Current studies on relation of fat to health

Effect of trans-unsaturated fats on experimental atherosclerosis in vervet monkeys

Vervet monkeys ( Ceropithecus aethiops pygerethrus ) were placed on semipurified diets containing 14% fat of which 3.2 or 6.0% was present as trans-unsaturated fatty acid (t-FA). Two groups were fed the high and low levels of t-FA for a year and two others were fed t-FA for 6 months and then returned to the control diet for 6 months more. One other group was fed the control diet for a year. The control diet contained 14% fat which was a mixture of 72% olive oil and 28% corn oil. There were no significant differences in weight gain. Monkeys fed 6% t-FA or control diets for one year had lowest liver weights. Serum cholesterol and triglycerides in monkeys fed 3.2% t-FA for one year were 134 and 55 mg/dl, respectively; in monkeys returned to control diet after 6 months on 6% t-FA the values were 146 and 50 g/dl. Serum and triglyceride levels for the other 3 groups were 166 +/- 2 and 70 +/- 2 mg/dl. Liver cholesterol levels ranged from 4.0 mg/g (3.2% t-FA) to 4.7 mg/g (control) and 4.8 mg/g (6% t-FA). Lecithin:cholesterol acyltransferase (LCAT) activity was 59.0 microM/h for controls and ranged from 52.4 microM/h (3.2% t-FA) to 73.4 microM/h (6% t-FA). Cholesterol synthesis by liver slices was not affected by diet when the substrate was acetate. When mevalonate was used, the monkeys fed either level of t-FA for 12 months exhibited greatly reduced (about 80%) cholesterogenesis. The levels of t-FA in serum and liver reflected the amount in the diet. After being returned to control diet levels of t-FA in serum and liver of monkeys (fed 3.2% t-FA) fell by 97 and 94%, respectively, and those in serum and liver of monkeys fed 6% t-FA fell by 65 and 91%. There were no significant differences in aortic atherosclerosis or arteriosclerosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of dietary fats on desaturase activities and the biosynthesis of fatty acids in rat-liver microsomes

Four groups of rats were fed diets containing 15% (w/w) high-oleic safflower oil (SFO, rich in cis-18:1 acids), a mixture of 80% partially hydrogenated soybean oil plus 20% corn oil (H + CO, rich in trans-18:1 acids), lard (L, rich in saturated fatty acids) and corn oil (Co, rich in 18:2 omega 6). Fatty acid composition of liver microsomes and activities of the delta 5, delta 6 and delta 9 desaturases were determined. Microsomal delta 6 desaturase activity and arachidonic acid were lower in the H + CO group compared with SFO of L. No difference was found in the delta 5 or delta 6 desaturase activity of CO and SFO groups. Thus, the oleic-acid level of the SFO diet had no effect on the metabolism of 18:2 omega 6. Fluorescent polarization studies, using trans-parinaric acid as a probe, showed no differences between the physical states of phospholipid vesicles made from lipids isolated from each group. We concluded that the trans-18:1 acids in partially hydrogenated soybean oil have a more inhibitory effect than saturated acids on EFA metabolism, even in the presence of adequate amounts of essential fatty acid.

A comparative study on the effect of cis (oleic, linoleic) and trans (elaidic, linoelaidic) fatty acids on the in vitro prostaglandin biosynthesis in human blood platelets from (1-14C) arachidonic acid

