.8-1.9 %). In muscle, the percentage of cis-9, trans-11 isomer ranged from 39.5 % to 41.8 % and that of trans-10, cis-12 isomer from 31.4 % to 33.4 % of total CLA. The incorporation of CLA isomers in the liver varied with dietary treatment, and the cis-9, trans-11 isomer seemed to be more efficiently incorporated than trans-10, cis-12. Sensory data indicated slight-to-moderate differences between the trout fed with and without CLA. The present results suggest that 250 g rainbow trout can incorporate CLA in both muscle and liver, contributing to the production of a functional food.     

An oil mixture with trans-10, cis-12 conjugated linoleic acid increases markers of inflammation and in vivo lipid peroxidation compared with cis-9, trans-11 conjugated linoleic acid in postmenopausal women

A mixture of trans-10, cis-12 (t10,c12) and cis-9, trans-11 (c9,t11) conjugated linoleic acid (CLA mixture) reduced atherosclerosis in animals, thus the effect of these isomers on endothelial dysfunctions leading to inflammation and atherosclerosis is of interest. We gave 75 healthy postmenopausal women a daily supplement of 5.5 g of oil rich in either CLA mixture, an oil rich in the naturally occurring c9,t11 CLA (CLA milk), respectively, or olive oil for 16 wk in a double-blind, randomized, parallel intervention study. We sampled blood and urine before and after the intervention. The ratios of total cholesterol:HDL cholesterol and concentrations of C-reactive protein, fibrinogen, and plasminogen activator inhibitor-1 were significantly higher in women supplemented with the CLA mixture than in those supplemented with CLA milk. Plasma triacylglycerol was significantly higher and HDL cholesterol was lower in women supplemented with the CLA mixture than with olive oil. Both CLA supplements increased lipid peroxidation, a marker of in vivo oxidative stress measured as urinary free 8-iso-prostaglandin F(2alpha). However, the CLA mixture increased lipid peroxidation more than the CLA milk did. The plasma cytokines interleukin-6 and tumor necrosis factor-alpha were not affected by the treatments, nor were any of the other variables measured. In conclusion, oil containing trans-10,cis-12 CLA has several adverse effects on classical and novel markers of coronary vascular disease, whereas the c9,t11 CLA isomer is more neutral, except for a small but significant increase in lipid peroxidation compared with olive oil.     

Inhibition of phospholipase A<Subscript>2</Subscript> activity by conjugated linoleic acids in human macrophages

The objective of this study was to assess the effect of conjugated linoleic acid isomers (CLAs) on the expression and activity of phospholipases A₂ (PLA₂) in human macrophages. Macrophages were incubated with 30 μM cis-9, trans-11 and trans-10, cis-12 CLAs for 48 h. After incubation, the total activity of phospholipases as well as the expression of mRNA for cytosolic (cPLA₂) and secretory (sPLA₂) phospholipases and activity of sPLA₂ were measured. Both CLA isomers reduced the total activity of PLA₂ (by 30.2%, P < 0.01 for cis-9, trans-11 CLA and by 30%, P < 0.001 for trans-10, cis-12 CLA). Trans-10, cis-12 CLA isomer downregulated the expression of mRNA of sPLA₂ and decreased the enzymatic activity of this enzyme (by 23%, P = 0.02) in macrophages. Conjugated linoleic acid isomers can significantly reduce the activity of PLA₂ in macrophages and downregulate sPLA₂ expression. The consequence of this effect may be reduction of releasing the arachidonic acid (AA) from the cellular membranes of macrophages. Supported by grant No. 3 P05B 117 23 from the State Committee for Scientific Research, Poland.     

Trans-10, cis-12-conjugated linoleic acid does not increase body fat loss induced by energy restriction

Very little evidence exists concerning the effects of conjugated linoleic acid (CLA) on body fat reduction induced by energy restriction. Moreover, although an effect of trans-10, cis-12-CLA on lipolysis has been suggested, it has not been consistently shown. The aims of the present study were to determine whether trans-10, cis-12-CLA increases the reduction of body fat induced by energy restriction, and to analyse its effect on lipolysis and adipose tissue lipase expression (hormone-sensitive lipase (HSL) and adipose tissue TAG lipase (ATGL)). Male Syrian Golden hamsters were fed a high-fat diet during 7 weeks in order to make them fatter. Then they were submitted to a mild energy restriction (25 %) without or with supplementation of 0.5 % trans-10, cis-12-CLA for 3 weeks. Basal glycerol release and lipolysis stimulated by several drugs acting at different levels of the lipolytic cascade were measured in epididymal adipose tissue. The expression of HSL and ATGL was assessed by real-time RT-PCR. No differences were found in adipose tissues size between the experimental groups. Medium adipocyte size and total number of adipocytes were similar in both experimental groups. Animals fed the CLA-enriched diet showed similar lipolytic rates as well as HSL and ATGL expressions to the controls. In conclusion, trans-10, cis-12-CLA does not promote adipose tissue lipid mobilisation nor does it heighten body fat reduction induced by energy restriction. Consequently, this CLA isomer does not seem to be a useful tool to be included in body weight-loss strategies followed in obesity treatment.     

