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 usc of dual and triple labeling methodology permitted a precise comparison of elaidic and oleic acid utilization. Elaidic acid (EI) was selectively concentrated in all th~ plasma phospholipids except for lysophosphatidylcholine. Three times more elaidic than oleic acid (On accumulated in the I-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. Over 5.5 billion Ib. of vegetable oil is hydrogenated annually for use in margarines, salad oils, cooking fats, and shortening (I). This hydrogenation process results in the formation of ca. 15% trans and positional fatty acid isomers (2-8). These oils are a major source of dietary fat, and it is estimated the average American diet contains ca. 8% trans fatty acid. Metabolism and biological effects of isomeric fatty acids have been studied in rats, monkeys, chickens, swine, rabbits, and man. The uptake and deposition of trans isomers into rat (9), swine (10), and human tissue (II) has been documented. Specific geometric and positional fatty acid isomers have been shown to be incorporated into egg yolk lipids (12-14 ), human blood plasma (15), rat liver (16-20), rat fetuses (21), rabbit serum lipids (22), and Escherichia coli membranes (22-27). Hydrogenated fats have been correlated with an increase in serum cholesterol and triglyceride levels in humans (28-32), increase in fragility of erythrocytes (17), alteration of the lipid transport function of rat mitochondria (17), increase in essential fatty acid requirements (33-34), increase in long chain unsaturated fatty acids content of rat phospholipid (35-36), increases in serum cholesterol levels in 1The mention of Hrm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other Hrms or similar products not mentioned. swine (37) and rabbits (38,39), alterations in membrane function in E. coli (26,27), and increase in rate of de novo fatty acid synthesis from acetate in rat liver (40). However, contradictory results have been reported by several researchers. For example, serum cholesterol levels in man have been reported both to be elevated and to remain unchanged by diets containing hydrogenated fats. Long term feeding studies have indicated no change in the growth, reproduction, longevity, or size of mice and rats fed hydrogenated fats (4146). . The results reported in previous investigations with human subjects have all involved hydrogenated fat that is a mixture of isomeric fats. This study specifically compares the utilization of olei~ to elaidic acid in human phospholipids and is an extension of previous data reported for human plasma neutral lipids (47).