Effect of triacylglycerol structure on absorption and metabolism of isotope-labeled palmitic and linoleic acids by humans

摘要

The effect of dietary TAG structure and fatty acid acyl TAG position on palmitic and linoleic acid metabolism was investigated in four middle-aged male subjects. The study design consisted of feeding diets containing 61 g/d of native lard (NL) or randomized lard (RL) for 28 d. Subjects then received an oral dose of either 1,3-tetradeuteriopalmitoyl-2-dideuteriolinoleoyl-rac-glycerol or a mixture of 1,3-dideuteriolinoleoyl-2-tetradeuteriopalmitoyl-rac-glycerol and 1,3-hexadeuteriopalmitoyl-2-tetradeuteriolinoleoyl-rac-glycerol. Methyl esters of plasma lipids isolated from blood samples drawn over a 2-d period were analyzed by GC-MS. Results showed that absorption of the H-2-fatty acids (H-2-FA) was not influenced by TAG position. The H-2-FA at the 2-acyl TAG position were 85 +/- 4.6% retained after absorption. Substantial migration of H-2-1 6:0 (31.2 +/- 8.6%) from the sn-2 TAG position to the sn-1,3 position and H-2-18:2n-6 (52.8 +/- 6.4%) from the sn-1,3 position to the sn-2 position of chylomicron TAG occurred after initial absorption and indicates the presence of a previously unrecognized isomerization mechanism. Incorporation and turnover of the 2H-FA in chylomicron TAG, plasma TAG, and plasma cholesterol esters were not influenced by TAG acyl position. Accretion of (2)H16:0 from the sn-2 TAG position in 1-acylphosphatidylcholine was 1.7 times higher than 2H-1 6:0 from the sn-1,3 TAG positions. Acyl TAG position did not influence 2H-1 8:2n-6 incorporation in PC. The concentration of H-2-18:2n-6-derived H-2-20:4n-6 in plasma PC from subjects fed the RL diet was 1.5 times higher than for subjects fed the NL diet, and this result suggests that diets containing 16:0 located at the sn-2 TAG position may inhibit 20:4n-6 synthesis. The overall conclusion is that selective rearrangement of chylomicron TAG structures diminishes but does not totally eliminate the metabolic and physiological effects of dietary TAG structure. [References: 42]