Metabolism of cis-12-octadecenoic acid and trans-9,trans-12-octadecadienoic acid and their influence on lipogenic enzyme activities in mouse liver

High carbohydrate (65% glucose) diets containing cis-12-octadecenoic acid (12c-18:1) or trans-9,trans-12-octadecadienoic acid (9t,12t-18:2) were fed to weanling mice to investigate the influence of fatty acid structure on six hepatic enzyme activities involved in lipid metabolism. Results with these diets were compared to those with diets containing no fatty acids, saturated fatty acids; cis-9-octadecenoic acid (9c-18:1) and cis-9,cis-12-octadecadienoic acid (9c,12c-18:2). These comparisons show saturated fatty acids, 9c-18:1, 12c-18:1, and 9t,12t-18:2, had little or no influence on the activity levels of fatty acid synthetase, malic enzyme (EC 1.1.1.40)citrate cleavage enzyme (EC 4.1.3.8), glucose-6-phosphate dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.44) and acetyl-CoA carboxylase (EC 6.4.1.2). Neither 12c-18:1 nor 9t,12t-18:2 produced the dramatic enzyme-lowering effect exhibited by the diet containing 9c,12c-18:2 when compared to the diet devoid of fat. Thus, both the 9 and 12 bonds must be present in the same molecule. Also, at least one and probably both bonds must be in the cis configuration to depress liver enzyme activities. Capillary gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were both used for analysis of the methyl esters derived from the hepatic lipids. The GC and GC-MS data provided (a) direct evidence for incorporation of both isomers into hepatic lipids and (b) indirect evidence that 9t,12t-18:2 lowered liver delta 9-desaturase activity. In addition, since these products were found in the complex liver lipids, there is no doubt that the various enzymes concerned with activation and acylation utilize both of these isomeric fatty acids as substrates.     

Metabolites of cis,trans, and trans,cis isomers of linoleic acid in mice and incorporation into tissue lipids

Metabolism of octadecadienoic acid isomers in weanling mice was studied by feeding fat-free diets supplemented with 2% by weight of cis-9,trans-12-octadecadienoic acid (c,t-18:2-d0), tetradeuterated trans-9,cis-12-octadecadienoic acid (t,c-18:2-d4) or dideuterated cis-9,cis-12-octadecadienoic acid (c,c-18:2-d2). Rates for conversion of c,t-18:2-d0 and c,c-18:2-d2 to c,t-20:4-d0 and c,c-20:4-d2 were identical and both were 5-times higher than conversion of t,c-18:2-d4 to t,c-20:4-d4. Accumulation of t,c-18:2-d4 in liver lipids was 2-4-times higher than for c,t-18:2-d0 or c,c-18:2-d2. The t,c-18:2 diet significantly increased with the 20:3(n-9) and total lipid concentrations in liver but not in heart, plasma or brain. The 20:3(n-9)/20:4(n-6) ratio in the liver lipids was 2-4-times higher for t,c-18:2-d4 than c,c-18:2-d2 fed mice. The position of the trans bond had a marked influence on the distribution of the various intermediate desaturation and elongation products. Intermediate metabolite data for the liver lipids indicated t,c-18:2-d4 was preferentially converted to 5c,11c,14t-20:3 ('dead end' product) rather than to t,c-20:4. Concentration of the 18:3(n-6) metabolite of c,t-18:2-d0 was about 10-times greater than the 18:3(n-6) metabolite of c,c-18:2-d2. Conversely, the concentration of the normal 20:3(n-6) metabolite from c,c-18:2-d2 was 4-times higher than the 20:3(n-6) metabolite of c,t-18:2-d0. Compared to the c,c-18:2 diet, the t,c- and c,t-18:2 diets significantly increased the total n-3, but not the total n-6 fatty acid content of heart lipids. These results illustrate that the position of the trans double-bond influences a variety of enzyme activities and the isomers differ in their physiological effects.     