Biohydrogenation of linolenic acid to stearic acid by the rumen microbial population yields multiple intermediate conjugated diene isomers

The current literature suggests that linolenic acid biohydrogenation converts to stearic acid without the formation of CLA. However, a multitude of CLA were identified in the rumen that are generally attributed to linoleic acid biohydrogenation. This study used a stable isotope tracer to investigate the biohydrogenation intermediates of (13)C-linolenic acid, including CLA. A continuous culture fermenter was used to maintain a mixed microbial population obtained from the rumen of cattle at pH 6.5 for 6 d. The mixed fermenter contents were then transferred to batch cultures containing either (13)C-labeled or unlabeled linolenic acid, which were run in triplicate for 0, 3, 24, and 48 h. The (13)C enrichment was determined by GC-MS. After 48 h of incubation, 8 CLA isomers were significantly enriched, suggesting that these CLA isomers originated directly from linolenic acid. The cis-10, cis-12 CLA isomer exhibited the highest enrichment (21.7%), followed by cis-9, cis-11 and trans-8, trans-10 CLA. The enrichment of these 2 CLA isomers ranged from 20.1 to 21.1% and the remaining 5 CLA including cis-9, trans-11 CLA were <15.0%. A multitude of nonconjugated and partially conjugated 18:2 and 18:3 isomers was enriched during the 48 h of incubation. The results of this study confirm that mixed ruminal microbes are capable of the formation of several CLA and 18:3 isomers from linolenic acid, indicating that linolenic acid biohydrogenation pathways are more complex than previously reported.     

trans-10,cis-12 conjugated linoleic acid inhibits the G1-S cell cycle progression in DU145 human prostate carcinoma cells

Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of linoleic acid, and has evidenced anti-cancer activities in experimental animal cancer models and in vitro studies. The two predominant isomers of CLA are cis-9,trans-11 CLA (c9t11) and trans-10,cis-12 CLA (t10c12). The present study was performed to study the effect of the individual CLA isomers on DU145 cell growth. The cells were incubated in serum-free medium with different concentrations of the fatty acids. Treatment of cells with t10c12 (at 2.5-10 micromol/L) resulted in a dose-dependent reduction in the numbers of viable cells, whereas c9t11 CLA at a concentration of 5 micromol/L slightly increased viable cell numbers at 3 days (P < .05). DNA flow cytometric analysis revealed that the treatment of DU145 cells with t10c12 for 24 hours induced a small but significant increase in the number of cells in the G1 phase, accompanied by a complementary decrease in cells in the S phase. c9t, however, had no effect on cell cycle progression. To determine the molecular mechanisms underlying t10c12-induced G1 arrest, the levels of cell cycle regulatory proteins were estimated by western blot analyses. t10c12 induced a marked increase in p21(CIP1/WAF1) protein levels in a dose-dependent manner. p27(KIP1) was not affected by t10c12. t10c12 moderately decreased cyclin A and cyclin D1 protein levels (P > .05). However, t10c12 did not affect the expression of cyclin-dependent kinase (CDK) 2, CDK4, or cyclin E. t10c12 increased p21(CIP1/WAF1) bound to CDK2 and attenuated CDK2 activity. These results indicate that t10c12-induced p21(CIP1/WAF1) binds to CDK, and inhibits the activity of this enzyme, which results in the observed decrease in the G1-S progression in DU145 cells.     

The effects of cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acids on delta4-desaturation in HepG2 cells

The objective of this study was to determine the effects of cis-9, trans-11 and trans-10, cis-12 CLA on the delta4-desaturation process in HepG2 cells. Experiments were conducted in which HepG2 cells were incubated with 25 micromol/L of those fatty acids and the concentrations of (n-6) and (n-3) polyunsaturated fatty acids in phosphatidyl choline and phosphatidyl ethanolamine were determined. In the presence of eicosapentaenoic acid, cells treated with trans-10, cis-12 CLA had a lower ratio of docosahexaenoic acid [22:6 (n-3)], the product of delta4-desaturation, to docosapentaenoic acid [22:5 (n-3)], the substrate of delta4-desaturation in both phospholipids, than control cells or cells treated with cis-9, trans-11 CLA (p < 0.05). This suggests that trans-10, cis-12 CLA suppresses the delta4-desaturation process in HepG2 cells.