<Emphasis Type="Italic">Trans</Emphasis>-18∶1 isomers in rat milk fat as effective biomarkers for the determination of individual isomeric <Emphasis Type="Italic">trans</Emphasis>-18∶1 acids in the dams' diet

Female rats were fed a diet containing by weight 10% partially hydrogenated sunflower oil, 2% sunflower oil, and 1% rapeseed oil during gestation and lactation. The trans-18∶1 isomer profile of the fat supplement was (in % of total trans 18∶1 acids in the fat supplement): Δ4, 0.5; Δ5, 1.0;Δ6–Δ8, 18∶0; Δ9 (elaidic), 13.5; Δ10, 22.2;Δ11 (vaccenic), 16.0; Δ12, 11.3; Δ13–Δ14, 12.8; Δ15, 2.5; and Δ16, 2.2 (total trans 18∶1 acids in the fat supplement: 40.6%). The cis 18∶1 isomer profile was (in % of total cis-18∶1 isomers):Δ6, Δ8, 2.1; Δ9 (oleics), 70.9; Δ10, 6.1; Δ11, 8.3; Δ12, 4.0; Δ13, 2.8; Δ14, 4.6, and Δ15, 1.2 (total cis-18∶1 acids in the fat supplement: 32.6%). Suckling rats from four litters were sacrificed at day 17 or 18 after birth, and their stomach content (milk) was analyzed. The trans-18∶1 isomer profile of milk was (relative proportions, in % of total): Δ4, 0.3; Δ5, 1.1; Δ6–Δ8, 16.8; Δ9, 15.3; Δ10, 22.0; Δ11, 16.7; Δ12, 11.8; Δ13–14, 11.8; Δ15, 2.5, and Δ16, 1.9 (total trans 18∶1 acids in milk: %). That of cis-18∶1 isomers was (proportions in % relative to total cis-18∶1 isomers): Δ6–Δ8, 4.7; Δ9, 72.5; Δ10, 4.0; Δ11, 8.0; Δ12, 7.1; Δ13, 1.9; Δ14, 1.0, and Δ15, 0.7 (total cis-18∶1 acids in milk: %). These results demonstrate that all isomeric acids, independent of the geometry and the position of the ethylenic bond, are incorporated into milk lipids. With regard to trans-18∶1 isomers, the distribution profile in milk is identical to that in the dams' diet, i.e., there is no discrimination against any positional isomer between their ingestiona nd their deposition into milk lipids. As a consequence, this study indicates that the trans-18∶1 isomer profile of milk reflects that in the dams' diet and supports our earlier hypothesis that the profile of trans-18∶1 isomers in milk can be used to deduce the relative contribution of ruminant fats and partially hydrogenated oils in the diet ot the total intake of trans-18∶1 isomers. On the other hand, the cis-18∶1 isomer profile in milk shows significant differences when compared to that in the dams' diet. Surprisingly, there are no major differences for the cis-Δ9 (oleic) and the cis-Δ11 (asclepic) isomers, which can be synthesized by the mother. However, there seems to be a significant positive selectivity for the group cis-Δ6–Δ8, and for the cis-Δ12 isomer, whereas a negative selectivity occurs for the Δ10 and Δ13 to Δ15 cis isomers. Dr. Robert L. Wolff Robert Wolff passed away at the age of 53 on the 10th of November, 2002. His know-how in the field of lipids was recognized internationally. He had the ability to lead his research projects in both the animal and vegetal worlds. His scientific achievement, more than 100 publications to his name in the field of trans fatty acids, made him highly esteemed by his colleagues. He was Conference Master at Bordeaux 1 University (France) up until 2001, at which time he joined the Nutritional Lipid Unit in I.N.R.A., Dijon (France). His mission there was to develop a research program on plasmalogens and their role in brain and muscle function, for which his analytical and biochemical skills were a guarantee of success. Unfortunately, his state of health did not allow him to complete this project. This publication is his final one.     

