Incorporation of deuterium labeled cis- and trans-9-octadecenoic acid in humans: plasma, erythrocyte, and platelet neutral lipids

A comparison of the metabolism of eighteen-carbon 13C-unsaturated fatty acids in healthy women

Altered use of different dietary fatty acids may contribute to several chronic diseases, including obesity, noninsulin-dependent diabetes mellitus, and cardiovascular disease. However, few comparative data are available to support this link, so the goal of the present study was to compare the metabolism of [(13)C]oleate, [(13)C]alpha-linolenate, [(13)C]elaidate, and [(13)C]linoleate through oxidation and incorporation into plasma lipid fractions and adipose tissue. Each tracer was given as a single oral bolus to six healthy women. Samples were collected over 8 days, and (13)C was analyzed using isotope ratio mass spectrometry. At 9 h postdose, cumulative oxidation was similar for [(13)C]elaidate, [(13)C]oleate, and [(13)C]alpha-linolenate (19 +/- 1%, 20 +/- 4%, and 19 +/- 3% dose, respectively). Significantly lower oxidation of [(13)C]linoleate (12 +/- 4% dose; P < 0.05) was accompanied by its higher incorporation into plasma phospholipids and cholesteryl esters. Abdominal adipose tissue was enriched with [(13)C]alpha-linolenate, [(13)C]elaidate, or [(13)C]linoleate within 6 h. The percentage linoleate in plasma phospholipids correlated positively with [(13)C]linoleate and [(13)C]elaidate oxidation, indicating a potential role of background diet. Conversion of [(13)C]linoleate and [(13)C]alpha-linolenate to longer chain polyunsaturates was a quantitatively minor route of utilization.

The proportion of trans monounsaturated fatty acids in serum triacylglycerols or platelet phospholipids as an objective indicator of their short-term intake in healthy men

Unfavourable effects of trans monounsaturated fatty acid (trans-C18:1) isomers on health variables have been reported. Reports on their actual intake, however, are scarce, because of the absence in many nutrient databases of values for trans-C18:1, and the wide variation in the level of trans fatty acids between different brands of the same product. We therefore examined whether the intake of trans-C18:1 is reflected by trans-C18:1 concentrations in serum triacylglycerols or platelet phospholipids. Thirty-eight men received two diets in random order. During the first experimental period twenty men consumed a Western-type control diet for six weeks, and eighteen men consumed a modified diet in which 70% of the fat was replaced by palm oil. After a wash-out period of 3 weeks, regimens were crossed over (second experimental period). The proportion of total fatty acids from trans-C18:1 in the diet decreased from 4.7 (SEM 0.27) during the control to 2.1 (SEM 0.16) on the modified diet (P < 0.001). Trans-C18:1 in serum triacylglycerols decreased from 3.5 (SEM 0.13) to 2.8 (SEM 0.11)% (P < 0.001), and in platelet phospholipids from 1.0 (SEM 0.06) to 0.7 (SEM 0.04)% (P < 0.001). After the first experimental period trans-C18:1 in the diet correlated with trans-C18:1 in serum triacylglycerols (r 0.41; P = 0.014), and platelet phospholipids (r 0.52; P = 0.001). Also, differences in the intake between the two periods correlated with changes in the proportion of trans-C18:1 in serum triacylglycerols (r 0.56; P = 0.001) and platelet phospholipids (r 0.58; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation of trans-8- and cis-8-octadecenoic acid isomers in human plasma and lipoprotein lipids

Mixtures of deuterium-labeled trans-8, cis-8 and cis-9-octadecenoic acids (8t-18:1, 8c-18:1, 9c-18:1) were fed as triglycerides (TG) to two adult male subjects. Blood samples were collected sequentially over a 48-hour period. Plasma and lipoprotein lipids were separated by thin layer chromatography and analyzed by gas chromatography-mass spectroscopy. Results indicate (i) absorption of the 8t- and 8c-18:1 isomers were similar to 9c-18:1; (ii) the 8t-18:1 isomer was cleared approximately 30% faster than 9c-18:1 from plasma TG; (iii) cholesterol ester samples contained 8.4 times less 8t-18:1 than 9c-18:1; (iv) incorporation at the 1-acyl phosphatidylcholine (PC) position was higher for 8t-18:1 and 8c-18:1 (2.2 and 1.7 times) than for 9c-18:1; and (v) discrimination at the 2-acyl PC position was 4.6-fold against 8t-18:1 and 1.3-fold against 8c-18:1 compared with 9c-18:1. Discrimination against uptake of the delta-8 isomers in both neutral and phospholipid classes suggests that both 8t- and 8c-18:1 may be preferentially oxidized relative to 9c-18:1. Except for triglycerides, data for each of the lipid classes from total plasma and individual lipoprotein samples were similar. These data indicate that differences for incorporation and turnover of the 8t- and 8c-18:1 isomers relative to 9c-18:1 are not substantially influenced by the lipoprotein classes. The maximum isotopic enrichment detected in the chylomicron triglycerides fractions was 60%, which indicates that a substantial amount of endogenous triglycerides was mobilized during absorption of the deuterated fats.

