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

Hydrogenated fat high in trans monoenes with an adequate level of linoleic acid has no effect on prostaglandin synthesis in rats

Our study was designed to determine whether hydrogenated fat high in trans monoenes concentration affected prostaglandin synthesis. Corn oil (CO), butter (B), hydrogenated vegetable oil (HF) and coating fat (CF) were used in this study. These fats were fed to rats for 10 wk at 10 g/100 g diet. The phospholipid (PL) fatty acid content of platelets, aorta and heart was determined by gas liquid chromatography, and the in vitro aorta production of prostacyclin (PGI2) from exogenous or endogenous arachidonic acid (AA) was measured using the radioimmuno-assay (RIA) method. Serum thromboxane B2 (TXB2) released by platelets as thromboxane A2 (TXA2) during incubation of whole blood was also measured by this method. In the group fed CF, AA was significantly lower in the PL of aorta, platelet and heart, and the ratio 20:3(n-9)/20:4(n-6) was greater than in the groups fed CO, B or HF, indicating that the group fed CF was essential fatty acid (EFA) deficient. Although AA was significantly lower in the aorta and platelet PL of the group fed HF compared to the group fed CO, that difference did not affect the amounts of PGI2 or TXB2 produced in these groups. The group fed CF had significantly less PGI2 and TXB2 released by aorta and platelets than the other groups. This was the result of the reduced level of AA and the presence of higher amounts of 20:3(n-9) acid in the PL, which might act as a competitive inhibitor for cyclooxygenase. The aortic production of PGI2 from exogenous AA did not differ among the groups indicating that prostaglandin synthetase was not affected by the dietary fat. We conclude that the consumption of hydrogenated fats high in trans 18:1 acids with adequate amount of linoleic acid had no effect on the amount of thromboxane or prostacyclin produced by platelet or aorta in vitro.

Controversies surrounding diet and breast cancer

What we know about prevention of breast cancer is related to lifetime oestrogen exposure and exposures to specific oestrogens at vulnerable periods of life. This can be influenced by diet. The strongest indicator of a diet-related effect to date is the fairly consistent increase in breast cancer among women who are tall or obese (Hunter & Willett, 1993). The other dietary factors summarized in Table 1 are less strongly associated with breast-cancer risk in epidemiological studies. The relationship between fat and breast-cancer risk has been extensively studied but remains somewhat uncertain. Fat, as a contributor to energy intakes and energy imbalance, is probably a factor in the higher breast-cancer rates in Western countries. Beyond its role as an energy source, the evidence for an independent effect of dietary fat on breast-cancer risk is weak. More focused analyses of the role of individual fatty acids, and on lipid-related pesticide exposures, may reveal strong effects which are currently masked by the use of inadequate exposure measures, as well as by measurement error. Currently, there is substantial evidence of a weak relationship with alcohol consumption, even at frequencies of drinking of less than once daily. The evidence of a protective role for antioxidants is weaker for breast cancer than for other cancers. This might by expected in a cancer which is not strongly associated with cigarette smoking. Specific foods are being studied for other potentially-active ingredients which may be involved in hormone metabolism, but conclusive results for soyabean or cruciferous vegetables are not yet available. Studying these relationships will continue to be a challenge for researchers because of the difficulties in measuring dietary exposures, which is complicated by the uncertainty of the relevant time frame for exposure assessment. While substantial attention has been focused on studying diet in relation to incidence, the potential for diet to reduce recurrence of breast cancer is thoroughly under-studied. There is little reason to believe that the factors which influence the incidence of breast cancer, perhaps during childhood and puberty, are the same as those which affect recurrence in adulthood. In this area, the very limited evidence available suggests that study of biologically-active fatty acids is promising.

Trans fatty acids: implications for health, analytical methods, incidence in edible fats and intake (a review)

Trans fatty acids (TFA) are supposed to be related to a variety of physiological effects. Numerous studies in this field are gathered and compared, which mainly deal with the influences on lipoprotein levels in plasma and their effects with regard to coronary heart diseases. Furthermore, the analytical accessibility of trans fatty acids by different methods is presented. Thus, the most reliable method for an exact quantitation of trans fatty acids in edible fats is the combination of Ag-TLC with GC. The contents of TFA, in particular trans-octadecenoic acids, in bovine and human milk fat, in partially hydrogenated vegetable fats and oils as well as in processed food from different countries, determined in numerous studies, are summarized. Especially results on the isomeric distribution of positional isomers of trans-octadecenoic acid may be of future interest, since negative metabolic activities might only originate from certain isomers. Finally, intake rates of TFA in several countries are presented. It can be concluded that there still is need for further nutritional studies and that the discussion about TFA should not neglect the comparison with the saturated fatty acids C12, C14 and C16.