Study of individual trans- and cis-16∶1 isomers in cow, goat, and ewe cheese fats by gas-liquid chromatography with emphasis on the trans-Δ3 isomer

Low-temperature gas-liquid chromatography (GLC) was applied to study the distribution profiles of isomeric trans-and cis-hexadecenoic acids in ruminant (cow, goat, and ewe) milk fat after their fractionation by argentation thin-layer chromatography (Ag-TLC). The fat was extracted from cheeses (12 samples of each species), the most common foods made with goat and ewe milks. The predominant trans-16∶1 isomer is palmitelaidic acid (the Δ9 isomer), but it does not exceed one-third of the total group, which itself represents 0.17% (cow), 0.16% (goat), and 0.26% (ewe) of the total fatty acids. The trans-Δ3 16∶1 isomer, which is reported for the first time in ruminant lipids and which likely comes from the animals' feed, is present at a level of ca. 10% of the trans-16∶1 acid group. Otherwise, all isomers with their ethylenic bond between positions Δ4 and Δ14 are observed in the three species studied, roughly showing the same relative distribution pattern. Quantitatively, the trans-16∶1 isomers only represent ca. 5% of the sum of the trans-16∶1 plus trans-18∶1 isomers, and they appear of little importance in comparison. It is inferred from this and recent studies that some previously reported data that were established for consumption assessments dealt in fact mainly with iso-17∶0 acid, which was confused with (and added to) trans-Δ9 (palmitelaidic) acid; consequently, these results were large overestimates. Regarding the cis-16∶1 acids, the Δ9 isomer is the prominent constituent as expected, but the second-most important isomer is the Δ13 isomer. It does not appear that trans-16∶1 isomers are from ruminant milk fats of great nutritional importance as compared with trans-18∶1 isomeric acids. As for trans-18∶1 isomers, the combination Ag-TLC/GLC is a necessary procedure to quantitate trans-16∶1 acids accurately and reliably. Ag-TLC allows removal of interfering branched 17∶0 acids and cis-16∶1 acids, and low-temperature GLC permits an accurate measurement of all individual isomers most of which with baseline resolution.     

Comparison of body weight and adipose tissue in male C57BI/6J mice fed diets with and withouttrans fatty acids

The effect of a diet containingtrans-fatty acids (tFA) on the fatty acid composition and fat accumulation in adipose tissue was investigated in mice. Male C57BI/6J mice were fed Control or Trans Diets that were similar, except that 50% of the 18∶1, which was allcis in the Control Diet, was replaced bytFA in the Trans Diet. At selected ages, body weight, epididymal fat pad weight, perirenal fat yield, adipose tissue cellularity and fatty acid composition were examined. Over the time period studied (2–24 mon), the proportion of 18∶0 and 16∶0 tended to decrease whilecis-18∶1 levels increased. Compared to the Control Diet, the Trans Diet resulted in adipose tissue lipids with higher percentages of 14∶0 and 18∶2n−6 and lower percentages ofcis-18∶1 and 20∶4n−6. In polar lipids,tFA replaced saturated fatty acids, whereastFA replacedcis-18∶1 in the nonpolar lipids. Body weights at 16 and 24 mon of age and epididymal fat pad weights at 8–24 mon of age were lower in mice fed the Trans Diet as compared to those fed the Control Diet. At the ages studied, the Trans Diet also resulted in lower values for perirenal fat weights, triacylglycerol to polar lipid ratios, and adipose cell size. The data suggest that chronic consumption oftFA affects lipid metabolism and results in decreased fat accumulation in murine adipose tissue.     

Incorporation oftrans long-chain n−3 polyunsaturated fatty acids in rat brain structures and retina

During heat treatment, polyunsaturated fatty acids and specifically 18∶3n−3 can undergo geometrical isomerization. In rat tissues, 18∶3 Δ9c, 12c, 15t, one of thetrans isomers of linolenic acid, can be desaturated and elongated to givetrans isomers of eicosapentaenoic and docosahexaenoic acids. The present study was undertaken to determine whether such compounds are incorporated into brain structures that are rich in n−3 long-chain polyunsaturated fatty acids. Two fractions enriched intrans isomers of α-linolenic acid were prepared and fed to female adult rats during gestation and lactation. The pups were killed at weaning. Synaptosomes, brain microvessees and retina were shown to contain the highest levels (about 0.5% of total fatty acids) of thetrans isomer of docosahexaenoic acid (22∶6 Δ4c, 7c, 10c, 13c, 16c, 19t). This compound was also observed in myelin and sciatic nerve, but to a lesser extent (0.1% of total fatty acids). However, the ratios of 22∶6trans to 22∶6cis were similar in all the tissues studied. When the diet was deficient in α-linolenic acid, the incorporation oftrans isomers was apparently doubled. However, comparison of the ratios oftrans 18∶3n−3 tocis 18∶3n−3 in the diet revealed that thecis n−3 fatty acids were more easily desaturated and elongated to 22∶6n−3 than the correspondingtrans n−3 fatty acids. An increase in 22∶5n−6 was thus observed, as has previously been described in n−3 fatty acid deficiency. These results encourage further studies to determine whether or not incorporations of suchtrans isomers into tissues may have physiological implications. Presented in part at the 32nd International Conference on the Biochemistry of Lipids, 1991, Granada, Spain. Delta nomenclature (Δ) is used fortrans polyunsaturated fatty acids to specify the position and geometry of ethylenic bonds. Polyunsaturated fatty acids containingtrans double bonds are abbreviated giving the locations of thetrans double bonds only; e.g., 20∶5 Δ17t 20∶5 Δ5c,8c,11c,14c,17t; 22∶5 Δ19t, 22∶5 Δ7c,10c,13c,16c,19t; 22∶6 Δ19t 22∶6 Δ4c,7c,10c,13c,16c,19t.     

