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

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Abstract
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.

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