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PubMed1987

The effect of linoleic acid on the sensitivity of human lymphocytes to cortisol and their capacity to catabolize the steroid.

We have shown previously that cortisol-sensitive lymphocytes (thymocytes) have a much lower capacity than cortisol-resistant cells to catabolize cortisol. In the present study, we attempt to demonstrate that inhibition of cortisol catabolism may make cortisol-resistant lymphocytes vulnerable to the steroid. Linoleic acid, which has the capacity to inhibit the catabolism of cortisol by lymphocytes, was used for this purpose. By using various concentrations of linoleic acid (20-60 micrograms/mL) we showed an inverse linear relationship between linoleic acid concentration and the rate of cortisol catabolism by lymphocytes. During this experiment which took 17 h the viability of cells did not change significantly (minimum viability 95%), even at the highest concentration of linoleic acid. Keeping the metabolism of cortisol at a level of 40% of that obtained by the control, by adding linoleic acid to lymphocyte cultures (50 micrograms/mL) and measuring the viability of the cells for a period of 3 days in the presence or absence of cortisol, we were able to show a rise in the death rate of the cells which started after 24 h of incubation owing to the presence of the steroid.

Humans↗
PubMed1994

The lipoxygenase activity of myoglobin. Oxidation of linoleic acid by the ferryl oxygen rather than protein radical.

Linoleic (9(Z),12(Z)-octadecadienoic) acid is oxidized by sperm whale myoglobin and H2O2 to an 84:16 (9S):(9R) enantiomer mixture of 9-hydroperoxy-10(E),12(Z)-octadecadienoic acid. Neither the 9,10- nor 12,13-epoxide of linoleic acid, nor 9-hydroxy-10(E),12(Z)-octadecadienoic nor 13-hydroperoxy-9(Z),11(E)-octadeca-dienoic acids, is detectably formed. Incubations with [(11R)-2H]- and [(11S)-2H]linoleic acids indicate that the pro-R hydrogen is abstracted 76% of the time. An H64V mutant in which access to the heme crevice is increased oxidizes linoleic acid exclusively by abstraction of the pro-R hydrogen to give the (9S)-hydroperoxide. Spectroscopic studies show that the Kd value for binding of linoleic acid to myoglobin is similar to the Km value for its oxidation and indicate that linoleic acid reduces the ferryl species to the ferric state. The stereochemical results, supported by 18O-labeling studies, definitively rule out a significant role for singlet oxygen in the myoglobin-catalyzed, H2O2-dependent oxidation of linoleic acid. The myoglobin protein radical formed with H2O2 also plays no part in the reaction because the Km and Vmax values for the oxidation of linoleic acid are similar for native myoglobin and two mutants (K102Q/Y103F/Y146F/Y151F and H64V/K102Q/Y103F/Y146F/Y151F) with no tyrosine residues. Furthermore, the rate of formation of the 9-hydroperoxide is not changed if the protein radical is allowed to decay before linoleic acid is added. The results establish that linoleic acid is oxidized within the heme crevice by reaction with the ferryl oxygen rather than a protein radical. They indicate, furthermore, that hydrogen abstraction and oxygen addition occur in an antarafacial manner and suggest a specific model for binding of linoleic acid within the myoglobin active site.

Animals↗
PubMed2002

Effect of linoleic acid metabolites on Na(+)/K(+) pump current in N20.1 oligodendrocytes: role of membrane fluidity.