Trans- and cis-octadecenoic acid isomers in the hump and milk lipids from Camelus dromedarius

The distribution profiles of individual trans- as well as cis-18∶1 isomers from the fat prepared from the hump adipose tissue and the milk from Camelus dromedarius (the single-humped Arabian species) are described. Gas-liquid chromatography on two capillary columns with different polarities and lengths were used for this purpose in combination with argentation thin-layer chromatography. A comparison of the profiles established is made with that of true ruminant fats. In the fats from the dromedarius as well as from true ruminants, the trans-18∶1 isomers have their ethylenic bonds in all positions between Δ4 and Δ16. The prominent trans isomer is the 11–18∶1 (vaccenic) acid in all species, and the complete distribution profiles are quite similar. Concerning the cis isomers, the prominent isomer is oleic acid, followed by cis-vaccenic acid, as in true ruminant fats. Other cis isomers encompass the Δ6–8 and the Δ12 to Δ15 isomers. Camelidae (suborder Tylopoda) and Bovidae (suborder Ruminantia) have evolved independently since the Eocene, that is for approximately 50 million years. Despite this considerable period, and the profound differences in anatomy, morphology, physiology, ecological and dietary habits between the extant species of these suborders, the rumen microflora has continued to synthesize the same trans- and cis-octadecenoic acid isomers, in comparable proportions, at least as deduced from their composition profiles. We conclude that the trans-18∶1 acid profile is not intrinsically species-dependent, but it can be affected by the nature and the proportions of dietary unsaturated fatty acids that themselves depend on the feed, and that may be species-specific.     

Characterization of trans-monounsaturated alkenyl chains in total plasmalogens (1-O-alk-1′-enyl-2-acyl glycerophospholipids) from sheep heart

In the present study, we investigated the alkenyl chains from sheep heart plasmalogens (1-O-alk-1′-enyl-2-acyl glycerophospholipids) after their conversion into trimethylene dioxyalkanyl (TMDOA) derivatives. Particular attention was given to monounsaturated alkenyl chains (C₁₈ mainly). For this purpose, a combination of silver ion TLC and GLC on highly polar, very long capillary columns was applied to TMDOA derivatives. Approximately 30 different alkenyl chains could be separated, and the main observation was that the component previously reported as a cis-9 18∶1 alkenyl chain in plasmalogens embraces in fact a wide range of trans and cis isomers, in amounts equal to 7.9 and 5.6%, respectively, of total alkenyl chains. Concerning the trans-monoenoate fraction, isomers with their ethylenic bond spanning from Δ6–Δ8 to Δ16 were tentatively identified on the basis of their distribution profile, which was similar to that of trans-18∶1 acids prepared and isolated from sheep adipose tissue. The main trans-monoenoic C₁₈ alkenyl chain in sheep heart plasmalogens would thus have its double bond in position 11, which seems logical, as alkenyl chains are derived from the corresponding alcohols, themselves issued from the corresponding FA, and in this particular case, vaccenic (trans-11 18∶1) acid. cis-Monoenoic C₁₈ alkenyl chains also appear more complex than realized earlier, showing in particular isomers with their ethylenic bond farther than the Δ9 position, in addition to the main isomer derived from oleic acid. Several trans-16∶1 alkenyl chains could be observed (totaling ca. 1%), but cis-16∶1 isomers were present in trace amounts only.     