Selective effects of isomeric cis and trans fatty acids on fatty acyl delta 9 and delta 6 desaturation by human skin fibroblasts

Human skin fibroblasts incorporate and actively desaturate long-chain fatty acids. Growth of these cells in lipid-free medium can be used to enhance delta 9 and delta 6 desaturation of [14C]stearate and [14C]linoleate, respectively. Medium supplementation with cis fatty acids inhibits delta 9 desaturation; effectiveness as inhibitors is linoleate (9c,12c-18:2) greater than oleate (9c-18:1) greater than vaccenate (11c-18:1). Linoelaidate (9t,12t-18:2), trans-vaccenate (11t-18:1) and saturated fatty acids are without effect; elaidate (9t-18:1) appears stimulatory. By contrast, the trans fatty acids elaidate and linoelaidate are potent inhibitors of delta 6 desaturation; inhibition by trans-vaccenate is 50% of that of elaidate. Desaturation of [14C]linoleate is only slightly inhibited by oleate, cis-vaccenate, or (6c,9c,12c)-linolenate. The relative effectiveness of isomeric cis- and trans-octadecenoic acids as inhibitors of delta 9 and delta 6 desaturation in intact human cells is different from that found in microsomal studies. The cell culture system can thus be important in evaluating physiological effects of isomeric fatty acids on cellular metabolic processes.     

Effects of conjugated linoleic acid on body fat accumulation and serum lipids in hamsters fed an atherogenic diet

Conjugated linoleic acid (CLA) refers to a mixture of naturally occurring positional and geometric isomers of linoleic acid that exist in dairy products and meat. The aim of the present work was to study the effects of c-9,t-11 and t-10,c-12 CLA isomers on body fat accumulation and serum lipids in hamsters fed an atherogenic diet. Hamsters were divided in four groups: one group was fed a chow diet (control) and the other three groups were given semi-purified atherogenic diets with 0.5% linoleic acid (LA), c-9,t-11 or t-10,c-12 CLA. Body weight and food intake were measured daily. After 6 weeks, adipose tissues from different anatomical locations and liver were dissected and weighed. Serum glucose, total cholesterol, HDL-c, LDL-c and triacylglycerol levels, as well as total and free cholesterol, triacylglycerol and phospholipid content in liver were determined by enzymatic methods. No differences in either energy intake or final body weight were found. The addition of t-10,c-12 CLA reduced fat accumulation and led to lower serum cholesterol, as compared with LA group. Nevertheless the level remained higher than in the control animals. The reduction in serum cholesterol was limited to LDL-c. This isomer also reduced triacylglycerol content in liver but did not modify serum triacylglycerol level. In summary, the present study demonstrates that t-10,c-12 CLA is the biologically active agent when anti-obesity and hypocholesterolaemic properties of CLA are considered. In contrast, the isomer c-9,t-11 has no effect on lipid metabolism in hamsters.     

Isomers of conjugated linoleic acids are synthesized via different mechanisms in ruminal digesta and bacteria

Digesta samples from the ovine rumen and pure ruminal bacteria were incubated with linoleic acid (LA) in deuterium oxide-containing buffer to investigate the mechanisms of the formation of conjugated linoleic acids (CLAs). Rumenic acid (RA; cis-9,trans-11-18:2), trans-9,trans-11-18:2, and trans-10,cis-12-18:2 were the major CLA intermediates formed from LA in ruminal digesta, with traces of trans-9,cis-11-18:2, cis-9,cis-11-18:2, and cis-10,cis-12-18:2. Mass spectrometry indicated an increase in the n+1 isotopomers of RA and other 9,11-CLA isomers, as a result of labeling at C-13, whereas 10,12 isomers contained minimal enrichment. In pure culture, Butyrivibrio fibrisolvens and Clostridium proteoclasticum produced mostly RA with minor amounts of other 9,11 isomers, all labeled at C-13. Increasing the deuterium enrichment in water led to an isotope effect, whereby (1)H was incorporated in preference to (2)H. In contrast, the type strain and a ruminal isolate of Propionibacterium acnes produced trans-10,cis-12-18:2 and other 10,12 isomers that were minimally labeled. Incubations with ruminal digesta provided no support for ricinoleic acid (12-OH,cis-9-18:1) as an intermediate of RA synthesis. We conclude that geometric isomers of 10,12-CLA are synthesized by a mechanism that differs from the synthesis of 9,11 isomers, the latter possibly initiated by hydrogen abstraction on C-11 catalyzed by a radical intermediate enzyme.     

Effect of fatty acids on growth of Japanese encephalitis virus cultivated in BHK-21 cells and phospholipid metabolism of the infected cells.