Metabolic derivatives of linoleic acid, both monoepoxides and diols, have been reported to be toxic in humans and multiple animal tissue preparations. A previous electrophysiological study has shown these compounds produce multiple effects on the electrical activity of rat ventricular myocytes. The hydrophobic nature of these compounds suggests the possibility that these effects may be due to nonspecific lipid interactions, i.e., changes in membrane fluidity. This study investigates membrane fluidity as a possible mechanism by which linoleic acid metabolites inhibit Na(+)/K(+) pump current (I(p)). This study showed that positional isomers 9,10- and 12,13-epoxy-octadecenoic acid (EOA) and 9,10- and 12,13-dihydroxy-OA (DHOA) inhibit I(p) in a dose-dependent manner in N20.1 mouse oligodendrocytes, with greater inhibition produced by EOAs. These compounds, at 10 microM, inhibited I(p) by 4.7 +/- 1.6, 18.2 +/- 0.5, 11.7 +/- 0.5, and 25.1 +/- 0.9% for 12,13-DHOA, 9,10-DHOA, 12,13-EOA, and 9,10-EOA, respectively, in oligodendrocytes. Fluorescence recovery after photobleaching measurements showed that both DHOA isomers produced a 7-8% increase in diffusion coefficient of the probe at 10 microM, whereas the diffusion coefficient was decreased by 5 and 13% by 9,10-EOA and 12,13-EOA, respectively. There was no apparent correlation between membrane fluidity and inhibition of I(p) by these four linoleic acid metabolites. These results indicate that membrane fluidity alone cannot explain the effects of these compounds on I(p) and suggest that they have a specific interaction with the Na(+)/K(+) pump.

Animals↗
PubMed1997

The growth inhibitory effect of conjugated linoleic acid on MCF-7 cells is related to estrogen response system.

Conjugated linoleic acid (CLA) has been shown to have a direct oncostatic action on MCF-7 human breast cancer cells in culture. However, the mechanism involved is not fully elucidated. In this study we have examined whether the inhibitor action is related to the estrogen responsiveness of MCF-7 cells. Our results demonstrate that CLA selectively inhibits proliferation of ER positive MCF-7 cells as compared with ER negative MDA-MB-231 cells. Cell cycle studies indicated that a higher percentage of CLA treated MCF-7 cells remained in the G0/G1 phase as compared to control and those treated with linoleic acid (LA). CLA also inhibited expression of c-myc in MCF-7 cells. These results demonstrate that CLA may inhibit MCF-7 cell growth by interfering with the hormone regulated mitogenic pathway. We are reporting for the first time the involvement of CLA, a dietary factor, in the regulation of hormone mediated mitogenic pathways in ER positive breast cancer cell proliferation in vitro.

Anticarcinogenic Agents↗
PubMed1983

Autoradiographic studies with albumin-bound 1-14C-linoleic acid in normal and essential fatty acid-deficient rats. A pilot study.

Young rats fed a diet providing 0.3, 3 or 10% of the energy as essential fatty acids (EFA) were given a single intravenous dose of albumin-bound 1-14C-linoleic acid. 1 animal from each group was killed at 1 and 18 h, respectively, after the injection and submitted to whole-body autoradiography. In general, the activities in the tissues were higher in the 0.3% group than in the other groups, whereas the differences between the 3% and the 10% group were small. In all groups the highest activity occurred in the brown fat. High activities were also noted in the liver, the adrenal cortex, the diaphragm, and the gastric and intestinal mucosa. The higher activities in the tissues of the rats fed 0.3% than in the tissues of those fed 3% or 10% EFA probably reflect a higher incorporation of fatty acids of the linoleic acid series into structural and other lipids in the former group due to the lack of EFA.

Adipose Tissue, Brown↗
PubMed2003

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.

Adipocytes↗
PubMed2000

Energy supplements rich in linoleic acid improve body weight and essential fatty acid status of cystic fibrosis patients.