Incorporation of dietarycis andtrans octadecenoate isomers in the lipid classes of various rat tissues

The percentage distribution of the geometrical and positional isomers in the hexadecenoates and octadecenoates isolated from triglycerides, phosphatidylcholines, and phosphatidylethanolamines of brain, heart, kidney, liver, lung, muscle, spleen, and adipose tissues from rats maintained four weeks on a semipurified diet supplemented with 15% partially hydrogenated safflower fatty acids, has been determined. Except for brain, octadecenoate percentages were increased in each of the lipid classes of all the tissues by the dietary fat. Although the diet did not contain detectable hexadecenoates, the 16∶1 fraction from the lipid classes of all the tissues was composed of 10–70% of thetrans isomers, indicating chain shortening of the dietary octadecenotes. Distribution ofcis andtrans positional isomers in triglyceride hexadecenoates was approximately the same in all tissues. Relatively high percentages of the Δ9, Δ10, and Δ11 isomers were observed, but the Δ8 was the predominatingtrans hexadecenoate isomer, indicating preferential chain shortening of thetrans δ10 octadecenoate.Trans octadecenoates were found in all tissues, but concentrations were dependent on tissue and lipid class. The distribution of thecis andtrans octadecenoate isomers was similar in all the tissue triglycerides, with the distribution of thetrans isomers resembling the diet. In contrast, the percentage distribution of thetrans octadecenoates in the phospholipid classes differed dramatically from the diet, and the distribution was dependent on both the tissue and lipid class. The Δ12, Δ13, and Δ14trans octadiet, suggesting an accumulation of these isomers. Although thecis Δ10 octadecenoate was a significant dietary component, this isomer was not incorporated significantly into any lipid class of any tissue. The metabolic fate of this isomer remains unknown.     

Trans fatty acids in adipose tissue of French women in relation to their dietary sources

This study reports the fatty acid composition of subcutaneous adipose tissue in French women with special emphasis on the content of trans fatty acids originating from two main dietary sources, ruminant fats and partially hydrogenated vegetable oils (PHVO). Adipose tissue trans fatty acid levels from 71 women, recruited between 1997 and 1998, were determined using a combination of capillary gas chromatography and silver nitrate thin-layer chromatography. Results indicate that on average cis monounsaturates accounted for 47.9% of total fatty acids, saturates for 32.2%, and linoleic acid for 14.4%. Cis n−3 polyunsaturates represented only 0.7%. Total content of trans fatty acids was 2.32±0.50%, consisting of trans 18∶1 (1.97±0.49%), trans 18∶2 (0.28±0.08%), and trans 16∶1 (0.06±0.03%). Trans 18∶3 isomers were not detectable. The level of trans fatty acids found in adipose tissue of French women was lower than those reported for Canada, the United States, and Northern European countries but higher than that determined in Spain. Therefore, trans fatty acid consumption in France appears to be intermediate between that of the United States or North Europe and that of Spain. Based on the equation of Enig et al., we estimated the mean daily trans 18∶1 acid intake of French women at 1.9 g per person. The major trans 18∶1 isomer in adipose tissue was Δ11trans, as in ruminant fats. Estimates of relative contribution of trans fatty acid intake were 55% from ruminant fats and 45% from PHVO. This pattern contrasts sharply with those established for Canada and the United States where PHVO is reported to be the major dietary source of trans fatty acids.     

Distributions of conjugated linoleic acid (CLA) isomers in tissue lipid classes of pigs fed a commercial CLA mixture determined by gas chromatography and silver ion-high-performance liquid chromatography

Pigs were fed a commercial conjugated linoleic acid (CLA) mixture, prepared by alkali isomerization of sunflower oil, at 2% of the basal diet, from 61.5 to 106 kg live weight, and were compared to pigs fed the same basal diet with 2% added sunflower oil. The total lipids from liver, heart, inner back fat, and omental fat of pigs fed the CLA diet were analyzed for the incorporation of CLA isomers into all the tissue lipid classes. A total of 10 lipid classes were isolated by three-directional thin-layer chromatography and analyzed by gas chromatography (GC) on long capillary columns and by silver-ion high-performance liquid chromatography (Ag⁺-HPLC); cholesterol was determined spectrophotometrically. Only trace amounts (<0.1%; by GC) of the 9,11–18∶2 cis/trans and trans, trans isomers were observed in pigs fed the control diet. Ten and twelve CLA isomers in the diet and in pig tissue lipids were sepatated by GC and Ag⁺-HPLC, respectively. The relative concentration of all the CLA isomers in the different lipid classes ranged from 1 to 6% of the total fatty acids. The four major cis/trans isomers (18.9% 11 cis, 13 trans-18∶2; 26.3% 10 trans, 12 cis-18∶2; 20.4% 9 cis, 11 trans-18∶2; and 16.1% 8 trans, 10 cis-18∶2) constituted 82% of the total CLA isomers in the dietary CLA mixture, and smaller amounts of the corresponding cis,cis (7.4%) and trans,trans (10.1%) isomers were present. The distribution of CLA isomers in inner back fat and in omental fat of the pigs was similar to that found in the diet. The liver triacylglycerols (TAG), free fatty acids (FFA), and cholesteryl esters showed a similar patterns to that found in the diet. The major liver phospholipids showed a marked increase of 9 cis,11 trans-18∶2, ranging from 36 to 54%, compared to that present in the diet. However, liver diphosphatidylglycerol (DPG) showed a high incorporation of the 11 cis,13 trans-18∶2 isomer (43%). All heart lipid classes, except TAG, showed a high content of 11 cis,13 trans-18∶2, which was in marked contrast to results in the liver. The relative proportion of 11 cis,13 trans-18∶2 ranged from 30% in the FFA to 77% in DPG. The second major isomer in all heart lipids was 9 cis,11 trans-18∶2. In both liver and heart lipids the relative proportions of both 10 trans,12 cis-18∶2 and 8 trans,10 cis-18∶2 were significantly lower compared to that found in the diet. The FFA in liver and heart showed the highest content of trans,trans isomers (31 to 36%) among all the lipid classes. The preferential accumulation of the 11 cis,13 trans-18∶2 into cardiac lipids, and in particular the major phospholipid in the inner mitochondrial membrane, DPG, in both heart and liver, appears unique and may be of concern. The levels of 11 cis,13 trans-18∶2 naturally found in foods have not been established.     