Dietary fatty acids affect the synthesis and thus ultimate availability of prostaglandin precursors. During processing of edible fats a significant portion of the naturally occurring cis fatty acids is changed to the respective trans isomers. Trans fatty acids could have a wide variety of effects including their effect on prostaglandin synthesis. A comparative study on the effect of cis (oleic and linoleic) fatty acids and their corresponding trans isomers (elaidic and linoelaidic acids) on the in vitro prostaglandin biosynthesis in human blood platelets was made. Linoleic acid (0.5, 1.0 mM) showed the same effect on the various arachidonic acid (AA) metabolites as reported earlier by us, that is, increased generation of prostaglandins and thromboxanes and reduced amounts of HHT and HETE (26). Linoelaidic acid at these two concentrations had the same effect but to a lesser extent. Both linoleic and linoelaidic acids at 0.25 mM concentration reduced TxB2 formation. Oleic and elaidic acids (0.5, 1.0 mM) decreased the formation of TxB2 though not significantly. With oleic acid, the results in respect of other AA metabolites were similar to those reported by us earlier (26). MDA was reduced significantly in the presence of linoleic, linoelaidic and oleic acids; cis isomers being more effective. In the presence of linoleic and linoelaidic acids, prostaglandin endoperoxides were reduced significantly; there was no change in the presence of oleic and elaidic acids. Thus fatty acids seem to affect the platelet cyclo-oxygenase activity; this being more pronounced in the case of cis fatty acids compared to their trans isomers. Reduction in cyclo-oxygenase activity also depends upon the number of double bonds in the acids.

Effects of dietary 9-trans, 12-trans linoleate on arachidonic acid metabolism in rat platelets

In order to determine the minimal amount of dietary 9-trans, 12-trans-linoleate which can decrease endoperoxide metabolites synthesized and their precursor in rat platelets, graded amounts (0, 0.1, 0.5, 1.0, 2.5%) of the trans-linoleate were fed to rats with a constant amount of all-cis-linoleate (2.5%) for 12 weeks. Arachidonic acid levels in platelet phospholipids of groups receiving the trans-linoleate at 2.5 and 1.0% were significantly (p less than 0.01) lower than that of the control receiving no trans-linoleate. Concentrations of TXB2 and PGF2 alpha in sera of the group receiving 2.5% trans-linoleate were significantly (p less than 0.05) lower than those of the control; however, there was no difference between the group receiving 1.0% trans-linoleate and the control. To determine whether the difference in serum concentration of endoperoxide metabolites could be manifested if rats were fed for longer period of time, 2 groups of rats were again fed diets containing 0 and 1.0% trans-linoleate, respectively, for 16 weeks. Arachidonic acid in platelet phospholipids of the group receiving the trans-linoleate was again significantly (p less than 0.01) lower than that of the control group. Concentrations of TXB2 and PGF2 alpha, and 12-hydroxyeicosatetraenoic acid formed in platelets, were smaller in the group receiving trans-linoleate than the control group; however, the difference was not statistically significant. These results indicated that all-trans-linoleate can reduce arachidonic acid metabolites formed in rat platelets when its dietary level is equal to or exceeds the level of all-cis-linoleate.

Incorporation into lipid classes of products from microsomal desaturation of isomeric trans-octadecenoic acids

The microsomal desaturation of positional isomers of trans-octadecenoic acids is effected by the delta 9-desaturase and, with concomitant geometric isomerization, cis,trans- and cis,cis-octadecadienoic acids of unusual structure are formed. Incorporation of the substrates and their products into lipids varied from 50.5% for incubations with 14-18:1 to 81.0% for 6-81:1. A detailed study of the composition of each of the major lipid classes, i.e., phospholipids, triacylglycerol and cholesteryl esters, as well as the composition of the free fatty acid fraction, revealed a complex picture. Generally, the c,c-18:2 products were enriched in the phospholipids fraction, whereas the c,t-18:2 appeared preferentially in cholesteryl esters. The 18:1 substrates themselves did not show marked preferences for any of the lipid classes. Phospholipase A2 action on phosphatidylcholine and phosphatidylethanolamine demonstrated enrichment of the c,c- and the c,t-18:2 products in the 2-position, whereas the 18:1 substrates were preferentially inserted into the 1-positions. The c,c- and c,t-18:2 formed by desaturation of t11-18:1 varied from this pattern, probably due to their conjugated double bond structures. Linoleic acid, c9,c12-18:2, formed during desaturation of t12-18:1, surprisingly showed enrichment in the 1-position of phosphatidylcholine. Incubation experiments with t5- and t6-isomers using liver microsomes from rats fed a corn-oil-supplemented diet showed conversion and incorporation rates similar to the rates obtained with microsomes from EFA-deficient rats. The fatty acid composition of lipid classes and the distribution of products and substrate between the 1- and 2-positions of phosphatidylcholine also agreed with results obtained using microsomes from EFA-deficient rats.

