Distribution of deuterium-labeledcis-andtrans-12-octadecenoic acids in human plasma and lipoprotein lipids

Triglycerides containingcis- andtrans-12-octadecenoic acid (12c-18∶1 and 12t-18∶1) andcis-9-octadecenoic acid (9c-18∶1) labeled with deuterium were fed to 2 young adult male subjects. These fatty isomers each contained a different number of deuterium labels, which allowed mass spectrometric analysis to distinguish among them after they were fed as a mixture. This approach results in a direct comparison of the absorption and distribution of these 3 monoenoic acids into blood plasma and lipoprotein lipids. Plasma lipid data indicated that all phospholipid fractions selectively incorporate 12c-18∶1 and 12t-18∶1 in preference to 9c-18∶1. Discrimination against 12c-18∶1 and 12t-18∶1 compared to 9c-18∶1 was found in the plasma neutral lipids, with a strong discrimination against 12t-18∶1 incorporation into the cholesteryl ester fraction. Considerable reduction in the percentage of linoleic and arachidonic acid was observed when 12–18∶1 isomers were incorporated in plasma triglyceride, phosphatidylcholine and sphingomyelin samples. Chylomicron lipid analyses indicated that all isomers were well absorbed. Variation was observed in the relative distribution of 12c-18∶1, 12t-18∶1 and 9c-18∶1 between the very low density, low density and high density lipoprotein lipid classes. No desaturation of 12c-18∶1 to linoleic acid was detected.