Identification of noveltrans isomers of 20∶5n−3 in liver lipids of rats fed a heated oil

Trans polyunsaturated n−3 fatty acids are formed as a result of the heat treatment of vegetable oils. It was demonstrated previously that the 18∶3 Δ9cis, 12cis, 15trans containing acis Δ9 ethylenic bond was converted to a geometrical isomer of 20∶5n−3, the 20∶5 Δ5cis, 8cis, 11cis, 14cis, 17trans. In the present study, we have identified two new isomers of eicosapentaenoic acid, the Δ11 monotrans and the Δ11, 17 ditrans isomers in liver of rats fed a heated oil. These are formed as a result of the conversion of two of the main isomers of linolenic acid which are present in refined and frying oils, the 18∶3 Δ9trans, 12cis, 15cis and the 18∶3 Δ9trans, 12cis, 15trans.     

trans fatty acids, 5. Fatty acid composition of lipids of the brain and other organs in suckling piglets

The effects of dietarytrans fatty acids on the fatty acid composition of the brain in comparison with other organs were studied in 3-wk-old suckling piglets. In Experiment (Expt.) 1 the piglets were delivered from sows fed partially hydrogenated fish oil (PHFO) (28%trans), partially hydrogenated soybean oil (PHSBO) (36%trans) or lard (0%trans). In Expt. 2 the piglets were delivered from sows fed PHFO, hydrogenated fish oil (HFO) (19%trans) or coconut fat (CF) (0%trans) with two levels of dietary linoleic acid (1 and 2.7%) according to factorial design. In both experiments the mother's milk was the piglets' only food. The level of incorporation oftrans fatty acids in the organs was dependent on the levels in the diets and independent of fat source (i.e., PHSBO, PHFO or HFO). Incorporation oftrans fatty acids into brain PE (phosphatidylethanolamine) was non-detectable in Expt. 1. In Expt. 2, small amounts (less than 0.5%) of 18∶1trans isomers were found in the brain, the level being slightly more on the lower level of dietary linoleic acid compared to the higher. In the other organs the percentage of 18∶1trans increased in the following order: heart PE, liver mitochondria PE, plasma lipids and subcutaneous adipose tissue. Small amounts of 20∶1trans were found in adipose tissue and plasma lipids. Other very long-chain fatty acids from PHFO or HFO (i.e., 20∶1cis and 22∶1cis+trans) were found in all organ lipids except for brain PE. Dietarytrans fatty acids increased the percentage of 22∶5n−6 in brain PE. Except for the brain and the heart, dietarytrans fatty acids reduced the percentage of saturated fatty acids and increased the percentage of monoenoic acids (includingtrans). The overall conclusion was that dietarytrans fatty acids had no noticeable effect on the brain PE composition but slight to moderate effects on the fatty acid profile of other organs of suckling piglets.     