Growth of Japanese encephalitis virus (JEV) in BHK-21 cells was stimulated in the presence of 20 to 40 mug of the sodium salt of oleic acid (cis-9-octadecenoic acid, 9-18:1) per ml supplemented in Waymouth medium. The stimulatory effect of the salt was highest when 9-18:1 was added after adsorption of the virus. Study of the effect of other fatty acids on growth of JEV showed the following results: the longer the chain length of the saturated fatty acid salt, the higher the stimulatory effect on viral growth. In contrast, polyunsaturated fatty acids had an inhibitory effect on viral growth. The effect of isomeric cis-octadecenoic acids on viral growth was variable, depending upon the position of the double bond. The cis-6-octadecenoic acid had the highest inhibitory effect on growth of JEV compared to other isomeric octadecenoic acids. The sodium salt of (1-14C) cis-9-octadecenoic acid (9-18:1, 20 mug/ml) was rapidly incorporated into control and JEV-infected cells. Specific radioactivity in phosphatidylcholine dropped 12 to 24 h after virus inoculation, whereas synthesis of phosphatidylethanolamine increased 12 to 24 h after virus inoculation in infected cells compared to uninfected cells. Results from these studies suggest that phospholipid metabolism of infected cells is markedly changed, which can be associated with altered fatty acid metabolism when using labeled 9-18:1 fatty acid as a marker.     

In vitro desaturation or elongation of monotrans isomers of linoleic acid by rat liver microsomes

Several nutritional studies have shown the in vivo conversion of the 9c,12t-18:2 and 9t,12c-18:2 into long chain polyunsaturated fatty acids (PUFA) containing 20 carbons (geometrical isomers of eicosadienoic and eicosatetraenoic acids). In the present work, some in vitro studies were carried out in order to have precise information on the conversion of these two isomers.In a first set of experiments, studies were focused on the in vitro 6 desaturation, the first regulatory step of the biosynthesis of n-6 long chain PUFA, from 9c,12c-18:2. Rat liver microsomes were prepared and incubated under desaturation conditions with [1-¹⁴C]-9c,12c-18:2 in presence of unlabelled 9c,12t-, 9t,12c- or 9t,12t-18:2. The data show that each trans isomer induced a decrease of the 6 desaturation of the [1-¹⁴C]-9c,12c-18:2, but the 9c,12t-18:2 was the most potent inhibitor (up to 63%). Rat liver microsomes were also incubated with [1-¹⁴C]-9c,12c-18:2, [1-¹⁴C]-9c,12t-18:2 or [1-¹⁴C]-9t,12c-18:2 under desaturation conditions. The results indicated that 18:2 9c,12t is a much better substrate for desaturase than 9t,12c-18:2. Moreover, the conversion levels of [1-¹⁴C]-9c,12t-18:2 was similar to what was observed for its all cis homologue, at low substrate concentration only. In a second set of experiments, in vitro elongation studies of each mono-trans 18:2 isomers and 9c,12c-18:2 were carried out. For that purpose, rat liver microsomes were incubated with [1-¹⁴C]-9c,12c-18:2, [1-¹⁴C]-9c,12t-18:2 or [1-¹⁴C]-9t,12c-18:2 under elongation conditions. The data show that [1-¹⁴C]-9t,12c-18:2 is better elongated than 9c,12c-18:2 while the amount of product formed from [1-¹⁴C]-9c,12t-18:2 was lower than was produced from the 9c,12c-18:2.Thus, the desaturation enzymes presented a higher affinity for the 9c,12t-18:2 whereas the elongation enzyme presented a higher affinity for the 9t,12c-18:2.     

Modification of the fatty acid composition of Escherichia coli by coexpression of a plant acyl-acyl carrier protein desaturase and ferredoxin.

Expression of a plant delta 6-palmitoyl (16:0)-acyl carrier protein desaturase in Escherichia coli resulted in the accumulation of the novel monounsaturated fatty acids delta 6-hexadecenoic acid (16:1 delta 6) and delta 8-octadecenoic acid. Amounts of 16:1 delta 6 accumulated by E. coli were increased more than twofold by the expression of a plant ferredoxin together with the delta 6-16:0-acyl carrier protein desaturase.     