BACKGROUND: Patients with cystic fibrosis who have steatorrhea frequently are underweight and have essential fatty acid (EFA) depletion, which is associated with a poor clinical course. It has been stated that poor EFA status is difficult to correct in patients with cystic fibrosis, and an impaired EFA metabolism with reduced synthesis of long-chain polyunsaturated fatty acids has been proposed. In this study, the effects of an oral energy supplement rich in linoleic acid were investigated in patients with cystic fibrosis who had a body weight below 95% of normal for height. METHODS: Thirty-six patients (16 girls) more than 4 years of age were randomized either to a control group (n = 20, age 13.3 +/- 3.8 years, mean +/- SD) receiving intensive dietary counseling only, or an intervention group (n = 16, age, 10.4 +/- 4.3 years) treated for 3 months with dietary counseling plus 628 +/- 254 mL (= kcal) per day of an energy supplement rich in fat (31% of energy) and linoleic acid (16% of energy). RESULTS: In contrast to the control group, the patients with supplemented diets achieved significant increases of energy intake (2189 +/- 731 kcal/day vs. 2733 +/- 762 kcal/day), weight for height (82.8% +/- 8.6% vs. 84.8% +/- 9.6% of normal), and body fat (5.1 +/- 1.7 kg vs. 5.8 +/- 2.2 kg) as well as the initially low values of plasma phospholipid linoleic acid (11.8% +/- 1.1% vs. 17.6% +/- 1.6% of total phospholipid fatty acids) and its main metabolite arachidonic acid (4.4% +/- 0.4% vs. 5.9% +/- 0.3%). CONCLUSIONS: Patients with cystic fibrosis with low body weight and poor EFA status benefit from EFA-rich energy supplements and can synthesize arachidonic acid from the precursor linoleic acid.

Adolescent↗
PubMed1989

Dietary saturated fat level alters the competition between alpha-linolenic and linoleic acid.

Male weanling rats were fed semi-synthetic diets high in saturated fat (beef tallow) vs high in linoleic acid (safflower oil) with or without high levels of alpha-linolenic acid (linseed oil) for a period of 28 days. The effect of feeding these diets on cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding linseed oil with beef tallow or safflower oil had no significant effect on serum levels of cholesterol. Serum cholesterol concentration was higher in animals fed the safflower oil diet than in animals fed the beef tallow diet without linseed oil. Feeding linseed oil lowered the cholesterol content in liver tissue for all dietary treatments tested. Consumption of linseed oil reduced the arachidonic acid content with concomitant increase in linoleic acid in serum and liver lipid fractions only when fed in combination with beef tallow, but not when fed with safflower oil. Similarly, omega 3 fatty acids (18:3 omega 3, 20:5 omega 3, 22:5 omega 3, 22:6 omega 3) replaced omega 6 fatty acids (20:4 omega 6, 22:4 omega 6, 22:5 omega 6) in serum and liver lipid fractions to a greater extent when linseed oil was fed with beef tallow than with safflower oil. The results suggest that the dietary ratio of linoleic acid to saturated fatty acids or of 18:3 omega 3 to 18:2 omega 6 may be important to determine the cholesterol and arachidonic acid lowering effect of dietary alpha-linolenic acid.

Animals↗
PubMed1995

Licorice-derived compounds inhibit linoleic acid (C:18:2 omega 6) desaturation in soybean chloroplasts.

Although glycyrrhizic acid, a major constituent of licorice root, has important pharmacological effects in humans, the biological activity of glycyrrhizic acid and its aglycone glycyrrhetinic acid in plants is unknown. Here we report that these licorice-derived compounds and the analog carbenoxolone inhibit desaturation of linoleic acid (C18:2 omega 6) in soybean chloroplasts using monogalactosyldiacylglycerol and phosphatidylcholine substrates in an in vitro assay for desaturase activity. At 10 nM glycyrrhetinic acid, there is significant inhibition of desaturation of linoleic acid suggesting that licorice-derived compounds could prove useful in investigating biochemical pathways of linoleic acid desaturation in plant chloroplasts and plant desaturase regulation, which has application in modification of plant response to environmental stress, as well as optimization of oil seed composition.

Carbohydrate Sequence↗
PubMed2005

Is conjugated linoleic acid (CLA) a protective factor in atherosclerosis? Study with the use of neural networks.