Trans fatty acids. 2. Fatty acid composition of the brain and other organs in the mature female pig

Female pigs were fed from three wk of age and up to two years a diet containing partially hydrogenated fish oil (PHFO, 28%trans monoenoic fatty acids), partially hydrogenated soybean oils (PHSBO, 36%trans fatty acids) or lard. No consistent differences were found between PHFO and PHSBO with regard to incorporation oftrans fatty acids in organ lipids, buttrans incorporations were highly organ-specific. Notrans fatty acids were detected in brain phosphatidylethanolamine (PE). The incorporation of monoenoictrans isomers, as a percentage of totalcis + trans, in other organs was highest in subcutaneous adipose tissue and liver mitochondria PE, followed by blood lipids with the lowest level in heart PE. The percentage oftrans isomers compared with that of dietary lipids was consistently lower for 20∶1, compared with 18∶1 in organs from PHFO-fed pigs. The only effect of dietarytrans fatty acids on the fatty acid pattern of brain PE was an increased level of 22∶5n−6. Heart PE and total serum lipids of pigs fed the hydrogenated fats contained higher levels of 18∶2n−6, and these lipids of the PHFO-fed group also contained slightly elevated amounts of 20∶3n−6, 18∶3n−3 and 20∶5n−3. Liver mitochondria PE of the PHFO group also contained higher levels of 20∶3n−6 and 22∶5n−6. Dietarytrans fatty acids caused a consistent decrease of saturated fatty acids compensated by increased levels of monoenes. Thus, it may be concluded that dietary long-chaintrans fatty acids in PHFO behaved similarly metabolically to 18∶1-trans in PHSBO in pigs, without noticeable influence on brain PE composition and with moderate to slight effects on the fatty acid profile of the other organs.     

Comparative studies on individual isomeric 18:1 acids in cow, goat, and ewe milk fats by low-temperature high-resolution capillary gas-liquid chromatography

The trans- as well as the cis-18∶1 isomer profiles were established in cow, goat, and ewe cheese fats, with the assumption that these are representative of the corresponding milks. Argentation thin-layer chromatography was combined with low-temperature high-resolution gas-liquid chromatography on 100-m highly polar capillary columns, thus adding precision to earlier data for these species. Despite differences in the absolute content of trans-18∶1 isomers between species, the relative profiles were essentially similar. Except for the minor trans Δ6–Δ8 group, all trans-18∶1 isomers with their ethylenic bonds between positions Δ4 and Δ16 (including the resolved critical pair Δ13/Δ14) were separated and quantitated individually. As expected, vaccenic (trans Δ9−18∶1) acid was the main isomer, accounting for as much as 37 to 50% of the total fraction. It was observed that the goat trans-18∶1 isomer profile was usually rather close to that of cows in winter (barn feeding), whereas that of the ewe shows a seasonal dependence. The trans-18∶1 profile of ewe milk fats from this study resembles that of cows in the transition period between winter and summer (pasture) feeding. Regarding the cis-18∶1 acid fraction, two isomers (oleic and cis-vaccenic acids) accounted for ca. 97% of that fraction for the three species, with the cis-Δ12 isomer ranked third. The analytical procedure employed here appears a convenient alternative to oxidative-based procedures (generally ozonolysis), taking less time and alleviating some draw-backs of the latter procedure.     

The effect of conjugated linoleic acid isomers on fatty acid profiles of liver and adipose tissues and their conversion to isomers of 16:2 and 18:3 conjugated fatty acids in rats

Conjugated linoleic acid (CLA) is a collective term that describes different isomers of linoleic acid with conjugated double bonds. Although the main dietary isomer is 9cis,11trans-18∶2, which is present in dairy products and ruminant fat, the biological effects of CLA generally have been studied using mixtures in which the 9cis,11trans- and the 10trans,12cis-18∶2 were present at similar levels. In the present work, we have studied the impact of each isomer (9cis,11trans- and 10trans,12cis-18∶2) given separately in the diet of rats for 6 wk. The 10trans,12cis-18∶2 decreased the triacylglycerol content of the liver (−32%) and increased the 18∶0 content at the expense of 18∶1n−9, suggesting an alteration of the Δ9 desaturase activity, as was already demonstrated in vitro. This was not observed when the 9cis,11trans-18∶2 was given in the diet. Moreover, the 10trans,12cis-18∶2 induced an increase in the C₂₂ polyunsaturated fatty acids in the liver lipids. The 10trans,12cis-18∶2 was mainly metabolized into conjugated 16∶2 and 18∶3, which have been identified. The 9cis,11trans isomer was preferentially metabolized into a conjugated 20∶3 isomer. Thus, the 9cis,11trans- and the 10trans,12cis-CLA isomers are metabolized differently and have distinct effects on the metabolism of polyunsaturated fatty acids in rat liver while altering liver triglyceride levels differentially.     