Trans fatty acid content of selected brands of West German nut-nougat cream

The fatty acid composition including trans fatty acids of 12 brands of nut-nougat creams were analyzed by capillary gas chromatography. The creams consisted mainly of sugar and partially hydrogenated vegetable oil. The lipid content, which was quantified gravimetrically, amounted to between 30 and 38.2% in the different brands. The fatty acid composition varied considerably between the different creams. Linoleic acid, the major polyunsaturated fatty acid (PUFA), ranged from 12 to 39%. Palmitic acid (16:0), which was the main fatty acid, varied from 9 to 27%. The total trans fatty acid content of the 12 creams ranged from 0.9 to 12.3%. Only two of the creams contained less than 1% of trans fatty acids; 18:1t was the trans fatty acid found in the greatest amounts, whereas 16:1t and 14:1t were only found in trace amounts. Three samples had amounts of 18:2tt, 18:2ct, and 18:2tc between 0.7 and 1.06%; only small amounts of linoleate isomers were detected in the other creams. Our results show that trans fatty acids are present in every brand of chocolate cream tested. Since the potential risk of arteriosclerosis and cancer resulting from the consumption of trans fatty acids is not yet clear, different ways of production should be used in order to eliminate them from the creams that are a preferred bread spread of infants and children.

Metabolism in humans of cis-12,trans-15-octadecadienoic acid relative to palmitic, stearic, oleic and linoleic acids

Mixtures of triglycerides containing deuterium-labeled hexadecanoic acid (16:0), octadecanoic acid (18:0), cis-9-octadecenoic acid (9c-18:1), cis-9,cis-12-octadecadienoic acid (9c, 12c-18:2) and cis-12,trans-15-octadecadienoic acid (12c,15t-18:2) were fed to two young-adult males. Plasma lipid classes were isolated from samples collected periodically over 48 hr. Incorporation and turnover of the deuterium-labeled fats in plasma lipids were followed by gas chromatography-mass spectrometry (GC-MS) analysis of the methyl ester derivatives. Absorption of the deuterated fats was followed by GC-MS analysis of chylomicron triglycerides isolated by ultracentrifugation. Results were the following: (i) endogenous fat contributed about 40% of the total fat incorporated into chylomicron triglycerides; (ii) elongation, desaturation and chain-shortened products from the deuterated fats were not detected; (iii) the polyunsaturated isomer 12c,15t-18:2 was metabolically more similar to saturated and 9c-18:1 fatty acids than to 9c,12c-18:2; (iv) relative incorporation of 9c,12c-18:2 into phospholipids did not increase proportionally with an increase of 9c,12c-18:2 in the mixture of deuterated fats fed; (v) absorption of 16:0, 18:0, 9c-18:1, 9c,12c-18:2 and 12c,15t-18:2 were similar; and (vi) data for the 1- and 2-acyl positions of phosphatidylcholine and for cholesteryl ester fractions reflected the known high specificity of phosphatidylcholine acyltransferase and lecithin:cholesteryl acyltransferase for 9c,12c-18:2. These results illustrate that incorporation of dietary fatty acids into human plasma lipid classes is selectively controlled and that incorporation of dietary 9c,12c-18:2 is limited. These results suggest that nutritional benefits of diets high in 9c,12c-18:2 may be of little value to normal subjects and that the 12c,15t-18:2 isomer in hydrogenated fat is not a nutritional liability at the present dietary level.

Absorption and distribution of deuterium-labeled trans- and cis-11-octadecenoic acid in human plasma and lipoprotein lipids

Triglycerides of deuterium-labeled trans-11-, trans-11-cis-11- and cis-9-octadecenoic acid (11t-18:1-2H, 11c-18:1-2H) were simultaneously fed to two young adult male subjects. Plasma lipids from blood samples collected periodically for 48 hr were analyzed by gas chromatography-mass spectroscopy. The results indicate the delta 11-18:1-2H acids and 9c-18:1-2H were equally well absorbed; relative turnover rates were higher for the delta 11-18-1-2H acids in plasma triglycerides; incorporation of the delta 11-18:1-2H acids into plasma phosphatidylcholine was similar to 9c-18:1-2H, but distribution at the 1- and 2-acyl positions was substantially different; esterification of cholesterol with 11t-18:1 was extremely low; chain shortening of the delta 11-18:1-2H acids was 2-3 times greater than for 9c-18:1-2H; no evidence for desaturation or elongation of the 18:1-2H acids was detected; and a 40% isotopic dilution of the 18:1-2H acids in the chylomicron triglyceride fraction indicated the presence of a substantial intestinal triglyceride pool. Based on our present knowledge, these metabolic results for delta 11-18:1 acids present in hydrogenated oils and animal fats indicate that the delta 11 isomers are no more likely than 9c-18:1 to contribute to dietary fat-related health problems.