PURPOSE: Conjugated linoleic acid (CLA) is a term used for positional and geometrical isomers of linoleic acid whose two unsaturated bonds are separated by one saturated bond (cis9trans11 and trans10cis12). Cooked meat and milk are among the richest dietary sources of CLA. Recently, much attention has been devoted to CLA due to its anti-cancer, anti-atherogenic, and anti-diabetic properties. MATERIAL AND METHODS: Our study group comprised 29 patients aged 45 to 75 years who were operated for atherosclerotic stenosis in the carotid arteries. RESULTS: Venous blood was collected after an overnight fast. Total cholesterol and triglycerides were assayed with enzymatic test kits. HDL-cholesterol was measured after precipitation with sodium magnesium phosphotungstate. LDL-cholesterol was calculated from total cholesterol, triglyceride and HDL-cholesterol concentrations using Friedewald's formula. A Perkin-Elmer gas chromatograph (model 8500) was used to analyze fatty acids methyl esters. Statistical analysis was performed with the Statistica Neural Networks software. Significantly lower plasma content of c9t11 CLA, linoleic, and arachidonic acids was found in the study group as compared with controls. Parametric analysis disclosed that c9t11 CLA concentrations depended on triglycerides and arachidonic acid in the study group and on linoleic acid and triglycerides in controls. An increase in total cholesterol concentration was associated with a decrease in the concentration of c9t11 CLA in the study group and a parallel increase in the control group.

Adult↗
PubMed1991

Isolation and identification of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone radical adducts formed by the decomposition of the hydroperoxides of linoleic acid, linolenic acid, and arachidonic acid by soybean lipoxygenase.

alpha-(4-Pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) radical adducts, which are formed in the reactions of soybean lipoxygenase with linoleic acid, arachidonic acid, and linolenic acid, were isolated using HPLC-ESR spectroscopy. Both linoleic acid and arachidonic acid gave one radical adduct, whereas in the case of linolenic acid, two radical adducts were isolated. These radical adducts all showed virtually identical uv spectra with lambda max at 292 and 220 nm in hexane. The absence of absorbance with lambda max at 234 nm indicates that a conjugated diene structure is not contained in these radical adducts. The mass spectra of the radical adducts formed from linoleic and arachidonic acids were identical and contained a molecular ion of m/z 264, consistent with the trapping of the pentyl radical by 4-POBN. Indeed, authentic 4-POBN pentyl radical adduct obtained from the reaction between pentylhydrazine and 4-POBN gave the same mass spectrum as the product obtained from the reaction of linoleic acid and arachidonic acid with 4-POBN. The two 4-POBN radical adducts formed in the linolenic acid reaction were shown by mass spectrometry to be isomers of pentenyl radicals. The 4-POBN-pentyl radical adduct was also detected in the reaction mixture of 13-hydroperoxy-linoleic acid, soybean lipoxygenase, and 4-POBN, indicating that the pentyl radical and pentenyl radical are formed by the decomposition of the hydroperoxides.

Arachidonic Acids↗
PubMed2003

The 10trans,12cis isomer of conjugated linoleic acid suppresses the development of hypertension in Otsuka Long-Evans Tokushima fatty rats.

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid found in beef, lamb, and dairy products. CLA has attracted considerable attention over the past several decades because of its potentially beneficial biological effects, including protective effects against several cancers, atherosclerosis, and obesity. Here we provide the first evidence that the 10trans,12cis-CLA isomer is able to suppress increases in blood pressure during the onset of obesity in OLETF rats. After 3 weeks of feeding with 10t,12c-CLA, systolic blood pressure was significantly lowered compared with rats fed linoleic acid or 9c,11t-CLA. Abdominal adipose tissue weight was also significantly lowered in rats fed 10t,12c-CLA, but not in those which were fed 9c,11t-CLA. In addition, we found that the relative mRNA expressions of angiotensinogen and leptin were suppressed by 10t,12c-CLA in adipose tissue. We speculate that the antihypertensive effect of 10t,12c-CLA can be attributed to the lowered secretion of hypertensive adipocytokines from abdominal adipose tissues.

Adipose Tissue↗
PubMedDate not supplied

Metabolic utilization of linoleic acid from fat emulsion in infants during total parenteral nutrition.