Follow-up of the Δ4 to Δ16 trans-18∶1 isomer profile and content in French processed foods containing partially hydrogenated vegetable oils during the period 1995–1999. Analytical and nutritional implications

A survey of the total content of trans-18∶1 acids and their detailed profile in French food lipids was conducted in 1995–1996, and 1999. For this purpose, 37 food items were chosen from their label indicating the presence of partially hydrogenated vegetable oils (PHVO) in their ingredients. The content as well as the detailed profile of these isomers was established by a combination of argentation thin-layer chromatography and gas-liquid chromatography (GLC) on long polar capillary columns. With regard to the mean trans-18∶1 acid contents of extracted PHVO, a significant decrease was observed between the two periods, i.e., from 26.9 to 11.8% of total fatty acids. However, only minor differences were noted in the mean relative distribution profiles of individual trans-18∶1 isomers with ethylenic bonds between positions Δ4 and Δ16 for the two periods. The predominant isomer was Δ9–18∶1 (elaidic) acid, in the wide range 15.2–46.1% (mean, 27.9±7.2%) of total trans-18∶1 acids, with the Δ10 isomer ranked second, with a mean of 21.3% (range, 11.6 to 27.4%). The content of the unresolved Δ6 to Δ8 isomer group was higher than the Δ11 isomer (vaccenic acid), representing on average 17.5 and 13.3%, respectively. Other isomers Δ4, Δ5, Δ12, Δ13/Δ14, Δ15, and Δ16, were less than 10% each: 1.0, 1.6, 7.4, 7.1, 1.8, and 1.0%, respectively. However, considering individual food items, it was noted that none of the extracted PHVO were identical to one another, indicating a considerable diversity of such fats available to the food industry. A comparison of data for French foods with similar data recently established for Germany indicates that no gross differences occur in PHVO used by food industries in both countries. Estimates for the absolute mean consumption of individual isomers from ruminant fats and PHVO are made for the French population and compared to similarly reconstructed hypothetical profiles for Germany and North America. Differences occur in the total intake of trans-18∶1 acids, but most important, in individual trans-18∶1 isomer intake, with a particular increase of the Δ6–Δ8 to Δ10 isomers with increasing consumption of PHVO. It is inferred from the present and earlier data that direct GLC of fatty acids is a faulty procedure that results (i) in variable underestimates of total trans-18∶1 acids, (ii) in a loss of information as regards the assessment of individual isomeric trans-18∶1 acids, and (iii) in the impossibility of comparing data obtained from human tissues if the relative contribution of dietary PHVO and ruminant fats is not known.     

Effect of pasture vs. concentrate diet on CLA isomer distribution in different tissue lipids of beef cattle

This study examined the effects of feeding pasture vs. concentrate on the distribution of CLA isomers in the lipids of longissimus and semitendinosus muscle, liver and heart muscle, and subcutaneous fat in beef bulls. Sixty-four German Holstein and German Simmental bulls were randomly allocated to either an indoor concentrate system or periods of pasture feeding followed by a finishing period on a concentrate containing linseed to enhance their beef content of n−3 PUFA and CLA. The concentrations of CLA isomers in the different tissues were determined by GC and silver ion HPLC. The diet affected the distribution of individual CLA isomers in the lipids of the different tissues. The concentration (mg/100 g fresh tissue) of the most prominent isomer, cis-9,trans-11 18∶2, was increased up to 1.5 times in liver and heart tissue of bulls fed on pasture as compared with concentrate. However, no diet effect was observed for cis-9,trans-11 18∶2 in the lipids of longissimus muscle and subcutaneous fat. In all tissues, the second-most abundant CLA isomer in concentratefed bulls was trans-7,cis-9 18∶2. In contrast, trans-11,cis-13 18∶2 was the second-most abundant CLA isomer in all investigated tissue lipids of pasture-fed bulls. The concentration of the trans-11,cis-13 18∶2 isomer was up to 15 times higher in tissues of pasture-fed bulls as compared with concentrate-fed animals. Furthermone, diet affected the concentrations of the CLA trans,trans 18∶2 isomers. Pasture feeding significantly increased the concentrations of some trans,trans 18∶2 isomers as compared with concentrate, predominantly trans-12,trans-14 18∶2 and trans-11,trans-13 18∶2. Overall, pasture feeding resulted in significantly increased concentrations of the sum of CLA isomers in the lipids of longissimus, muscle, subcutaneous fat, heart and liver muscle of German Holstein and German Simmental bulls, but not in semitendinosus muscle.     