Occurrence of positional isomers of octadecenoic and hexadecenoic acids in human depot fat

Positional isomers of hexadecenoic aud octadecenoic acids of human adipose tissue have been separated by gas-liquid chromatography and their amounts determined by oxidative cleavage (MnO(4) and IO(4)). The following isomeric octadecenoic acids were present: 7-octadecenoic acid (0.4%), 8- (1.9%), 9- (73.0%), 10- (2.5%), 11- (19.0%) and 12- (3.2%). The hexadecenoic acids have also been shown to be a mixture of positional isomers, in which the cis-9-isomer predominates. 10-Hexadecenoic and 12-octadecenoic acids could conceivably be precursors of linoleic acid. The following branched fatty acids have also been determined in human depot fat: 13-methyltetradecanoic, 12-methyltetradecanoic, 14-methylpentadecanoic, 14-methylhexadecanoic, and 16-methylheptadecanoic acid. They were present in percentages of 0.02-0.6% and their identification rests solely on comparison of their gas-liquid chromatographic retention times with those of synthetic compounds.     

The effect of two isomeric octadecenoic acids on the lipid metabolism and growth of Novikoff hepatoma cells.

The origin and metabolism of octadecenoic acid (18 : 1) was examined in intact Novikoff rat hepatoma cells by using labeled precursors and two isomeric octadecenoic acids which differed in their abilities to stimulate cell growth in a serum-free medium. The isomers (ci-6-18 : 1 and cis-9-18 : 1) were measured in the cellular lipid by ozonolysis and reduction of the ozonides. The results indicate that the 18 : 1 fatty acid accumulated in the cell lipid by uptake of the preformed acid from the medium. The cis-9-18 : 1 to 16 : 1 and 20 : 1 fatty acids by chain shortening and chain elongation. Both isomers inhibited de novo fatty acid synthesis from acetate by cells suspended in a serum-free medium. The isomers did not exert coordinate control of both fatty acid and cholesterol biosynthesis in the Novikoff cells.     

Isomerization of stable isotopically labeled elaidic acid to cis and trans monoenes by ruminal microbes

A previous study showed that oleic acid was converted by mixed ruminal microbes to stearic acid and also converted to a multitude of trans octadecenoic acid isomers. This study traced the metabolism of one of these trans C18:1 isomers upon its incubation with mixed ruminal microbes. Unlabeled and labeled (18-[13C]trans-9 C18:1) elaidic acid were each added to four in vitro batch cultures with three cultures inoculated with mixed ruminal bacteria and one uninoculated culture. Samples were taken at 0, 12, 24, and 48 h and analyzed for 13C enrichment in component fatty acids by gas chromatography-mass spectrometry. At 0 h of incubation, enrichment was detected only in elaidic acid. By 48 h of incubation, 13C enrichment was 18% (P < 0.01) for stearic acid, 7% to 30% (P < 0.01) for all trans C18:1 isomers having double bonds between carbons six through 16, and 5% to 10% for cis-9 and cis-11 monoenes. After 48 h, 13C enrichment in the uninoculated cultures was only detected in the added elaidic acid. This study shows trans fatty acids exposed to active ruminal cultures are converted to stearic acid but also undergo enzymic isomerization yielding a multitude of positional and geometric isomers.     

Epimerization of benzo[a]pyrene-tetrols after acid hydrolysis, implications for determination of benzo[a]pyrene adducts in protein and DNA

