Incorporation of deuterium-labeled trans- and cis-I 3-octadecenoic acids in human plasma lipids'

The absorption and distribution of deuterated transand cis-l S-octadecenoic acid (1 3t-18: 1 and 13c-18: 1) in plasma lipids were compared to deuterated cis-9-octadecenoic acid (9c18: 1) in two young adult male subjects. A mixture of triglycerides was fed in a multiple-labeled experiment where each triglyceride contained a fatty acid labeled with a different number of deuterium atoms. Analysis of human plasma lipids by mass spectroscopy allowed the distribution of the two 13octadecenoic acid isomers to be directly compared to cis-9octadecenoic acid. Plasma lipids selectively excluded both the 13t18: 1 and 13c-18: 1 isomers relative to 9c-18: 1 in all neutral and phospholipid fractions. Discrimination against incorporation of the 13t-18: 1 isomer into plasma cholesteryl ester and 2-acyl phosphatidylcholine was nearly absolute. The 1 -acyl phosphatidylcholine fraction exhibited a large positive selectivity for the 13t-18: 1 isomer. Differences in the relative distribution of the trans and cis 1318: 1 isomers vs. 9c-18: 1 in the various lipoprotein lipid classes were found. Analysis of the chylomicron triglyceride component of the plasma lipids indicated all three fatty acids were equally well absorbed.Emken, E. A., R. 0. Adlof, W. K. Rohwedder, and R. M. Gulley. Incorporation of deuterium-labeled transand cis-13octadecenoic acids in human plasma lipids./. Lipid Res. 1983. 24: 34-46. Supplementary key words lipid metabolism deuterium-labeled isomeric fatty acids Soybean oil is the most important source of visible dietary fat in the United States and is an excellent source of polyunsaturated fatty acids (1-3). About 75% of the edible soybean oil produced is partially hydrogenated during processing to improve flavor stability and to increase the melting point or solid fat index. Partial hydrogenation or hardening of soy oil allows it to be formulated into margarines and shortenings. Part of the increase in melting point is a result of the formation of positional and trans fatty acid isomers. Analysis of commercial salad oils, margarines, and shortenings has identified the 8 through 13 positional cis and trans isomers as the major monounsaturated fatty acids in hydrogenated soybean oil (4, 5). These fatty acid isomers are incorporated into animal (617) and human tissue lipids (1 8-23), and their metabolism and biochemistry have been the subject of recent reviews (24-26). Little human data now exists on the metabolism of specific positional fatty acid isomers that can be used to determine the validity of animal and in vitro data for predicting human metabolic response to specific fatty acid isomers. To provide human data for evaluating possible nutritional and metabolic effects of fatty acid isomers, the absorption, distribution, and disappearance of deuterium labeled cisand truns-13-octadecenoic acid compared to cis-9-octadecenoic acid in human plasma and lipoprotein lipid classes were determined using a triple-labeled experimental approach.