Conversion of 18∶3 Δ9cis, 12cis, 15trans in rat liver microsomes

Several years ago, it was established that the Δ15 trans isomer of α-linolenic acid is converted in vivo into fatty acids containing 20 and 22 carbons (geometrical isomers of eicosapentaenoic and docosahexaenoic acids). The present study focused on the in vitro Δ6 desaturation, the first step of the biosynthesis of the n-3 long-chain polyunsaturated fatty acids from 18:3n-3. For that purpose, rat liver microsomes were prepared and incubated with radiolabeled 18∶3 Δ9cis, 12cis, 15cis (18∶3 c,c,c) or 18∶3 Δ9cis, 12cis, 15trans (18∶3c,c,t) under desaturation conditions. The data show that 18∶3c,c,t is converted at a lower rate compared with α-linolenic acid. The product of conversion of 18∶3 c,c,t may be 18∶4 Δ6cis, 9cis, 12cis, 15trans resulting from a Δ6 desaturation of the trans substrate. Moreover, the conversion of radiolabeled 18∶3c,c,t was strongly decreased by the presence of 18∶3c,c,c (up to 48%) while the 18∶3c,c,t only slightly decreased the conversion of radiolabeled 18∶3c,c,c. Thus, the desaturation enzyme presented a higher affinity for the native all-cis n-3 substrate.     

Phospholipid content and fatty acid composition of human heart

Phospholipid content and fatty acid composition of human heart were determined on 36 biopsy specimens collected during open heart surgery. The main phospholipid classes, phosphatidylcholine (PC), phosphatidylethanolamine (PE), diphosphatidylglycerol (DPG), and sphingomyelin (SPH) were separated by HPLC, quantified, and converted to fatty acid methyl esters which were chromatographed on capillary GLC columns. Sex and age (mainly 40–70) of patients had no significant influence on the relative distribution of phospholipid classes and only a slight effect on fatty acid composition. Incorporation oftrans 18∶1 in phospholipid classes was low.cis andtrans octadecenoic isomers seemed to be selectively incorporated, the Δ9 and Δ11cis ortrans isomers being predominant. Human and rat data were compared, and some species differences were noticed. In human PC, palmitic acid is higher and stearic acid much lower than in rat PC. Saturated dimethyl acetals (16∶0 and 18∶0) in PC and PE were greater for humans. Incorporation of 20∶4 n−6 in human PE is higher than in rat PE.     

Dietary fats containing concentrates ofcis ortrans octadecenoates and the patterns of polyunsaturated fatty acids of liver phosphatidylcholine and phosphatidylethanolamine

The effects of the mixedcis- 18∶1 isomers and mixedtrans-18∶1 isomers present in partially hydrogenated soybean oil (PHSO) upon the patterns of polyunsaturated fatty acids (PUFA) in liver phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were studied in rats fed concentrates ofcis- 18∶1 ortrans- 18∶1 isomers isolated as triacylglycerides from PHSO. Thecis- 18∶1 andtrans- 18∶1 concentrates were fed at levels equal to those present in PHSO fed at 17.9% of the diet. All diets contained the required amounts of both linoleic and linolenic acids. Thetrans- 18∶1 concentrate was found to suppress the levels of 20∶4ω6 and 20∶3ω9, and to increase the levels of 18∶2ω6 and 20∶5ω3 in PC and PE. Thecis- 18∶1 concentrate suppressed 20∶4ω6 in PC, 20∶5ω3 in PC and PE, and 18∶2ω6 was more effective than thetrans concentrate in suppressing 22∶6ω3. Thetrans- 18∶1 concentrate was more effective in suppressing 20∶4ω6. Thetrans-18∶ isomers appear to modify PUFA metabolism by inhibition of PUFA synthesis, whereas thecis- 18∶1isomers appear to compete with 2-position fatty acyl transfer and to inhibit ω3 PUFA acylation.     

Biosynthesis of conjugated linoleic acid in humans

This paper deals with the reanalysis of serum lipids from previous studies in which deuterated fatty acids were administered to a single person. Samples were reanalyzed to determine if the deuterated fatty acids were converted to deuterium-labeled conjugated linoleic acid (CLA, 9c, 11t-18∶2) or other CLA isomers. We found 11-trans-octadecenoate (fed as the triglyceride) was converted (Δ9 desaturase) to CLA, at a CLA enrichment ofca. 30%. The 11-cis-octadecenoate isomer was also converted to 9c, 11c-18∶2, but at <10% the concentration of the 11t-18∶1 isomer. No evidence (within our limits of detection) for conversion of 10-cis-or 10-trans-octadecenoate to the 10,12-CLA isomers (Δ12 desaturase) was found. No evidence for the conversion of 9-cis, 12-cis-octadecadienoate to CLA (via isomerase enzyme) was found. Although these data come from isomerase enzyme) was found. Although these data come from four single human subject studies, data from some 30 similar human studies have convinced us that the existence of a metabolic pathway in one subject may be extrapolated to the normal adult population.