Trans fatty acids may impair biosynthesis of long-chain polyunsaturates and growth in man

Human diet contains large amounts of trans fatty acids originating primarily from hydrogenated fats. Consumption of trans fatty acids is considered safe for man, but side effects, including impaired biosynthesis of long-chain polyunsaturated fatty acids with 20 and 22 carbon atoms and reduced growth have been observed in animals. We studied whether or not there are indications of untoward effects of trans fatty acids in 29 premature infants (birth weight 1700 +/- 127 g, gestational age 33.6 +/- 1.4 weeks, mean +/- SD). Plasma samples obtained on day 4 of life were analysed for fatty acid composition. Trans octadecenoic acid and total trans fatty acids in plasma lipid fractions (% wt/wt) were not related to the precursor essential fatty acids linoleic and alpha-linolenic acids but correlated inversely to n - 3 and n - 6 long-chain polyunsaturated fatty acids and to the product/substrate ratios of long-chain polyunsaturate biosynthesis. Trans fatty acids were also inversely correlated to birth weight but not to gestational age. These data indicate a potential impairment of essential fatty acid metabolism and early growth by trans isomers in man, and question the safety of high dietary trans isomer intakes during pregnancy and the perinatal period.

[Supply, metabolism and biological effects of trans-isomeric fatty acids in infants]

Consumption of trans-fatty acids increased markedly during this century due to the widespread use of partially hydrogenated fats. A sensitive analytical method was developed which enables the precise determination of 7 trans-isomers in small sample volumes. With this method we documented the materno-fetal transfer of trans-fatty acids across the human placenta. The content in human milk depends on maternal diet and is lower in Germany than in the Sudan. The distribution in fore- and hind-milk, in milk fat fractions and within the triglyceride molecule was determined. The content of trans-fatty acids is lower in commercial and home-made infant formulae than in human milk, although there is a certain batch to batch variation in formulae. Infants absorb dietary trans-isomers and incorporate them into endogenous lipids, subcutaneous tissue and cell membranes. Trans-fatty acids in plasma lipids are significantly higher in infants fed human milk than in those fed formulae. African children have a lower exposure than Germans. The relative contribution of trans-octadecenoic acid is lower in plasma sterol esters than in triglycerides and phospholipids, pointing to a negative selectivity of plasmatic cholesterol esterification with this fatty acid. Thus, a high supply of trans-octadecenoic acid might have negative effects on the cholesterol levels. In premature infants we found an inverse correlation between trans-fatty acid exposure and birthweight, thus interference with intrauterine growth appears possible. A possible causative factor could be impaired biosynthesis of long-chain polyunsaturated fatty acids by trans-isomers, for which we found strong indications. The results of our investigations the question whether the consumption of trans-fatty acids in pregnant and lactating women and in infants is nutritionally safe.

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.

The role of linoleic acid and its metabolites in the lowering of plasma cholesterol and the prevention of cardiovascular disease

An increase in linoleic acid intake lowers plasma cholesterol and is one of the safest methods for achieving this end. However, the amounts that must be consumed are large. Linoleic acid is metabolized via several routes and it is probable that a metabolite, rather than linoleic acid itself, is responsible for the cholesterol-lowering effect. If that metabolite could be identified, safe, drug-free, cholesterol-lowering might be achieved with much lower doses. Evidence is reviewed which suggests that a long-chain polyunsaturated fatty acid and/or a prostaglandin metabolite may be responsible for the cholesterol-controlling action of linoleic acid. Such metabolites may be effective also in controlling other risk factors for cardiovascular disease, such as elevated blood pressure and enhanced platelet aggregation. Epidemiological studies suggest that low levels of those metabolites, especially dihomogammalinolenic acid and arachidonic acid, are powerful independent risk factors for development of ischaemic heart disease. Further research in this area is urgently needed now that it is broadly accepted that cholesterol-lowering does indeed reduce the risk of cardiovascular disease.

Reduction in thromboxane formation by n-3 fatty acids enriched lung microsomes from rat and guinea pig following the ingestion of dietary menhaden oil

Feeding rats and guinea pigs on a diet containing 5% menhaden oil altered the fatty acid composition of lung microsomes. The lung microsomal phospholipids contained increased amounts of n-3 fatty acids, eicosapentaenoic (20:5) and docosahexaenoic acid (20:6), following the ingestion of menhaden oil. There was a concomitant decrease in arachidonic acid (20:4) levels in rat lung microsomes, but no significant change of this fatty acid was observed in the microsomes from guinea pigs. The ability of lung microsomes to convert 14C-arachidonic acid into thromboxane (TXB) was reduced by the enrichment of n-3 fatty acids in the microsomal lipids.

Dietary trilinoelaidate: effects on the in vitro biosynthesis of different prostaglandins in brain, lung and stomach fundus of rats

The effects of dietary trilinoelaidate on the biosynthesis of different prostaglandins (PG's) from [1-14C]-arachidonic acid by brain, lung, and stomach fundus homogenates of rats were determined. Rats were fed diets containing hydrogenated tallow (essential fatty acid deficient), trilinoelaidin at 0 (control), 10 and 50 weight percent of the total dietary fat and sacrificed at the end of eleven weeks. Brain, lung and stomach fundus of rats receiving trilinoelaidin at a level of 50 weight percent of the total dietary fat and the essential fatty acids deficient diet showed increased activity for the in vitro conversion of exogenous arachidonic acid to PG's compared to controls.

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.