Determination of benzo[a]pyrene-DNA or protein adducts with high performance liquid chromatography (HPLC) after acid hydrolysis at high temperature (90 degrees C) enables four isomers of benzo[a]pyrene tetrahydrotetrol to be identified and quantitated. We have investigated the effect of acid treatment of benzo[a]pyrene-tetrahydrotetrol isomers using HPLC and nuclear magnetic resonance spectroscopy (NMR) analysis. By HPLC, we found reversible epimerization of (+/-)-benzo[a]pyrene-r-7,t-8,9, 10-tetrahydrotetrol to (+/-)-benzo[a]pyrene-r-7,t-8,9, c-10-tetrahydrotetrol and of (+/-)-benzo[a]pyrene-r-7,t-8,c-9, t-10-tetrahydrotetrol to (+/-)-benzo[a]pyrene-r-7,t-8,c-9, 10-tetrahydrotetrol, but no interconversion between the two isomer groups. After acid hydrolysis, we found an equilibrium of 87% (+/-)-benzo[a]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol and 9% (+/-)-benzo[a]pyrene-r-7,t-8,9,10-tetrahydrotetrol and 68% (+/-)-benzo[a]pyrene-r-7,t-8,c-9,10-tetrahydrotetrol and 20% (+/-)-benzo[a]pyrene-r-7,t-8,c-9,t-10-tetrahydrotetrol. Minor amounts of two unknown compounds with similar chromatographic characteristics were also found. We have established a NMR method for determination of underivatized (+/-)-benzo[a]pyrene-r-7,t-8,9, c-10-tetrahydrotetrol and (+/-)-benzo[a]pyrene-r-7,t-8,9, 10-tetrahydrotetrol confirming the epimerization of (+/-)-benzo[a]pyrene-r-7,t-8,9,10-tetrahydrotetrol to (+/-)-benzo[a]pyrene-r-7,t-8,9,c-10- tetrahydrotetrol. (+/-)-Benzo[a]pyrene-r-7,t-8,9,10-tetrahydrotetrol was treated with aqueous hydrochloric acid in tetrahydro- furan-d8 to give (+/-)-benzo[a]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol at 57 degrees C while observing the 1H NMR resonances at 500 MHz. Gradient-selected correlation spectroscopy (COSY), heteronuclear multiple quantum correlation (HMQC) and heteronuclear multiple bond correlation (HMBC) experiments were performed to confirm the assignments of the aliphatic hydrogens in the product (+/-)-benzo[a]pyrene-r-7,t-8,9, c-10-terahydrotetrol. Thus, when analyzing benzo[a]pyrene-DNA or protein adducts by cleaving the adducts with acid hydrolysis, the only ratio of biological significance is between (+/-)-benzo[a]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol plus (+/-)-benzo[a]pyrene-r-7,t-8,9,10-tetrahydrotetrol and (+/-)-benzo[a]pyrene-r-7,t-8,c-9,10-tetrahydrotetrol plus (+/-)-benzo[a]pyrene-r-7,t-8,c-9,t-10-tetrahydrotetrol, due to interconversion (epimerization) at C-10.     

Oxidation and esterification of cis- and trans-isomers of octadecenoic and octadecadienoic acids in isolated rat liver

The metabolism of 9-octadecenoic and 9,12-octadecadienoic acids with different geometrical configurations was compared in isolated perfused rat liver. More ketone bodies were produced when the trans-isomers were infused. In contrast, only the cis-isomer augmented the triacylglycerol secretion almost entirely as very-low-density lipoprotein (VLDL). Although these responses were independent of the difference in the degree of unsaturation in both the cis- and trans-isomers, the trans-monoenic acid compared to the trans-dienic acid was incorporated more readily into perfusate and hepatic lipids. Quantitative information was obtained with radioactive tracer experiments. The hepatic uptakes of 9-[10-14C]octadecenoic acids were comparable in the cis- and trans-isomers. The trans-octadecenoic acid compared to the cis counterpart was oxidized more readily and incorporated more into liver phospholipid but less into perfusate and liver triacylglycerol. These reciprocal responses counterbalanced each other. The lower rates of triacylglycerol synthesis and secretion in the liver perfused with the trans-octadecenoic acid was confirmed using [2- 3H]glycerol as a tracer. The marked difference in the channelling of cis- and trans-fatty acids in the pathways of oxidation and esterification seems to modify the VLDL secretion in perfused rat liver. Present observations indicate a considerable difference in the fate of unsaturated fatty acids with different configurations. trans-Fatty acids are expected to be an efficient energy source in animal tissues and may not be hyperlipidemic.     

Fatty acids of pulmonary surfactant phosphatidylcholine from fetal rabbit lung tissue in culture. Biosynthesis of n-10 monoenoic fatty acids