The metabolic utilization of linoleic acid (C18:2w6) from intravenous (iv) soybean oil emulsion via its conversion to higher homologues and prostaglandin biosynthesis was studied in 21 infants. The infants were of normal birth weight, in good clinical and metabolic condition, and aged from 1-4 months. They all received total parenteral nutrition after birth for more than 1 month; the only lipid was provided by iv Intralipid 20%, at levels approximating 350 mg/kg/24 h of linoleic acid (2.5% of the infants' total daily energy intake). Study of the fatty acids of plasma and erythrocyte phospholipids in these infants, compared to healthy controls of the same age (N = 26), showed that 350 mg/kg/24 hr of C18:2w6 supply resulted in normalization of erythrocyte phospholipid fatty acid distribution. This was particularly true of the higher homologues of C18:2w6 (C18:3w6, C20:3w6, and C20:4w6). This suggested that delta 6 and delta 5 desaturation activities are normal in these conditions with this C18:2w6 supply. These results were confirmed by the study of 24-hr urinary excretion of prostaglandins PGE1 and PGE2. With 350 mg/kg/24 hr of C18:2w6 supply their urinary levels were not significantly different from those observed in normal children of the same age receiving an equivalent oral C18:2w6 intake.

Erythrocytes↗
PubMed1978

Reappraisal of linoleic acid requirement of the young infant, with particular regard to use of modified cows' milk formulae.

Most infants in the UK are bottle fed with cows' milk formulae that are alleged to provide less than the minimum requirement for linoleic acid, i.e. 1% of the total dietary energy. 20 term infants fed solely on a modified cows' milk formula that provided 0.55% of the energy from linoleic acid were therefore examined for evidence of deficiency. Rates of growth in length and weight, measured during the first 3 months of life, were identical with those of 20 wholly breast-fed infants. Voluntary food intakes (kcal/kg per day) followed the normal pattern. The fatty acid composition of the plasma lipids showed changes characteristic of a low intake of linoleic acid, but triene:tetraene ratios did not indicate a deficiency state, and clinical signs of deficiency were not observed. These findings suggest that the requirement for linoleic acid is substantially less than was formerly believed. The small amount of alpha-linolenic acid present in cows' milk may however exert a sparing effect on linoleic acid.

Animals↗
PubMed1976

A study of cow's milk containing high levels of linoleic acid: isolation and properties of the fat-globule membrane.

Properties of whole milk and milk fractions from cows fed a diet that gave a greatly increased proportion of unsaturated fatty acid residues (especially of linoleic acid) in the milk lipids were studied, and this milk (high-linoleic milk) was compared with milk from cows on a control diet (control milk). The milk fractions were isolated by high-speed centrifugation of whole milk or cream and were examined by chemical analysis and electron microscopy. During centrifugation the globules of milk fat were disrupted and the membranes (fat-globule 'ghosts') floated as a layer beneath the free lipid. Membrane proteins from the 2 sorts of milk gave the same electrophoretic pattern and the amino acid compositions were the same. Lipid analysis of the membrane fraction from high-linoleic milk showed the expected increase in the proportion of unsaturated fatty acid residues in the neutral lipids, but there was an unexpected decrease in the proportion of unsaturated residues in the membrane phospholipids. No differences were found between high-linoleic and control milk in the ultrastructure of the milk-fat globules or the isolated membranes.

Amino Acids↗
PubMed2004

Conjugated linoleic acid modulation of cell membrane in leukemia cells.

