Membrane lipid composition and cellular function.

Intake of trans fatty acids and risk of coronary heart disease among women

Trans isomers of fatty acids, formed by the partial hydrogenation of vegetable oils to produce margarine and vegetable shortening, increase the ratio of plasma low-density-lipopratein to highdensity-lipoprotein cholesterol, so it is possible that they adversely influence risk of coronary heart disease (CHD). To investigate this possibility, we studied dietary data from participants in the Nurses' Health Study. We calculated intake of trans fatty acids fram dietary questionnaires completed by 85 095 women without diagnosed CHD, strake, diabetes, or hypercholesteralaemia in 1980. During 8 years of follow-up, there were 431 cases of new CHD (non-fatal myocardial infarction or death from CHD). After adjustment for age and total energy intake, intake of trans isomers was directly related to risk of CHD (relative risk for highest vs lowest quintile 1·50 [95% CI 1'12-2'00]. p for trend =:= 0·001). Additional control for established CH 0 risk factors, multivitamin use, and intakes of saturated fat, monounsaturated fat, and linoleic acid, dietary cholesterol. vitamins Eor C, carotene, or fibre did not change the relative risk substantially. The association was stronger for the 69 181 women whose margarine consumption over the previous 10 years had been stable (1'67 [1'05-2'66], p for trend =0'002). Intakes of foods that are major sources of trans isomers (margarine, cookies [biscuits], cake, and white bread) were each significantly associated with higher risks of CHD. These findings support the hypothesis that consumption of partially hydrogenated vegetable oils may contribute to occurrence of CHD.

Intake of trans fatty acids and risk of coronary heart disease arnong wornen

Essential fatty acids in growth and development

Essential fatty acids (EFA), which are not synthesized in animal and human tissues, belong to the n-6 and n-3 families of polyunsaturated fatty acids (PUFA), derived from linoleic acid (LA, 18:2n-6) and alpha-linolenic acid (LNA, 18:3n-3). Optimal requirements are 3-6% of ingested energy for LA and 0.5-1% for LNA in adults. Requirements in LNA are higher in development. Dietary sources of LA and LNA are principally plants, while arachidonic acid (AA, 20:4n-6) is found in products from terrestrian animals, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in products from marine animals. EFA are principally present in dietary triacylglycerols, which should be hydrolyzed by lipases in gastric and intestinal lumen. DHA seems to be released more slowly than the others. Its intestinal absorption is delayed but not decreased. Long-chain PUFAs are incorporated in noticeable amounts in chylomicron phospholipids. However, their uptake by tissues is no more rapid than uptake of shorter chain PUFA. In tissues, LA and LNA, which constitute the major part of dietary EFA, should be converted into fatty acids of longer and more unsaturated chain by alternate desaturation (delta 6, delta 5, delta 4)-elongation reactions. Animal tissues are more active in this biosynthesis than human tissues. Liver is one of the most active organs and its role is critical in providing less active tissues, particularly the brain, with long-chain PUFA secreted in VLDL (very low density lipoprotein). In liver, many nutritional, hormonal and physiological factors act on the PUFA biosynthesis. Dietary fatty acids exert a great influence and are often inhibitory. Dietary LNA inhibits delta 6 desaturation of LA. The desaturation products AA, EPA, and DHA inhibit delta 6 desaturation of LA and delta 5 desaturation of DGLA (dihomo-gamma-linolenic acid). With regard to hormones, insulin and thyroxin are necessary to delta 6 and delta 5 desaturation activities, whereas other hormones (glucagon, epinephrine, ACTH, glucocorticoids) inhibit desaturation. Concerning the physiological factors, the age of individuals is critical. In the fetus, the liver and the brain are capable of converting LA and LNA into longer-chain EFA, but these are also delivered by the mother, after synthesis in the maternal liver and placenta. Just after birth, in animals, the delta 6 desaturation activity increases in the liver and decreases in the brain. In aging, the capacity of the whole liver to desaturate LA and DGLA is equal at 1.5 and 25 months of age in rats fed a balanced diet throughout their life and the AA and DHA content of tissue phospholipids is unchanged in aging.(ABSTRACT TRUNCATED AT 400 WORDS)

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The metabolism and availability of essential fatty acids in animal and human tissues.

Fatty acyl Δ6 desaturation activity of cultured human endothelial cells modulation by fetal bovine serum

Selective effects of isomeric cis and trans fatty acids on fatty acyl Δ9 and Δ6 desaturation by human skin fibroblasts

Incorporation of exogenous [14C] arachidonate by human skin fibroblasts was found to be significantly greater than that of either [14C]linoleate or alpha-[14C] linolenate. Arachidonate was preferentially esterified in the PI + PS and PE classes of phospholipids. Over 40% of the incorporated [14C] arachidonate was chain elongated in 24 hours. Cells were also grown in lipid-free medium to enhance PUFA desaturation and elongation and the utilization of various omega 6 and omega 3 metabolites examined. Whereas [14C] linoleate partitioned approximately 50:50 between PL and TAG, eicosatrienoate (20:3 omega 6) was selectively sequestered in TAG. Arachidonate and docosatetraenoate (22:4 omega 6) were preferentially incorporated into phospholipids; the PI + PS fraction was most highly enriched with arachidonate. Modification of alpha-[14C] linolenate was more extensive than that of [14C] linoleate. Docosapentaenoate (22:5 omega 3) was the major omega 3 [14C] PUFA of PI + PS and PE. Eicosapentaeonate was not selectively incorporated into phospholipids; within phospholipids the 20:5 omega 3 was primarily in PC. These results indicate that human skin fibroblasts exhibit acyl specificity in the esterification of polyunsaturated fatty acids, including preferential utilization of arachidonate rather than other prostaglandin precursors in the PI + PS fraction.

M.Candace Whitehurst

Papers

Fatty acyl Δ6 desaturation activity of cultured human endothelial cells modulation by fetal bovine serum

Selective effects of isomeric cis and trans fatty acids on fatty acyl Δ9 and Δ6 desaturation by human skin fibroblasts

Selective utilization of omega 6 and omega 3 polyunsaturated fatty acids by human skin fibroblasts.