We have previously reported that fetal rabbit lung tissue in organ culture produces a lamellar body material (pulmonary surfactant) with a lower percentage of disaturated phosphatidylcholine than is typically found in rabbit lung in vivo (Longmuir, K.J., C. Resele-Tiden, and L. Sykes. 1985. Biochim. Biophys. Acta. 833: 135-143). This investigation was conducted to identify all fatty acids present in the lamellar body phosphatidylcholine, and to determine whether the low level of disaturated phosphatidylcholine is due to excessive unsaturated fatty acid at position sn-1, sn-2, or both. Fetal rabbit lung tissue, 23 days gestation, was maintained in culture for 7 days in defined (serum-free) medium. Phospholipids were labeled in culture with [1-14C]acetate or [U-14C]glycerol (to follow de novo fatty acid biosynthesis), or with [1-14C]palmitic acid (to follow incorporation of exogenously supplied fatty acid). Radiolabeled fatty acid methyl esters obtained from lamellar body phosphatidylcholine were first separated by reverse-phase thin-layer chromatography (TLC) into two fractions of 1) 14:0 + 16:1 and 2) 16:0 + 18:1. Complete separation of the individual saturated and monoenoic fatty acids was achieved by silver nitrate TLC of the two fractions. Monoenoic fatty acid double bond position was determined by permanganate-periodate oxidation followed by HPLC of the carboxylic acid phenacyl esters. Lamellar body phosphatidylcholine contained four monoenoic fatty acids: 1) palmitoleic acid, 16:1 cis-9; 2) oleic acid, 18:1 cis-9; 3) cis-vaccenic acid, 18:1 cis-11; and 4) 6-hexadecenoic acid, 16:1 cis-6. In addition, 8-octadecenoic acid, 18:1 cis-8, was found in the fatty acids of the tissue homogenate. The abnormally low disaturated phosphatidylcholine content in lamellar body material was the result of abnormally high levels of monoenoic fatty acid (principally 16:1 cis-9) found at position sn-2. Position sn-1 contained normal levels of saturated fatty acid. The biosynthesis of the unusual n-10 fatty acids was observed from the start of culture throughout the entire 7-day culture period, and was observed in incubations of tissue slices of day 23 fetal rabbit lung. This is the first report of the biosynthesis of n-10 fatty acids (16:1 cis-6 and 18:1 cis-8) in a mammalian tissue other than skin, where these fatty acids are found in the secretory product (sebum) of sebaceous glands.     

Sequential enzymes of linoleic acid oxidation in corn germ: lipoxygenase and linoleate hydroperoxide isomerase

Linoleic acid oxidation catalyzed by lipoxygenase (lipoxidase) activity in extracts of defatted corn germ does not terminate in the product, linoleic acid hydroperoxide, unless the lipoxygenase is first partially purified. If purification is not attempted, the hydroperoxide product exists only as a barely detectable intermediate in the synthesis of three products. One of these was identified as 9-hydroxy-10-oxo-cis-12-octadecenoic acid formed from the hydroperoxide by the enzyme, linoleate hydroperoxide isomerase. Another product, 13-hydroxy-10-oxo-trans-11-octadecenoic acid, is believed to be formed by an isomerase also. The third product was the linoleate ester of one of the hydroxy-oxo-fatty acids, 9-(cis-9,cis-12-octadecadienoyl)-10-oxo-cis-12-octadecenoic acid. It is not known if the synthesis of the ester is enzyme-catalyzed. When a mixture of 13-hydroperoxy-cis-9,trans-11-octa-decadienoic acid and 9-hydroperoxy-trans-10,cis-12-octa-decadienoic acid from soybean lipoxygenase oxidation of linoleic acid was used as a substrate, 13-hydroxy-12-oxo-cis-9-octadecenoic acid and 9-hydroxy-12-oxo-trans-10-octadecenoic acid were formed as the major products of catalysis by linoleate hydroperoxide isomerase(s) from corn. Smaller quantities of 9-hydroxy-10-oxo-cis-12-octadecenoic acid and 13-hydroxy-10-oxo-trans-11-octadecenoic acid were also formed.     

Cis and trans conformational changes of bacterial fatty acids in comparison with analogs of animal and vegetable origin

The conditions of the formations of trans isomers of fatty acids, depending on the method of processing and storage of the raw material of microbial, plant and animal origin, were investigated. In the composition of lipids, except for the main trans-isomer elaidic acid, nonsignificant amounts of trans -2-hexen-4-ynal, trans-2-formlcyclopro-panecarboxylate, methyl octadeca-9-yn-l1-trans-enoate, trans-2, 2-dimethyl-3-(2-propenyl)-ethyl ester, trans-9-octadecenoic acid, and trans-1,5-heptadiene, and mixed isomers of methyloctadeca-9-yn-11-trans-enoate,-methyl-9-cis, 11-trans-octadecadienoate, l-[trans-4-(2-iodo-ethyl) cyclohexyl]-trans-4-pentylcyclo-hexane and cis-9, and trans 11-octadecenoic acid. The major trans elaidic acid component was detected in natural objects of different origin in quantities not exceeding 0.05–0.11%. The combination of thermal processing with other parameters, especially enzymatic treatment, led to an increased proportion of trans isomers. The content of trans isomers is usually proportional to the time of storage of materials.     