This study compared the cellular uptake of pure conjugated linoleic acid isomers (CLA(9c,11t) and CLA(9c,11c)) to linoleic acid (LA) and their effects on polyunsaturated fatty acid (PUFA) synthesis, its metabolism into conjugated long chain fatty acids (FAs) by desaturation and chain-elongation as well as cell proliferation and the associated anticarcinogenic effects on various human leukemia cell lines (K562, REH, CCRF-CEM and U937 cells). Furthermore, selective effects of this individual isomers of CLA on desaturation steps involved in the biosynthesis of PUFAs associated with cell growth were investigated. CLA isomers supplemented in the culture medium was readily incorporated and esterified into phospholipids (PLs) in the four cell lines in a concentration- and time-dependent manner. The incorporation of the specific CLA isomers in PLs was similar to LA. All four incubating leukemia cells (40 microM CLA for 48 h) showed very high cellular CLA content in PLs (range: 32-63 g FA/100 g total phospholipid fatty acid) affected by the nature of CLA and the cell type. Supplementation with CLA or LA altered also cell membrane composition by n-6 PUFA synthesis. Accordingly, CLA metabolism interferes with LA metabolism. We were able to show that CLA isomers are converted by the leukemia cells of the same metabolic pathway into conjugated diene fatty acids (CDFAs) as LA into non-conjugated PUFAs. In this view, the gas chromatography-flame ionization detector detection of major CDFAs (CD-18:3, CD-20:2 and CD-20:3) in cell membrane of CLA-treated cultures resulted from successive Delta6-desaturation, elongation and Delta5-desaturation of CLA isomers. However, in comparison to LA, relatively lower amounts of elongation and/or desaturation metabolites were detected for CLA(9c,11t), and only minor amounts or trace CDFAs were observed for CLA(9c,11c). Furthermore, CLA(9c,11t) revealed only very low levels of CD-20:4 FA and no CLA(9c,11c)-conversion could be detected. The metabolization of CLA indicated that CLA(9c,11c) 60 microM) had the CLA type dependent antiproliferative effects. Thus, the 9cis,11trans- and the 9cis,11cis-CLA isomers regulate cell growth and survival in different leukemia cell types through their existence alone and/or by their inhibitory effects of desaturase activity.

Cell Line, Tumor↗
PubMed1995

Stereocontrolled hydrolysis of the linoleic acid monoepoxide regioisomers catalyzed by soybean epoxide hydrolase.

Soybean fatty acid epoxide hydrolase (EC 3.3.2.3) was found to possess remarkable and unique stereochemical features. After complete hydrolysis, this enzyme converts racemic or enantiomerically enriched cis-9,10-epoxy-12(Z)-octadecenoic and cis-12,13-epoxyocta-9(Z)-decenoic acids, i.e. the two regioisomers of linoleic acid monoepoxides, into their corresponding 9R, 10R- and 12R, 13R-dihydrodiols with a high enantiomeric excess (> 90%). A straightforward chiral-phase HPLC technique was developed that gives an easy access to the stereochemistry of these reaction products. These results are discussed in terms of a possible model for the substrate binding site of this enzyme.

Epoxide Hydrolases↗
PubMed1988

Dietary linoleic acid and rat neutrophil adhesion and chemotaxis.

We studied adherence and chemotaxis of peritoneal neutrophils from rats fed a diet providing 0.3, 3 or 10% of the energy as linoleic acid. Whereas neutrophils from the 0.3% group showed biochemical evidence of essential fatty acid deficiency (EFAD), cells from the 10% group (the high essential fatty acid (HEFA) group) exhibited a 38% increase of linoleic acid compared to the control group (3% group). EFAD neutrophils showed a significantly lower hyperadherence in response to the ionophore A23187 relative to controls. Also, the fMLP induced response was slightly lower, whereas adherence responses to PMA were unaffected. fMLP induced chemotaxis was only 42% of controls. In HEFA neutrophils, hyperadherence to PMA was significantly diminished, and fMLP or ionophore A23187 stimulation resulted only in a slightly lower hyperadherence compared to controls. Chemotaxis in response to fMLP was significantly decreased. Spontaneous adherence and migration as well as hyperadherence and chemotaxis in response to LTB4 did not differ from controls for any of the groups. This study shows that manipulation of the dietary content of linoleic acid can alter neutrophil functions such as adherence and chemotaxis.

Animals↗