In vivo distribution and turnover of trans- and cis-10-octadecenoic acid isomers in human plasma lipids

Triacylglycerols containing deuterium-labeled trans-10- and cis-10-octadecenoic acid (10t-18:1, 10c-18:1) plus the triacylglycerol of deuterated cis-9-octadecenoic acid (9c-18:1) were fed as a mixture to two young, adult male subjects. Analysis by mass spectroscopy of the labeled fats in blood samples collected periodically for 48 h allowed the uptake, distribution and turnover of both 10-octadecenoic acid isomers to be directly compared to 9c-18:1. A feature of this study is that actual weight data for the labeled fats were obtained. These data allowed plasma triacylglycerol turnover rates of 3.47-5.13 mg/min per kg to be estimated. Plasma and chylomicron triacylglycerol data also provided evidence that absorption of the deuterated fats mobilized 10-12 g of a triacylglycerol pool present in the intestinal cells. Other results are summarized as follows: the 10t-, 10c- and 9c-18:1 fatty acids were equally well absorbed, both delta 10-18:1 isomers were oxidized more rapidly than 9c-18:1, conversion of the delta 10-18:1 isomers into their corresponding 16:1 isomers was about 3-times faster than for 9c-18:1, the delta 10-18:1 isomers were preferentially incorporated at the 1-acyl and excluded from the 2-acyl position of phosphatidylcholine, esterification of cholesterol with the delta 10-18:1 fatty acids was 2.5-4.3-times slower than for 9c-18:1 and desaturation and elongation rates for the delta 10-18:1 acids were very low.

Analysis of deuterium labeled blood lipids by chemical ionization mass spectrometry

A quantitative analytical method has been developed to analyze methyl esters of blood fatty acids derived from human subjects fed deuterium-labeled fats. The GCMS computer method provides for the analysis of the fed deuterium-labeled fatty acids, the naturally occurring blood fatty acids and new fatty acids formed by chain elongation or shortening of the fed labeled fats. Approximately 20 fatty acids including 16, 17, 18 and 20 carbon chain acids were analyzed with a relative standard deviation of 0.02 at the microgram level and a sensitivity of less than one nanogram. The method uses capillary GC to separate the fatty acid esters and isobutane chemical ionization mass spectrometry with multiple ion detection to determine the isotopic constituents of the GC peaks. The technique provides for the determination of overlapping GC peaks labeled with 2, 4 and 6 deuterium atoms and makes extensive use of computers both for data acquisition and processing.

Distribution of deuterium-labeled cis- and trans-12-octadecenoic acids in human plasma and lipoprotein lipids

Triglycerides containing cis- and trans-12-octadecenoic acid (12c-18:1 and 12t-18:1) and cis-9-octadecenoic acid (9c-18:1) labeled with deuterium were fed to 2 young adult male subjects. These fatty isomers each contained a different number of deuterium lables, which allowed mass spectrometric analysis to distinguish among them after they were fed as a mixture. This approach results in a direct comparison of the absorption and distribution of these 3 monenoic acids into blood plasma and lipoprotein lipids. Plasma lipid data indicated that all phospholipid fractions selectively incorporate 12c-18:1 and 12t-18:1 in preference to 9c-18:1. Discrimination against 12c-18:1 and 12t-18:1 compared to 9c-18:1 was found in the plasma neutral lipids, with a strong discrimination against 12t-18:1 incorporation into the cholesteryl ester fraction. Considerable reduction in the percentage of linoleic and arachidonic acid was observed when 12-18:1 isomers were incorporated in plasma triglyceride, phosphatidylcholine and spingomyelin samples. Chylomicron lipid analyses indicated that all isomers were well absorbed. Variation was observed in the relative distribution of 12c-18:1, 12t-18:1 and 9c-18:1 between the very low density, low density and high density lipoprotein lipid classes. No desaturation of 12c-18:1 to linoleic acid was detected.

Incorporation of deuterium-labeled cis- and trans-9-octadecenoic acids in humans: plasma, erythrocyte, and platelet phospholipids

The objective of this study was to follow the uptake and distribution of oleic and elaidic acids into human erythrocytes, platelets, and plasma phospholipids. The use of dual and triple labeling methodology permitted a precise comparison of elaidic and oleic acid utilization. Elaidic acid (EI) was selectively concentrated in all the plasma phospholipids except for lysophosphatidylcholine. Three times more elaidic than oleic acid (OI) accumulated in the 1-acyl position of phosphatidylcholine, as determined by hydrolysis with phospholipase A2. Rapid incorporation and removal of elaidate were observed for all samples. These results support the concept that enzymes responsible for acylation of phospholipids are sensitive to double bond configuration and the physical properties of the fatty acid moieties. Labeled fatty acid levels in red cell and platelet phospholipids were much lower than for plasma phospholipids, indicating a relatively slow rate for the in vivo incorporation of fatty acids into blood cell membrane phospholipids. No isotope effect was found when oleic acid labeled with deuterium on the double bond was used.