Dietary trans fatty acids modulate erythrocyte membrane fatty acyl composition and insulin binding in monkeys

The substitution of trans- for half of the cis-monounsaturated fatty acids in the diet of Macaca fasicularis monkeys resulted in alterations in erythrocyte fatty acid composition and insulin receptor properties but not in membrane fluidity. Both cis and trans diets contained 10% fat and similar fatty acid compositions, except that approximately 50% of the cis-octadecenoate (c-18:1) in the cis diet was replaced with trans-octadecenoate isomers (t-18:1) in the trans diet. Compared with the cis diet, the trans diet resulted in the incorporation of approximately 11% t-18:1, an approximately 50% decrease in c-18:1, an approximately 16% decrease in total saturated fatty acids, and an approximately 20% increase in 18:2(n-6) in erythrocyte membrane lipids. The increase in 18:2(n-6) may reflect on homeostatic mechanisms designed to maintain overall membrane fluidity, as no diet-related changes in fluidity were observed with diphenylhexatriene steady state fluorescence polarization. Values observed for insulin binding and insulin receptor number were higher and binding affinity was lower in monkeys fed the cis diet. In the absence of an effect on overall membrane fluidity, altered receptor activity suggests that insulin receptor activity is dynamic, requiring specific fluid membrane subdomains or highly specific fatty acid-protein interactions.     

Enantioselectivity of the hydrolysis of linoleic acid monoepoxides catalyzed by soybean fatty acid epoxide hydrolase.

Soybean epoxide hydrolase efficiently catalyzes the hydration of the two positional isomers of linoleic acid monoepoxides into their corresponding vic-diols. Kinetic analysis of the progress curves, obtained at low substrate concentrations (i.e. [So] much less than Km), and analysis of the residual substrates by chiral-phase HPLC, indicate that the hydrolase is highly enantioselective, i.e. cis-9R,10S-epoxy-12(Z)-octadecenoic and cis-12R,13S-epoxy-9(Z)-octadecenoic acids are preferentially hydrolyzed (the enantioselectivity ratios are 15 and 28, respectively). Importantly, these two enantiomers are the one formed preponderantly by epoxidation of linoleic acid by peroxygenase, a hydroperoxide-dependent oxidase we have previously described in soybean (Blée, E., and Schuber, F., Biochem. Biophys. Res. Commun. (1990) 173, 1354-1360).     

Conjugated linoleic acid and atherosclerosis: studies in animal models

Conjugated linoleic acids (CLA) are isomeric forms of linoleic acid (LA) containing two conjugated sites of unsaturation. The most abundant dietary form of CLA is the cis-9,trans-11 (c-9,t-11) isomer that is found in the fatty tissues and milk of ruminant animals. CLA can also be acquired by ingestion of supplements, which are usually equimolar mixtures of the c-9,t-11 and t-10,c-12 CLA. For more than a decade, the potential for CLA to modify atherosclerosis in animal models has been examined. However, to date, the studies have failed to reach consensus on whether CLA can be effective in reducing the incidence or severity of atherosclerotic lesions, or whether or not plasma lipid and lipoprotein levels can be improved with CLA supplementation. This review will examine the evidence for and against a role for CLA in atherosclerosis, with a focus on the rabbit, the hamster, and the apoE-deficient mouse.     

Trans fat diet causes decreased brood size and shortened lifespan in Caenorhabditis elegans delta-6-desaturase mutant fat-3

Trans-fatty acids (TFAs) enter the diet through industrial processes and can cause adverse human health effects. The present study was aimed to examine the effects of dietary cis- and trans-fatty acids on the model organism Caenorhabditis elegans. Cis- or trans-18:1n9 triglycerides (25 μM) caused no apparent changes in the numbers of viable progeny of wild-type N2 animals. However, in fat-3 mutants lacking delta-6-desaturase, the trans-isomer caused modest decreases in lifespan and progeny after three generations. Long-chain polyunsaturated fatty acids (PUFA) profiles were significantly altered in fat-3 mutants compared to wild type but were not altered after exposure to dietary cis- or trans-18:1n9. Genome-wide expression analysis of fat-3 mutants revealed hundreds of changes. Several genes involved in fat metabolism (acs-2, fat-7, mdt-15) were significantly increased by cis- or trans-18:1n9 without discrimination between isomers. These results provide support for the hypothesis that dietary trans fats are detrimental to development and aging.