Desaturation of isomeric trans-octadecenoic acids by rat liver microsomes

Desaturation of twelve labeled positional isomers of trans-18 : 1 acids was investigated using enzymes of liver microsomes from essential-fatty-acid-deficient rats. Oleic acid was used as model for comparison and for optimizing the incubation conditions. Each positional isomer desaturated at a unique rate. The trans-6- and trans-13-octadecenoic acids gave mostly trans-6, cis-9- and cis-9,-trans-13-18 : 2 acids, respectively. The trans-5-isomer gave mostly cis-5, cis-9-18 : 2 acid. The trans-4-isomer gave a mixture of trans-4, cis-9- + cis-4, cis-9-18 : 2, trans-11-isomer gave cis-9, trans-11- + cis-9, cis-11-18 : 2; trans-12-isomer gave cis-9, trans-12- + cis-9, cis-12-18 : 2, and trans-14-isomer have cis-9,-trans-14- + cis-9, cis-14-18 : 2 acid. The trans-8-, trans-9-, and trans-10-isomers were not measurably desaturated. The site of desaturation of the trans-18 : 1 isomer was the 9-position, indicating action of delta 9 desaturase. Thus the isomeric trans-18 : 1 acids present in partially hydrogenated fats can be converted to cis, trans- or trans, cis- and cis, cis-18 : 2 isomers, and trans-18 : 1 isomers in food may have effects upon metabolic control because of the products derived from them.

Incorporation of saturated and cis- and trans-unsaturated long chain fatty acids in rat myocytes and increased susceptibility to arrhythmias

Neonatal rat heart myocytes cultured for 3 days in fatty acid-enriched (5 X 10(5) M stearate, oleate, elaidate, linoleate, linoelaidate or arachidonate at a 3 : 1, fatty acid (FA/albumin ratio) were analyzed by high-pressure liquid chromatography (HPLC) for the FA content of their neutral lipid, glyco-cardiolipid and phospholipid fractions and were tested for their susceptibility to arrhythmias produced by hypoxic/normoxic medium changes. Increases in the relative amount of FA in the above lipid fractions were generally in the order: elaidate = linoelaidate greater than linoleate = arachidonate greater than stearate = oleate. Cell morphology was unaffected by such treatment, but the cultures were more susceptible to induced arrhythmias. Cultures enriched with trans-FA, elaidate or linoelaidate, became markedly arrhythmic; arrhythmias in stearate-enriched cultures were of short duration; whereas the other FA produced intermediate increases. Susceptibility to arrhythmias could not be correlated with polyunsaturated fatty acid (PUFA/saturated fatty acid (SATFA) ratios of FA in the phospholipid fraction.

Prostaglandins and their precursors in tissues from rats fed on trans, trans-linoleate

Feeding trans,trans-9,12-linoleate to rats as 50 and 100% of the dietary fat decreased the concentrations of n-6 fatty acids, i.e. 18:2, 20:3 and 20:4, in heart, kidney, lung, adipose tissue and platelets of rats. The concentrations of prostaglandin products prostaglandins E1, E2 and F2 alpha in serum were significantly decreased in rats receiving high concentrations of dietary trans, trans-linoleate.

Kidney lipids: changes caused by dietary 9-trans, 12-trans-octadecadienoate

Trans,trans-linoleate at 50 and 100% of dietary fat decreased kidney size and altered its composition. Trans,trans-linoleate as the sole source of dietary fat impaired growth and caused more severe symptoms of essential fatty acid deficiency than was observed with hydrogenated coconut oil (HCO). The concentration of renal cholesterol, phospholipids (PL), triglycerides (TG) and cholesteryl esters (CE) were also decreased. Linoleic (18:2), homo-gamma-linolenic acid (20:3n6) and arachidonic acid (20:4n6) were significantly depressed in lipid classes, especially in PL and CE, by dietary trans,trans-linoleate. The increase in eicosatrienoate (20:3n9), especially in PL and CE of kidneys of rats fed HCO (essential fatty acid deficient), was slight in rats fed 100% trans,trans-linoleate, indicating that the trans,trans acid probably inhibited acyl elongation and desaturation.

The effect of elaidic acid incorporation upon the lipid composition of Ehrlich Ascites tumor cells and of the host's liver

The incorporation of elaidic acid into Ehrlich ascites tumor cells (EATC) upon feeding the host an elaidic acid-rich diet has been investigated in the present study. The EATC lipids contained only one-half the concentration of elaidic acid found in the lipids of either the host livers or of livers from normal mice. On the other hand, elaidic acid incorporation into tumor cells was close to that of ascites fluid. This incorporation was mainly into phospholipids; the highest into choline phospholipids and ethanolamine phospholipids. Some changes in the EATC fatty acid composition were noted due to this incorporation. EATC phospholipids had reduced polyunsaturated fatty acids as compared with oleic acid-grown cells. The same was true with respect to ascites fluid phospholipids, but neutral lipids were not altered. Tumor development was accompanied by an increase in elaidic acid of the host's liver. Elaidic acid incorporation into tumor cells resulted in a reduction in the amount of all major lipids in the tumor. In contrast, elaidic acid had no effect on lipid composition of livers from normal mice and and-tumor bearing mice, and also had no effect upon the lipids of the ascites fluid that bathes the tumor cells. The incorporation of elaidic acid into the lipids of EATC, normal liver and host liver did not affect the relative composition of phospholipids in these tissues. The development of the tumor did result in decreases in triacylglycerols and esterified cholesterol, and increases in phospholipids and free cholesterol in the livers of host animals.

Distribution of isomeric octadecenoic fatty acids in milk fat

Milk fat octadecenoic acids were isolated by preparative gas-liquid chromatography of their methyl esters and separated into cis and trans isomers by argentation thin-layer chromatography. The distribution of the double bonds in the two fractions was determined by reductive ozonolysis. Cis octadecenoic acids had double bonds in positions 6 to 14. The cis-9 isomer was the most abundant isomer representing approximately 95% of the total. Trans octadecenoic acids had double bonds in positions 6 to 16, the predominant isomer being trans-11 octadecenoic acid. Data illustrating the range of variation in the distribution of positional isomers of octadecenoic acid for herd milk fat and butter are presented. There was no obvious seasonal variation in the distribution pattern. Fat from perirenal and subcutaneous adipose tissue of a dairy cow had composition similar to that of butter samples.

Effects of dietary saturated and trans fatty acids on tissue lipid composition and serum LCAT activity in the rat

Groups of rats were fed from weaning with diets containing 5% by wt of hydrogenated coconut oil (HCO), safflower oil, or a concentrate of ethyl elaidate and linolelaidate (TRANS) as the sole source of dietary fat. Fatty acid composition of the lipid classes from serum, liver, heart, and kidney was determined, and the serum lecithin: cholesterol acyl transferase (LCAT) activities were assayed for each animal. Serum LCAT activity was increased by both the HCO and TRANS diets in the early stages of the development of an essential fatty acid (EFA) deficiency but was suppressed in the animals of the TRANS group as they became older. The HCO and TRANS groups exhibited changes in tissue lipid fatty acid composition, as well as reduced growth, characteristic of an EFA deficiency. Coversion of oleic acid to eicosatrienoic acid was impaired in the animals fed the TRANS diet, greatly increasing the octadecenoic acid content of the tissue lipids at the expense of eicosatrienoic acid. The TRANS diet also suppressed incorporation of eicosatrienoic acid into cholesteryl esters of tissue and serum, indicating that, when fed as the sole source of unsaturated fat, trans fatty acids influenced the metabolism of unsaturated fatty acids and cholesterol.